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4344 lines
143 KiB
4344 lines
143 KiB
====================== |
|
Writing an ALSA Driver |
|
====================== |
|
|
|
:Author: Takashi Iwai <[email protected]> |
|
|
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Preface |
|
======= |
|
|
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This document describes how to write an `ALSA (Advanced Linux Sound |
|
Architecture) <http://www.alsa-project.org/>`__ driver. The document |
|
focuses mainly on PCI soundcards. In the case of other device types, the |
|
API might be different, too. However, at least the ALSA kernel API is |
|
consistent, and therefore it would be still a bit help for writing them. |
|
|
|
This document targets people who already have enough C language skills |
|
and have basic linux kernel programming knowledge. This document doesn't |
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explain the general topic of linux kernel coding and doesn't cover |
|
low-level driver implementation details. It only describes the standard |
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way to write a PCI sound driver on ALSA. |
|
|
|
This document is still a draft version. Any feedback and corrections, |
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please!! |
|
|
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File Tree Structure |
|
=================== |
|
|
|
General |
|
------- |
|
|
|
The file tree structure of ALSA driver is depicted below. |
|
|
|
:: |
|
|
|
sound |
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/core |
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/oss |
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/seq |
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/oss |
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/include |
|
/drivers |
|
/mpu401 |
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/opl3 |
|
/i2c |
|
/synth |
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/emux |
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/pci |
|
/(cards) |
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/isa |
|
/(cards) |
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/arm |
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/ppc |
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/sparc |
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/usb |
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/pcmcia /(cards) |
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/soc |
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/oss |
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|
|
|
|
core directory |
|
-------------- |
|
|
|
This directory contains the middle layer which is the heart of ALSA |
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drivers. In this directory, the native ALSA modules are stored. The |
|
sub-directories contain different modules and are dependent upon the |
|
kernel config. |
|
|
|
core/oss |
|
~~~~~~~~ |
|
|
|
The codes for PCM and mixer OSS emulation modules are stored in this |
|
directory. The rawmidi OSS emulation is included in the ALSA rawmidi |
|
code since it's quite small. The sequencer code is stored in |
|
``core/seq/oss`` directory (see `below <core/seq/oss_>`__). |
|
|
|
core/seq |
|
~~~~~~~~ |
|
|
|
This directory and its sub-directories are for the ALSA sequencer. This |
|
directory contains the sequencer core and primary sequencer modules such |
|
like snd-seq-midi, snd-seq-virmidi, etc. They are compiled only when |
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``CONFIG_SND_SEQUENCER`` is set in the kernel config. |
|
|
|
core/seq/oss |
|
~~~~~~~~~~~~ |
|
|
|
This contains the OSS sequencer emulation codes. |
|
|
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include directory |
|
----------------- |
|
|
|
This is the place for the public header files of ALSA drivers, which are |
|
to be exported to user-space, or included by several files at different |
|
directories. Basically, the private header files should not be placed in |
|
this directory, but you may still find files there, due to historical |
|
reasons :) |
|
|
|
drivers directory |
|
----------------- |
|
|
|
This directory contains code shared among different drivers on different |
|
architectures. They are hence supposed not to be architecture-specific. |
|
For example, the dummy pcm driver and the serial MIDI driver are found |
|
in this directory. In the sub-directories, there is code for components |
|
which are independent from bus and cpu architectures. |
|
|
|
drivers/mpu401 |
|
~~~~~~~~~~~~~~ |
|
|
|
The MPU401 and MPU401-UART modules are stored here. |
|
|
|
drivers/opl3 and opl4 |
|
~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
The OPL3 and OPL4 FM-synth stuff is found here. |
|
|
|
i2c directory |
|
------------- |
|
|
|
This contains the ALSA i2c components. |
|
|
|
Although there is a standard i2c layer on Linux, ALSA has its own i2c |
|
code for some cards, because the soundcard needs only a simple operation |
|
and the standard i2c API is too complicated for such a purpose. |
|
|
|
synth directory |
|
--------------- |
|
|
|
This contains the synth middle-level modules. |
|
|
|
So far, there is only Emu8000/Emu10k1 synth driver under the |
|
``synth/emux`` sub-directory. |
|
|
|
pci directory |
|
------------- |
|
|
|
This directory and its sub-directories hold the top-level card modules |
|
for PCI soundcards and the code specific to the PCI BUS. |
|
|
|
The drivers compiled from a single file are stored directly in the pci |
|
directory, while the drivers with several source files are stored on |
|
their own sub-directory (e.g. emu10k1, ice1712). |
|
|
|
isa directory |
|
------------- |
|
|
|
This directory and its sub-directories hold the top-level card modules |
|
for ISA soundcards. |
|
|
|
arm, ppc, and sparc directories |
|
------------------------------- |
|
|
|
They are used for top-level card modules which are specific to one of |
|
these architectures. |
|
|
|
usb directory |
|
------------- |
|
|
|
This directory contains the USB-audio driver. In the latest version, the |
|
USB MIDI driver is integrated in the usb-audio driver. |
|
|
|
pcmcia directory |
|
---------------- |
|
|
|
The PCMCIA, especially PCCard drivers will go here. CardBus drivers will |
|
be in the pci directory, because their API is identical to that of |
|
standard PCI cards. |
|
|
|
soc directory |
|
------------- |
|
|
|
This directory contains the codes for ASoC (ALSA System on Chip) |
|
layer including ASoC core, codec and machine drivers. |
|
|
|
oss directory |
|
------------- |
|
|
|
Here contains OSS/Lite codes. |
|
All codes have been deprecated except for dmasound on m68k as of |
|
writing this. |
|
|
|
|
|
Basic Flow for PCI Drivers |
|
========================== |
|
|
|
Outline |
|
------- |
|
|
|
The minimum flow for PCI soundcards is as follows: |
|
|
|
- define the PCI ID table (see the section `PCI Entries`_). |
|
|
|
- create ``probe`` callback. |
|
|
|
- create ``remove`` callback. |
|
|
|
- create a struct pci_driver structure |
|
containing the three pointers above. |
|
|
|
- create an ``init`` function just calling the |
|
:c:func:`pci_register_driver()` to register the pci_driver |
|
table defined above. |
|
|
|
- create an ``exit`` function to call the |
|
:c:func:`pci_unregister_driver()` function. |
|
|
|
Full Code Example |
|
----------------- |
|
|
|
The code example is shown below. Some parts are kept unimplemented at |
|
this moment but will be filled in the next sections. The numbers in the |
|
comment lines of the :c:func:`snd_mychip_probe()` function refer |
|
to details explained in the following section. |
|
|
|
:: |
|
|
|
#include <linux/init.h> |
|
#include <linux/pci.h> |
|
#include <linux/slab.h> |
|
#include <sound/core.h> |
|
#include <sound/initval.h> |
|
|
|
/* module parameters (see "Module Parameters") */ |
|
/* SNDRV_CARDS: maximum number of cards supported by this module */ |
|
static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX; |
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static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR; |
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static bool enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP; |
|
|
|
/* definition of the chip-specific record */ |
|
struct mychip { |
|
struct snd_card *card; |
|
/* the rest of the implementation will be in section |
|
* "PCI Resource Management" |
|
*/ |
|
}; |
|
|
|
/* chip-specific destructor |
|
* (see "PCI Resource Management") |
|
*/ |
|
static int snd_mychip_free(struct mychip *chip) |
|
{ |
|
.... /* will be implemented later... */ |
|
} |
|
|
|
/* component-destructor |
|
* (see "Management of Cards and Components") |
|
*/ |
|
static int snd_mychip_dev_free(struct snd_device *device) |
|
{ |
|
return snd_mychip_free(device->device_data); |
|
} |
|
|
|
/* chip-specific constructor |
|
* (see "Management of Cards and Components") |
|
*/ |
|
static int snd_mychip_create(struct snd_card *card, |
|
struct pci_dev *pci, |
|
struct mychip **rchip) |
|
{ |
|
struct mychip *chip; |
|
int err; |
|
static const struct snd_device_ops ops = { |
|
.dev_free = snd_mychip_dev_free, |
|
}; |
|
|
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*rchip = NULL; |
|
|
|
/* check PCI availability here |
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* (see "PCI Resource Management") |
|
*/ |
|
.... |
|
|
|
/* allocate a chip-specific data with zero filled */ |
|
chip = kzalloc(sizeof(*chip), GFP_KERNEL); |
|
if (chip == NULL) |
|
return -ENOMEM; |
|
|
|
chip->card = card; |
|
|
|
/* rest of initialization here; will be implemented |
|
* later, see "PCI Resource Management" |
|
*/ |
|
.... |
|
|
|
err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); |
|
if (err < 0) { |
|
snd_mychip_free(chip); |
|
return err; |
|
} |
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|
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*rchip = chip; |
|
return 0; |
|
} |
|
|
|
/* constructor -- see "Driver Constructor" sub-section */ |
|
static int snd_mychip_probe(struct pci_dev *pci, |
|
const struct pci_device_id *pci_id) |
|
{ |
|
static int dev; |
|
struct snd_card *card; |
|
struct mychip *chip; |
|
int err; |
|
|
|
/* (1) */ |
|
if (dev >= SNDRV_CARDS) |
|
return -ENODEV; |
|
if (!enable[dev]) { |
|
dev++; |
|
return -ENOENT; |
|
} |
|
|
|
/* (2) */ |
|
err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, |
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0, &card); |
|
if (err < 0) |
|
return err; |
|
|
|
/* (3) */ |
|
err = snd_mychip_create(card, pci, &chip); |
|
if (err < 0) |
|
goto error; |
|
|
|
/* (4) */ |
|
strcpy(card->driver, "My Chip"); |
|
strcpy(card->shortname, "My Own Chip 123"); |
|
sprintf(card->longname, "%s at 0x%lx irq %i", |
|
card->shortname, chip->port, chip->irq); |
|
|
|
/* (5) */ |
|
.... /* implemented later */ |
|
|
|
/* (6) */ |
|
err = snd_card_register(card); |
|
if (err < 0) |
|
goto error; |
|
|
|
/* (7) */ |
|
pci_set_drvdata(pci, card); |
|
dev++; |
|
return 0; |
|
|
|
error: |
|
snd_card_free(card); |
|
return err; |
|
} |
|
|
|
/* destructor -- see the "Destructor" sub-section */ |
|
static void snd_mychip_remove(struct pci_dev *pci) |
|
{ |
|
snd_card_free(pci_get_drvdata(pci)); |
|
} |
|
|
|
|
|
|
|
Driver Constructor |
|
------------------ |
|
|
|
The real constructor of PCI drivers is the ``probe`` callback. The |
|
``probe`` callback and other component-constructors which are called |
|
from the ``probe`` callback cannot be used with the ``__init`` prefix |
|
because any PCI device could be a hotplug device. |
|
|
|
In the ``probe`` callback, the following scheme is often used. |
|
|
|
1) Check and increment the device index. |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static int dev; |
|
.... |
|
if (dev >= SNDRV_CARDS) |
|
return -ENODEV; |
|
if (!enable[dev]) { |
|
dev++; |
|
return -ENOENT; |
|
} |
|
|
|
|
|
where ``enable[dev]`` is the module option. |
|
|
|
Each time the ``probe`` callback is called, check the availability of |
|
the device. If not available, simply increment the device index and |
|
returns. dev will be incremented also later (`step 7 |
|
<7) Set the PCI driver data and return zero._>`__). |
|
|
|
2) Create a card instance |
|
~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
struct snd_card *card; |
|
int err; |
|
.... |
|
err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, |
|
0, &card); |
|
|
|
|
|
The details will be explained in the section `Management of Cards and |
|
Components`_. |
|
|
|
3) Create a main component |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
In this part, the PCI resources are allocated. |
|
|
|
:: |
|
|
|
struct mychip *chip; |
|
.... |
|
err = snd_mychip_create(card, pci, &chip); |
|
if (err < 0) |
|
goto error; |
|
|
|
The details will be explained in the section `PCI Resource |
|
Management`_. |
|
|
|
When something goes wrong, the probe function needs to deal with the |
|
error. In this example, we have a single error handling path placed |
|
at the end of the function. |
|
|
|
:: |
|
|
|
error: |
|
snd_card_free(card); |
|
return err; |
|
|
|
Since each component can be properly freed, the single |
|
:c:func:`snd_card_free()` call should suffice in most cases. |
|
|
|
|
|
4) Set the driver ID and name strings. |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
strcpy(card->driver, "My Chip"); |
|
strcpy(card->shortname, "My Own Chip 123"); |
|
sprintf(card->longname, "%s at 0x%lx irq %i", |
|
card->shortname, chip->port, chip->irq); |
|
|
|
The driver field holds the minimal ID string of the chip. This is used |
|
by alsa-lib's configurator, so keep it simple but unique. Even the |
|
same driver can have different driver IDs to distinguish the |
|
functionality of each chip type. |
|
|
|
The shortname field is a string shown as more verbose name. The longname |
|
field contains the information shown in ``/proc/asound/cards``. |
|
|
|
5) Create other components, such as mixer, MIDI, etc. |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
Here you define the basic components such as `PCM <PCM Interface_>`__, |
|
mixer (e.g. `AC97 <API for AC97 Codec_>`__), MIDI (e.g. |
|
`MPU-401 <MIDI (MPU401-UART) Interface_>`__), and other interfaces. |
|
Also, if you want a `proc file <Proc Interface_>`__, define it here, |
|
too. |
|
|
|
6) Register the card instance. |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
err = snd_card_register(card); |
|
if (err < 0) |
|
goto error; |
|
|
|
Will be explained in the section `Management of Cards and |
|
Components`_, too. |
|
|
|
7) Set the PCI driver data and return zero. |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
pci_set_drvdata(pci, card); |
|
dev++; |
|
return 0; |
|
|
|
In the above, the card record is stored. This pointer is used in the |
|
remove callback and power-management callbacks, too. |
|
|
|
Destructor |
|
---------- |
|
|
|
The destructor, remove callback, simply releases the card instance. Then |
|
the ALSA middle layer will release all the attached components |
|
automatically. |
|
|
|
It would be typically just calling :c:func:`snd_card_free()`: |
|
|
|
:: |
|
|
|
static void snd_mychip_remove(struct pci_dev *pci) |
|
{ |
|
snd_card_free(pci_get_drvdata(pci)); |
|
} |
|
|
|
|
|
The above code assumes that the card pointer is set to the PCI driver |
|
data. |
|
|
|
Header Files |
|
------------ |
|
|
|
For the above example, at least the following include files are |
|
necessary. |
|
|
|
:: |
|
|
|
#include <linux/init.h> |
|
#include <linux/pci.h> |
|
#include <linux/slab.h> |
|
#include <sound/core.h> |
|
#include <sound/initval.h> |
|
|
|
where the last one is necessary only when module options are defined |
|
in the source file. If the code is split into several files, the files |
|
without module options don't need them. |
|
|
|
In addition to these headers, you'll need ``<linux/interrupt.h>`` for |
|
interrupt handling, and ``<linux/io.h>`` for I/O access. If you use the |
|
:c:func:`mdelay()` or :c:func:`udelay()` functions, you'll need |
|
to include ``<linux/delay.h>`` too. |
|
|
|
The ALSA interfaces like the PCM and control APIs are defined in other |
|
``<sound/xxx.h>`` header files. They have to be included after |
|
``<sound/core.h>``. |
|
|
|
Management of Cards and Components |
|
================================== |
|
|
|
Card Instance |
|
------------- |
|
|
|
For each soundcard, a “card” record must be allocated. |
|
|
|
A card record is the headquarters of the soundcard. It manages the whole |
|
list of devices (components) on the soundcard, such as PCM, mixers, |
|
MIDI, synthesizer, and so on. Also, the card record holds the ID and the |
|
name strings of the card, manages the root of proc files, and controls |
|
the power-management states and hotplug disconnections. The component |
|
list on the card record is used to manage the correct release of |
|
resources at destruction. |
|
|
|
As mentioned above, to create a card instance, call |
|
:c:func:`snd_card_new()`. |
|
|
|
:: |
|
|
|
struct snd_card *card; |
|
int err; |
|
err = snd_card_new(&pci->dev, index, id, module, extra_size, &card); |
|
|
|
|
|
The function takes six arguments: the parent device pointer, the |
|
card-index number, the id string, the module pointer (usually |
|
``THIS_MODULE``), the size of extra-data space, and the pointer to |
|
return the card instance. The extra_size argument is used to allocate |
|
card->private_data for the chip-specific data. Note that these data are |
|
allocated by :c:func:`snd_card_new()`. |
|
|
|
The first argument, the pointer of struct device, specifies the parent |
|
device. For PCI devices, typically ``&pci->`` is passed there. |
|
|
|
Components |
|
---------- |
|
|
|
After the card is created, you can attach the components (devices) to |
|
the card instance. In an ALSA driver, a component is represented as a |
|
struct snd_device object. A component |
|
can be a PCM instance, a control interface, a raw MIDI interface, etc. |
|
Each such instance has one component entry. |
|
|
|
A component can be created via :c:func:`snd_device_new()` |
|
function. |
|
|
|
:: |
|
|
|
snd_device_new(card, SNDRV_DEV_XXX, chip, &ops); |
|
|
|
This takes the card pointer, the device-level (``SNDRV_DEV_XXX``), the |
|
data pointer, and the callback pointers (``&ops``). The device-level |
|
defines the type of components and the order of registration and |
|
de-registration. For most components, the device-level is already |
|
defined. For a user-defined component, you can use |
|
``SNDRV_DEV_LOWLEVEL``. |
|
|
|
This function itself doesn't allocate the data space. The data must be |
|
allocated manually beforehand, and its pointer is passed as the |
|
argument. This pointer (``chip`` in the above example) is used as the |
|
identifier for the instance. |
|
|
|
Each pre-defined ALSA component such as ac97 and pcm calls |
|
:c:func:`snd_device_new()` inside its constructor. The destructor |
|
for each component is defined in the callback pointers. Hence, you don't |
|
need to take care of calling a destructor for such a component. |
|
|
|
If you wish to create your own component, you need to set the destructor |
|
function to the dev_free callback in the ``ops``, so that it can be |
|
released automatically via :c:func:`snd_card_free()`. The next |
|
example will show an implementation of chip-specific data. |
|
|
|
Chip-Specific Data |
|
------------------ |
|
|
|
Chip-specific information, e.g. the I/O port address, its resource |
|
pointer, or the irq number, is stored in the chip-specific record. |
|
|
|
:: |
|
|
|
struct mychip { |
|
.... |
|
}; |
|
|
|
|
|
In general, there are two ways of allocating the chip record. |
|
|
|
1. Allocating via :c:func:`snd_card_new()`. |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
As mentioned above, you can pass the extra-data-length to the 5th |
|
argument of :c:func:`snd_card_new()`, i.e. |
|
|
|
:: |
|
|
|
err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, |
|
sizeof(struct mychip), &card); |
|
|
|
struct mychip is the type of the chip record. |
|
|
|
In return, the allocated record can be accessed as |
|
|
|
:: |
|
|
|
struct mychip *chip = card->private_data; |
|
|
|
With this method, you don't have to allocate twice. The record is |
|
released together with the card instance. |
|
|
|
2. Allocating an extra device. |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
After allocating a card instance via :c:func:`snd_card_new()` |
|
(with ``0`` on the 4th arg), call :c:func:`kzalloc()`. |
|
|
|
:: |
|
|
|
struct snd_card *card; |
|
struct mychip *chip; |
|
err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, |
|
0, &card); |
|
..... |
|
chip = kzalloc(sizeof(*chip), GFP_KERNEL); |
|
|
|
The chip record should have the field to hold the card pointer at least, |
|
|
|
:: |
|
|
|
struct mychip { |
|
struct snd_card *card; |
|
.... |
|
}; |
|
|
|
|
|
Then, set the card pointer in the returned chip instance. |
|
|
|
:: |
|
|
|
chip->card = card; |
|
|
|
Next, initialize the fields, and register this chip record as a |
|
low-level device with a specified ``ops``, |
|
|
|
:: |
|
|
|
static const struct snd_device_ops ops = { |
|
.dev_free = snd_mychip_dev_free, |
|
}; |
|
.... |
|
snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); |
|
|
|
:c:func:`snd_mychip_dev_free()` is the device-destructor |
|
function, which will call the real destructor. |
|
|
|
:: |
|
|
|
static int snd_mychip_dev_free(struct snd_device *device) |
|
{ |
|
return snd_mychip_free(device->device_data); |
|
} |
|
|
|
where :c:func:`snd_mychip_free()` is the real destructor. |
|
|
|
The demerit of this method is the obviously more amount of codes. |
|
The merit is, however, you can trigger the own callback at registering |
|
and disconnecting the card via setting in snd_device_ops. |
|
About the registering and disconnecting the card, see the subsections |
|
below. |
|
|
|
|
|
Registration and Release |
|
------------------------ |
|
|
|
After all components are assigned, register the card instance by calling |
|
:c:func:`snd_card_register()`. Access to the device files is |
|
enabled at this point. That is, before |
|
:c:func:`snd_card_register()` is called, the components are safely |
|
inaccessible from external side. If this call fails, exit the probe |
|
function after releasing the card via :c:func:`snd_card_free()`. |
|
|
|
For releasing the card instance, you can call simply |
|
:c:func:`snd_card_free()`. As mentioned earlier, all components |
|
are released automatically by this call. |
|
|
|
For a device which allows hotplugging, you can use |
|
:c:func:`snd_card_free_when_closed()`. This one will postpone |
|
the destruction until all devices are closed. |
|
|
|
PCI Resource Management |
|
======================= |
|
|
|
Full Code Example |
|
----------------- |
|
|
|
In this section, we'll complete the chip-specific constructor, |
|
destructor and PCI entries. Example code is shown first, below. |
|
|
|
:: |
|
|
|
struct mychip { |
|
struct snd_card *card; |
|
struct pci_dev *pci; |
|
|
|
unsigned long port; |
|
int irq; |
|
}; |
|
|
|
static int snd_mychip_free(struct mychip *chip) |
|
{ |
|
/* disable hardware here if any */ |
|
.... /* (not implemented in this document) */ |
|
|
|
/* release the irq */ |
|
if (chip->irq >= 0) |
|
free_irq(chip->irq, chip); |
|
/* release the I/O ports & memory */ |
|
pci_release_regions(chip->pci); |
|
/* disable the PCI entry */ |
|
pci_disable_device(chip->pci); |
|
/* release the data */ |
|
kfree(chip); |
|
return 0; |
|
} |
|
|
|
/* chip-specific constructor */ |
|
static int snd_mychip_create(struct snd_card *card, |
|
struct pci_dev *pci, |
|
struct mychip **rchip) |
|
{ |
|
struct mychip *chip; |
|
int err; |
|
static const struct snd_device_ops ops = { |
|
.dev_free = snd_mychip_dev_free, |
|
}; |
|
|
|
*rchip = NULL; |
|
|
|
/* initialize the PCI entry */ |
|
err = pci_enable_device(pci); |
|
if (err < 0) |
|
return err; |
|
/* check PCI availability (28bit DMA) */ |
|
if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 || |
|
pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) { |
|
printk(KERN_ERR "error to set 28bit mask DMA\n"); |
|
pci_disable_device(pci); |
|
return -ENXIO; |
|
} |
|
|
|
chip = kzalloc(sizeof(*chip), GFP_KERNEL); |
|
if (chip == NULL) { |
|
pci_disable_device(pci); |
|
return -ENOMEM; |
|
} |
|
|
|
/* initialize the stuff */ |
|
chip->card = card; |
|
chip->pci = pci; |
|
chip->irq = -1; |
|
|
|
/* (1) PCI resource allocation */ |
|
err = pci_request_regions(pci, "My Chip"); |
|
if (err < 0) { |
|
kfree(chip); |
|
pci_disable_device(pci); |
|
return err; |
|
} |
|
chip->port = pci_resource_start(pci, 0); |
|
if (request_irq(pci->irq, snd_mychip_interrupt, |
|
IRQF_SHARED, KBUILD_MODNAME, chip)) { |
|
printk(KERN_ERR "cannot grab irq %d\n", pci->irq); |
|
snd_mychip_free(chip); |
|
return -EBUSY; |
|
} |
|
chip->irq = pci->irq; |
|
card->sync_irq = chip->irq; |
|
|
|
/* (2) initialization of the chip hardware */ |
|
.... /* (not implemented in this document) */ |
|
|
|
err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); |
|
if (err < 0) { |
|
snd_mychip_free(chip); |
|
return err; |
|
} |
|
|
|
*rchip = chip; |
|
return 0; |
|
} |
|
|
|
/* PCI IDs */ |
|
static struct pci_device_id snd_mychip_ids[] = { |
|
{ PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, |
|
PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, }, |
|
.... |
|
{ 0, } |
|
}; |
|
MODULE_DEVICE_TABLE(pci, snd_mychip_ids); |
|
|
|
/* pci_driver definition */ |
|
static struct pci_driver driver = { |
|
.name = KBUILD_MODNAME, |
|
.id_table = snd_mychip_ids, |
|
.probe = snd_mychip_probe, |
|
.remove = snd_mychip_remove, |
|
}; |
|
|
|
/* module initialization */ |
|
static int __init alsa_card_mychip_init(void) |
|
{ |
|
return pci_register_driver(&driver); |
|
} |
|
|
|
/* module clean up */ |
|
static void __exit alsa_card_mychip_exit(void) |
|
{ |
|
pci_unregister_driver(&driver); |
|
} |
|
|
|
module_init(alsa_card_mychip_init) |
|
module_exit(alsa_card_mychip_exit) |
|
|
|
EXPORT_NO_SYMBOLS; /* for old kernels only */ |
|
|
|
Some Hafta's |
|
------------ |
|
|
|
The allocation of PCI resources is done in the ``probe`` function, and |
|
usually an extra :c:func:`xxx_create()` function is written for this |
|
purpose. |
|
|
|
In the case of PCI devices, you first have to call the |
|
:c:func:`pci_enable_device()` function before allocating |
|
resources. Also, you need to set the proper PCI DMA mask to limit the |
|
accessed I/O range. In some cases, you might need to call |
|
:c:func:`pci_set_master()` function, too. |
|
|
|
Suppose the 28bit mask, and the code to be added would be like: |
|
|
|
:: |
|
|
|
err = pci_enable_device(pci); |
|
if (err < 0) |
|
return err; |
|
if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 || |
|
pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) { |
|
printk(KERN_ERR "error to set 28bit mask DMA\n"); |
|
pci_disable_device(pci); |
|
return -ENXIO; |
|
} |
|
|
|
|
|
Resource Allocation |
|
------------------- |
|
|
|
The allocation of I/O ports and irqs is done via standard kernel |
|
functions. These resources must be released in the destructor |
|
function (see below). |
|
|
|
Now assume that the PCI device has an I/O port with 8 bytes and an |
|
interrupt. Then struct mychip will have the |
|
following fields: |
|
|
|
:: |
|
|
|
struct mychip { |
|
struct snd_card *card; |
|
|
|
unsigned long port; |
|
int irq; |
|
}; |
|
|
|
|
|
For an I/O port (and also a memory region), you need to have the |
|
resource pointer for the standard resource management. For an irq, you |
|
have to keep only the irq number (integer). But you need to initialize |
|
this number as -1 before actual allocation, since irq 0 is valid. The |
|
port address and its resource pointer can be initialized as null by |
|
:c:func:`kzalloc()` automatically, so you don't have to take care of |
|
resetting them. |
|
|
|
The allocation of an I/O port is done like this: |
|
|
|
:: |
|
|
|
err = pci_request_regions(pci, "My Chip"); |
|
if (err < 0) { |
|
kfree(chip); |
|
pci_disable_device(pci); |
|
return err; |
|
} |
|
chip->port = pci_resource_start(pci, 0); |
|
|
|
It will reserve the I/O port region of 8 bytes of the given PCI device. |
|
The returned value, ``chip->res_port``, is allocated via |
|
:c:func:`kmalloc()` by :c:func:`request_region()`. The pointer |
|
must be released via :c:func:`kfree()`, but there is a problem with |
|
this. This issue will be explained later. |
|
|
|
The allocation of an interrupt source is done like this: |
|
|
|
:: |
|
|
|
if (request_irq(pci->irq, snd_mychip_interrupt, |
|
IRQF_SHARED, KBUILD_MODNAME, chip)) { |
|
printk(KERN_ERR "cannot grab irq %d\n", pci->irq); |
|
snd_mychip_free(chip); |
|
return -EBUSY; |
|
} |
|
chip->irq = pci->irq; |
|
|
|
where :c:func:`snd_mychip_interrupt()` is the interrupt handler |
|
defined `later <PCM Interrupt Handler_>`__. Note that |
|
``chip->irq`` should be defined only when :c:func:`request_irq()` |
|
succeeded. |
|
|
|
On the PCI bus, interrupts can be shared. Thus, ``IRQF_SHARED`` is used |
|
as the interrupt flag of :c:func:`request_irq()`. |
|
|
|
The last argument of :c:func:`request_irq()` is the data pointer |
|
passed to the interrupt handler. Usually, the chip-specific record is |
|
used for that, but you can use what you like, too. |
|
|
|
I won't give details about the interrupt handler at this point, but at |
|
least its appearance can be explained now. The interrupt handler looks |
|
usually like the following: |
|
|
|
:: |
|
|
|
static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) |
|
{ |
|
struct mychip *chip = dev_id; |
|
.... |
|
return IRQ_HANDLED; |
|
} |
|
|
|
After requesting the IRQ, you can passed it to ``card->sync_irq`` |
|
field: |
|
:: |
|
|
|
card->irq = chip->irq; |
|
|
|
This allows PCM core automatically performing |
|
:c:func:`synchronize_irq()` at the necessary timing like ``hw_free``. |
|
See the later section `sync_stop callback`_ for details. |
|
|
|
Now let's write the corresponding destructor for the resources above. |
|
The role of destructor is simple: disable the hardware (if already |
|
activated) and release the resources. So far, we have no hardware part, |
|
so the disabling code is not written here. |
|
|
|
To release the resources, the “check-and-release” method is a safer way. |
|
For the interrupt, do like this: |
|
|
|
:: |
|
|
|
if (chip->irq >= 0) |
|
free_irq(chip->irq, chip); |
|
|
|
Since the irq number can start from 0, you should initialize |
|
``chip->irq`` with a negative value (e.g. -1), so that you can check |
|
the validity of the irq number as above. |
|
|
|
When you requested I/O ports or memory regions via |
|
:c:func:`pci_request_region()` or |
|
:c:func:`pci_request_regions()` like in this example, release the |
|
resource(s) using the corresponding function, |
|
:c:func:`pci_release_region()` or |
|
:c:func:`pci_release_regions()`. |
|
|
|
:: |
|
|
|
pci_release_regions(chip->pci); |
|
|
|
When you requested manually via :c:func:`request_region()` or |
|
:c:func:`request_mem_region()`, you can release it via |
|
:c:func:`release_resource()`. Suppose that you keep the resource |
|
pointer returned from :c:func:`request_region()` in |
|
chip->res_port, the release procedure looks like: |
|
|
|
:: |
|
|
|
release_and_free_resource(chip->res_port); |
|
|
|
Don't forget to call :c:func:`pci_disable_device()` before the |
|
end. |
|
|
|
And finally, release the chip-specific record. |
|
|
|
:: |
|
|
|
kfree(chip); |
|
|
|
We didn't implement the hardware disabling part in the above. If you |
|
need to do this, please note that the destructor may be called even |
|
before the initialization of the chip is completed. It would be better |
|
to have a flag to skip hardware disabling if the hardware was not |
|
initialized yet. |
|
|
|
When the chip-data is assigned to the card using |
|
:c:func:`snd_device_new()` with ``SNDRV_DEV_LOWLELVEL`` , its |
|
destructor is called at the last. That is, it is assured that all other |
|
components like PCMs and controls have already been released. You don't |
|
have to stop PCMs, etc. explicitly, but just call low-level hardware |
|
stopping. |
|
|
|
The management of a memory-mapped region is almost as same as the |
|
management of an I/O port. You'll need three fields like the |
|
following: |
|
|
|
:: |
|
|
|
struct mychip { |
|
.... |
|
unsigned long iobase_phys; |
|
void __iomem *iobase_virt; |
|
}; |
|
|
|
and the allocation would be like below: |
|
|
|
:: |
|
|
|
err = pci_request_regions(pci, "My Chip"); |
|
if (err < 0) { |
|
kfree(chip); |
|
return err; |
|
} |
|
chip->iobase_phys = pci_resource_start(pci, 0); |
|
chip->iobase_virt = ioremap(chip->iobase_phys, |
|
pci_resource_len(pci, 0)); |
|
|
|
and the corresponding destructor would be: |
|
|
|
:: |
|
|
|
static int snd_mychip_free(struct mychip *chip) |
|
{ |
|
.... |
|
if (chip->iobase_virt) |
|
iounmap(chip->iobase_virt); |
|
.... |
|
pci_release_regions(chip->pci); |
|
.... |
|
} |
|
|
|
Of course, a modern way with :c:func:`pci_iomap()` will make things a |
|
bit easier, too. |
|
|
|
:: |
|
|
|
err = pci_request_regions(pci, "My Chip"); |
|
if (err < 0) { |
|
kfree(chip); |
|
return err; |
|
} |
|
chip->iobase_virt = pci_iomap(pci, 0, 0); |
|
|
|
which is paired with :c:func:`pci_iounmap()` at destructor. |
|
|
|
|
|
PCI Entries |
|
----------- |
|
|
|
So far, so good. Let's finish the missing PCI stuff. At first, we need a |
|
struct pci_device_id table for |
|
this chipset. It's a table of PCI vendor/device ID number, and some |
|
masks. |
|
|
|
For example, |
|
|
|
:: |
|
|
|
static struct pci_device_id snd_mychip_ids[] = { |
|
{ PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, |
|
PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, }, |
|
.... |
|
{ 0, } |
|
}; |
|
MODULE_DEVICE_TABLE(pci, snd_mychip_ids); |
|
|
|
The first and second fields of the struct pci_device_id are the vendor |
|
and device IDs. If you have no reason to filter the matching devices, you can |
|
leave the remaining fields as above. The last field of the |
|
struct pci_device_id contains private data for this entry. You can specify |
|
any value here, for example, to define specific operations for supported |
|
device IDs. Such an example is found in the intel8x0 driver. |
|
|
|
The last entry of this list is the terminator. You must specify this |
|
all-zero entry. |
|
|
|
Then, prepare the struct pci_driver |
|
record: |
|
|
|
:: |
|
|
|
static struct pci_driver driver = { |
|
.name = KBUILD_MODNAME, |
|
.id_table = snd_mychip_ids, |
|
.probe = snd_mychip_probe, |
|
.remove = snd_mychip_remove, |
|
}; |
|
|
|
The ``probe`` and ``remove`` functions have already been defined in |
|
the previous sections. The ``name`` field is the name string of this |
|
device. Note that you must not use a slash “/” in this string. |
|
|
|
And at last, the module entries: |
|
|
|
:: |
|
|
|
static int __init alsa_card_mychip_init(void) |
|
{ |
|
return pci_register_driver(&driver); |
|
} |
|
|
|
static void __exit alsa_card_mychip_exit(void) |
|
{ |
|
pci_unregister_driver(&driver); |
|
} |
|
|
|
module_init(alsa_card_mychip_init) |
|
module_exit(alsa_card_mychip_exit) |
|
|
|
Note that these module entries are tagged with ``__init`` and ``__exit`` |
|
prefixes. |
|
|
|
That's all! |
|
|
|
PCM Interface |
|
============= |
|
|
|
General |
|
------- |
|
|
|
The PCM middle layer of ALSA is quite powerful and it is only necessary |
|
for each driver to implement the low-level functions to access its |
|
hardware. |
|
|
|
For accessing to the PCM layer, you need to include ``<sound/pcm.h>`` |
|
first. In addition, ``<sound/pcm_params.h>`` might be needed if you |
|
access to some functions related with hw_param. |
|
|
|
Each card device can have up to four pcm instances. A pcm instance |
|
corresponds to a pcm device file. The limitation of number of instances |
|
comes only from the available bit size of the Linux's device numbers. |
|
Once when 64bit device number is used, we'll have more pcm instances |
|
available. |
|
|
|
A pcm instance consists of pcm playback and capture streams, and each |
|
pcm stream consists of one or more pcm substreams. Some soundcards |
|
support multiple playback functions. For example, emu10k1 has a PCM |
|
playback of 32 stereo substreams. In this case, at each open, a free |
|
substream is (usually) automatically chosen and opened. Meanwhile, when |
|
only one substream exists and it was already opened, the successful open |
|
will either block or error with ``EAGAIN`` according to the file open |
|
mode. But you don't have to care about such details in your driver. The |
|
PCM middle layer will take care of such work. |
|
|
|
Full Code Example |
|
----------------- |
|
|
|
The example code below does not include any hardware access routines but |
|
shows only the skeleton, how to build up the PCM interfaces. |
|
|
|
:: |
|
|
|
#include <sound/pcm.h> |
|
.... |
|
|
|
/* hardware definition */ |
|
static struct snd_pcm_hardware snd_mychip_playback_hw = { |
|
.info = (SNDRV_PCM_INFO_MMAP | |
|
SNDRV_PCM_INFO_INTERLEAVED | |
|
SNDRV_PCM_INFO_BLOCK_TRANSFER | |
|
SNDRV_PCM_INFO_MMAP_VALID), |
|
.formats = SNDRV_PCM_FMTBIT_S16_LE, |
|
.rates = SNDRV_PCM_RATE_8000_48000, |
|
.rate_min = 8000, |
|
.rate_max = 48000, |
|
.channels_min = 2, |
|
.channels_max = 2, |
|
.buffer_bytes_max = 32768, |
|
.period_bytes_min = 4096, |
|
.period_bytes_max = 32768, |
|
.periods_min = 1, |
|
.periods_max = 1024, |
|
}; |
|
|
|
/* hardware definition */ |
|
static struct snd_pcm_hardware snd_mychip_capture_hw = { |
|
.info = (SNDRV_PCM_INFO_MMAP | |
|
SNDRV_PCM_INFO_INTERLEAVED | |
|
SNDRV_PCM_INFO_BLOCK_TRANSFER | |
|
SNDRV_PCM_INFO_MMAP_VALID), |
|
.formats = SNDRV_PCM_FMTBIT_S16_LE, |
|
.rates = SNDRV_PCM_RATE_8000_48000, |
|
.rate_min = 8000, |
|
.rate_max = 48000, |
|
.channels_min = 2, |
|
.channels_max = 2, |
|
.buffer_bytes_max = 32768, |
|
.period_bytes_min = 4096, |
|
.period_bytes_max = 32768, |
|
.periods_min = 1, |
|
.periods_max = 1024, |
|
}; |
|
|
|
/* open callback */ |
|
static int snd_mychip_playback_open(struct snd_pcm_substream *substream) |
|
{ |
|
struct mychip *chip = snd_pcm_substream_chip(substream); |
|
struct snd_pcm_runtime *runtime = substream->runtime; |
|
|
|
runtime->hw = snd_mychip_playback_hw; |
|
/* more hardware-initialization will be done here */ |
|
.... |
|
return 0; |
|
} |
|
|
|
/* close callback */ |
|
static int snd_mychip_playback_close(struct snd_pcm_substream *substream) |
|
{ |
|
struct mychip *chip = snd_pcm_substream_chip(substream); |
|
/* the hardware-specific codes will be here */ |
|
.... |
|
return 0; |
|
|
|
} |
|
|
|
/* open callback */ |
|
static int snd_mychip_capture_open(struct snd_pcm_substream *substream) |
|
{ |
|
struct mychip *chip = snd_pcm_substream_chip(substream); |
|
struct snd_pcm_runtime *runtime = substream->runtime; |
|
|
|
runtime->hw = snd_mychip_capture_hw; |
|
/* more hardware-initialization will be done here */ |
|
.... |
|
return 0; |
|
} |
|
|
|
/* close callback */ |
|
static int snd_mychip_capture_close(struct snd_pcm_substream *substream) |
|
{ |
|
struct mychip *chip = snd_pcm_substream_chip(substream); |
|
/* the hardware-specific codes will be here */ |
|
.... |
|
return 0; |
|
} |
|
|
|
/* hw_params callback */ |
|
static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream, |
|
struct snd_pcm_hw_params *hw_params) |
|
{ |
|
/* the hardware-specific codes will be here */ |
|
.... |
|
return 0; |
|
} |
|
|
|
/* hw_free callback */ |
|
static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream) |
|
{ |
|
/* the hardware-specific codes will be here */ |
|
.... |
|
return 0; |
|
} |
|
|
|
/* prepare callback */ |
|
static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream) |
|
{ |
|
struct mychip *chip = snd_pcm_substream_chip(substream); |
|
struct snd_pcm_runtime *runtime = substream->runtime; |
|
|
|
/* set up the hardware with the current configuration |
|
* for example... |
|
*/ |
|
mychip_set_sample_format(chip, runtime->format); |
|
mychip_set_sample_rate(chip, runtime->rate); |
|
mychip_set_channels(chip, runtime->channels); |
|
mychip_set_dma_setup(chip, runtime->dma_addr, |
|
chip->buffer_size, |
|
chip->period_size); |
|
return 0; |
|
} |
|
|
|
/* trigger callback */ |
|
static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream, |
|
int cmd) |
|
{ |
|
switch (cmd) { |
|
case SNDRV_PCM_TRIGGER_START: |
|
/* do something to start the PCM engine */ |
|
.... |
|
break; |
|
case SNDRV_PCM_TRIGGER_STOP: |
|
/* do something to stop the PCM engine */ |
|
.... |
|
break; |
|
default: |
|
return -EINVAL; |
|
} |
|
} |
|
|
|
/* pointer callback */ |
|
static snd_pcm_uframes_t |
|
snd_mychip_pcm_pointer(struct snd_pcm_substream *substream) |
|
{ |
|
struct mychip *chip = snd_pcm_substream_chip(substream); |
|
unsigned int current_ptr; |
|
|
|
/* get the current hardware pointer */ |
|
current_ptr = mychip_get_hw_pointer(chip); |
|
return current_ptr; |
|
} |
|
|
|
/* operators */ |
|
static struct snd_pcm_ops snd_mychip_playback_ops = { |
|
.open = snd_mychip_playback_open, |
|
.close = snd_mychip_playback_close, |
|
.hw_params = snd_mychip_pcm_hw_params, |
|
.hw_free = snd_mychip_pcm_hw_free, |
|
.prepare = snd_mychip_pcm_prepare, |
|
.trigger = snd_mychip_pcm_trigger, |
|
.pointer = snd_mychip_pcm_pointer, |
|
}; |
|
|
|
/* operators */ |
|
static struct snd_pcm_ops snd_mychip_capture_ops = { |
|
.open = snd_mychip_capture_open, |
|
.close = snd_mychip_capture_close, |
|
.hw_params = snd_mychip_pcm_hw_params, |
|
.hw_free = snd_mychip_pcm_hw_free, |
|
.prepare = snd_mychip_pcm_prepare, |
|
.trigger = snd_mychip_pcm_trigger, |
|
.pointer = snd_mychip_pcm_pointer, |
|
}; |
|
|
|
/* |
|
* definitions of capture are omitted here... |
|
*/ |
|
|
|
/* create a pcm device */ |
|
static int snd_mychip_new_pcm(struct mychip *chip) |
|
{ |
|
struct snd_pcm *pcm; |
|
int err; |
|
|
|
err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm); |
|
if (err < 0) |
|
return err; |
|
pcm->private_data = chip; |
|
strcpy(pcm->name, "My Chip"); |
|
chip->pcm = pcm; |
|
/* set operators */ |
|
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, |
|
&snd_mychip_playback_ops); |
|
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, |
|
&snd_mychip_capture_ops); |
|
/* pre-allocation of buffers */ |
|
/* NOTE: this may fail */ |
|
snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV, |
|
&chip->pci->dev, |
|
64*1024, 64*1024); |
|
return 0; |
|
} |
|
|
|
|
|
PCM Constructor |
|
--------------- |
|
|
|
A pcm instance is allocated by the :c:func:`snd_pcm_new()` |
|
function. It would be better to create a constructor for pcm, namely, |
|
|
|
:: |
|
|
|
static int snd_mychip_new_pcm(struct mychip *chip) |
|
{ |
|
struct snd_pcm *pcm; |
|
int err; |
|
|
|
err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm); |
|
if (err < 0) |
|
return err; |
|
pcm->private_data = chip; |
|
strcpy(pcm->name, "My Chip"); |
|
chip->pcm = pcm; |
|
.... |
|
return 0; |
|
} |
|
|
|
The :c:func:`snd_pcm_new()` function takes four arguments. The |
|
first argument is the card pointer to which this pcm is assigned, and |
|
the second is the ID string. |
|
|
|
The third argument (``index``, 0 in the above) is the index of this new |
|
pcm. It begins from zero. If you create more than one pcm instances, |
|
specify the different numbers in this argument. For example, ``index = |
|
1`` for the second PCM device. |
|
|
|
The fourth and fifth arguments are the number of substreams for playback |
|
and capture, respectively. Here 1 is used for both arguments. When no |
|
playback or capture substreams are available, pass 0 to the |
|
corresponding argument. |
|
|
|
If a chip supports multiple playbacks or captures, you can specify more |
|
numbers, but they must be handled properly in open/close, etc. |
|
callbacks. When you need to know which substream you are referring to, |
|
then it can be obtained from struct snd_pcm_substream data passed to each |
|
callback as follows: |
|
|
|
:: |
|
|
|
struct snd_pcm_substream *substream; |
|
int index = substream->number; |
|
|
|
|
|
After the pcm is created, you need to set operators for each pcm stream. |
|
|
|
:: |
|
|
|
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, |
|
&snd_mychip_playback_ops); |
|
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, |
|
&snd_mychip_capture_ops); |
|
|
|
The operators are defined typically like this: |
|
|
|
:: |
|
|
|
static struct snd_pcm_ops snd_mychip_playback_ops = { |
|
.open = snd_mychip_pcm_open, |
|
.close = snd_mychip_pcm_close, |
|
.hw_params = snd_mychip_pcm_hw_params, |
|
.hw_free = snd_mychip_pcm_hw_free, |
|
.prepare = snd_mychip_pcm_prepare, |
|
.trigger = snd_mychip_pcm_trigger, |
|
.pointer = snd_mychip_pcm_pointer, |
|
}; |
|
|
|
All the callbacks are described in the Operators_ subsection. |
|
|
|
After setting the operators, you probably will want to pre-allocate the |
|
buffer and set up the managed allocation mode. |
|
For that, simply call the following: |
|
|
|
:: |
|
|
|
snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV, |
|
&chip->pci->dev, |
|
64*1024, 64*1024); |
|
|
|
It will allocate a buffer up to 64kB as default. Buffer management |
|
details will be described in the later section `Buffer and Memory |
|
Management`_. |
|
|
|
Additionally, you can set some extra information for this pcm in |
|
``pcm->info_flags``. The available values are defined as |
|
``SNDRV_PCM_INFO_XXX`` in ``<sound/asound.h>``, which is used for the |
|
hardware definition (described later). When your soundchip supports only |
|
half-duplex, specify like this: |
|
|
|
:: |
|
|
|
pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX; |
|
|
|
|
|
... And the Destructor? |
|
----------------------- |
|
|
|
The destructor for a pcm instance is not always necessary. Since the pcm |
|
device will be released by the middle layer code automatically, you |
|
don't have to call the destructor explicitly. |
|
|
|
The destructor would be necessary if you created special records |
|
internally and needed to release them. In such a case, set the |
|
destructor function to ``pcm->private_free``: |
|
|
|
:: |
|
|
|
static void mychip_pcm_free(struct snd_pcm *pcm) |
|
{ |
|
struct mychip *chip = snd_pcm_chip(pcm); |
|
/* free your own data */ |
|
kfree(chip->my_private_pcm_data); |
|
/* do what you like else */ |
|
.... |
|
} |
|
|
|
static int snd_mychip_new_pcm(struct mychip *chip) |
|
{ |
|
struct snd_pcm *pcm; |
|
.... |
|
/* allocate your own data */ |
|
chip->my_private_pcm_data = kmalloc(...); |
|
/* set the destructor */ |
|
pcm->private_data = chip; |
|
pcm->private_free = mychip_pcm_free; |
|
.... |
|
} |
|
|
|
|
|
|
|
Runtime Pointer - The Chest of PCM Information |
|
---------------------------------------------- |
|
|
|
When the PCM substream is opened, a PCM runtime instance is allocated |
|
and assigned to the substream. This pointer is accessible via |
|
``substream->runtime``. This runtime pointer holds most information you |
|
need to control the PCM: the copy of hw_params and sw_params |
|
configurations, the buffer pointers, mmap records, spinlocks, etc. |
|
|
|
The definition of runtime instance is found in ``<sound/pcm.h>``. Here |
|
are the contents of this file: |
|
|
|
:: |
|
|
|
struct _snd_pcm_runtime { |
|
/* -- Status -- */ |
|
struct snd_pcm_substream *trigger_master; |
|
snd_timestamp_t trigger_tstamp; /* trigger timestamp */ |
|
int overrange; |
|
snd_pcm_uframes_t avail_max; |
|
snd_pcm_uframes_t hw_ptr_base; /* Position at buffer restart */ |
|
snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/ |
|
|
|
/* -- HW params -- */ |
|
snd_pcm_access_t access; /* access mode */ |
|
snd_pcm_format_t format; /* SNDRV_PCM_FORMAT_* */ |
|
snd_pcm_subformat_t subformat; /* subformat */ |
|
unsigned int rate; /* rate in Hz */ |
|
unsigned int channels; /* channels */ |
|
snd_pcm_uframes_t period_size; /* period size */ |
|
unsigned int periods; /* periods */ |
|
snd_pcm_uframes_t buffer_size; /* buffer size */ |
|
unsigned int tick_time; /* tick time */ |
|
snd_pcm_uframes_t min_align; /* Min alignment for the format */ |
|
size_t byte_align; |
|
unsigned int frame_bits; |
|
unsigned int sample_bits; |
|
unsigned int info; |
|
unsigned int rate_num; |
|
unsigned int rate_den; |
|
|
|
/* -- SW params -- */ |
|
struct timespec tstamp_mode; /* mmap timestamp is updated */ |
|
unsigned int period_step; |
|
unsigned int sleep_min; /* min ticks to sleep */ |
|
snd_pcm_uframes_t start_threshold; |
|
snd_pcm_uframes_t stop_threshold; |
|
snd_pcm_uframes_t silence_threshold; /* Silence filling happens when |
|
noise is nearest than this */ |
|
snd_pcm_uframes_t silence_size; /* Silence filling size */ |
|
snd_pcm_uframes_t boundary; /* pointers wrap point */ |
|
|
|
snd_pcm_uframes_t silenced_start; |
|
snd_pcm_uframes_t silenced_size; |
|
|
|
snd_pcm_sync_id_t sync; /* hardware synchronization ID */ |
|
|
|
/* -- mmap -- */ |
|
volatile struct snd_pcm_mmap_status *status; |
|
volatile struct snd_pcm_mmap_control *control; |
|
atomic_t mmap_count; |
|
|
|
/* -- locking / scheduling -- */ |
|
spinlock_t lock; |
|
wait_queue_head_t sleep; |
|
struct timer_list tick_timer; |
|
struct fasync_struct *fasync; |
|
|
|
/* -- private section -- */ |
|
void *private_data; |
|
void (*private_free)(struct snd_pcm_runtime *runtime); |
|
|
|
/* -- hardware description -- */ |
|
struct snd_pcm_hardware hw; |
|
struct snd_pcm_hw_constraints hw_constraints; |
|
|
|
/* -- timer -- */ |
|
unsigned int timer_resolution; /* timer resolution */ |
|
|
|
/* -- DMA -- */ |
|
unsigned char *dma_area; /* DMA area */ |
|
dma_addr_t dma_addr; /* physical bus address (not accessible from main CPU) */ |
|
size_t dma_bytes; /* size of DMA area */ |
|
|
|
struct snd_dma_buffer *dma_buffer_p; /* allocated buffer */ |
|
|
|
#if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE) |
|
/* -- OSS things -- */ |
|
struct snd_pcm_oss_runtime oss; |
|
#endif |
|
}; |
|
|
|
|
|
For the operators (callbacks) of each sound driver, most of these |
|
records are supposed to be read-only. Only the PCM middle-layer changes |
|
/ updates them. The exceptions are the hardware description (hw) DMA |
|
buffer information and the private data. Besides, if you use the |
|
standard managed buffer allocation mode, you don't need to set the |
|
DMA buffer information by yourself. |
|
|
|
In the sections below, important records are explained. |
|
|
|
Hardware Description |
|
~~~~~~~~~~~~~~~~~~~~ |
|
|
|
The hardware descriptor (struct snd_pcm_hardware) contains the definitions of |
|
the fundamental hardware configuration. Above all, you'll need to define this |
|
in the `PCM open callback`_. Note that the runtime instance holds the copy of |
|
the descriptor, not the pointer to the existing descriptor. That is, |
|
in the open callback, you can modify the copied descriptor |
|
(``runtime->hw``) as you need. For example, if the maximum number of |
|
channels is 1 only on some chip models, you can still use the same |
|
hardware descriptor and change the channels_max later: |
|
|
|
:: |
|
|
|
struct snd_pcm_runtime *runtime = substream->runtime; |
|
... |
|
runtime->hw = snd_mychip_playback_hw; /* common definition */ |
|
if (chip->model == VERY_OLD_ONE) |
|
runtime->hw.channels_max = 1; |
|
|
|
Typically, you'll have a hardware descriptor as below: |
|
|
|
:: |
|
|
|
static struct snd_pcm_hardware snd_mychip_playback_hw = { |
|
.info = (SNDRV_PCM_INFO_MMAP | |
|
SNDRV_PCM_INFO_INTERLEAVED | |
|
SNDRV_PCM_INFO_BLOCK_TRANSFER | |
|
SNDRV_PCM_INFO_MMAP_VALID), |
|
.formats = SNDRV_PCM_FMTBIT_S16_LE, |
|
.rates = SNDRV_PCM_RATE_8000_48000, |
|
.rate_min = 8000, |
|
.rate_max = 48000, |
|
.channels_min = 2, |
|
.channels_max = 2, |
|
.buffer_bytes_max = 32768, |
|
.period_bytes_min = 4096, |
|
.period_bytes_max = 32768, |
|
.periods_min = 1, |
|
.periods_max = 1024, |
|
}; |
|
|
|
- The ``info`` field contains the type and capabilities of this |
|
pcm. The bit flags are defined in ``<sound/asound.h>`` as |
|
``SNDRV_PCM_INFO_XXX``. Here, at least, you have to specify whether |
|
the mmap is supported and which interleaved format is |
|
supported. When the hardware supports mmap, add the |
|
``SNDRV_PCM_INFO_MMAP`` flag here. When the hardware supports the |
|
interleaved or the non-interleaved formats, |
|
``SNDRV_PCM_INFO_INTERLEAVED`` or ``SNDRV_PCM_INFO_NONINTERLEAVED`` |
|
flag must be set, respectively. If both are supported, you can set |
|
both, too. |
|
|
|
In the above example, ``MMAP_VALID`` and ``BLOCK_TRANSFER`` are |
|
specified for the OSS mmap mode. Usually both are set. Of course, |
|
``MMAP_VALID`` is set only if the mmap is really supported. |
|
|
|
The other possible flags are ``SNDRV_PCM_INFO_PAUSE`` and |
|
``SNDRV_PCM_INFO_RESUME``. The ``PAUSE`` bit means that the pcm |
|
supports the “pause” operation, while the ``RESUME`` bit means that |
|
the pcm supports the full “suspend/resume” operation. If the |
|
``PAUSE`` flag is set, the ``trigger`` callback below must handle |
|
the corresponding (pause push/release) commands. The suspend/resume |
|
trigger commands can be defined even without the ``RESUME`` |
|
flag. See `Power Management`_ section for details. |
|
|
|
When the PCM substreams can be synchronized (typically, |
|
synchronized start/stop of a playback and a capture streams), you |
|
can give ``SNDRV_PCM_INFO_SYNC_START``, too. In this case, you'll |
|
need to check the linked-list of PCM substreams in the trigger |
|
callback. This will be described in the later section. |
|
|
|
- ``formats`` field contains the bit-flags of supported formats |
|
(``SNDRV_PCM_FMTBIT_XXX``). If the hardware supports more than one |
|
format, give all or'ed bits. In the example above, the signed 16bit |
|
little-endian format is specified. |
|
|
|
- ``rates`` field contains the bit-flags of supported rates |
|
(``SNDRV_PCM_RATE_XXX``). When the chip supports continuous rates, |
|
pass ``CONTINUOUS`` bit additionally. The pre-defined rate bits are |
|
provided only for typical rates. If your chip supports |
|
unconventional rates, you need to add the ``KNOT`` bit and set up |
|
the hardware constraint manually (explained later). |
|
|
|
- ``rate_min`` and ``rate_max`` define the minimum and maximum sample |
|
rate. This should correspond somehow to ``rates`` bits. |
|
|
|
- ``channel_min`` and ``channel_max`` define, as you might already |
|
expected, the minimum and maximum number of channels. |
|
|
|
- ``buffer_bytes_max`` defines the maximum buffer size in |
|
bytes. There is no ``buffer_bytes_min`` field, since it can be |
|
calculated from the minimum period size and the minimum number of |
|
periods. Meanwhile, ``period_bytes_min`` and define the minimum and |
|
maximum size of the period in bytes. ``periods_max`` and |
|
``periods_min`` define the maximum and minimum number of periods in |
|
the buffer. |
|
|
|
The “period” is a term that corresponds to a fragment in the OSS |
|
world. The period defines the size at which a PCM interrupt is |
|
generated. This size strongly depends on the hardware. Generally, |
|
the smaller period size will give you more interrupts, that is, |
|
more controls. In the case of capture, this size defines the input |
|
latency. On the other hand, the whole buffer size defines the |
|
output latency for the playback direction. |
|
|
|
- There is also a field ``fifo_size``. This specifies the size of the |
|
hardware FIFO, but currently it is neither used in the driver nor |
|
in the alsa-lib. So, you can ignore this field. |
|
|
|
PCM Configurations |
|
~~~~~~~~~~~~~~~~~~ |
|
|
|
Ok, let's go back again to the PCM runtime records. The most |
|
frequently referred records in the runtime instance are the PCM |
|
configurations. The PCM configurations are stored in the runtime |
|
instance after the application sends ``hw_params`` data via |
|
alsa-lib. There are many fields copied from hw_params and sw_params |
|
structs. For example, ``format`` holds the format type chosen by the |
|
application. This field contains the enum value |
|
``SNDRV_PCM_FORMAT_XXX``. |
|
|
|
One thing to be noted is that the configured buffer and period sizes |
|
are stored in “frames” in the runtime. In the ALSA world, ``1 frame = |
|
channels \* samples-size``. For conversion between frames and bytes, |
|
you can use the :c:func:`frames_to_bytes()` and |
|
:c:func:`bytes_to_frames()` helper functions. |
|
|
|
:: |
|
|
|
period_bytes = frames_to_bytes(runtime, runtime->period_size); |
|
|
|
Also, many software parameters (sw_params) are stored in frames, too. |
|
Please check the type of the field. ``snd_pcm_uframes_t`` is for the |
|
frames as unsigned integer while ``snd_pcm_sframes_t`` is for the |
|
frames as signed integer. |
|
|
|
DMA Buffer Information |
|
~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
The DMA buffer is defined by the following four fields, ``dma_area``, |
|
``dma_addr``, ``dma_bytes`` and ``dma_private``. The ``dma_area`` |
|
holds the buffer pointer (the logical address). You can call |
|
:c:func:`memcpy()` from/to this pointer. Meanwhile, ``dma_addr`` holds |
|
the physical address of the buffer. This field is specified only when |
|
the buffer is a linear buffer. ``dma_bytes`` holds the size of buffer |
|
in bytes. ``dma_private`` is used for the ALSA DMA allocator. |
|
|
|
If you use either the managed buffer allocation mode or the standard |
|
API function :c:func:`snd_pcm_lib_malloc_pages()` for allocating the buffer, |
|
these fields are set by the ALSA middle layer, and you should *not* |
|
change them by yourself. You can read them but not write them. On the |
|
other hand, if you want to allocate the buffer by yourself, you'll |
|
need to manage it in hw_params callback. At least, ``dma_bytes`` is |
|
mandatory. ``dma_area`` is necessary when the buffer is mmapped. If |
|
your driver doesn't support mmap, this field is not |
|
necessary. ``dma_addr`` is also optional. You can use dma_private as |
|
you like, too. |
|
|
|
Running Status |
|
~~~~~~~~~~~~~~ |
|
|
|
The running status can be referred via ``runtime->status``. This is |
|
the pointer to the struct snd_pcm_mmap_status record. |
|
For example, you can get the current |
|
DMA hardware pointer via ``runtime->status->hw_ptr``. |
|
|
|
The DMA application pointer can be referred via ``runtime->control``, |
|
which points to the struct snd_pcm_mmap_control record. |
|
However, accessing directly to this value is not recommended. |
|
|
|
Private Data |
|
~~~~~~~~~~~~ |
|
|
|
You can allocate a record for the substream and store it in |
|
``runtime->private_data``. Usually, this is done in the `PCM open |
|
callback`_. Don't mix this with ``pcm->private_data``. The |
|
``pcm->private_data`` usually points to the chip instance assigned |
|
statically at the creation of PCM, while the ``runtime->private_data`` |
|
points to a dynamic data structure created at the PCM open |
|
callback. |
|
|
|
:: |
|
|
|
static int snd_xxx_open(struct snd_pcm_substream *substream) |
|
{ |
|
struct my_pcm_data *data; |
|
.... |
|
data = kmalloc(sizeof(*data), GFP_KERNEL); |
|
substream->runtime->private_data = data; |
|
.... |
|
} |
|
|
|
|
|
The allocated object must be released in the `close callback`_. |
|
|
|
Operators |
|
--------- |
|
|
|
OK, now let me give details about each pcm callback (``ops``). In |
|
general, every callback must return 0 if successful, or a negative |
|
error number such as ``-EINVAL``. To choose an appropriate error |
|
number, it is advised to check what value other parts of the kernel |
|
return when the same kind of request fails. |
|
|
|
The callback function takes at least the argument with |
|
struct snd_pcm_substream pointer. To retrieve the chip |
|
record from the given substream instance, you can use the following |
|
macro. |
|
|
|
:: |
|
|
|
int xxx() { |
|
struct mychip *chip = snd_pcm_substream_chip(substream); |
|
.... |
|
} |
|
|
|
The macro reads ``substream->private_data``, which is a copy of |
|
``pcm->private_data``. You can override the former if you need to |
|
assign different data records per PCM substream. For example, the |
|
cmi8330 driver assigns different ``private_data`` for playback and |
|
capture directions, because it uses two different codecs (SB- and |
|
AD-compatible) for different directions. |
|
|
|
PCM open callback |
|
~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static int snd_xxx_open(struct snd_pcm_substream *substream); |
|
|
|
This is called when a pcm substream is opened. |
|
|
|
At least, here you have to initialize the ``runtime->hw`` |
|
record. Typically, this is done by like this: |
|
|
|
:: |
|
|
|
static int snd_xxx_open(struct snd_pcm_substream *substream) |
|
{ |
|
struct mychip *chip = snd_pcm_substream_chip(substream); |
|
struct snd_pcm_runtime *runtime = substream->runtime; |
|
|
|
runtime->hw = snd_mychip_playback_hw; |
|
return 0; |
|
} |
|
|
|
where ``snd_mychip_playback_hw`` is the pre-defined hardware |
|
description. |
|
|
|
You can allocate a private data in this callback, as described in |
|
`Private Data`_ section. |
|
|
|
If the hardware configuration needs more constraints, set the hardware |
|
constraints here, too. See Constraints_ for more details. |
|
|
|
close callback |
|
~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static int snd_xxx_close(struct snd_pcm_substream *substream); |
|
|
|
|
|
Obviously, this is called when a pcm substream is closed. |
|
|
|
Any private instance for a pcm substream allocated in the ``open`` |
|
callback will be released here. |
|
|
|
:: |
|
|
|
static int snd_xxx_close(struct snd_pcm_substream *substream) |
|
{ |
|
.... |
|
kfree(substream->runtime->private_data); |
|
.... |
|
} |
|
|
|
ioctl callback |
|
~~~~~~~~~~~~~~ |
|
|
|
This is used for any special call to pcm ioctls. But usually you can |
|
leave it as NULL, then PCM core calls the generic ioctl callback |
|
function :c:func:`snd_pcm_lib_ioctl()`. If you need to deal with the |
|
unique setup of channel info or reset procedure, you can pass your own |
|
callback function here. |
|
|
|
hw_params callback |
|
~~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static int snd_xxx_hw_params(struct snd_pcm_substream *substream, |
|
struct snd_pcm_hw_params *hw_params); |
|
|
|
This is called when the hardware parameter (``hw_params``) is set up |
|
by the application, that is, once when the buffer size, the period |
|
size, the format, etc. are defined for the pcm substream. |
|
|
|
Many hardware setups should be done in this callback, including the |
|
allocation of buffers. |
|
|
|
Parameters to be initialized are retrieved by |
|
:c:func:`params_xxx()` macros. |
|
|
|
When you set up the managed buffer allocation mode for the substream, |
|
a buffer is already allocated before this callback gets |
|
called. Alternatively, you can call a helper function below for |
|
allocating the buffer, too. |
|
|
|
:: |
|
|
|
snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(hw_params)); |
|
|
|
:c:func:`snd_pcm_lib_malloc_pages()` is available only when the |
|
DMA buffers have been pre-allocated. See the section `Buffer Types`_ |
|
for more details. |
|
|
|
Note that this and ``prepare`` callbacks may be called multiple times |
|
per initialization. For example, the OSS emulation may call these |
|
callbacks at each change via its ioctl. |
|
|
|
Thus, you need to be careful not to allocate the same buffers many |
|
times, which will lead to memory leaks! Calling the helper function |
|
above many times is OK. It will release the previous buffer |
|
automatically when it was already allocated. |
|
|
|
Another note is that this callback is non-atomic (schedulable) as |
|
default, i.e. when no ``nonatomic`` flag set. This is important, |
|
because the ``trigger`` callback is atomic (non-schedulable). That is, |
|
mutexes or any schedule-related functions are not available in |
|
``trigger`` callback. Please see the subsection Atomicity_ for |
|
details. |
|
|
|
hw_free callback |
|
~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static int snd_xxx_hw_free(struct snd_pcm_substream *substream); |
|
|
|
This is called to release the resources allocated via |
|
``hw_params``. |
|
|
|
This function is always called before the close callback is called. |
|
Also, the callback may be called multiple times, too. Keep track |
|
whether the resource was already released. |
|
|
|
When you have set up the managed buffer allocation mode for the PCM |
|
substream, the allocated PCM buffer will be automatically released |
|
after this callback gets called. Otherwise you'll have to release the |
|
buffer manually. Typically, when the buffer was allocated from the |
|
pre-allocated pool, you can use the standard API function |
|
:c:func:`snd_pcm_lib_malloc_pages()` like: |
|
|
|
:: |
|
|
|
snd_pcm_lib_free_pages(substream); |
|
|
|
prepare callback |
|
~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static int snd_xxx_prepare(struct snd_pcm_substream *substream); |
|
|
|
This callback is called when the pcm is “prepared”. You can set the |
|
format type, sample rate, etc. here. The difference from ``hw_params`` |
|
is that the ``prepare`` callback will be called each time |
|
:c:func:`snd_pcm_prepare()` is called, i.e. when recovering after |
|
underruns, etc. |
|
|
|
Note that this callback is now non-atomic. You can use |
|
schedule-related functions safely in this callback. |
|
|
|
In this and the following callbacks, you can refer to the values via |
|
the runtime record, ``substream->runtime``. For example, to get the |
|
current rate, format or channels, access to ``runtime->rate``, |
|
``runtime->format`` or ``runtime->channels``, respectively. The |
|
physical address of the allocated buffer is set to |
|
``runtime->dma_area``. The buffer and period sizes are in |
|
``runtime->buffer_size`` and ``runtime->period_size``, respectively. |
|
|
|
Be careful that this callback will be called many times at each setup, |
|
too. |
|
|
|
trigger callback |
|
~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static int snd_xxx_trigger(struct snd_pcm_substream *substream, int cmd); |
|
|
|
This is called when the pcm is started, stopped or paused. |
|
|
|
Which action is specified in the second argument, |
|
``SNDRV_PCM_TRIGGER_XXX`` in ``<sound/pcm.h>``. At least, the ``START`` |
|
and ``STOP`` commands must be defined in this callback. |
|
|
|
:: |
|
|
|
switch (cmd) { |
|
case SNDRV_PCM_TRIGGER_START: |
|
/* do something to start the PCM engine */ |
|
break; |
|
case SNDRV_PCM_TRIGGER_STOP: |
|
/* do something to stop the PCM engine */ |
|
break; |
|
default: |
|
return -EINVAL; |
|
} |
|
|
|
When the pcm supports the pause operation (given in the info field of |
|
the hardware table), the ``PAUSE_PUSH`` and ``PAUSE_RELEASE`` commands |
|
must be handled here, too. The former is the command to pause the pcm, |
|
and the latter to restart the pcm again. |
|
|
|
When the pcm supports the suspend/resume operation, regardless of full |
|
or partial suspend/resume support, the ``SUSPEND`` and ``RESUME`` |
|
commands must be handled, too. These commands are issued when the |
|
power-management status is changed. Obviously, the ``SUSPEND`` and |
|
``RESUME`` commands suspend and resume the pcm substream, and usually, |
|
they are identical to the ``STOP`` and ``START`` commands, respectively. |
|
See the `Power Management`_ section for details. |
|
|
|
As mentioned, this callback is atomic as default unless ``nonatomic`` |
|
flag set, and you cannot call functions which may sleep. The |
|
``trigger`` callback should be as minimal as possible, just really |
|
triggering the DMA. The other stuff should be initialized |
|
``hw_params`` and ``prepare`` callbacks properly beforehand. |
|
|
|
sync_stop callback |
|
~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static int snd_xxx_sync_stop(struct snd_pcm_substream *substream); |
|
|
|
This callback is optional, and NULL can be passed. It's called after |
|
the PCM core stops the stream and changes the stream state |
|
``prepare``, ``hw_params`` or ``hw_free``. |
|
Since the IRQ handler might be still pending, we need to wait until |
|
the pending task finishes before moving to the next step; otherwise it |
|
might lead to a crash due to resource conflicts or access to the freed |
|
resources. A typical behavior is to call a synchronization function |
|
like :c:func:`synchronize_irq()` here. |
|
|
|
For majority of drivers that need only a call of |
|
:c:func:`synchronize_irq()`, there is a simpler setup, too. |
|
While keeping NULL to ``sync_stop`` PCM callback, the driver can set |
|
``card->sync_irq`` field to store the valid interrupt number after |
|
requesting an IRQ, instead. Then PCM core will look call |
|
:c:func:`synchronize_irq()` with the given IRQ appropriately. |
|
|
|
If the IRQ handler is released at the card destructor, you don't need |
|
to clear ``card->sync_irq``, as the card itself is being released. |
|
So, usually you'll need to add just a single line for assigning |
|
``card->sync_irq`` in the driver code unless the driver re-acquires |
|
the IRQ. When the driver frees and re-acquires the IRQ dynamically |
|
(e.g. for suspend/resume), it needs to clear and re-set |
|
``card->sync_irq`` again appropriately. |
|
|
|
pointer callback |
|
~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream) |
|
|
|
This callback is called when the PCM middle layer inquires the current |
|
hardware position on the buffer. The position must be returned in |
|
frames, ranging from 0 to ``buffer_size - 1``. |
|
|
|
This is called usually from the buffer-update routine in the pcm |
|
middle layer, which is invoked when :c:func:`snd_pcm_period_elapsed()` |
|
is called in the interrupt routine. Then the pcm middle layer updates |
|
the position and calculates the available space, and wakes up the |
|
sleeping poll threads, etc. |
|
|
|
This callback is also atomic as default. |
|
|
|
copy_user, copy_kernel and fill_silence ops |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
These callbacks are not mandatory, and can be omitted in most cases. |
|
These callbacks are used when the hardware buffer cannot be in the |
|
normal memory space. Some chips have their own buffer on the hardware |
|
which is not mappable. In such a case, you have to transfer the data |
|
manually from the memory buffer to the hardware buffer. Or, if the |
|
buffer is non-contiguous on both physical and virtual memory spaces, |
|
these callbacks must be defined, too. |
|
|
|
If these two callbacks are defined, copy and set-silence operations |
|
are done by them. The detailed will be described in the later section |
|
`Buffer and Memory Management`_. |
|
|
|
ack callback |
|
~~~~~~~~~~~~ |
|
|
|
This callback is also not mandatory. This callback is called when the |
|
``appl_ptr`` is updated in read or write operations. Some drivers like |
|
emu10k1-fx and cs46xx need to track the current ``appl_ptr`` for the |
|
internal buffer, and this callback is useful only for such a purpose. |
|
|
|
This callback is atomic as default. |
|
|
|
page callback |
|
~~~~~~~~~~~~~ |
|
|
|
This callback is optional too. The mmap calls this callback to get the |
|
page fault address. |
|
|
|
Since the recent changes, you need no special callback any longer for |
|
the standard SG-buffer or vmalloc-buffer. Hence this callback should |
|
be rarely used. |
|
|
|
mmap calllback |
|
~~~~~~~~~~~~~~ |
|
|
|
This is another optional callback for controlling mmap behavior. |
|
Once when defined, PCM core calls this callback when a page is |
|
memory-mapped instead of dealing via the standard helper. |
|
If you need special handling (due to some architecture or |
|
device-specific issues), implement everything here as you like. |
|
|
|
|
|
PCM Interrupt Handler |
|
--------------------- |
|
|
|
The rest of pcm stuff is the PCM interrupt handler. The role of PCM |
|
interrupt handler in the sound driver is to update the buffer position |
|
and to tell the PCM middle layer when the buffer position goes across |
|
the prescribed period size. To inform this, call the |
|
:c:func:`snd_pcm_period_elapsed()` function. |
|
|
|
There are several types of sound chips to generate the interrupts. |
|
|
|
Interrupts at the period (fragment) boundary |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
This is the most frequently found type: the hardware generates an |
|
interrupt at each period boundary. In this case, you can call |
|
:c:func:`snd_pcm_period_elapsed()` at each interrupt. |
|
|
|
:c:func:`snd_pcm_period_elapsed()` takes the substream pointer as |
|
its argument. Thus, you need to keep the substream pointer accessible |
|
from the chip instance. For example, define ``substream`` field in the |
|
chip record to hold the current running substream pointer, and set the |
|
pointer value at ``open`` callback (and reset at ``close`` callback). |
|
|
|
If you acquire a spinlock in the interrupt handler, and the lock is used |
|
in other pcm callbacks, too, then you have to release the lock before |
|
calling :c:func:`snd_pcm_period_elapsed()`, because |
|
:c:func:`snd_pcm_period_elapsed()` calls other pcm callbacks |
|
inside. |
|
|
|
Typical code would be like: |
|
|
|
:: |
|
|
|
|
|
static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) |
|
{ |
|
struct mychip *chip = dev_id; |
|
spin_lock(&chip->lock); |
|
.... |
|
if (pcm_irq_invoked(chip)) { |
|
/* call updater, unlock before it */ |
|
spin_unlock(&chip->lock); |
|
snd_pcm_period_elapsed(chip->substream); |
|
spin_lock(&chip->lock); |
|
/* acknowledge the interrupt if necessary */ |
|
} |
|
.... |
|
spin_unlock(&chip->lock); |
|
return IRQ_HANDLED; |
|
} |
|
|
|
|
|
|
|
High frequency timer interrupts |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
This happens when the hardware doesn't generate interrupts at the period |
|
boundary but issues timer interrupts at a fixed timer rate (e.g. es1968 |
|
or ymfpci drivers). In this case, you need to check the current hardware |
|
position and accumulate the processed sample length at each interrupt. |
|
When the accumulated size exceeds the period size, call |
|
:c:func:`snd_pcm_period_elapsed()` and reset the accumulator. |
|
|
|
Typical code would be like the following. |
|
|
|
:: |
|
|
|
|
|
static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) |
|
{ |
|
struct mychip *chip = dev_id; |
|
spin_lock(&chip->lock); |
|
.... |
|
if (pcm_irq_invoked(chip)) { |
|
unsigned int last_ptr, size; |
|
/* get the current hardware pointer (in frames) */ |
|
last_ptr = get_hw_ptr(chip); |
|
/* calculate the processed frames since the |
|
* last update |
|
*/ |
|
if (last_ptr < chip->last_ptr) |
|
size = runtime->buffer_size + last_ptr |
|
- chip->last_ptr; |
|
else |
|
size = last_ptr - chip->last_ptr; |
|
/* remember the last updated point */ |
|
chip->last_ptr = last_ptr; |
|
/* accumulate the size */ |
|
chip->size += size; |
|
/* over the period boundary? */ |
|
if (chip->size >= runtime->period_size) { |
|
/* reset the accumulator */ |
|
chip->size %= runtime->period_size; |
|
/* call updater */ |
|
spin_unlock(&chip->lock); |
|
snd_pcm_period_elapsed(substream); |
|
spin_lock(&chip->lock); |
|
} |
|
/* acknowledge the interrupt if necessary */ |
|
} |
|
.... |
|
spin_unlock(&chip->lock); |
|
return IRQ_HANDLED; |
|
} |
|
|
|
|
|
|
|
On calling :c:func:`snd_pcm_period_elapsed()` |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
In both cases, even if more than one period are elapsed, you don't have |
|
to call :c:func:`snd_pcm_period_elapsed()` many times. Call only |
|
once. And the pcm layer will check the current hardware pointer and |
|
update to the latest status. |
|
|
|
Atomicity |
|
--------- |
|
|
|
One of the most important (and thus difficult to debug) problems in |
|
kernel programming are race conditions. In the Linux kernel, they are |
|
usually avoided via spin-locks, mutexes or semaphores. In general, if a |
|
race condition can happen in an interrupt handler, it has to be managed |
|
atomically, and you have to use a spinlock to protect the critical |
|
session. If the critical section is not in interrupt handler code and if |
|
taking a relatively long time to execute is acceptable, you should use |
|
mutexes or semaphores instead. |
|
|
|
As already seen, some pcm callbacks are atomic and some are not. For |
|
example, the ``hw_params`` callback is non-atomic, while ``trigger`` |
|
callback is atomic. This means, the latter is called already in a |
|
spinlock held by the PCM middle layer. Please take this atomicity into |
|
account when you choose a locking scheme in the callbacks. |
|
|
|
In the atomic callbacks, you cannot use functions which may call |
|
:c:func:`schedule()` or go to :c:func:`sleep()`. Semaphores and |
|
mutexes can sleep, and hence they cannot be used inside the atomic |
|
callbacks (e.g. ``trigger`` callback). To implement some delay in such a |
|
callback, please use :c:func:`udelay()` or :c:func:`mdelay()`. |
|
|
|
All three atomic callbacks (trigger, pointer, and ack) are called with |
|
local interrupts disabled. |
|
|
|
The recent changes in PCM core code, however, allow all PCM operations |
|
to be non-atomic. This assumes that the all caller sides are in |
|
non-atomic contexts. For example, the function |
|
:c:func:`snd_pcm_period_elapsed()` is called typically from the |
|
interrupt handler. But, if you set up the driver to use a threaded |
|
interrupt handler, this call can be in non-atomic context, too. In such |
|
a case, you can set ``nonatomic`` filed of struct snd_pcm object |
|
after creating it. When this flag is set, mutex and rwsem are used internally |
|
in the PCM core instead of spin and rwlocks, so that you can call all PCM |
|
functions safely in a non-atomic |
|
context. |
|
|
|
Constraints |
|
----------- |
|
|
|
If your chip supports unconventional sample rates, or only the limited |
|
samples, you need to set a constraint for the condition. |
|
|
|
For example, in order to restrict the sample rates in the some supported |
|
values, use :c:func:`snd_pcm_hw_constraint_list()`. You need to |
|
call this function in the open callback. |
|
|
|
:: |
|
|
|
static unsigned int rates[] = |
|
{4000, 10000, 22050, 44100}; |
|
static struct snd_pcm_hw_constraint_list constraints_rates = { |
|
.count = ARRAY_SIZE(rates), |
|
.list = rates, |
|
.mask = 0, |
|
}; |
|
|
|
static int snd_mychip_pcm_open(struct snd_pcm_substream *substream) |
|
{ |
|
int err; |
|
.... |
|
err = snd_pcm_hw_constraint_list(substream->runtime, 0, |
|
SNDRV_PCM_HW_PARAM_RATE, |
|
&constraints_rates); |
|
if (err < 0) |
|
return err; |
|
.... |
|
} |
|
|
|
|
|
|
|
There are many different constraints. Look at ``sound/pcm.h`` for a |
|
complete list. You can even define your own constraint rules. For |
|
example, let's suppose my_chip can manage a substream of 1 channel if |
|
and only if the format is ``S16_LE``, otherwise it supports any format |
|
specified in struct snd_pcm_hardware> (or in any other |
|
constraint_list). You can build a rule like this: |
|
|
|
:: |
|
|
|
static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params, |
|
struct snd_pcm_hw_rule *rule) |
|
{ |
|
struct snd_interval *c = hw_param_interval(params, |
|
SNDRV_PCM_HW_PARAM_CHANNELS); |
|
struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); |
|
struct snd_interval ch; |
|
|
|
snd_interval_any(&ch); |
|
if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) { |
|
ch.min = ch.max = 1; |
|
ch.integer = 1; |
|
return snd_interval_refine(c, &ch); |
|
} |
|
return 0; |
|
} |
|
|
|
|
|
Then you need to call this function to add your rule: |
|
|
|
:: |
|
|
|
snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS, |
|
hw_rule_channels_by_format, NULL, |
|
SNDRV_PCM_HW_PARAM_FORMAT, -1); |
|
|
|
The rule function is called when an application sets the PCM format, and |
|
it refines the number of channels accordingly. But an application may |
|
set the number of channels before setting the format. Thus you also need |
|
to define the inverse rule: |
|
|
|
:: |
|
|
|
static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params, |
|
struct snd_pcm_hw_rule *rule) |
|
{ |
|
struct snd_interval *c = hw_param_interval(params, |
|
SNDRV_PCM_HW_PARAM_CHANNELS); |
|
struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); |
|
struct snd_mask fmt; |
|
|
|
snd_mask_any(&fmt); /* Init the struct */ |
|
if (c->min < 2) { |
|
fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE; |
|
return snd_mask_refine(f, &fmt); |
|
} |
|
return 0; |
|
} |
|
|
|
|
|
... and in the open callback: |
|
|
|
:: |
|
|
|
snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT, |
|
hw_rule_format_by_channels, NULL, |
|
SNDRV_PCM_HW_PARAM_CHANNELS, -1); |
|
|
|
One typical usage of the hw constraints is to align the buffer size |
|
with the period size. As default, ALSA PCM core doesn't enforce the |
|
buffer size to be aligned with the period size. For example, it'd be |
|
possible to have a combination like 256 period bytes with 999 buffer |
|
bytes. |
|
|
|
Many device chips, however, require the buffer to be a multiple of |
|
periods. In such a case, call |
|
:c:func:`snd_pcm_hw_constraint_integer()` for |
|
``SNDRV_PCM_HW_PARAM_PERIODS``. |
|
|
|
:: |
|
|
|
snd_pcm_hw_constraint_integer(substream->runtime, |
|
SNDRV_PCM_HW_PARAM_PERIODS); |
|
|
|
This assures that the number of periods is integer, hence the buffer |
|
size is aligned with the period size. |
|
|
|
The hw constraint is a very much powerful mechanism to define the |
|
preferred PCM configuration, and there are relevant helpers. |
|
I won't give more details here, rather I would like to say, “Luke, use |
|
the source.” |
|
|
|
Control Interface |
|
================= |
|
|
|
General |
|
------- |
|
|
|
The control interface is used widely for many switches, sliders, etc. |
|
which are accessed from user-space. Its most important use is the mixer |
|
interface. In other words, since ALSA 0.9.x, all the mixer stuff is |
|
implemented on the control kernel API. |
|
|
|
ALSA has a well-defined AC97 control module. If your chip supports only |
|
the AC97 and nothing else, you can skip this section. |
|
|
|
The control API is defined in ``<sound/control.h>``. Include this file |
|
if you want to add your own controls. |
|
|
|
Definition of Controls |
|
---------------------- |
|
|
|
To create a new control, you need to define the following three |
|
callbacks: ``info``, ``get`` and ``put``. Then, define a |
|
struct snd_kcontrol_new record, such as: |
|
|
|
:: |
|
|
|
|
|
static struct snd_kcontrol_new my_control = { |
|
.iface = SNDRV_CTL_ELEM_IFACE_MIXER, |
|
.name = "PCM Playback Switch", |
|
.index = 0, |
|
.access = SNDRV_CTL_ELEM_ACCESS_READWRITE, |
|
.private_value = 0xffff, |
|
.info = my_control_info, |
|
.get = my_control_get, |
|
.put = my_control_put |
|
}; |
|
|
|
|
|
The ``iface`` field specifies the control type, |
|
``SNDRV_CTL_ELEM_IFACE_XXX``, which is usually ``MIXER``. Use ``CARD`` |
|
for global controls that are not logically part of the mixer. If the |
|
control is closely associated with some specific device on the sound |
|
card, use ``HWDEP``, ``PCM``, ``RAWMIDI``, ``TIMER``, or ``SEQUENCER``, |
|
and specify the device number with the ``device`` and ``subdevice`` |
|
fields. |
|
|
|
The ``name`` is the name identifier string. Since ALSA 0.9.x, the |
|
control name is very important, because its role is classified from |
|
its name. There are pre-defined standard control names. The details |
|
are described in the `Control Names`_ subsection. |
|
|
|
The ``index`` field holds the index number of this control. If there |
|
are several different controls with the same name, they can be |
|
distinguished by the index number. This is the case when several |
|
codecs exist on the card. If the index is zero, you can omit the |
|
definition above. |
|
|
|
The ``access`` field contains the access type of this control. Give |
|
the combination of bit masks, ``SNDRV_CTL_ELEM_ACCESS_XXX``, |
|
there. The details will be explained in the `Access Flags`_ |
|
subsection. |
|
|
|
The ``private_value`` field contains an arbitrary long integer value |
|
for this record. When using the generic ``info``, ``get`` and ``put`` |
|
callbacks, you can pass a value through this field. If several small |
|
numbers are necessary, you can combine them in bitwise. Or, it's |
|
possible to give a pointer (casted to unsigned long) of some record to |
|
this field, too. |
|
|
|
The ``tlv`` field can be used to provide metadata about the control; |
|
see the `Metadata`_ subsection. |
|
|
|
The other three are `Control Callbacks`_. |
|
|
|
Control Names |
|
------------- |
|
|
|
There are some standards to define the control names. A control is |
|
usually defined from the three parts as “SOURCE DIRECTION FUNCTION”. |
|
|
|
The first, ``SOURCE``, specifies the source of the control, and is a |
|
string such as “Master”, “PCM”, “CD” and “Line”. There are many |
|
pre-defined sources. |
|
|
|
The second, ``DIRECTION``, is one of the following strings according to |
|
the direction of the control: “Playback”, “Capture”, “Bypass Playback” |
|
and “Bypass Capture”. Or, it can be omitted, meaning both playback and |
|
capture directions. |
|
|
|
The third, ``FUNCTION``, is one of the following strings according to |
|
the function of the control: “Switch”, “Volume” and “Route”. |
|
|
|
The example of control names are, thus, “Master Capture Switch” or “PCM |
|
Playback Volume”. |
|
|
|
There are some exceptions: |
|
|
|
Global capture and playback |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
“Capture Source”, “Capture Switch” and “Capture Volume” are used for the |
|
global capture (input) source, switch and volume. Similarly, “Playback |
|
Switch” and “Playback Volume” are used for the global output gain switch |
|
and volume. |
|
|
|
Tone-controls |
|
~~~~~~~~~~~~~ |
|
|
|
tone-control switch and volumes are specified like “Tone Control - XXX”, |
|
e.g. “Tone Control - Switch”, “Tone Control - Bass”, “Tone Control - |
|
Center”. |
|
|
|
3D controls |
|
~~~~~~~~~~~ |
|
|
|
3D-control switches and volumes are specified like “3D Control - XXX”, |
|
e.g. “3D Control - Switch”, “3D Control - Center”, “3D Control - Space”. |
|
|
|
Mic boost |
|
~~~~~~~~~ |
|
|
|
Mic-boost switch is set as “Mic Boost” or “Mic Boost (6dB)”. |
|
|
|
More precise information can be found in |
|
``Documentation/sound/designs/control-names.rst``. |
|
|
|
Access Flags |
|
------------ |
|
|
|
The access flag is the bitmask which specifies the access type of the |
|
given control. The default access type is |
|
``SNDRV_CTL_ELEM_ACCESS_READWRITE``, which means both read and write are |
|
allowed to this control. When the access flag is omitted (i.e. = 0), it |
|
is considered as ``READWRITE`` access as default. |
|
|
|
When the control is read-only, pass ``SNDRV_CTL_ELEM_ACCESS_READ`` |
|
instead. In this case, you don't have to define the ``put`` callback. |
|
Similarly, when the control is write-only (although it's a rare case), |
|
you can use the ``WRITE`` flag instead, and you don't need the ``get`` |
|
callback. |
|
|
|
If the control value changes frequently (e.g. the VU meter), |
|
``VOLATILE`` flag should be given. This means that the control may be |
|
changed without `Change notification`_. Applications should poll such |
|
a control constantly. |
|
|
|
When the control is inactive, set the ``INACTIVE`` flag, too. There are |
|
``LOCK`` and ``OWNER`` flags to change the write permissions. |
|
|
|
Control Callbacks |
|
----------------- |
|
|
|
info callback |
|
~~~~~~~~~~~~~ |
|
|
|
The ``info`` callback is used to get detailed information on this |
|
control. This must store the values of the given |
|
struct snd_ctl_elem_info object. For example, |
|
for a boolean control with a single element: |
|
|
|
:: |
|
|
|
|
|
static int snd_myctl_mono_info(struct snd_kcontrol *kcontrol, |
|
struct snd_ctl_elem_info *uinfo) |
|
{ |
|
uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN; |
|
uinfo->count = 1; |
|
uinfo->value.integer.min = 0; |
|
uinfo->value.integer.max = 1; |
|
return 0; |
|
} |
|
|
|
|
|
|
|
The ``type`` field specifies the type of the control. There are |
|
``BOOLEAN``, ``INTEGER``, ``ENUMERATED``, ``BYTES``, ``IEC958`` and |
|
``INTEGER64``. The ``count`` field specifies the number of elements in |
|
this control. For example, a stereo volume would have count = 2. The |
|
``value`` field is a union, and the values stored are depending on the |
|
type. The boolean and integer types are identical. |
|
|
|
The enumerated type is a bit different from others. You'll need to set |
|
the string for the currently given item index. |
|
|
|
:: |
|
|
|
static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol, |
|
struct snd_ctl_elem_info *uinfo) |
|
{ |
|
static char *texts[4] = { |
|
"First", "Second", "Third", "Fourth" |
|
}; |
|
uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED; |
|
uinfo->count = 1; |
|
uinfo->value.enumerated.items = 4; |
|
if (uinfo->value.enumerated.item > 3) |
|
uinfo->value.enumerated.item = 3; |
|
strcpy(uinfo->value.enumerated.name, |
|
texts[uinfo->value.enumerated.item]); |
|
return 0; |
|
} |
|
|
|
The above callback can be simplified with a helper function, |
|
:c:func:`snd_ctl_enum_info()`. The final code looks like below. |
|
(You can pass ``ARRAY_SIZE(texts)`` instead of 4 in the third argument; |
|
it's a matter of taste.) |
|
|
|
:: |
|
|
|
static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol, |
|
struct snd_ctl_elem_info *uinfo) |
|
{ |
|
static char *texts[4] = { |
|
"First", "Second", "Third", "Fourth" |
|
}; |
|
return snd_ctl_enum_info(uinfo, 1, 4, texts); |
|
} |
|
|
|
|
|
Some common info callbacks are available for your convenience: |
|
:c:func:`snd_ctl_boolean_mono_info()` and |
|
:c:func:`snd_ctl_boolean_stereo_info()`. Obviously, the former |
|
is an info callback for a mono channel boolean item, just like |
|
:c:func:`snd_myctl_mono_info()` above, and the latter is for a |
|
stereo channel boolean item. |
|
|
|
get callback |
|
~~~~~~~~~~~~ |
|
|
|
This callback is used to read the current value of the control and to |
|
return to user-space. |
|
|
|
For example, |
|
|
|
:: |
|
|
|
|
|
static int snd_myctl_get(struct snd_kcontrol *kcontrol, |
|
struct snd_ctl_elem_value *ucontrol) |
|
{ |
|
struct mychip *chip = snd_kcontrol_chip(kcontrol); |
|
ucontrol->value.integer.value[0] = get_some_value(chip); |
|
return 0; |
|
} |
|
|
|
|
|
|
|
The ``value`` field depends on the type of control as well as on the |
|
info callback. For example, the sb driver uses this field to store the |
|
register offset, the bit-shift and the bit-mask. The ``private_value`` |
|
field is set as follows: |
|
|
|
:: |
|
|
|
.private_value = reg | (shift << 16) | (mask << 24) |
|
|
|
and is retrieved in callbacks like |
|
|
|
:: |
|
|
|
static int snd_sbmixer_get_single(struct snd_kcontrol *kcontrol, |
|
struct snd_ctl_elem_value *ucontrol) |
|
{ |
|
int reg = kcontrol->private_value & 0xff; |
|
int shift = (kcontrol->private_value >> 16) & 0xff; |
|
int mask = (kcontrol->private_value >> 24) & 0xff; |
|
.... |
|
} |
|
|
|
In the ``get`` callback, you have to fill all the elements if the |
|
control has more than one elements, i.e. ``count > 1``. In the example |
|
above, we filled only one element (``value.integer.value[0]``) since |
|
it's assumed as ``count = 1``. |
|
|
|
put callback |
|
~~~~~~~~~~~~ |
|
|
|
This callback is used to write a value from user-space. |
|
|
|
For example, |
|
|
|
:: |
|
|
|
|
|
static int snd_myctl_put(struct snd_kcontrol *kcontrol, |
|
struct snd_ctl_elem_value *ucontrol) |
|
{ |
|
struct mychip *chip = snd_kcontrol_chip(kcontrol); |
|
int changed = 0; |
|
if (chip->current_value != |
|
ucontrol->value.integer.value[0]) { |
|
change_current_value(chip, |
|
ucontrol->value.integer.value[0]); |
|
changed = 1; |
|
} |
|
return changed; |
|
} |
|
|
|
|
|
|
|
As seen above, you have to return 1 if the value is changed. If the |
|
value is not changed, return 0 instead. If any fatal error happens, |
|
return a negative error code as usual. |
|
|
|
As in the ``get`` callback, when the control has more than one |
|
elements, all elements must be evaluated in this callback, too. |
|
|
|
Callbacks are not atomic |
|
~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
All these three callbacks are basically not atomic. |
|
|
|
Control Constructor |
|
------------------- |
|
|
|
When everything is ready, finally we can create a new control. To create |
|
a control, there are two functions to be called, |
|
:c:func:`snd_ctl_new1()` and :c:func:`snd_ctl_add()`. |
|
|
|
In the simplest way, you can do like this: |
|
|
|
:: |
|
|
|
err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip)); |
|
if (err < 0) |
|
return err; |
|
|
|
where ``my_control`` is the struct snd_kcontrol_new object defined above, |
|
and chip is the object pointer to be passed to kcontrol->private_data which |
|
can be referred to in callbacks. |
|
|
|
:c:func:`snd_ctl_new1()` allocates a new struct snd_kcontrol instance, and |
|
:c:func:`snd_ctl_add()` assigns the given control component to the |
|
card. |
|
|
|
Change Notification |
|
------------------- |
|
|
|
If you need to change and update a control in the interrupt routine, you |
|
can call :c:func:`snd_ctl_notify()`. For example, |
|
|
|
:: |
|
|
|
snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, id_pointer); |
|
|
|
This function takes the card pointer, the event-mask, and the control id |
|
pointer for the notification. The event-mask specifies the types of |
|
notification, for example, in the above example, the change of control |
|
values is notified. The id pointer is the pointer of struct snd_ctl_elem_id |
|
to be notified. You can find some examples in ``es1938.c`` or ``es1968.c`` |
|
for hardware volume interrupts. |
|
|
|
Metadata |
|
-------- |
|
|
|
To provide information about the dB values of a mixer control, use on of |
|
the ``DECLARE_TLV_xxx`` macros from ``<sound/tlv.h>`` to define a |
|
variable containing this information, set the ``tlv.p`` field to point to |
|
this variable, and include the ``SNDRV_CTL_ELEM_ACCESS_TLV_READ`` flag |
|
in the ``access`` field; like this: |
|
|
|
:: |
|
|
|
static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0); |
|
|
|
static struct snd_kcontrol_new my_control = { |
|
... |
|
.access = SNDRV_CTL_ELEM_ACCESS_READWRITE | |
|
SNDRV_CTL_ELEM_ACCESS_TLV_READ, |
|
... |
|
.tlv.p = db_scale_my_control, |
|
}; |
|
|
|
|
|
The :c:func:`DECLARE_TLV_DB_SCALE()` macro defines information |
|
about a mixer control where each step in the control's value changes the |
|
dB value by a constant dB amount. The first parameter is the name of the |
|
variable to be defined. The second parameter is the minimum value, in |
|
units of 0.01 dB. The third parameter is the step size, in units of 0.01 |
|
dB. Set the fourth parameter to 1 if the minimum value actually mutes |
|
the control. |
|
|
|
The :c:func:`DECLARE_TLV_DB_LINEAR()` macro defines information |
|
about a mixer control where the control's value affects the output |
|
linearly. The first parameter is the name of the variable to be defined. |
|
The second parameter is the minimum value, in units of 0.01 dB. The |
|
third parameter is the maximum value, in units of 0.01 dB. If the |
|
minimum value mutes the control, set the second parameter to |
|
``TLV_DB_GAIN_MUTE``. |
|
|
|
API for AC97 Codec |
|
================== |
|
|
|
General |
|
------- |
|
|
|
The ALSA AC97 codec layer is a well-defined one, and you don't have to |
|
write much code to control it. Only low-level control routines are |
|
necessary. The AC97 codec API is defined in ``<sound/ac97_codec.h>``. |
|
|
|
Full Code Example |
|
----------------- |
|
|
|
:: |
|
|
|
struct mychip { |
|
.... |
|
struct snd_ac97 *ac97; |
|
.... |
|
}; |
|
|
|
static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97, |
|
unsigned short reg) |
|
{ |
|
struct mychip *chip = ac97->private_data; |
|
.... |
|
/* read a register value here from the codec */ |
|
return the_register_value; |
|
} |
|
|
|
static void snd_mychip_ac97_write(struct snd_ac97 *ac97, |
|
unsigned short reg, unsigned short val) |
|
{ |
|
struct mychip *chip = ac97->private_data; |
|
.... |
|
/* write the given register value to the codec */ |
|
} |
|
|
|
static int snd_mychip_ac97(struct mychip *chip) |
|
{ |
|
struct snd_ac97_bus *bus; |
|
struct snd_ac97_template ac97; |
|
int err; |
|
static struct snd_ac97_bus_ops ops = { |
|
.write = snd_mychip_ac97_write, |
|
.read = snd_mychip_ac97_read, |
|
}; |
|
|
|
err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus); |
|
if (err < 0) |
|
return err; |
|
memset(&ac97, 0, sizeof(ac97)); |
|
ac97.private_data = chip; |
|
return snd_ac97_mixer(bus, &ac97, &chip->ac97); |
|
} |
|
|
|
|
|
AC97 Constructor |
|
---------------- |
|
|
|
To create an ac97 instance, first call :c:func:`snd_ac97_bus()` |
|
with an ``ac97_bus_ops_t`` record with callback functions. |
|
|
|
:: |
|
|
|
struct snd_ac97_bus *bus; |
|
static struct snd_ac97_bus_ops ops = { |
|
.write = snd_mychip_ac97_write, |
|
.read = snd_mychip_ac97_read, |
|
}; |
|
|
|
snd_ac97_bus(card, 0, &ops, NULL, &pbus); |
|
|
|
The bus record is shared among all belonging ac97 instances. |
|
|
|
And then call :c:func:`snd_ac97_mixer()` with an struct snd_ac97_template |
|
record together with the bus pointer created above. |
|
|
|
:: |
|
|
|
struct snd_ac97_template ac97; |
|
int err; |
|
|
|
memset(&ac97, 0, sizeof(ac97)); |
|
ac97.private_data = chip; |
|
snd_ac97_mixer(bus, &ac97, &chip->ac97); |
|
|
|
where chip->ac97 is a pointer to a newly created ``ac97_t`` |
|
instance. In this case, the chip pointer is set as the private data, |
|
so that the read/write callback functions can refer to this chip |
|
instance. This instance is not necessarily stored in the chip |
|
record. If you need to change the register values from the driver, or |
|
need the suspend/resume of ac97 codecs, keep this pointer to pass to |
|
the corresponding functions. |
|
|
|
AC97 Callbacks |
|
-------------- |
|
|
|
The standard callbacks are ``read`` and ``write``. Obviously they |
|
correspond to the functions for read and write accesses to the |
|
hardware low-level codes. |
|
|
|
The ``read`` callback returns the register value specified in the |
|
argument. |
|
|
|
:: |
|
|
|
static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97, |
|
unsigned short reg) |
|
{ |
|
struct mychip *chip = ac97->private_data; |
|
.... |
|
return the_register_value; |
|
} |
|
|
|
Here, the chip can be cast from ``ac97->private_data``. |
|
|
|
Meanwhile, the ``write`` callback is used to set the register |
|
value |
|
|
|
:: |
|
|
|
static void snd_mychip_ac97_write(struct snd_ac97 *ac97, |
|
unsigned short reg, unsigned short val) |
|
|
|
|
|
These callbacks are non-atomic like the control API callbacks. |
|
|
|
There are also other callbacks: ``reset``, ``wait`` and ``init``. |
|
|
|
The ``reset`` callback is used to reset the codec. If the chip |
|
requires a special kind of reset, you can define this callback. |
|
|
|
The ``wait`` callback is used to add some waiting time in the standard |
|
initialization of the codec. If the chip requires the extra waiting |
|
time, define this callback. |
|
|
|
The ``init`` callback is used for additional initialization of the |
|
codec. |
|
|
|
Updating Registers in The Driver |
|
-------------------------------- |
|
|
|
If you need to access to the codec from the driver, you can call the |
|
following functions: :c:func:`snd_ac97_write()`, |
|
:c:func:`snd_ac97_read()`, :c:func:`snd_ac97_update()` and |
|
:c:func:`snd_ac97_update_bits()`. |
|
|
|
Both :c:func:`snd_ac97_write()` and |
|
:c:func:`snd_ac97_update()` functions are used to set a value to |
|
the given register (``AC97_XXX``). The difference between them is that |
|
:c:func:`snd_ac97_update()` doesn't write a value if the given |
|
value has been already set, while :c:func:`snd_ac97_write()` |
|
always rewrites the value. |
|
|
|
:: |
|
|
|
snd_ac97_write(ac97, AC97_MASTER, 0x8080); |
|
snd_ac97_update(ac97, AC97_MASTER, 0x8080); |
|
|
|
:c:func:`snd_ac97_read()` is used to read the value of the given |
|
register. For example, |
|
|
|
:: |
|
|
|
value = snd_ac97_read(ac97, AC97_MASTER); |
|
|
|
:c:func:`snd_ac97_update_bits()` is used to update some bits in |
|
the given register. |
|
|
|
:: |
|
|
|
snd_ac97_update_bits(ac97, reg, mask, value); |
|
|
|
Also, there is a function to change the sample rate (of a given register |
|
such as ``AC97_PCM_FRONT_DAC_RATE``) when VRA or DRA is supported by the |
|
codec: :c:func:`snd_ac97_set_rate()`. |
|
|
|
:: |
|
|
|
snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100); |
|
|
|
|
|
The following registers are available to set the rate: |
|
``AC97_PCM_MIC_ADC_RATE``, ``AC97_PCM_FRONT_DAC_RATE``, |
|
``AC97_PCM_LR_ADC_RATE``, ``AC97_SPDIF``. When ``AC97_SPDIF`` is |
|
specified, the register is not really changed but the corresponding |
|
IEC958 status bits will be updated. |
|
|
|
Clock Adjustment |
|
---------------- |
|
|
|
In some chips, the clock of the codec isn't 48000 but using a PCI clock |
|
(to save a quartz!). In this case, change the field ``bus->clock`` to |
|
the corresponding value. For example, intel8x0 and es1968 drivers have |
|
their own function to read from the clock. |
|
|
|
Proc Files |
|
---------- |
|
|
|
The ALSA AC97 interface will create a proc file such as |
|
``/proc/asound/card0/codec97#0/ac97#0-0`` and ``ac97#0-0+regs``. You |
|
can refer to these files to see the current status and registers of |
|
the codec. |
|
|
|
Multiple Codecs |
|
--------------- |
|
|
|
When there are several codecs on the same card, you need to call |
|
:c:func:`snd_ac97_mixer()` multiple times with ``ac97.num=1`` or |
|
greater. The ``num`` field specifies the codec number. |
|
|
|
If you set up multiple codecs, you either need to write different |
|
callbacks for each codec or check ``ac97->num`` in the callback |
|
routines. |
|
|
|
MIDI (MPU401-UART) Interface |
|
============================ |
|
|
|
General |
|
------- |
|
|
|
Many soundcards have built-in MIDI (MPU401-UART) interfaces. When the |
|
soundcard supports the standard MPU401-UART interface, most likely you |
|
can use the ALSA MPU401-UART API. The MPU401-UART API is defined in |
|
``<sound/mpu401.h>``. |
|
|
|
Some soundchips have a similar but slightly different implementation of |
|
mpu401 stuff. For example, emu10k1 has its own mpu401 routines. |
|
|
|
MIDI Constructor |
|
---------------- |
|
|
|
To create a rawmidi object, call :c:func:`snd_mpu401_uart_new()`. |
|
|
|
:: |
|
|
|
struct snd_rawmidi *rmidi; |
|
snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags, |
|
irq, &rmidi); |
|
|
|
|
|
The first argument is the card pointer, and the second is the index of |
|
this component. You can create up to 8 rawmidi devices. |
|
|
|
The third argument is the type of the hardware, ``MPU401_HW_XXX``. If |
|
it's not a special one, you can use ``MPU401_HW_MPU401``. |
|
|
|
The 4th argument is the I/O port address. Many backward-compatible |
|
MPU401 have an I/O port such as 0x330. Or, it might be a part of its own |
|
PCI I/O region. It depends on the chip design. |
|
|
|
The 5th argument is a bitflag for additional information. When the I/O |
|
port address above is part of the PCI I/O region, the MPU401 I/O port |
|
might have been already allocated (reserved) by the driver itself. In |
|
such a case, pass a bit flag ``MPU401_INFO_INTEGRATED``, and the |
|
mpu401-uart layer will allocate the I/O ports by itself. |
|
|
|
When the controller supports only the input or output MIDI stream, pass |
|
the ``MPU401_INFO_INPUT`` or ``MPU401_INFO_OUTPUT`` bitflag, |
|
respectively. Then the rawmidi instance is created as a single stream. |
|
|
|
``MPU401_INFO_MMIO`` bitflag is used to change the access method to MMIO |
|
(via readb and writeb) instead of iob and outb. In this case, you have |
|
to pass the iomapped address to :c:func:`snd_mpu401_uart_new()`. |
|
|
|
When ``MPU401_INFO_TX_IRQ`` is set, the output stream isn't checked in |
|
the default interrupt handler. The driver needs to call |
|
:c:func:`snd_mpu401_uart_interrupt_tx()` by itself to start |
|
processing the output stream in the irq handler. |
|
|
|
If the MPU-401 interface shares its interrupt with the other logical |
|
devices on the card, set ``MPU401_INFO_IRQ_HOOK`` (see |
|
`below <MIDI Interrupt Handler_>`__). |
|
|
|
Usually, the port address corresponds to the command port and port + 1 |
|
corresponds to the data port. If not, you may change the ``cport`` |
|
field of struct snd_mpu401 manually afterward. |
|
However, struct snd_mpu401 pointer is |
|
not returned explicitly by :c:func:`snd_mpu401_uart_new()`. You |
|
need to cast ``rmidi->private_data`` to struct snd_mpu401 explicitly, |
|
|
|
:: |
|
|
|
struct snd_mpu401 *mpu; |
|
mpu = rmidi->private_data; |
|
|
|
and reset the ``cport`` as you like: |
|
|
|
:: |
|
|
|
mpu->cport = my_own_control_port; |
|
|
|
The 6th argument specifies the ISA irq number that will be allocated. If |
|
no interrupt is to be allocated (because your code is already allocating |
|
a shared interrupt, or because the device does not use interrupts), pass |
|
-1 instead. For a MPU-401 device without an interrupt, a polling timer |
|
will be used instead. |
|
|
|
MIDI Interrupt Handler |
|
---------------------- |
|
|
|
When the interrupt is allocated in |
|
:c:func:`snd_mpu401_uart_new()`, an exclusive ISA interrupt |
|
handler is automatically used, hence you don't have anything else to do |
|
than creating the mpu401 stuff. Otherwise, you have to set |
|
``MPU401_INFO_IRQ_HOOK``, and call |
|
:c:func:`snd_mpu401_uart_interrupt()` explicitly from your own |
|
interrupt handler when it has determined that a UART interrupt has |
|
occurred. |
|
|
|
In this case, you need to pass the private_data of the returned rawmidi |
|
object from :c:func:`snd_mpu401_uart_new()` as the second |
|
argument of :c:func:`snd_mpu401_uart_interrupt()`. |
|
|
|
:: |
|
|
|
snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs); |
|
|
|
|
|
RawMIDI Interface |
|
================= |
|
|
|
Overview |
|
-------- |
|
|
|
The raw MIDI interface is used for hardware MIDI ports that can be |
|
accessed as a byte stream. It is not used for synthesizer chips that do |
|
not directly understand MIDI. |
|
|
|
ALSA handles file and buffer management. All you have to do is to write |
|
some code to move data between the buffer and the hardware. |
|
|
|
The rawmidi API is defined in ``<sound/rawmidi.h>``. |
|
|
|
RawMIDI Constructor |
|
------------------- |
|
|
|
To create a rawmidi device, call the :c:func:`snd_rawmidi_new()` |
|
function: |
|
|
|
:: |
|
|
|
struct snd_rawmidi *rmidi; |
|
err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi); |
|
if (err < 0) |
|
return err; |
|
rmidi->private_data = chip; |
|
strcpy(rmidi->name, "My MIDI"); |
|
rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT | |
|
SNDRV_RAWMIDI_INFO_INPUT | |
|
SNDRV_RAWMIDI_INFO_DUPLEX; |
|
|
|
The first argument is the card pointer, the second argument is the ID |
|
string. |
|
|
|
The third argument is the index of this component. You can create up to |
|
8 rawmidi devices. |
|
|
|
The fourth and fifth arguments are the number of output and input |
|
substreams, respectively, of this device (a substream is the equivalent |
|
of a MIDI port). |
|
|
|
Set the ``info_flags`` field to specify the capabilities of the |
|
device. Set ``SNDRV_RAWMIDI_INFO_OUTPUT`` if there is at least one |
|
output port, ``SNDRV_RAWMIDI_INFO_INPUT`` if there is at least one |
|
input port, and ``SNDRV_RAWMIDI_INFO_DUPLEX`` if the device can handle |
|
output and input at the same time. |
|
|
|
After the rawmidi device is created, you need to set the operators |
|
(callbacks) for each substream. There are helper functions to set the |
|
operators for all the substreams of a device: |
|
|
|
:: |
|
|
|
snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops); |
|
snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops); |
|
|
|
The operators are usually defined like this: |
|
|
|
:: |
|
|
|
static struct snd_rawmidi_ops snd_mymidi_output_ops = { |
|
.open = snd_mymidi_output_open, |
|
.close = snd_mymidi_output_close, |
|
.trigger = snd_mymidi_output_trigger, |
|
}; |
|
|
|
These callbacks are explained in the `RawMIDI Callbacks`_ section. |
|
|
|
If there are more than one substream, you should give a unique name to |
|
each of them: |
|
|
|
:: |
|
|
|
struct snd_rawmidi_substream *substream; |
|
list_for_each_entry(substream, |
|
&rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams, |
|
list { |
|
sprintf(substream->name, "My MIDI Port %d", substream->number + 1); |
|
} |
|
/* same for SNDRV_RAWMIDI_STREAM_INPUT */ |
|
|
|
RawMIDI Callbacks |
|
----------------- |
|
|
|
In all the callbacks, the private data that you've set for the rawmidi |
|
device can be accessed as ``substream->rmidi->private_data``. |
|
|
|
If there is more than one port, your callbacks can determine the port |
|
index from the struct snd_rawmidi_substream data passed to each |
|
callback: |
|
|
|
:: |
|
|
|
struct snd_rawmidi_substream *substream; |
|
int index = substream->number; |
|
|
|
RawMIDI open callback |
|
~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static int snd_xxx_open(struct snd_rawmidi_substream *substream); |
|
|
|
|
|
This is called when a substream is opened. You can initialize the |
|
hardware here, but you shouldn't start transmitting/receiving data yet. |
|
|
|
RawMIDI close callback |
|
~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static int snd_xxx_close(struct snd_rawmidi_substream *substream); |
|
|
|
Guess what. |
|
|
|
The ``open`` and ``close`` callbacks of a rawmidi device are |
|
serialized with a mutex, and can sleep. |
|
|
|
Rawmidi trigger callback for output substreams |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up); |
|
|
|
|
|
This is called with a nonzero ``up`` parameter when there is some data |
|
in the substream buffer that must be transmitted. |
|
|
|
To read data from the buffer, call |
|
:c:func:`snd_rawmidi_transmit_peek()`. It will return the number |
|
of bytes that have been read; this will be less than the number of bytes |
|
requested when there are no more data in the buffer. After the data have |
|
been transmitted successfully, call |
|
:c:func:`snd_rawmidi_transmit_ack()` to remove the data from the |
|
substream buffer: |
|
|
|
:: |
|
|
|
unsigned char data; |
|
while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) { |
|
if (snd_mychip_try_to_transmit(data)) |
|
snd_rawmidi_transmit_ack(substream, 1); |
|
else |
|
break; /* hardware FIFO full */ |
|
} |
|
|
|
If you know beforehand that the hardware will accept data, you can use |
|
the :c:func:`snd_rawmidi_transmit()` function which reads some |
|
data and removes them from the buffer at once: |
|
|
|
:: |
|
|
|
while (snd_mychip_transmit_possible()) { |
|
unsigned char data; |
|
if (snd_rawmidi_transmit(substream, &data, 1) != 1) |
|
break; /* no more data */ |
|
snd_mychip_transmit(data); |
|
} |
|
|
|
If you know beforehand how many bytes you can accept, you can use a |
|
buffer size greater than one with the ``snd_rawmidi_transmit*()`` functions. |
|
|
|
The ``trigger`` callback must not sleep. If the hardware FIFO is full |
|
before the substream buffer has been emptied, you have to continue |
|
transmitting data later, either in an interrupt handler, or with a |
|
timer if the hardware doesn't have a MIDI transmit interrupt. |
|
|
|
The ``trigger`` callback is called with a zero ``up`` parameter when |
|
the transmission of data should be aborted. |
|
|
|
RawMIDI trigger callback for input substreams |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up); |
|
|
|
|
|
This is called with a nonzero ``up`` parameter to enable receiving data, |
|
or with a zero ``up`` parameter do disable receiving data. |
|
|
|
The ``trigger`` callback must not sleep; the actual reading of data |
|
from the device is usually done in an interrupt handler. |
|
|
|
When data reception is enabled, your interrupt handler should call |
|
:c:func:`snd_rawmidi_receive()` for all received data: |
|
|
|
:: |
|
|
|
void snd_mychip_midi_interrupt(...) |
|
{ |
|
while (mychip_midi_available()) { |
|
unsigned char data; |
|
data = mychip_midi_read(); |
|
snd_rawmidi_receive(substream, &data, 1); |
|
} |
|
} |
|
|
|
|
|
drain callback |
|
~~~~~~~~~~~~~~ |
|
|
|
:: |
|
|
|
static void snd_xxx_drain(struct snd_rawmidi_substream *substream); |
|
|
|
|
|
This is only used with output substreams. This function should wait |
|
until all data read from the substream buffer have been transmitted. |
|
This ensures that the device can be closed and the driver unloaded |
|
without losing data. |
|
|
|
This callback is optional. If you do not set ``drain`` in the struct |
|
snd_rawmidi_ops structure, ALSA will simply wait for 50 milliseconds |
|
instead. |
|
|
|
Miscellaneous Devices |
|
===================== |
|
|
|
FM OPL3 |
|
------- |
|
|
|
The FM OPL3 is still used in many chips (mainly for backward |
|
compatibility). ALSA has a nice OPL3 FM control layer, too. The OPL3 API |
|
is defined in ``<sound/opl3.h>``. |
|
|
|
FM registers can be directly accessed through the direct-FM API, defined |
|
in ``<sound/asound_fm.h>``. In ALSA native mode, FM registers are |
|
accessed through the Hardware-Dependent Device direct-FM extension API, |
|
whereas in OSS compatible mode, FM registers can be accessed with the |
|
OSS direct-FM compatible API in ``/dev/dmfmX`` device. |
|
|
|
To create the OPL3 component, you have two functions to call. The first |
|
one is a constructor for the ``opl3_t`` instance. |
|
|
|
:: |
|
|
|
struct snd_opl3 *opl3; |
|
snd_opl3_create(card, lport, rport, OPL3_HW_OPL3_XXX, |
|
integrated, &opl3); |
|
|
|
The first argument is the card pointer, the second one is the left port |
|
address, and the third is the right port address. In most cases, the |
|
right port is placed at the left port + 2. |
|
|
|
The fourth argument is the hardware type. |
|
|
|
When the left and right ports have been already allocated by the card |
|
driver, pass non-zero to the fifth argument (``integrated``). Otherwise, |
|
the opl3 module will allocate the specified ports by itself. |
|
|
|
When the accessing the hardware requires special method instead of the |
|
standard I/O access, you can create opl3 instance separately with |
|
:c:func:`snd_opl3_new()`. |
|
|
|
:: |
|
|
|
struct snd_opl3 *opl3; |
|
snd_opl3_new(card, OPL3_HW_OPL3_XXX, &opl3); |
|
|
|
Then set ``command``, ``private_data`` and ``private_free`` for the |
|
private access function, the private data and the destructor. The |
|
``l_port`` and ``r_port`` are not necessarily set. Only the command |
|
must be set properly. You can retrieve the data from the |
|
``opl3->private_data`` field. |
|
|
|
After creating the opl3 instance via :c:func:`snd_opl3_new()`, |
|
call :c:func:`snd_opl3_init()` to initialize the chip to the |
|
proper state. Note that :c:func:`snd_opl3_create()` always calls |
|
it internally. |
|
|
|
If the opl3 instance is created successfully, then create a hwdep device |
|
for this opl3. |
|
|
|
:: |
|
|
|
struct snd_hwdep *opl3hwdep; |
|
snd_opl3_hwdep_new(opl3, 0, 1, &opl3hwdep); |
|
|
|
The first argument is the ``opl3_t`` instance you created, and the |
|
second is the index number, usually 0. |
|
|
|
The third argument is the index-offset for the sequencer client assigned |
|
to the OPL3 port. When there is an MPU401-UART, give 1 for here (UART |
|
always takes 0). |
|
|
|
Hardware-Dependent Devices |
|
-------------------------- |
|
|
|
Some chips need user-space access for special controls or for loading |
|
the micro code. In such a case, you can create a hwdep |
|
(hardware-dependent) device. The hwdep API is defined in |
|
``<sound/hwdep.h>``. You can find examples in opl3 driver or |
|
``isa/sb/sb16_csp.c``. |
|
|
|
The creation of the ``hwdep`` instance is done via |
|
:c:func:`snd_hwdep_new()`. |
|
|
|
:: |
|
|
|
struct snd_hwdep *hw; |
|
snd_hwdep_new(card, "My HWDEP", 0, &hw); |
|
|
|
where the third argument is the index number. |
|
|
|
You can then pass any pointer value to the ``private_data``. If you |
|
assign a private data, you should define the destructor, too. The |
|
destructor function is set in the ``private_free`` field. |
|
|
|
:: |
|
|
|
struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL); |
|
hw->private_data = p; |
|
hw->private_free = mydata_free; |
|
|
|
and the implementation of the destructor would be: |
|
|
|
:: |
|
|
|
static void mydata_free(struct snd_hwdep *hw) |
|
{ |
|
struct mydata *p = hw->private_data; |
|
kfree(p); |
|
} |
|
|
|
The arbitrary file operations can be defined for this instance. The file |
|
operators are defined in the ``ops`` table. For example, assume that |
|
this chip needs an ioctl. |
|
|
|
:: |
|
|
|
hw->ops.open = mydata_open; |
|
hw->ops.ioctl = mydata_ioctl; |
|
hw->ops.release = mydata_release; |
|
|
|
And implement the callback functions as you like. |
|
|
|
IEC958 (S/PDIF) |
|
--------------- |
|
|
|
Usually the controls for IEC958 devices are implemented via the control |
|
interface. There is a macro to compose a name string for IEC958 |
|
controls, :c:func:`SNDRV_CTL_NAME_IEC958()` defined in |
|
``<include/asound.h>``. |
|
|
|
There are some standard controls for IEC958 status bits. These controls |
|
use the type ``SNDRV_CTL_ELEM_TYPE_IEC958``, and the size of element is |
|
fixed as 4 bytes array (value.iec958.status[x]). For the ``info`` |
|
callback, you don't specify the value field for this type (the count |
|
field must be set, though). |
|
|
|
“IEC958 Playback Con Mask” is used to return the bit-mask for the IEC958 |
|
status bits of consumer mode. Similarly, “IEC958 Playback Pro Mask” |
|
returns the bitmask for professional mode. They are read-only controls. |
|
|
|
Meanwhile, “IEC958 Playback Default” control is defined for getting and |
|
setting the current default IEC958 bits. |
|
|
|
Due to historical reasons, both variants of the Playback Mask and the |
|
Playback Default controls can be implemented on either a |
|
``SNDRV_CTL_ELEM_IFACE_PCM`` or a ``SNDRV_CTL_ELEM_IFACE_MIXER`` iface. |
|
Drivers should expose the mask and default on the same iface though. |
|
|
|
In addition, you can define the control switches to enable/disable or to |
|
set the raw bit mode. The implementation will depend on the chip, but |
|
the control should be named as “IEC958 xxx”, preferably using the |
|
:c:func:`SNDRV_CTL_NAME_IEC958()` macro. |
|
|
|
You can find several cases, for example, ``pci/emu10k1``, |
|
``pci/ice1712``, or ``pci/cmipci.c``. |
|
|
|
Buffer and Memory Management |
|
============================ |
|
|
|
Buffer Types |
|
------------ |
|
|
|
ALSA provides several different buffer allocation functions depending on |
|
the bus and the architecture. All these have a consistent API. The |
|
allocation of physically-contiguous pages is done via |
|
:c:func:`snd_malloc_xxx_pages()` function, where xxx is the bus |
|
type. |
|
|
|
The allocation of pages with fallback is |
|
:c:func:`snd_malloc_xxx_pages_fallback()`. This function tries |
|
to allocate the specified pages but if the pages are not available, it |
|
tries to reduce the page sizes until enough space is found. |
|
|
|
The release the pages, call :c:func:`snd_free_xxx_pages()` |
|
function. |
|
|
|
Usually, ALSA drivers try to allocate and reserve a large contiguous |
|
physical space at the time the module is loaded for the later use. This |
|
is called “pre-allocation”. As already written, you can call the |
|
following function at pcm instance construction time (in the case of PCI |
|
bus). |
|
|
|
:: |
|
|
|
snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, |
|
&pci->dev, size, max); |
|
|
|
where ``size`` is the byte size to be pre-allocated and the ``max`` is |
|
the maximum size to be changed via the ``prealloc`` proc file. The |
|
allocator will try to get an area as large as possible within the |
|
given size. |
|
|
|
The second argument (type) and the third argument (device pointer) are |
|
dependent on the bus. For normal devices, pass the device pointer |
|
(typically identical as ``card->dev``) to the third argument with |
|
``SNDRV_DMA_TYPE_DEV`` type. For the continuous buffer unrelated to the |
|
bus can be pre-allocated with ``SNDRV_DMA_TYPE_CONTINUOUS`` type. |
|
You can pass NULL to the device pointer in that case, which is the |
|
default mode implying to allocate with ``GFP_KERNEL`` flag. |
|
If you need a different GFP flag, you can pass it by encoding the flag |
|
into the device pointer via a special macro |
|
:c:func:`snd_dma_continuous_data()`. |
|
For the scatter-gather buffers, use ``SNDRV_DMA_TYPE_DEV_SG`` with the |
|
device pointer (see the `Non-Contiguous Buffers`_ section). |
|
|
|
Once the buffer is pre-allocated, you can use the allocator in the |
|
``hw_params`` callback: |
|
|
|
:: |
|
|
|
snd_pcm_lib_malloc_pages(substream, size); |
|
|
|
Note that you have to pre-allocate to use this function. |
|
|
|
Most of drivers use, though, rather the newly introduced "managed |
|
buffer allocation mode" instead of the manual allocation or release. |
|
This is done by calling :c:func:`snd_pcm_set_managed_buffer_all()` |
|
instead of :c:func:`snd_pcm_lib_preallocate_pages_for_all()`. |
|
|
|
:: |
|
|
|
snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV, |
|
&pci->dev, size, max); |
|
|
|
where passed arguments are identical in both functions. |
|
The difference in the managed mode is that PCM core will call |
|
:c:func:`snd_pcm_lib_malloc_pages()` internally already before calling |
|
the PCM ``hw_params`` callback, and call :c:func:`snd_pcm_lib_free_pages()` |
|
after the PCM ``hw_free`` callback automatically. So the driver |
|
doesn't have to call these functions explicitly in its callback any |
|
longer. This made many driver code having NULL ``hw_params`` and |
|
``hw_free`` entries. |
|
|
|
External Hardware Buffers |
|
------------------------- |
|
|
|
Some chips have their own hardware buffers and the DMA transfer from the |
|
host memory is not available. In such a case, you need to either 1) |
|
copy/set the audio data directly to the external hardware buffer, or 2) |
|
make an intermediate buffer and copy/set the data from it to the |
|
external hardware buffer in interrupts (or in tasklets, preferably). |
|
|
|
The first case works fine if the external hardware buffer is large |
|
enough. This method doesn't need any extra buffers and thus is more |
|
effective. You need to define the ``copy_user`` and ``copy_kernel`` |
|
callbacks for the data transfer, in addition to ``fill_silence`` |
|
callback for playback. However, there is a drawback: it cannot be |
|
mmapped. The examples are GUS's GF1 PCM or emu8000's wavetable PCM. |
|
|
|
The second case allows for mmap on the buffer, although you have to |
|
handle an interrupt or a tasklet to transfer the data from the |
|
intermediate buffer to the hardware buffer. You can find an example in |
|
the vxpocket driver. |
|
|
|
Another case is when the chip uses a PCI memory-map region for the |
|
buffer instead of the host memory. In this case, mmap is available only |
|
on certain architectures like the Intel one. In non-mmap mode, the data |
|
cannot be transferred as in the normal way. Thus you need to define the |
|
``copy_user``, ``copy_kernel`` and ``fill_silence`` callbacks as well, |
|
as in the cases above. The examples are found in ``rme32.c`` and |
|
``rme96.c``. |
|
|
|
The implementation of the ``copy_user``, ``copy_kernel`` and |
|
``silence`` callbacks depends upon whether the hardware supports |
|
interleaved or non-interleaved samples. The ``copy_user`` callback is |
|
defined like below, a bit differently depending whether the direction |
|
is playback or capture: |
|
|
|
:: |
|
|
|
static int playback_copy_user(struct snd_pcm_substream *substream, |
|
int channel, unsigned long pos, |
|
void __user *src, unsigned long count); |
|
static int capture_copy_user(struct snd_pcm_substream *substream, |
|
int channel, unsigned long pos, |
|
void __user *dst, unsigned long count); |
|
|
|
In the case of interleaved samples, the second argument (``channel``) is |
|
not used. The third argument (``pos``) points the current position |
|
offset in bytes. |
|
|
|
The meaning of the fourth argument is different between playback and |
|
capture. For playback, it holds the source data pointer, and for |
|
capture, it's the destination data pointer. |
|
|
|
The last argument is the number of bytes to be copied. |
|
|
|
What you have to do in this callback is again different between playback |
|
and capture directions. In the playback case, you copy the given amount |
|
of data (``count``) at the specified pointer (``src``) to the specified |
|
offset (``pos``) on the hardware buffer. When coded like memcpy-like |
|
way, the copy would be like: |
|
|
|
:: |
|
|
|
my_memcpy_from_user(my_buffer + pos, src, count); |
|
|
|
For the capture direction, you copy the given amount of data (``count``) |
|
at the specified offset (``pos``) on the hardware buffer to the |
|
specified pointer (``dst``). |
|
|
|
:: |
|
|
|
my_memcpy_to_user(dst, my_buffer + pos, count); |
|
|
|
Here the functions are named as ``from_user`` and ``to_user`` because |
|
it's the user-space buffer that is passed to these callbacks. That |
|
is, the callback is supposed to copy from/to the user-space data |
|
directly to/from the hardware buffer. |
|
|
|
Careful readers might notice that these callbacks receive the |
|
arguments in bytes, not in frames like other callbacks. It's because |
|
it would make coding easier like the examples above, and also it makes |
|
easier to unify both the interleaved and non-interleaved cases, as |
|
explained in the following. |
|
|
|
In the case of non-interleaved samples, the implementation will be a bit |
|
more complicated. The callback is called for each channel, passed by |
|
the second argument, so totally it's called for N-channels times per |
|
transfer. |
|
|
|
The meaning of other arguments are almost same as the interleaved |
|
case. The callback is supposed to copy the data from/to the given |
|
user-space buffer, but only for the given channel. For the detailed |
|
implementations, please check ``isa/gus/gus_pcm.c`` or |
|
"pci/rme9652/rme9652.c" as examples. |
|
|
|
The above callbacks are the copy from/to the user-space buffer. There |
|
are some cases where we want copy from/to the kernel-space buffer |
|
instead. In such a case, ``copy_kernel`` callback is called. It'd |
|
look like: |
|
|
|
:: |
|
|
|
static int playback_copy_kernel(struct snd_pcm_substream *substream, |
|
int channel, unsigned long pos, |
|
void *src, unsigned long count); |
|
static int capture_copy_kernel(struct snd_pcm_substream *substream, |
|
int channel, unsigned long pos, |
|
void *dst, unsigned long count); |
|
|
|
As found easily, the only difference is that the buffer pointer is |
|
without ``__user`` prefix; that is, a kernel-buffer pointer is passed |
|
in the fourth argument. Correspondingly, the implementation would be |
|
a version without the user-copy, such as: |
|
|
|
:: |
|
|
|
my_memcpy(my_buffer + pos, src, count); |
|
|
|
Usually for the playback, another callback ``fill_silence`` is |
|
defined. It's implemented in a similar way as the copy callbacks |
|
above: |
|
|
|
:: |
|
|
|
static int silence(struct snd_pcm_substream *substream, int channel, |
|
unsigned long pos, unsigned long count); |
|
|
|
The meanings of arguments are the same as in the ``copy_user`` and |
|
``copy_kernel`` callbacks, although there is no buffer pointer |
|
argument. In the case of interleaved samples, the channel argument has |
|
no meaning, as well as on ``copy_*`` callbacks. |
|
|
|
The role of ``fill_silence`` callback is to set the given amount |
|
(``count``) of silence data at the specified offset (``pos``) on the |
|
hardware buffer. Suppose that the data format is signed (that is, the |
|
silent-data is 0), and the implementation using a memset-like function |
|
would be like: |
|
|
|
:: |
|
|
|
my_memset(my_buffer + pos, 0, count); |
|
|
|
In the case of non-interleaved samples, again, the implementation |
|
becomes a bit more complicated, as it's called N-times per transfer |
|
for each channel. See, for example, ``isa/gus/gus_pcm.c``. |
|
|
|
Non-Contiguous Buffers |
|
---------------------- |
|
|
|
If your hardware supports the page table as in emu10k1 or the buffer |
|
descriptors as in via82xx, you can use the scatter-gather (SG) DMA. ALSA |
|
provides an interface for handling SG-buffers. The API is provided in |
|
``<sound/pcm.h>``. |
|
|
|
For creating the SG-buffer handler, call |
|
:c:func:`snd_pcm_set_managed_buffer()` or |
|
:c:func:`snd_pcm_set_managed_buffer_all()` with |
|
``SNDRV_DMA_TYPE_DEV_SG`` in the PCM constructor like other PCI |
|
pre-allocator. You need to pass ``&pci->dev``, where pci is |
|
the struct pci_dev pointer of the chip as |
|
well. |
|
|
|
:: |
|
|
|
snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_DEV_SG, |
|
&pci->dev, size, max); |
|
|
|
The ``struct snd_sg_buf`` instance is created as |
|
``substream->dma_private`` in turn. You can cast the pointer like: |
|
|
|
:: |
|
|
|
struct snd_sg_buf *sgbuf = (struct snd_sg_buf *)substream->dma_private; |
|
|
|
Then in :c:func:`snd_pcm_lib_malloc_pages()` call, the common SG-buffer |
|
handler will allocate the non-contiguous kernel pages of the given size |
|
and map them onto the virtually contiguous memory. The virtual pointer |
|
is addressed in runtime->dma_area. The physical address |
|
(``runtime->dma_addr``) is set to zero, because the buffer is |
|
physically non-contiguous. The physical address table is set up in |
|
``sgbuf->table``. You can get the physical address at a certain offset |
|
via :c:func:`snd_pcm_sgbuf_get_addr()`. |
|
|
|
If you need to release the SG-buffer data explicitly, call the |
|
standard API function :c:func:`snd_pcm_lib_free_pages()` as usual. |
|
|
|
Vmalloc'ed Buffers |
|
------------------ |
|
|
|
It's possible to use a buffer allocated via :c:func:`vmalloc()`, for |
|
example, for an intermediate buffer. In the recent version of kernel, |
|
you can simply allocate it via standard |
|
:c:func:`snd_pcm_lib_malloc_pages()` and co after setting up the |
|
buffer preallocation with ``SNDRV_DMA_TYPE_VMALLOC`` type. |
|
|
|
:: |
|
|
|
snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_VMALLOC, |
|
NULL, 0, 0); |
|
|
|
The NULL is passed to the device pointer argument, which indicates |
|
that the default pages (GFP_KERNEL and GFP_HIGHMEM) will be |
|
allocated. |
|
|
|
Also, note that zero is passed to both the size and the max size |
|
arguments here. Since each vmalloc call should succeed at any time, |
|
we don't need to pre-allocate the buffers like other continuous |
|
pages. |
|
|
|
If you need the 32bit DMA allocation, pass the device pointer encoded |
|
by :c:func:`snd_dma_continuous_data()` with ``GFP_KERNEL|__GFP_DMA32`` |
|
argument. |
|
|
|
:: |
|
|
|
snd_pcm_set_managed_buffer_all(pcm, SNDRV_DMA_TYPE_VMALLOC, |
|
snd_dma_continuous_data(GFP_KERNEL | __GFP_DMA32), 0, 0); |
|
|
|
Proc Interface |
|
============== |
|
|
|
ALSA provides an easy interface for procfs. The proc files are very |
|
useful for debugging. I recommend you set up proc files if you write a |
|
driver and want to get a running status or register dumps. The API is |
|
found in ``<sound/info.h>``. |
|
|
|
To create a proc file, call :c:func:`snd_card_proc_new()`. |
|
|
|
:: |
|
|
|
struct snd_info_entry *entry; |
|
int err = snd_card_proc_new(card, "my-file", &entry); |
|
|
|
where the second argument specifies the name of the proc file to be |
|
created. The above example will create a file ``my-file`` under the |
|
card directory, e.g. ``/proc/asound/card0/my-file``. |
|
|
|
Like other components, the proc entry created via |
|
:c:func:`snd_card_proc_new()` will be registered and released |
|
automatically in the card registration and release functions. |
|
|
|
When the creation is successful, the function stores a new instance in |
|
the pointer given in the third argument. It is initialized as a text |
|
proc file for read only. To use this proc file as a read-only text file |
|
as it is, set the read callback with a private data via |
|
:c:func:`snd_info_set_text_ops()`. |
|
|
|
:: |
|
|
|
snd_info_set_text_ops(entry, chip, my_proc_read); |
|
|
|
where the second argument (``chip``) is the private data to be used in |
|
the callbacks. The third parameter specifies the read buffer size and |
|
the fourth (``my_proc_read``) is the callback function, which is |
|
defined like |
|
|
|
:: |
|
|
|
static void my_proc_read(struct snd_info_entry *entry, |
|
struct snd_info_buffer *buffer); |
|
|
|
In the read callback, use :c:func:`snd_iprintf()` for output |
|
strings, which works just like normal :c:func:`printf()`. For |
|
example, |
|
|
|
:: |
|
|
|
static void my_proc_read(struct snd_info_entry *entry, |
|
struct snd_info_buffer *buffer) |
|
{ |
|
struct my_chip *chip = entry->private_data; |
|
|
|
snd_iprintf(buffer, "This is my chip!\n"); |
|
snd_iprintf(buffer, "Port = %ld\n", chip->port); |
|
} |
|
|
|
The file permissions can be changed afterwards. As default, it's set as |
|
read only for all users. If you want to add write permission for the |
|
user (root as default), do as follows: |
|
|
|
:: |
|
|
|
entry->mode = S_IFREG | S_IRUGO | S_IWUSR; |
|
|
|
and set the write buffer size and the callback |
|
|
|
:: |
|
|
|
entry->c.text.write = my_proc_write; |
|
|
|
For the write callback, you can use :c:func:`snd_info_get_line()` |
|
to get a text line, and :c:func:`snd_info_get_str()` to retrieve |
|
a string from the line. Some examples are found in |
|
``core/oss/mixer_oss.c``, core/oss/and ``pcm_oss.c``. |
|
|
|
For a raw-data proc-file, set the attributes as follows: |
|
|
|
:: |
|
|
|
static const struct snd_info_entry_ops my_file_io_ops = { |
|
.read = my_file_io_read, |
|
}; |
|
|
|
entry->content = SNDRV_INFO_CONTENT_DATA; |
|
entry->private_data = chip; |
|
entry->c.ops = &my_file_io_ops; |
|
entry->size = 4096; |
|
entry->mode = S_IFREG | S_IRUGO; |
|
|
|
For the raw data, ``size`` field must be set properly. This specifies |
|
the maximum size of the proc file access. |
|
|
|
The read/write callbacks of raw mode are more direct than the text mode. |
|
You need to use a low-level I/O functions such as |
|
:c:func:`copy_from_user()` and :c:func:`copy_to_user()` to transfer the data. |
|
|
|
:: |
|
|
|
static ssize_t my_file_io_read(struct snd_info_entry *entry, |
|
void *file_private_data, |
|
struct file *file, |
|
char *buf, |
|
size_t count, |
|
loff_t pos) |
|
{ |
|
if (copy_to_user(buf, local_data + pos, count)) |
|
return -EFAULT; |
|
return count; |
|
} |
|
|
|
If the size of the info entry has been set up properly, ``count`` and |
|
``pos`` are guaranteed to fit within 0 and the given size. You don't |
|
have to check the range in the callbacks unless any other condition is |
|
required. |
|
|
|
Power Management |
|
================ |
|
|
|
If the chip is supposed to work with suspend/resume functions, you need |
|
to add power-management code to the driver. The additional code for |
|
power-management should be ifdef-ed with ``CONFIG_PM``, or annotated |
|
with __maybe_unused attribute; otherwise the compiler will complain |
|
you. |
|
|
|
If the driver *fully* supports suspend/resume that is, the device can be |
|
properly resumed to its state when suspend was called, you can set the |
|
``SNDRV_PCM_INFO_RESUME`` flag in the pcm info field. Usually, this is |
|
possible when the registers of the chip can be safely saved and restored |
|
to RAM. If this is set, the trigger callback is called with |
|
``SNDRV_PCM_TRIGGER_RESUME`` after the resume callback completes. |
|
|
|
Even if the driver doesn't support PM fully but partial suspend/resume |
|
is still possible, it's still worthy to implement suspend/resume |
|
callbacks. In such a case, applications would reset the status by |
|
calling :c:func:`snd_pcm_prepare()` and restart the stream |
|
appropriately. Hence, you can define suspend/resume callbacks below but |
|
don't set ``SNDRV_PCM_INFO_RESUME`` info flag to the PCM. |
|
|
|
Note that the trigger with SUSPEND can always be called when |
|
:c:func:`snd_pcm_suspend_all()` is called, regardless of the |
|
``SNDRV_PCM_INFO_RESUME`` flag. The ``RESUME`` flag affects only the |
|
behavior of :c:func:`snd_pcm_resume()`. (Thus, in theory, |
|
``SNDRV_PCM_TRIGGER_RESUME`` isn't needed to be handled in the trigger |
|
callback when no ``SNDRV_PCM_INFO_RESUME`` flag is set. But, it's better |
|
to keep it for compatibility reasons.) |
|
|
|
In the earlier version of ALSA drivers, a common power-management layer |
|
was provided, but it has been removed. The driver needs to define the |
|
suspend/resume hooks according to the bus the device is connected to. In |
|
the case of PCI drivers, the callbacks look like below: |
|
|
|
:: |
|
|
|
static int __maybe_unused snd_my_suspend(struct device *dev) |
|
{ |
|
.... /* do things for suspend */ |
|
return 0; |
|
} |
|
static int __maybe_unused snd_my_resume(struct device *dev) |
|
{ |
|
.... /* do things for suspend */ |
|
return 0; |
|
} |
|
|
|
The scheme of the real suspend job is as follows. |
|
|
|
1. Retrieve the card and the chip data. |
|
|
|
2. Call :c:func:`snd_power_change_state()` with |
|
``SNDRV_CTL_POWER_D3hot`` to change the power status. |
|
|
|
3. If AC97 codecs are used, call :c:func:`snd_ac97_suspend()` for |
|
each codec. |
|
|
|
4. Save the register values if necessary. |
|
|
|
5. Stop the hardware if necessary. |
|
|
|
A typical code would be like: |
|
|
|
:: |
|
|
|
static int __maybe_unused mychip_suspend(struct device *dev) |
|
{ |
|
/* (1) */ |
|
struct snd_card *card = dev_get_drvdata(dev); |
|
struct mychip *chip = card->private_data; |
|
/* (2) */ |
|
snd_power_change_state(card, SNDRV_CTL_POWER_D3hot); |
|
/* (3) */ |
|
snd_ac97_suspend(chip->ac97); |
|
/* (4) */ |
|
snd_mychip_save_registers(chip); |
|
/* (5) */ |
|
snd_mychip_stop_hardware(chip); |
|
return 0; |
|
} |
|
|
|
|
|
The scheme of the real resume job is as follows. |
|
|
|
1. Retrieve the card and the chip data. |
|
|
|
2. Re-initialize the chip. |
|
|
|
3. Restore the saved registers if necessary. |
|
|
|
4. Resume the mixer, e.g. calling :c:func:`snd_ac97_resume()`. |
|
|
|
5. Restart the hardware (if any). |
|
|
|
6. Call :c:func:`snd_power_change_state()` with |
|
``SNDRV_CTL_POWER_D0`` to notify the processes. |
|
|
|
A typical code would be like: |
|
|
|
:: |
|
|
|
static int __maybe_unused mychip_resume(struct pci_dev *pci) |
|
{ |
|
/* (1) */ |
|
struct snd_card *card = dev_get_drvdata(dev); |
|
struct mychip *chip = card->private_data; |
|
/* (2) */ |
|
snd_mychip_reinit_chip(chip); |
|
/* (3) */ |
|
snd_mychip_restore_registers(chip); |
|
/* (4) */ |
|
snd_ac97_resume(chip->ac97); |
|
/* (5) */ |
|
snd_mychip_restart_chip(chip); |
|
/* (6) */ |
|
snd_power_change_state(card, SNDRV_CTL_POWER_D0); |
|
return 0; |
|
} |
|
|
|
Note that, at the time this callback gets called, the PCM stream has |
|
been already suspended via its own PM ops calling |
|
:c:func:`snd_pcm_suspend_all()` internally. |
|
|
|
OK, we have all callbacks now. Let's set them up. In the initialization |
|
of the card, make sure that you can get the chip data from the card |
|
instance, typically via ``private_data`` field, in case you created the |
|
chip data individually. |
|
|
|
:: |
|
|
|
static int snd_mychip_probe(struct pci_dev *pci, |
|
const struct pci_device_id *pci_id) |
|
{ |
|
.... |
|
struct snd_card *card; |
|
struct mychip *chip; |
|
int err; |
|
.... |
|
err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, |
|
0, &card); |
|
.... |
|
chip = kzalloc(sizeof(*chip), GFP_KERNEL); |
|
.... |
|
card->private_data = chip; |
|
.... |
|
} |
|
|
|
When you created the chip data with :c:func:`snd_card_new()`, it's |
|
anyway accessible via ``private_data`` field. |
|
|
|
:: |
|
|
|
static int snd_mychip_probe(struct pci_dev *pci, |
|
const struct pci_device_id *pci_id) |
|
{ |
|
.... |
|
struct snd_card *card; |
|
struct mychip *chip; |
|
int err; |
|
.... |
|
err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE, |
|
sizeof(struct mychip), &card); |
|
.... |
|
chip = card->private_data; |
|
.... |
|
} |
|
|
|
If you need a space to save the registers, allocate the buffer for it |
|
here, too, since it would be fatal if you cannot allocate a memory in |
|
the suspend phase. The allocated buffer should be released in the |
|
corresponding destructor. |
|
|
|
And next, set suspend/resume callbacks to the pci_driver. |
|
|
|
:: |
|
|
|
static SIMPLE_DEV_PM_OPS(snd_my_pm_ops, mychip_suspend, mychip_resume); |
|
|
|
static struct pci_driver driver = { |
|
.name = KBUILD_MODNAME, |
|
.id_table = snd_my_ids, |
|
.probe = snd_my_probe, |
|
.remove = snd_my_remove, |
|
.driver.pm = &snd_my_pm_ops, |
|
}; |
|
|
|
Module Parameters |
|
================= |
|
|
|
There are standard module options for ALSA. At least, each module should |
|
have the ``index``, ``id`` and ``enable`` options. |
|
|
|
If the module supports multiple cards (usually up to 8 = ``SNDRV_CARDS`` |
|
cards), they should be arrays. The default initial values are defined |
|
already as constants for easier programming: |
|
|
|
:: |
|
|
|
static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX; |
|
static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR; |
|
static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP; |
|
|
|
If the module supports only a single card, they could be single |
|
variables, instead. ``enable`` option is not always necessary in this |
|
case, but it would be better to have a dummy option for compatibility. |
|
|
|
The module parameters must be declared with the standard |
|
``module_param()``, ``module_param_array()`` and |
|
:c:func:`MODULE_PARM_DESC()` macros. |
|
|
|
The typical coding would be like below: |
|
|
|
:: |
|
|
|
#define CARD_NAME "My Chip" |
|
|
|
module_param_array(index, int, NULL, 0444); |
|
MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard."); |
|
module_param_array(id, charp, NULL, 0444); |
|
MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard."); |
|
module_param_array(enable, bool, NULL, 0444); |
|
MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard."); |
|
|
|
Also, don't forget to define the module description and the license. |
|
Especially, the recent modprobe requires to define the |
|
module license as GPL, etc., otherwise the system is shown as “tainted”. |
|
|
|
:: |
|
|
|
MODULE_DESCRIPTION("Sound driver for My Chip"); |
|
MODULE_LICENSE("GPL"); |
|
|
|
|
|
Device-Managed Resources |
|
======================== |
|
|
|
In the examples above, all resources are allocated and released |
|
manually. But human beings are lazy in nature, especially developers |
|
are lazier. So there are some ways to automate the release part; it's |
|
the (device-)managed resources aka devres or devm family. For |
|
example, an object allocated via :c:func:`devm_kmalloc()` will be |
|
freed automatically at unbinding the device. |
|
|
|
ALSA core provides also the device-managed helper, namely, |
|
:c:func:`snd_devm_card_new()` for creating a card object. |
|
Call this functions instead of the normal :c:func:`snd_card_new()`, |
|
and you can forget the explicit :c:func:`snd_card_free()` call, as |
|
it's called automagically at error and removal paths. |
|
|
|
One caveat is that the call of :c:func:`snd_card_free()` would be put |
|
at the beginning of the call chain only after you call |
|
:c:func:`snd_card_register()`. |
|
|
|
Also, the ``private_free`` callback is always called at the card free, |
|
so be careful to put the hardware clean-up procedure in |
|
``private_free`` callback. It might be called even before you |
|
actually set up at an earlier error path. For avoiding such an |
|
invalid initialization, you can set ``private_free`` callback after |
|
:c:func:`snd_card_register()` call succeeds. |
|
|
|
Another thing to be remarked is that you should use device-managed |
|
helpers for each component as much as possible once when you manage |
|
the card in that way. Mixing up with the normal and the managed |
|
resources may screw up the release order. |
|
|
|
|
|
How To Put Your Driver Into ALSA Tree |
|
===================================== |
|
|
|
General |
|
------- |
|
|
|
So far, you've learned how to write the driver codes. And you might have |
|
a question now: how to put my own driver into the ALSA driver tree? Here |
|
(finally :) the standard procedure is described briefly. |
|
|
|
Suppose that you create a new PCI driver for the card “xyz”. The card |
|
module name would be snd-xyz. The new driver is usually put into the |
|
alsa-driver tree, ``sound/pci`` directory in the case of PCI |
|
cards. |
|
|
|
In the following sections, the driver code is supposed to be put into |
|
Linux kernel tree. The two cases are covered: a driver consisting of a |
|
single source file and one consisting of several source files. |
|
|
|
Driver with A Single Source File |
|
-------------------------------- |
|
|
|
1. Modify sound/pci/Makefile |
|
|
|
Suppose you have a file xyz.c. Add the following two lines |
|
|
|
:: |
|
|
|
snd-xyz-objs := xyz.o |
|
obj-$(CONFIG_SND_XYZ) += snd-xyz.o |
|
|
|
2. Create the Kconfig entry |
|
|
|
Add the new entry of Kconfig for your xyz driver. config SND_XYZ |
|
tristate "Foobar XYZ" depends on SND select SND_PCM help Say Y here |
|
to include support for Foobar XYZ soundcard. To compile this driver |
|
as a module, choose M here: the module will be called snd-xyz. the |
|
line, select SND_PCM, specifies that the driver xyz supports PCM. In |
|
addition to SND_PCM, the following components are supported for |
|
select command: SND_RAWMIDI, SND_TIMER, SND_HWDEP, |
|
SND_MPU401_UART, SND_OPL3_LIB, SND_OPL4_LIB, SND_VX_LIB, |
|
SND_AC97_CODEC. Add the select command for each supported |
|
component. |
|
|
|
Note that some selections imply the lowlevel selections. For example, |
|
PCM includes TIMER, MPU401_UART includes RAWMIDI, AC97_CODEC |
|
includes PCM, and OPL3_LIB includes HWDEP. You don't need to give |
|
the lowlevel selections again. |
|
|
|
For the details of Kconfig script, refer to the kbuild documentation. |
|
|
|
Drivers with Several Source Files |
|
--------------------------------- |
|
|
|
Suppose that the driver snd-xyz have several source files. They are |
|
located in the new subdirectory, sound/pci/xyz. |
|
|
|
1. Add a new directory (``sound/pci/xyz``) in ``sound/pci/Makefile`` |
|
as below |
|
|
|
:: |
|
|
|
obj-$(CONFIG_SND) += sound/pci/xyz/ |
|
|
|
|
|
2. Under the directory ``sound/pci/xyz``, create a Makefile |
|
|
|
:: |
|
|
|
snd-xyz-objs := xyz.o abc.o def.o |
|
obj-$(CONFIG_SND_XYZ) += snd-xyz.o |
|
|
|
3. Create the Kconfig entry |
|
|
|
This procedure is as same as in the last section. |
|
|
|
|
|
Useful Functions |
|
================ |
|
|
|
:c:func:`snd_printk()` and friends |
|
---------------------------------- |
|
|
|
.. note:: This subsection describes a few helper functions for |
|
decorating a bit more on the standard :c:func:`printk()` & co. |
|
However, in general, the use of such helpers is no longer recommended. |
|
If possible, try to stick with the standard functions like |
|
:c:func:`dev_err()` or :c:func:`pr_err()`. |
|
|
|
ALSA provides a verbose version of the :c:func:`printk()` function. |
|
If a kernel config ``CONFIG_SND_VERBOSE_PRINTK`` is set, this function |
|
prints the given message together with the file name and the line of the |
|
caller. The ``KERN_XXX`` prefix is processed as well as the original |
|
:c:func:`printk()` does, so it's recommended to add this prefix, |
|
e.g. snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\\n"); |
|
|
|
There are also :c:func:`printk()`'s for debugging. |
|
:c:func:`snd_printd()` can be used for general debugging purposes. |
|
If ``CONFIG_SND_DEBUG`` is set, this function is compiled, and works |
|
just like :c:func:`snd_printk()`. If the ALSA is compiled without |
|
the debugging flag, it's ignored. |
|
|
|
:c:func:`snd_printdd()` is compiled in only when |
|
``CONFIG_SND_DEBUG_VERBOSE`` is set. |
|
|
|
:c:func:`snd_BUG()` |
|
------------------- |
|
|
|
It shows the ``BUG?`` message and stack trace as well as |
|
:c:func:`snd_BUG_ON()` at the point. It's useful to show that a |
|
fatal error happens there. |
|
|
|
When no debug flag is set, this macro is ignored. |
|
|
|
:c:func:`snd_BUG_ON()` |
|
---------------------- |
|
|
|
:c:func:`snd_BUG_ON()` macro is similar with |
|
:c:func:`WARN_ON()` macro. For example, snd_BUG_ON(!pointer); or |
|
it can be used as the condition, if (snd_BUG_ON(non_zero_is_bug)) |
|
return -EINVAL; |
|
|
|
The macro takes an conditional expression to evaluate. When |
|
``CONFIG_SND_DEBUG``, is set, if the expression is non-zero, it shows |
|
the warning message such as ``BUG? (xxx)`` normally followed by stack |
|
trace. In both cases it returns the evaluated value. |
|
|
|
Acknowledgments |
|
=============== |
|
|
|
I would like to thank Phil Kerr for his help for improvement and |
|
corrections of this document. |
|
|
|
Kevin Conder reformatted the original plain-text to the DocBook format. |
|
|
|
Giuliano Pochini corrected typos and contributed the example codes in |
|
the hardware constraints section.
|
|
|