FreeModbus学习——接收状态机xMBRTUReceiveFSM

news2025/10/31 16:46:01

FreeModbus版本：1.6

接收状态机xMBRTUReceiveFSM

在协议栈初始化时，会发现有两个接收函数

peMBFrameReceiveCur = eMBRTUReceive;

pxMBFrameCBByteReceived = xMBRTUReceiveFSM;

那么这两个接收函数哪个是状态机？它俩有什么区别呢？
在这里插入图片描述
xMBRTUReceiveFSM这个是接收状态机函数。

FSM是finite-state machine的缩写，即有限状态机。

看一下这个函数在哪里调用
pxMBFrameCBByteReceived = xMBRTUReceiveFSM;

在portserial.c文件中，会发现pxMBFrameCBByteReceived 被prvvUARTRxISR调用。
在这里插入图片描述
prvvUARTRxISR这个函数是串口接收中断时调用的。

串口接收中断由用户实现，比如这样
在这里插入图片描述
所以接收状态机的调用顺序是这样的

接收到字节 →
中断服务函数 →
prvvUARTRxISR →
pxMBFrameCBByteReceived →
xMBRTUReceiveFSM

先看一下接收状态机都有什么状态

typedef enum
{
    STATE_RX_INIT,              /*!< Receiver is in initial state. */
    STATE_RX_IDLE,              /*!< Receiver is in idle state. */
    STATE_RX_RCV,               /*!< Frame is beeing received. */
    STATE_RX_ERROR              /*!< If the frame is invalid. */
} eMBRcvState;

分别是初始化态，空闲态，接收态，错误态。

来看一下接收状态机的实现xMBRTUReceiveFSM

BOOL
xMBRTUReceiveFSM( void )
{
    BOOL            xTaskNeedSwitch = FALSE;
    UCHAR           ucByte;

    assert( eSndState == STATE_TX_IDLE );

    /* Always read the character. */
    ( void )xMBPortSerialGetByte( ( CHAR * ) & ucByte );

    switch ( eRcvState )
    {
        /* If we have received a character in the init state we have to
         * wait until the frame is finished.
         */
    case STATE_RX_INIT:
        vMBPortTimersEnable(  );
        break;

        /* In the error state we wait until all characters in the
         * damaged frame are transmitted.
         */
    case STATE_RX_ERROR:
        vMBPortTimersEnable(  );
        break;

        /* In the idle state we wait for a new character. If a character
         * is received the t1.5 and t3.5 timers are started and the
         * receiver is in the state STATE_RX_RECEIVCE.
         */
    case STATE_RX_IDLE:
        usRcvBufferPos = 0;
        ucRTUBuf[usRcvBufferPos++] = ucByte;
        eRcvState = STATE_RX_RCV;

        /* Enable t3.5 timers. */
        vMBPortTimersEnable(  );
        break;

        /* We are currently receiving a frame. Reset the timer after
         * every character received. If more than the maximum possible
         * number of bytes in a modbus frame is received the frame is
         * ignored.
         */
    case STATE_RX_RCV:
        if( usRcvBufferPos < MB_SER_PDU_SIZE_MAX )
        {
            ucRTUBuf[usRcvBufferPos++] = ucByte;
        }
        else
        {
            eRcvState = STATE_RX_ERROR;
        }
        vMBPortTimersEnable(  );
        break;
    }
    return xTaskNeedSwitch;
}