HAL_UART_Transmit

HAL_UART_Transmit_DMA 异常

patch1582 提问时间：2026-7-21 14:45 / 未解决

问答
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我想用 DMA 通过串口输出单个字符。首先将 DMA 配置为普通单次模式，初始化代码如下： huart2.Instance = USART2; huart2.Init.BaudRate = 115200; huart2.Init.WordLength = UART_WORDLENGTH_8B; huart2.Init.StopBits = UART_STOPBITS_1; huart2.Init.Parity = UART_PARITY_NONE; huart2.Init.Mode = UART_MODE_TX_RX; huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE; huart2.Init.OverSampling = UART_OVERSAMPLING_16; HAL_UART_Init(&huart2);

hdma_usart2_tx.Instance = DMA1_Stream6; hdma_usart2_tx.Init.Channel = DMA_CHANNEL_4; hdma_usart2_tx.Init.Direction = DMA_MEMORY_TO_PERIPH; hdma_usart2_tx.Init.PeriphInc = DMA_PINC_DISABLE; hdma_usart2_tx.Init.MemInc = DMA_MINC_ENABLE; hdma_usart2_tx.Init.PeriphDataAlignment = DMA_PDATAALIGN_BYTE; hdma_usart2_tx.Init.MemDataAlignment = DMA_MDATAALIGN_BYTE; hdma_usart2_tx.Init.Mode = DMA_NORMAL; hdma_usart2_tx.Init.Priority = DMA_PRIORITY_LOW; hdma_usart2_tx.Init.FIFOMode = DMA_FIFOMODE_DISABLE; HAL_DMA_Init(&hdma_usart2_tx);

__HAL_LINKDMA(huart,hdmatx,hdma_usart2_tx); 主循环之外只添加了这段发送代码，while (1) 里只有 LED 闪烁逻辑： HAL_UART_Transmit_DMA(&huart2,(uint8_t)"a",1); HAL_UART_Transmit_DMA(&huart2,(uint8_t)"b",1); 普通 DMA 模式下，串口只输出一次字符a，随后 LED 开始闪烁，字符b没有输出。如果改成发送长字符串再加两个单字符： char testMessage[] = "test output of a longer string\r\n"; HAL_UART_Transmit_DMA(&huart2,(uint8_t)&testMessage,sizeof(testMessage)-1); HAL_UART_Transmit_DMA(&huart2,(uint8_t)"a",1); HAL_UART_Transmit_DMA(&huart2,(uint8_t*)"b",1); 最终只能收到完整字符串，a和b依旧不会发送出来。如果把 DMA 配置改成循环模式（DMA_CIRCULAR），其余初始化不变，再次执行单次发送代码：

HAL_UART_Transmit_DMA(&huart2,(uint8_t)"a",1); HAL_UART_Transmit_DMA(&huart2,(uint8_t)"b",1); 串口会持续不断重复输出a，LED 同步闪烁，b不出现。如果同样搭配长字符串一起发送：

char testMessage[] = "test output of a longer string\r\n"; HAL_UART_Transmit_DMA(&huart2,(uint8_t)&testMessage,sizeof(testMessage)-1); HAL_UART_Transmit_DMA(&huart2,(uint8_t)"a",1); HAL_UART_Transmit_DMA(&huart2,(uint8_t*)"b",1); 字符串会无限循环重复发送，a和b依旧无输出。查阅手册 UM1725《STM32F4xx HAL 驱动说明》846 页关于串口 DMA 的描述： Send an amount of data in non blocking mode (DMA) using HAL_UART_Transmit_DMA() At transmission end of half transfer HAL_UART_TxHalfCpltCallback is executed and user can add his own code by customization of function pointer HAL_UART_TxHalfCpltCallback At transmission end of transfer HAL_UART_TxCpltCallback is executed and user can add his own code by customization of function pointer HAL_UART_TxCpltCallback 为什么 DMA 模式只能发送一次数据，后续所有发送请求全部失效；循环 DMA 模式会无限重复第一条发送内容，后面的发送指令不生效？麻烦各位帮忙解答一下。