LPC5500的SDK中提供了非常丰富的串口例程(如下图所示)：

但是，偏偏没有串口DMA发送+中断接收这种组合。

实话说小编觉得这种组合才是大部分MCU场景中最常用的。尤其是对一些RX数据量不大(比如只是解析一些命令)但是TX数据量大的应用(比如定时，高频发送数据)再合适不过，该架构模型简单，非常容易理解。

本篇文章就手把手教大家分分钟撸一个DMA发送+中断接收的例程：

我们复制一个dma_transfer例程作为模板，重命名为dma_tx_int_rx(名字无所谓，自己起即可)。打开，编译下载运行一下，确保原版demo在自己的板子上可以顺利的运行，咱们把前期工作都铺垫好。

下面我们开始改代码：dma_transfer原版代码是TX和RX都是dma传输，我们只需要将RX改为中断接收数据即可。

首先将USART_TransferCreateHandleDMA函数修改下，将所有RX DMA有关的东西去掉，handler填NULL就可以。这样usart_dma driver就不会处理RX DMA有关的操作了：

USART_TransferCreateHandleDMA(DEMO_USART,  &g_uartDmaHandle, USART_UserCallback, NULL，&g_uartTxDmaHandle, NULL);

2. 开启usart RX中断，没啥可说的，常规操作：

/* Enable RX interrupt. */

USART_EnableInterrupts(DEMO_USART, kUSART_RxLevelInterruptEnable | kUSART_RxErrorInterruptEnable);
EnableIRQ(DEMO_USART_IRQn);

3. 在app层定义(接管)串口硬件中断,并在中断中处理串口RX接收到的数据：

#define DEMO_USART_IRQHandler FLEXCOMM0_IRQHandler
#define DEMO_USART_IRQn     FLEXCOMM0_IRQn



void DEMO_USART_IRQHandler(void)
{
   uint8_t data;
   /* If new data arrived. */
   if ((kUSART_RxFifoNotEmptyFlag | kUSART_RxError | kUSART_RxFifoFullFlag) & USART_GetStatusFlags(DEMO_USART))
   {
       data = USART_ReadByte(DEMO_USART);
       PRINTF("usart rx interrupt:%c\r\n", data);

       if(data == 's')

       {

          /* Send g_tipString out. */

          xfer.data     = g_tipString;

          xfer.dataSize = sizeof(g_tipString) - 1;


          g_uartDmaHandle.txState = kUSART_TxIdle;

          USART_TransferSendDMA(DEMO_USART, &g_uartDmaHandle, &xfer);

      }

   }

   if ((0U != (DEMO_USART->INTENSET &  USART_INTENSET_TXIDLEEN_MASK)) && (0U != (DEMO_USART->INTSTAT & USART_INTSTAT_TXIDLE_MASK)))

   {

      USART_TransferDMAHandleIRQ(DEMO_USART, &g_uartDmaHandle);

   }

}

注意，这里需要在硬件串口中断里判断TXIDLE中断，并调用USART_TransferDMAHandleIRQ。这是仿照fsl_usart_dma.c中的写法(fsl_usart_dma中开启了TXIDLE中断，并使用TXIDLE中断来调用dma handle用户回调函数，现在硬件串口中断已经被app层接管，所以我们同样要实现这部分功能)。

4. 测试：改好代码，下载运行：当串口敲入任意键时候，程序都会回显接收到数据，当按键”s”时，会调用USART_TransferSendDMA函数使用DMA发送一串数据，并进入DMA发送完成回调函数。

代码清单

以下是完整代码清单(可以直接复制到usart_dma_transfer.c里运行)：

/*
* Copyright (c) 2016, Freescale Semiconductor, Inc.

* Copyright 2016-2017 NXP

* All rights reserved.

*

* SPDX-License-Identifier:  BSD-3-Clause

*/

#include "pin_mux.h"

#include "board.h"

#include "fsl_usart.h"

#include "fsl_usart_dma.h"

#include "fsl_dma.h"

#include "fsl_debug_console.h"


#include 

#include "fsl_power.h"


#define DEMO_USART                USART0

#define DEMO_USART_CLK_SRC        kCLOCK_Flexcomm0

#define DEMO_USART_CLK_FREQ       CLOCK_GetFlexCommClkFreq(0U)

#define USART_RX_DMA_CHANNEL      4

#define USART_TX_DMA_CHANNEL      5

#define EXAMPLE_UART_DMA_BASEADDR DMA0

#define DEMO_USART_IRQHandler FLEXCOMM0_IRQHandler

#define DEMO_USART_IRQn       FLEXCOMM0_IRQn

#define ECHO_BUFFER_LENGTH 8


usart_transfer_t xfer;

usart_dma_handle_t g_uartDmaHandle;

dma_handle_t g_uartTxDmaHandle;

uint8_t g_tipString[]                  = "This string is send from UART_DMA\r\n";

#define kUSART_TxIdle 0

void USART_UserCallback(USART_Type *base, usart_dma_handle_t *handle, status_t status, void *userData)

{

   userData = userData;

   if (kStatus_USART_TxIdle == status)

   {

       PRINTF("USART_UserCallback, status:0x%X\r\n", status);

   }

}

void DEMO_USART_IRQHandler(void)
{
   uint8_t data;
   /* If new data arrived. */
   if ((kUSART_RxFifoNotEmptyFlag | kUSART_RxError | kUSART_RxFifoFullFlag) & USART_GetStatusFlags(DEMO_USART))
   {
       data = USART_ReadByte(DEMO_USART);
       PRINTF("usart rx interrupt:%c\r\n", data);

       if(data == 's')

       {

          /* Send g_tipString out. */

          xfer.data     = g_tipString;

          xfer.dataSize = sizeof(g_tipString) - 1;


          g_uartDmaHandle.txState = kUSART_TxIdle;

          USART_TransferSendDMA(DEMO_USART, &g_uartDmaHandle, &xfer);

      }

   }

   if ((0U != (DEMO_USART->INTENSET &  USART_INTENSET_TXIDLEEN_MASK)) && (0U != (DEMO_USART->INTSTAT & USART_INTSTAT_TXIDLE_MASK)))

   {

      USART_TransferDMAHandleIRQ(DEMO_USART, &g_uartDmaHandle);

   }

}

int main(void)

{

   usart_config_t    config;

  

   /* set BOD VBAT level to 1.65V */

   POWER_SetBodVbatLevel(kPOWER_BodVbatLevel1650mv, kPOWER_BodHystLevel50mv, false);

   /* attach 12 MHz clock to FLEXCOMM0 (debug console) */

   CLOCK_AttachClk(kFRO12M_to_FLEXCOMM0);

  

   BOARD_InitBootPins();

   BOARD_InitBootClocks();

   BOARD_InitDebugConsole();

  

   PRINTF("USART: TX DMA, RX INTERRUPT\r\n");

   PRINTF("press 's' for DMA TX tranmsit\r\n");

  

   USART_GetDefaultConfig(&config);

   config.baudRate_Bps = BOARD_DEBUG_UART_BAUDRATE;

   config.enableTx     = true;

   config.enableRx     = true;

  

   USART_Init(DEMO_USART, &config, DEMO_USART_CLK_FREQ);

  

   /* Configure DMA. */

   DMA_Init(EXAMPLE_UART_DMA_BASEADDR);

   DMA_EnableChannel(EXAMPLE_UART_DMA_BASEADDR, USART_TX_DMA_CHANNEL);

   DMA_EnableChannel(EXAMPLE_UART_DMA_BASEADDR, USART_RX_DMA_CHANNEL);

   DMA_CreateHandle(&g_uartTxDmaHandle, EXAMPLE_UART_DMA_BASEADDR, USART_TX_DMA_CHANNEL);

   USART_TransferCreateHandleDMA(DEMO_USART, &g_uartDmaHandle, USART_UserCallback, NULL, &g_uartTxDmaHandle, NULL);

 

   /* Send g_tipString out. */

   xfer.data     = g_tipString;

   xfer.dataSize = sizeof(g_tipString) - 1;

   USART_TransferSendDMA(DEMO_USART, &g_uartDmaHandle, &xfer);

  

   /* Enable RX interrupt. */

   USART_EnableInterrupts(DEMO_USART, kUSART_RxLevelInterruptEnable | kUSART_RxErrorInterruptEnable);

   EnableIRQ(DEMO_USART_IRQn);