查看“Serial TTY line discipline”的源代码

本文提供有关 Linux® TTY 框架的信息。 它说明了如何使用线路规则激活“ UART”接口，以及如何从用户和内核空间访问它。<br />

==Framework purpose==
UART是几种设备类型（例如蓝牙，NFC，FM收音机和GPS设备）的通用接口。 <br/>
从内核版本4.12开始，TTY框架中引入了串行设备总线（也称为Serdev），以改善提供给连接到串行端口的设备的接口。 请参考 [[Serial TTY overview]]文章，以详细了解TTY框架的用途。尽管如此，仍然有可能（即使不推荐）使用行规“驱动程序”。
本文重点介绍提供给连接到串行端口的设备的线路规范接口。

==System overview==
[[File:Serial TTY Line Discipline overview.png|center|link=]]
<br/>

===Components description===
''From client application to hardware''
* Application: customer application to read/write data from the peripheral connected on the serial port.

* [[TTY tools]]: tools provided by Linux community, such as '''stty''', '''ldattach''', '''inputattach''', '''tty''', '''ttys''', '''agetty''', '''mingetty''', '''kermit''' and '''minicom'''.
{{ReviewsComments|FGA W1941: I can't find TTY tools in above figure. Is it relevant here?.}}
* Termios: API<ref name="termios API">[http://man7.org/linux/man-pages/man3/termios.3.html termios API], Linux Programmer's Manual termios API Documentation (user land API with serial devices)</ref> which offers an interface to develop an application using serial drivers.
*Client subsystem: kernel subsystem client of '''TTY''' core (Example:  a Bluetooth device)
{{ReviewsComments|FGA W1941: I can't find "Client subsystem" in above figure.}}
* TTY framework: high-level TTY structures management, including {{CodeSource | Linux kernel | drivers/tty/tty_io.c | '''tty character device driver'''}}, {{CodeSource | Linux kernel | drivers/tty | '''TTY core functions'''}}, [[Serial TTY line discipline| '''line discipline''']].
{{ReviewsComments|FGA W1941: "TTY framework" -> "TTY Core" in above figure ?}}
* Serial framework: low-level serial driver management, including the {{CodeSource | Linux kernel | drivers/tty/serial/serial_core.c | '''serial core''' functions}}.
{{ReviewsComments|FGA W1941: "Serial framework" -> "Serial Core" in above figure ?}}
* USART driver: {{CodeSource | Linux kernel | drivers/tty/serial/stm32-usart.c | stm32-usart}} '''low-level serial driver''' for all stm32 family devices.

* [[USART internal peripheral| STM32 USART]]: '''STM32 frontend IP''' connected to the external devices through a serial port
{{ReviewsComments|FGA W1941: Maybe worth adding the external device in the above figure ?}}

===APIs description===

The TTY provides only '''character device interface''' (named /dev/ttyX) to user space.
The main API for user space TTY client applications is provided by the portable POSIX terminal interface termios, which relies on /dev/ttyX interface for TTY link configuration.<br/>

The '''termios API'''<ref name="termios API"/> is a user land API, and its functions describe a general terminal interface that is provided to control asynchronous communications ports. <br/>

The POSIX termios API abstracts the low-level details of the hardware, and provides a simple yet complete programming interface that can be used for advanced projects. It is a wrapper on '''character device API''' <ref> [http://bootlin.com/doc/accessing-hardware.pdf Character device API overview], ''Accessing hardware from userspace'' training, Bootlin documentation</ref> ioctl operations.<br/>

{{Info|A [[Serial TTY line discipline|'''line discipline''']] driver can be used when a serial interface is needed at kernel level.}}
For example, a kernel driver maybe needed to control an external device through an U(S)ART port.
{{ReviewsComments|FGA W1941: I rephrased above note, can you please double-ckeck ?}}
* The '''line discipline''' will be responsible for:
** creating this new kernel API
** routing data flow between serial core and new kernel API <br/>

{{ReviewsComments|FGA W1941: No how to use section, nor examples ? Is it deliberate ?<br/>
FGA W1941: Maybe worth pointing out some existing examples in the kernel ?}}

==References==
<references />

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[[Category:Serial TTY|6]]
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