自动改变为RS-485通信RTS

问题描述

我试图建立半双工通信在我的计划。我已经使用RTS标志（TIOCM_RTS）来传输之间来回切换，并接受我的RS485收发器。和发送/接收数据，我需要手动更改RTS标志：

1. 设置RTS为高。




2. 发送数据。




3. 设置RTS为低。

     INT setRTS（INT级）{
       INT状态;
       的ioctl（ser_port，TIOCMGET，＆安培;状态）;
       如果（水平）{
           状态| = TIOCM_RTS;
       }其他{
           状态和放大器; =〜TIOCM_RTS;
       }
       的ioctl（ser_port，TIOCMSET，＆安培;状态）;
       返回1;
   }
    

我的问题是：不应该在Linux内核能够自动切换RTS？
而如何保证数据调用之前被送到setRTS（0）？

解决方案

Yes, there is kernel framework for this starting in Linux 3.0.
There are two ioctls in include/uapi/asm-generic/ioctls.h:

#define TIOCGRS485      0x542E
#define TIOCSRS485      0x542F

to retrieve and configure a tty serial port driver in RS-485 mode.
These ioctls use the struct serial_rs485:

 /*
  * Serial interface for controlling RS485 settings on chips with suitable
  * support. Set with TIOCSRS485 and get with TIOCGRS485 if supported by your
  * platform. The set function returns the new state, with any unsupported bits
  * reverted appropriately.
  */

 struct serial_rs485 {
         __u32   flags;                  /* RS485 feature flags */
 #define SER_RS485_ENABLED               (1 << 0)        /* If enabled */
 #define SER_RS485_RTS_ON_SEND           (1 << 1)        /* Logical level for
                                                            RTS pin when
                                                            sending */
 #define SER_RS485_RTS_AFTER_SEND        (1 << 2)        /* Logical level for
                                                            RTS pin after sent*/
 #define SER_RS485_RX_DURING_TX          (1 << 4)
         __u32   delay_rts_before_send;  /* Delay before send (milliseconds) */
         __u32   delay_rts_after_send;   /* Delay after send (milliseconds) */
         __u32   padding[5];             /* Memory is cheap, new structs
                                            are a royal PITA .. */
 };

I've used this RS-485 capabilty on Atmel and Etrax SoCs, but otherwise implementation of these ioctls in Linux UART/USART drivers is very sparse.
If your driver doesn't have it, then consider implementing it yourself. You could use the implementation in drivers/tty/serial/atmel_serial.c as a guide. Also read the Linux kernel document for RS485.

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