云途 串口发送阻塞与非阻塞API

云途MCU串口数据发送常用的有两套API（其实有三套）

LINFlexD_UART_DRV_SendData
LINFlexD_UART_DRV_SendDataBlocking

下面简要说明一下带blocking的这个API，为了简明，我把API做了一下删减

status_t LINFlexD_UART_DRV_SendDataBlocking(uint32_t instance,
                                            const uint8_t * txBuff,
                                            uint32_t txSize,
                                            uint32_t timeout)
{

    linflexd_uart_state_t * uartState;
    status_t retVal;

    uartState = (linflexd_uart_state_t *)s_uartLINFlexDStatePtr[instance];
    retVal = STATUS_SUCCESS;

    /* Indicates this is a blocking transaction. */
    uartState->isTxBlocking = true;
    /* Reset signal before transfer */
    //这里会尝试获取txcomplete信号量，
    (void)OSIF_SemaWait(&(uartState->txComplete), 0);

        /* Start the transmission process using DMA */
        //真正发送数据的入口API
        retVal = LINFlexD_UART_DRV_StartSendUsingDma(instance, txBuff, txSize);

    if (retVal == STATUS_SUCCESS)
    {
        //等待信号量
        /* Wait until to transmit is complete. */
        retVal = OSIF_SemaWait(&uartState->txComplete, timeout);

        /* Finish the transmission if timeout expired */
        if (retVal == STATUS_TIMEOUT)
        {
            uartState->isTxBlocking = false;
            uartState->transmitStatus = STATUS_TIMEOUT;

            LINFlexD_UART_DRV_CompleteSendUsingDma(((void *)instance), DMA_CHN_NORMAL);

        }
    }

    return retVal;
}

在上面这个API中，发送完成后底层驱动会释放信号量txComplete（send前会尝试获取）,一般用freertos的都建议用带block的API

补充：之前我在看关于串口回调函数事件的时候有一个点非常困惑,UART_EVENT_TX_EMPTY和UART_EVENT_END_TRANSFER难道不是一个事件吗？TX的fifo为空，应该是代表了传输完成；今天突然看到Linflexd_Uart_Continuous_Transmission_Demo例程才反应过来，tx fifo为空本次传输的的8个字节传输完成了。硬件已准备好接收下一个待发送的字节，一般用在逐字节流式传输。如果是整个传输任务（如多字节发送完成）此时触发的是UART_EVENT_END_TRANSFER事件

typedef enum
{
    UART_EVENT_RX_FULL      = 0x00U,    /*!< Rx buffer is full */
    UART_EVENT_TX_EMPTY     = 0x01U,    /*!< Tx buffer is empty */
    UART_EVENT_END_TRANSFER = 0x02U,    /*!< The current transfer is ending */
    UART_EVENT_ERROR        = 0x03U,    /*!< An error occured during transfer */
    UART_EVENT_TIMEOUT      = 0x04U,    /*!< Uart TimeOut */

} uart_event_t;

水平有限，有什么疏漏之处欢迎指问