Serial TTY line discipline

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。

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。
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

Components description

从客户端应用程序到硬件

• 应用程序：客户应用程序，用于从串行端口上连接的外围设备读取/写入数据。

• TTY tools: Linux社区提供的工具，例 stty, ldattach, inputattach, tty, ttys, agetty, mingetty, kermit and minicom.

• Termios: API 提供使用串行驱动程序开发应用程序的接口。
• 客户端子系统：TTY内核的内核子系统客户端（示例：蓝牙设备）

• TTY框架：高层TTY结构管理，包括 drivers/tty/tty_io.c | |}} tty character device driver , drivers/tty | |}} TTY core functions , line discipline.

• 串行框架：低级串行驱动程序管理，包括drivers/tty/serial/serial_core.c | |}} serial core functions .

• USART驱动程序：drivers/tty/serial/stm32-usart.c | |}} stm32-usart '“低级串行驱动程序'”，用于所有stm32系列设备。
• STM32 USART: STM32前端IP 通过串行端口连接到外部设备

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.

The termios API is a user land API, and its functions describe a general terminal interface that is provided to control asynchronous communications ports.

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 ioctl operations.

A 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. <securetransclude src="ProtectedTemplate:ReviewsComments" params="FGA W1941: I rephrased above note, can you please double-ckeck ?"></securetransclude>{{#set:Has reviews comments=true}}

• The line discipline will be responsible for:
  • creating this new kernel API
  • routing data flow between serial core and new kernel API
    

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References