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174 lines
7.2 KiB
174 lines
7.2 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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=============================== |
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Linux Drivers for Baycom Modems |
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=============================== |
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Thomas M. Sailer, HB9JNX/AE4WA, <[email protected]> |
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The drivers for the baycom modems have been split into |
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separate drivers as they did not share any code, and the driver |
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and device names have changed. |
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This document describes the Linux Kernel Drivers for simple Baycom style |
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amateur radio modems. |
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The following drivers are available: |
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==================================== |
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baycom_ser_fdx: |
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This driver supports the SER12 modems either full or half duplex. |
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Its baud rate may be changed via the ``baud`` module parameter, |
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therefore it supports just about every bit bang modem on a |
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serial port. Its devices are called bcsf0 through bcsf3. |
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This is the recommended driver for SER12 type modems, |
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however if you have a broken UART clone that does not have working |
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delta status bits, you may try baycom_ser_hdx. |
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baycom_ser_hdx: |
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This is an alternative driver for SER12 type modems. |
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It only supports half duplex, and only 1200 baud. Its devices |
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are called bcsh0 through bcsh3. Use this driver only if baycom_ser_fdx |
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does not work with your UART. |
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baycom_par: |
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This driver supports the par96 and picpar modems. |
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Its devices are called bcp0 through bcp3. |
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baycom_epp: |
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This driver supports the EPP modem. |
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Its devices are called bce0 through bce3. |
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This driver is work-in-progress. |
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The following modems are supported: |
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======= ======================================================================== |
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ser12 This is a very simple 1200 baud AFSK modem. The modem consists only |
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of a modulator/demodulator chip, usually a TI TCM3105. The computer |
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is responsible for regenerating the receiver bit clock, as well as |
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for handling the HDLC protocol. The modem connects to a serial port, |
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hence the name. Since the serial port is not used as an async serial |
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port, the kernel driver for serial ports cannot be used, and this |
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driver only supports standard serial hardware (8250, 16450, 16550) |
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par96 This is a modem for 9600 baud FSK compatible to the G3RUH standard. |
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The modem does all the filtering and regenerates the receiver clock. |
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Data is transferred from and to the PC via a shift register. |
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The shift register is filled with 16 bits and an interrupt is signalled. |
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The PC then empties the shift register in a burst. This modem connects |
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to the parallel port, hence the name. The modem leaves the |
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implementation of the HDLC protocol and the scrambler polynomial to |
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the PC. |
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picpar This is a redesign of the par96 modem by Henning Rech, DF9IC. The modem |
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is protocol compatible to par96, but uses only three low power ICs |
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and can therefore be fed from the parallel port and does not require |
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an additional power supply. Furthermore, it incorporates a carrier |
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detect circuitry. |
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EPP This is a high-speed modem adaptor that connects to an enhanced parallel |
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port. |
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Its target audience is users working over a high speed hub (76.8kbit/s). |
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eppfpga This is a redesign of the EPP adaptor. |
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======= ======================================================================== |
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All of the above modems only support half duplex communications. However, |
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the driver supports the KISS (see below) fullduplex command. It then simply |
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starts to send as soon as there's a packet to transmit and does not care |
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about DCD, i.e. it starts to send even if there's someone else on the channel. |
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This command is required by some implementations of the DAMA channel |
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access protocol. |
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The Interface of the drivers |
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============================ |
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Unlike previous drivers, these drivers are no longer character devices, |
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but they are now true kernel network interfaces. Installation is therefore |
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simple. Once installed, four interfaces named bc{sf,sh,p,e}[0-3] are available. |
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sethdlc from the ax25 utilities may be used to set driver states etc. |
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Users of userland AX.25 stacks may use the net2kiss utility (also available |
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in the ax25 utilities package) to convert packets of a network interface |
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to a KISS stream on a pseudo tty. There's also a patch available from |
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me for WAMPES which allows attaching a kernel network interface directly. |
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Configuring the driver |
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====================== |
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Every time a driver is inserted into the kernel, it has to know which |
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modems it should access at which ports. This can be done with the setbaycom |
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utility. If you are only using one modem, you can also configure the |
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driver from the insmod command line (or by means of an option line in |
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``/etc/modprobe.d/*.conf``). |
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Examples:: |
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modprobe baycom_ser_fdx mode="ser12*" iobase=0x3f8 irq=4 |
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sethdlc -i bcsf0 -p mode "ser12*" io 0x3f8 irq 4 |
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Both lines configure the first port to drive a ser12 modem at the first |
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serial port (COM1 under DOS). The * in the mode parameter instructs the driver |
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to use the software DCD algorithm (see below):: |
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insmod baycom_par mode="picpar" iobase=0x378 |
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sethdlc -i bcp0 -p mode "picpar" io 0x378 |
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Both lines configure the first port to drive a picpar modem at the |
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first parallel port (LPT1 under DOS). (Note: picpar implies |
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hardware DCD, par96 implies software DCD). |
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The channel access parameters can be set with sethdlc -a or kissparms. |
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Note that both utilities interpret the values slightly differently. |
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Hardware DCD versus Software DCD |
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================================ |
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To avoid collisions on the air, the driver must know when the channel is |
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busy. This is the task of the DCD circuitry/software. The driver may either |
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utilise a software DCD algorithm (options=1) or use a DCD signal from |
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the hardware (options=0). |
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======= ================================================================= |
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ser12 if software DCD is utilised, the radio's squelch should always be |
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open. It is highly recommended to use the software DCD algorithm, |
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as it is much faster than most hardware squelch circuitry. The |
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disadvantage is a slightly higher load on the system. |
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par96 the software DCD algorithm for this type of modem is rather poor. |
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The modem simply does not provide enough information to implement |
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a reasonable DCD algorithm in software. Therefore, if your radio |
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feeds the DCD input of the PAR96 modem, the use of the hardware |
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DCD circuitry is recommended. |
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picpar the picpar modem features a builtin DCD hardware, which is highly |
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recommended. |
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======= ================================================================= |
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Compatibility with the rest of the Linux kernel |
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=============================================== |
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The serial driver and the baycom serial drivers compete |
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for the same hardware resources. Of course only one driver can access a given |
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interface at a time. The serial driver grabs all interfaces it can find at |
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startup time. Therefore the baycom drivers subsequently won't be able to |
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access a serial port. You might therefore find it necessary to release |
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a port owned by the serial driver with 'setserial /dev/ttyS# uart none', where |
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# is the number of the interface. The baycom drivers do not reserve any |
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ports at startup, unless one is specified on the 'insmod' command line. Another |
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method to solve the problem is to compile all drivers as modules and |
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leave it to kmod to load the correct driver depending on the application. |
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The parallel port drivers (baycom_par, baycom_epp) now use the parport subsystem |
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to arbitrate the ports between different client drivers. |
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vy 73s de |
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Tom Sailer, [email protected] |
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hb9jnx @ hb9w.ampr.org
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