Serial TTY line discipline

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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

Serial TTY Line Discipline overview.png


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[1] 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)

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[1] 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 [2] ioctl operations.

Info.png 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

  1. 1.01.1 termios API, Linux Programmer's Manual termios API Documentation (user land API with serial devices)
  2. Character device API overview, Accessing hardware from userspace training, Bootlin documentation