STM32的USART使用DMA--操作

注意：DMA的中断产生条件中，TC=transfer complete interrupt产生，需要DMA的buffer满才会产生。

只有当DMA内存中的数据个数达到20个时候才能产生中断。定义如下。DMA_InitStructure.DMA_BufferSize = 20;//sizeof(Ch3DMABuffer);

static usart3_dma_config(void)

{

DMA_InitTypeDef DMA_InitStructure;

NVIC_InitTypeDef NVIC_InitStructure;

RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1,ENABLE);

/* DMA1 Channel3 (triggered by USART1 Rx event) Config */

DMA_DeInit(DMA1_Channel3);

DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&USART3->DR;

DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)Ch3DMABuffer;

DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;

DMA_InitStructure.DMA_BufferSize = 20;//sizeof(Ch3DMABuffer);

DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;

DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;

DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;

DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;

DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;

DMA_InitStructure.DMA_Priority = DMA_Priority_Low;

DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;

DMA_Init(DMA1_Channel3, &DMA_InitStructure);

/* Enable the End of Transfer Interrupt after */

DMA_ITConfig( DMA1_Channel3, DMA_IT_TC, ENABLE );

DMA_ITConfig(DMA1_Channel3,DMA_IT_TE,ENABLE);

USART_DMACmd(USART3,USART_DMAReq_Rx,ENABLE);

/* Enable DMA Channel3 */

DMA_Cmd(DMA1_Channel3, ENABLE);

NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);

NVIC_InitStructure.NVIC_IRQChannel = DMA1_Channel3_IRQn;

NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;

NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;

NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;

NVIC_Init(&NVIC_InitStructure);

}

注意在中断中，更新buffersize时，先关闭dma，设置好buffersize后，再开启dma

void DMA1_Channel3_IRQHandler(void)

{

uint16_t dma_len;

//static uint16_t rDMARear = sizeof(Ch3DMABuffer);

DMA_ClearITPendingBit(DMA1_IT_TC3);

DMA_ClearITPendingBit(DMA1_IT_TE3);

DMA_Cmd(DMA1_Channel3,DISABLE);

dma_len = DMA_GetCurrDataCounter(DMA1_Channel3);

//if(dma_len

usart3_rxbuff.len = dma_len;

DMA_SetCurrDataCounter(DMA1_Channel3,50);

DMA_Cmd(DMA1_Channel3,ENABLE);

usart3_rxbuff.rxend = 1;

}

------------------------部分理解参考如下内容-----------------------

USART1的DMA发送比较简单，在要发送之前，重新设置好DMA_BufferSize的大小，然后启动DMA就行了。不过在设置这一值时，得先关闭DMA通道。代码如下：

DMA_ClearFlag(DMA1_FLAG_TC4); //清DMA发送完成标志

DMA_Cmd(DMA1_Channel4, DISABLE); //停止DMA

DMA1_Channel4->CNDTR = sizeof(TxBuffer1) / sizeof(TxBuffer1[0]);//重设传输长度

DMA_Cmd(DMA1_Channel4, ENABLE); //启动DMA

USART1的DMA接收：如果向USART1发送了数据，则数据会通过DMA传输至初始化DMA接收通道时设置好的内存地址处。据说数据的解析会比较麻烦，因为你不知道什么时候一条完整的指令传输完了，怎么做可以参考这两处：http://bbs.21ic.com/viewthread.php?tid=124248&highlight=USART+DMA

http://bbs.21ic.com/viewthread.php?tid=109346&highlight=USART+DMA

试了一下接收通道DMA1_Channel5的DMA1_IT_TC5中断，有一点和我预料的不一样，初始化该通道时不是也设置过一个DMA_BufferSize值吗，只有接收满了这个DMA_BufferSize大小的数据后，才会产生DMA1_IT_TC5中断，而不是接收一个字节的数据就会产生一个DMA1_IT_TC5中断。