LPC5500

串口DMA

LPC5500的SDK中提供了非常豐富的串口例程(如下圖所示)：

但是，偏偏沒有串口DMA發送+中斷接收這種組合。

實話說小編覺得這種組合才是大部分MCU場景中最常用的。尤其是對一些RX數據量不大(比如只是解析一些命令)但是TX數據量大的應用(比如定時，高頻發送數據)再合適不過，該架構模型簡單，非常容易理解。

本篇文章就手把手教大家分分鐘擼一個DMA發送+中斷接收的例程：

我們復制一個dma_transfer例程作為模板，重命名為dma_tx_int_rx(名字無所謂，自己起即可)。打開，編譯下載運行一下，確保原版demo在自己的板子上可以順利的運行，咱們把前期工作都鋪墊好。

下面我們開始改代碼：dma_transfer原版代碼是TX和RX都是dma傳輸，我們只需要將RX改為中斷接收數據即可。

首先將USART_TransferCreateHandleDMA函數修改下，將所有RX DMA有關的東西去掉，handler填NULL就可以。這樣usart_dma driver就不會處理RX DMA有關的操作了：

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

2. 開啟usart RX中斷，沒啥可說的，常規操作：

/* Enable RX interrupt. */

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

3. 在app層定義(接管)串口硬件中斷,并在中斷中處理串口RX接收到的數據：

#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:%crn", 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，這里需要在硬件串口中斷里判斷TXIDLE中斷，并調用USART_TransferDMAHandleIRQ。這是仿照fsl_usart_dma.c中的寫法(fsl_usart_dma中開啟了TXIDLE中斷，并使用TXIDLE中斷來調用dma handle用戶回調函數，現在硬件串口中斷已經被app層接管，所以我們同樣要實現這部分功能)。

4. 測試：改好代碼，下載運行：當串口敲入任意鍵時候，程序都會回顯接收到數據，當按鍵”s”時，會調用USART_TransferSendDMA函數使用DMA發送一串數據，并進入DMA發送完成回調函數。

代碼清單

以下是完整代碼清單(可以直接復制到usart_dma_transfer.c里運行)：

/*
* 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_DMArn";

#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%Xrn", 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:%crn", 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 INTERRUPTrn");

   PRINTF("press 's' for DMA TX tranmsitrn");

  

   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);

來源：恩智浦MCU加油站

審核編輯：湯梓紅