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(fā)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(shù)據(jù)量不大(比如只是解析一些命令)但是TX數(shù)據(jù)量大的應(yīng)用(比如定時，高頻發(fā)送數(shù)據(jù))再合適不過，該架構(gòu)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(fā)送+中斷接收的例程：

我們復(fù)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(shù)據(jù)即可。

1. 首先將USART_TransferCreateHandleDMA函數(shù)修改下，將所有RX DMA有關(guān)的東西去掉，handler填NULL就可以。這樣usart_dmadriver就不會處理RX DMA有關(guān)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(guī)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(shù)據(jù)：

#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 ", 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(diào)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(diào)用dma handle用戶回調(diào)函數(shù)，現(xiàn)在硬件串口中斷已經(jīng)被app層接管，所以我們同樣要實現(xiàn)這部分功能)。

4. 測試：改好代碼，下載運行：當(dāng)串口敲入任意鍵時候，程序都會回顯接收到數(shù)據(jù)，當(dāng)按鍵”s”時，會調(diào)用USART_TransferSendDMA函數(shù)使用DMA發(fā)送一串?dāng)?shù)據(jù)，并進入DMA發(fā)送完成回調(diào)函數(shù)。

代碼清單

以下是完整代碼清單(可以直接復(fù)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_DMA ";

#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 ", 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 ", 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 ");

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

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);

while(1);

}