分享正文之前推薦一個(gè)嵌入式招聘信息的平臺(tái)：

概述

基本原理

單消息代碼描述

xMessageBufferSend()
{
    /* If a time out is specified and there isn't enough
    space in the message buffer to send the data, then
    enter the blocked state to wait for more space. */
    if( time out != 0 )
    {
        while( there is insufficient space in the buffer &&
               not timed out waiting )
        {
            Enter the blocked state to wait for space in the buffer
        }
    }


    if( there is enough space in the buffer )
    {
        write data to buffer
        sbSEND_COMPLETED()
    }
}

xMessageBufferReceive()
{
    /* If a time out is specified and the buffer doesn't
    contain any data that can be read, then enter the
    blocked state to wait for the buffer to contain data. */
    if( time out != 0 )
    {
        while( there is no data in the buffer &&
               not timed out waiting )
        {
            Enter the blocked state to wait for data
        }
    }


    if( there is data in the buffer )
    {
        read data from buffer
        sbRECEIVE_COMPLETED()
    }
}

多消息代碼描述

• 如果硬件允許，則每個(gè)消息緩沖區(qū)可以使用不同的中斷線，從而使中斷服務(wù)程序和消息緩沖區(qū)之間保持一對(duì)一的映射。
• 中斷服務(wù)例程可以簡(jiǎn)單地查詢每個(gè)消息緩沖區(qū)以查看其是否包含數(shù)據(jù)。
• 可以通過(guò)傳遞元數(shù)據(jù)（消息是什么，消息的預(yù)期接收者是什么等等）以及實(shí)際數(shù)據(jù)的單個(gè)消息緩沖區(qū)來(lái)代替多個(gè)消息緩沖區(qū)。

/* Added to FreeRTOSConfig.h to override the default implementation. */
#define sbSEND_COMPLETED( pxStreamBuffer ) vGenerateCoreToCoreInterrupt( pxStreamBuffer )


/* Implemented in a C file. */
void vGenerateCoreToCoreInterrupt( MessageBufferHandle_t xUpdatedBuffer )
{
size_t BytesWritten.


    /* Called by the implementation of sbSEND_COMPLETED() in FreeRTOSConfig.h.
    If this function was called because data was written to any message buffer
    other than the control message buffer then write the handle of the message
    buffer that contains data to the control message buffer, then raise an
    interrupt in the other core.  If this function was called because data was
    written to the control message buffer then do nothing. */
    if( xUpdatedBuffer != xControlMessageBuffer )
    {
        BytesWritten = xMessageBufferSend(  xControlMessageBuffer,
                                            &xUpdatedBuffer,
                                            sizeof( xUpdatedBuffer ),
                                            0 );


        /* If the bytes could not be written then the control message buffer
        is too small! */
        configASSERT( BytesWritten == sizeof( xUpdatedBuffer );


        /* Generate interrupt in the other core (pseudocode). */
        GenerateInterrupt();
    }
}

void InterruptServiceRoutine( void )
{
MessageBufferHandle_t xUpdatedMessageBuffer;
BaseType_t xHigherPriorityTaskWoken = pdFALSE;


    /* Receive the handle of the message buffer that contains data from the
    control message buffer.  Ensure to drain the buffer before returning. */
    while( xMessageBufferReceiveFromISR( xControlMessageBuffer,
                                         &xUpdatedMessageBuffer,
                                         sizeof( xUpdatedMessageBuffer ),
                                         &xHigherPriorityTaskWoken )
                                           == sizeof( xUpdatedMessageBuffer ) )
    {
        /* Call the API function that sends a notification to any task that is
        blocked on the xUpdatedMessageBuffer message buffer waiting for data to
        arrive. */
        xMessageBufferSendCompletedFromISR( xUpdatedMessageBuffer,
                                            &xHigherPriorityTaskWoken );
    }


    /* Normal FreeRTOS "yield from interrupt" semantics, where
    xHigherPriorityTaskWoken is initialised to pdFALSE and will then get set to
    pdTRUE if the interrupt unblocks a task that has a priority above that of
    the currently executing task. */
    portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
}