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63 lines
2.3 KiB
63 lines
2.3 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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=== |
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TTY |
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=== |
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Teletypewriter (TTY) layer takes care of all those serial devices. Including |
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the virtual ones like pseudoterminal (PTY). |
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TTY structures |
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============== |
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There are several major TTY structures. Every TTY device in a system has a |
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corresponding struct tty_port. These devices are maintained by a TTY driver |
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which is struct tty_driver. This structure describes the driver but also |
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contains a reference to operations which could be performed on the TTYs. It is |
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struct tty_operations. Then, upon open, a struct tty_struct is allocated and |
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lives until the final close. During this time, several callbacks from struct |
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tty_operations are invoked by the TTY layer. |
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Every character received by the kernel (both from devices and users) is passed |
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through a preselected :doc:`tty_ldisc` (in |
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short ldisc; in C, struct tty_ldisc_ops). Its task is to transform characters |
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as defined by a particular ldisc or by user too. The default one is n_tty, |
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implementing echoes, signal handling, jobs control, special characters |
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processing, and more. The transformed characters are passed further to |
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user/device, depending on the source. |
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In-detail description of the named TTY structures is in separate documents: |
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.. toctree:: |
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:maxdepth: 2 |
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tty_driver |
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tty_port |
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tty_struct |
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tty_ldisc |
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tty_buffer |
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n_tty |
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tty_internals |
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Writing TTY Driver |
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================== |
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Before one starts writing a TTY driver, they must consider |
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:doc:`Serial <../driver-api/serial/driver>` and :doc:`USB Serial |
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<../usb/usb-serial>` layers |
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first. Drivers for serial devices can often use one of these specific layers to |
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implement a serial driver. Only special devices should be handled directly by |
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the TTY Layer. If you are about to write such a driver, read on. |
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A *typical* sequence a TTY driver performs is as follows: |
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#. Allocate and register a TTY driver (module init) |
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#. Create and register TTY devices as they are probed (probe function) |
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#. Handle TTY operations and events like interrupts (TTY core invokes the |
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former, the device the latter) |
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#. Remove devices as they are going away (remove function) |
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#. Unregister and free the TTY driver (module exit) |
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Steps regarding driver, i.e. 1., 3., and 5. are described in detail in |
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:doc:`tty_driver`. For the other two (devices handling), look into |
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:doc:`tty_port`.
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