请教关于 freemodbus的 usTimerT35_50us

发布于 2021-11-22 20:46:56 浏览：1150 订阅该版

```c
eMBErrorCode
eMBMasterRTUInit(UCHAR ucPort, ULONG ulBaudRate, eMBParity eParity )
{
    eMBErrorCode    eStatus = MB_ENOERR;
    ULONG           usTimerT35_50us;

ENTER_CRITICAL_SECTION(  );

/* Modbus RTU uses 8 Databits. */
    if( xMBMasterPortSerialInit( ucPort, ulBaudRate, 8, eParity ) != TRUE )
    {
        eStatus = MB_EPORTERR;
    }
    else
    {
        /* If baudrate > 19200 then we should use the fixed timer values
         * t35 = 1750us. Otherwise t35 must be 3.5 times the character time.
         */
        if( ulBaudRate > 19200 )
        {
            **usTimerT35_50us = 35;       /* 1800us. */**
        }
        else
        {
            /* The timer reload value for a character is given by:
             *
             * ChTimeValue = Ticks_per_1s / ( Baudrate / 11 )
             *             = 11 * Ticks_per_1s / Baudrate
             *             = 220000 / Baudrate
             * The reload for t3.5 is 1.5 times this value and similary
             * for t3.5.
             */
            usTimerT35_50us = ( 7UL * 220000UL ) / ( 2UL * ulBaudRate );
        }
        if( xMBMasterPortTimersInit( ( USHORT ) usTimerT35_50us ) != TRUE )
        {
            eStatus = MB_EPORTERR;
        }
    }
    EXIT_CRITICAL_SECTION(  );

return eStatus;
}
```
然后在xMBMasterPortTimersInit 创建软定时器，问题来了
我的波特率是57600，那么t35是1750us,由于RT_TICK_PER_SECOND = 1000，即1ms
此时无法实现1750us超时值，因为tick是1000us，这样的情况是
- 方案一：把软定时器超时值设为2ms 
- 方案二：还是需要改为硬定时器，想问一下大佬 我准备改成使用硬件定时器，并把相关涉及到软定时器的启动 停止 控制改为硬件定时器的接口
哪位大佬指导一下