串口不定长接收在项目中经常用到，像MODBUS串口服务器中就会经常传来一大帧数据，数据的长度不定，通常人们的做法是采用环形队列接收的方式，以特定的结束标志位如0x0d 0x0a等用以判断一帧数据的结束，但实际上STM32这种高级的ARM单片机是带有空闲中断和DMA的，不需要用环形队列这种纯软件的做法实现不定长接收，直接用空闲中断+DMA就可以实现了，非常简单，小白也能一看就懂。
首先是要初始化串口不定长接收，比如打开空闲中断，打开DMA，这里我选的是板上的USB转TTL串口即串口3，对应的接收DMA为DMA1流1:
代码如下：
void UART3_Init(int baud)
{
__HAL_RCC_GPIOB_CLK_ENABLE();
__HAL_RCC_USART3_CLK_ENABLE();
__HAL_RCC_DMA1_CLK_ENABLE();
GPIO_InitStruct.Pin = GPIO_PIN_10|GPIO_PIN_11;
GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
GPIO_InitStruct.Pull = GPIO_PULLUP;
GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH;
GPIO_InitStruct.Alternate = GPIO_AF7_USART3;
HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);
huart3.Instance = USART3;
huart3.Init.BaudRate = baud;
huart3.Init.WordLength = UART_WORDLENGTH_8B;
huart3.Init.StopBits = UART_STOPBITS_1;
huart3.Init.Parity = UART_PARITY_NONE;
huart3.Init.Mode = UART_MODE_TX_RX;
huart3.Init.HwFlowCtl = UART_HWCONTROL_NONE;
huart3.Init.OverSampling = UART_OVERSAMPLING_16;
HAL_UART_Init(&huart3);
__HAL_UART_ENABLE_IT(&huart3,UART_IT_IDLE);
HAL_NVIC_SetPriority(USART3_IRQn,0,0);
HAL_NVIC_EnableIRQ(USART3_IRQn);
hdma_usart3_rx.Instance = DMA1_Stream1;
hdma_usart3_rx.Init.Channel = DMA_CHANNEL_4;
hdma_usart3_rx.Init.Direction = DMA_PERIPH_TO_MEMORY;
hdma_usart3_rx.Init.PeriphInc = DMA_PINC_DISABLE;
hdma_usart3_rx.Init.MemInc = DMA_MINC_ENABLE;
hdma_usart3_rx.Init.PeriphDataAlignment = DMA_PDATAALIGN_BYTE;
hdma_usart3_rx.Init.MemDataAlignment = DMA_MDATAALIGN_BYTE;
hdma_usart3_rx.Init.Mode = DMA_NORMAL;
hdma_usart3_rx.Init.Priority = DMA_PRIORITY_LOW;
hdma_usart3_rx.Init.FIFOMode = DMA_FIFOMODE_DISABLE;
HAL_DMA_Init(&hdma_usart3_rx);
__HAL_LINKDMA(&huart3,hdmarx,hdma_usart3_rx);
}
void USART3_IRQHandler()
{
int temp;
if(__HAL_UART_GET_FLAG(&huart3,UART_FLAG_IDLE))
{
__HAL_UART_CLEAR_IDLEFLAG(&huart3);
HAL_UART_DMAStop(&huart3);
temp=__HAL_DMA_GET_COUNTER(&hdma_usart3_rx);
rx_len_uart3=BUFFERSIZE-temp;
rx_flag_uart3=1;
}
}
在主循环中加入以下语句以让单片机轮询串口不定长接收的标志位，并在液晶彩屏上显示出来：
void UART_DMA_Get()
{
int i;
if(rx_flag_uart1==1)
{
printf("rx_len=%d\n\n",rx_len_uart1);
printf("%s\n\n",rx_buf_uart1);
rx_len_uart1=0;
rx_flag_uart1=0;
}
if(rx_flag_uart3==1)
{
printf("rx_len=%d\n\n",rx_len_uart3);
for(i=0;i<rx_len_uart3;i++)
{
if(rx_buf_uart3=='\r'||rx_buf_uart3=='\n')
rx_buf_uart3=0;
}
printf("%s\n\n",rx_buf_uart3);
SPILCD_DrawString(0,128," ",BLACK,CYAN,ZF32_NORMAL);
SPILCD_DrawString(0,128,rx_buf_uart3,BLACK,CYAN,ZF32_NORMAL);
rx_len_uart3=0;
rx_flag_uart3=0;
}
HAL_UART_Receive_DMA(&huart1,(uint8_t*)rx_buf_uart1,BUFFERSIZE);
HAL_UART_Receive_DMA(&huart3,(uint8_t*)rx_buf_uart3,BUFFERSIZE);
}
看看效果，可以看到，上位机串口程序那边发什么，显示屏就显示什么：
本文转载于【F407开发板】串口空闲中断+DMA实现不定长接收&处理
http://www.stmcu.org.cn/module/forum/thread-619033-1-1.html
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