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使用STM32CubeMX生成初始化代码。
问题：
HAL_UART_Transmit_DMA函数只能调用一次，第二次就返回状态HAL_UART_STATE_BUSY 0x02。
原因：
stm32l1xx_hal_uart.c开头有描述
(##) DMA Configuration if you need to use DMA process (HAL_UART_Transmit_DMA()
and HAL_UART_Receive_DMA() APIs):
(+++) Declare a DMA handle structure for the Tx/Rx channel.
(+++) Enable the DMAx interface clock.
(+++) Configure the declared DMA handle structure with the required
Tx/Rx parameters.
(+++) Configure the DMA Tx/Rx channel.
(+++) Associate the initialized DMA handle to the UART DMA Tx/Rx handle.
(+++) Configure the priority and enable the NVIC for the transfer complete
interrupt on the DMA Tx/Rx channel.
(+++) Configure the USARTx interrupt priority and enable the NVIC USART IRQ handle
(used for last byte sending completion detection in DMA non circular mode)
配置USARTx中断优先级，启用NVIC USART中断句柄（使用DMA非循环模式时，用来检测最后一个字节发送完毕）
/**
* @brief DMA UART transmit process complete callback
* @param hdma: DMA handle
* @retval None
*/
01523 static void UART_DMATransmitCplt(DMA_HandleTypeDef *hdma)
{
UART_HandleTypeDef* huart = ( UART_HandleTypeDef* )((DMA_HandleTypeDef* )hdma)->Parent;
huart->TxXferCount = 0;
/* Disable the DMA transfer for transmit request by setting the DMAT bit
in the UART CR3 register */
huart->Instance->CR3 &= (uint32_t)~((uint32_t)USART_CR3_DMAT);
/* Wait for UART TC Flag */
if(UART_WaitOnFlagUntilTimeout(huart, UART_FLAG_TC, RESET, HAL_UART_TXDMA_TIMEOUTVALUE) != HAL_OK)
{
/* Timeout Occured */
huart->State = HAL_UART_STATE_TIMEOUT;
HAL_UART_ErrorCallback(huart);
}
else
{
/* No Timeout */
/* Check if a receive process is ongoing or not */
if(huart->State == HAL_UART_STATE_BUSY_TX_RX)
{
huart->State = HAL_UART_STATE_BUSY_RX;
}
else
{
huart->State = HAL_UART_STATE_READY;
}
HAL_UART_TxCpltCallback(huart);
}
}
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