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旭日X3派開發板提供了40PIN標準接口，方便用戶擴展外圍設備。其中物理引腳編號8和10為串口通信發送和接收使用(8-TXD，10-RXD)。

40PIN引腳功能和位置編號如下：

串口轉USB設備引腳和功能描述如下：

我們可以使用3根杜邦線 + 一個串口轉USB設備(旭日X3派開發包附贈) + 一臺筆記本電腦 + putty(串口工具)搭建串口通信開發環境。

如下圖示：

1）6號管腳和串口轉USB GND連接

2）8號管腳和串口轉USB RXD連接

3）10號管腳和串口轉USB TXD連接

從40PIN管腳功能圖我們知道，8號和10號管腳為UART3，對應的設備文件為 /dev/ttyS3。

環境搭建完成后，我們來編寫一個簡單的程序庫操作串口。

//頭文件

#ifndef SERIAL_H#define SERIAL_Htypedef struct Serial Serial;struct Serial{ int (*Open)(Serial *pDevice, const char *sDevice, int baudrate); void (*Close)(Serial *pDevice); int (*Write)(Serial *pDevice, const char *buf, int len); int (*Read)(Serial *pDevice, char *buf, int len);};Serial* CreateSerialDevice();void DestroySerialDevice(Serial *pDevice);#endif //SERIAL

//實現文件

#include #include #include #include #include #include #include #include "serial.h"typedef struct SerialImpl{ Serial base; int handle; int baudrate; char sDevice[64];}SerialImpl;int speed_arr[] = {B1500000, B1152000, B1000000, B921600, B576000, B500000, B460800, B230400, B115200, B57600, B38400, B19200, B9600, B4800, B2400, B1800, B1200, B600, B300, B200, B150, B134, B110, B75, B50, B0};int baudrate_arr[] = {1500000, 1152000, 1000000, 921600, 576000, 500000, 460800, 230400, 115200, 57600, 38400, 19200, 9600, 4800, 2400, 1800, 1200, 600, 300, 200, 150, 134, 110, 75, 50, 0};int serial_setting(Serial *pDevice, int baudrate);void serial_close(Serial *pDevice);int serial_comspeed_get(int baudrate){ for (int i = 0; i < sizeof(baudrate_arr)/ sizeof(baudrate_arr[0]); ++i) { if (baudrate_arr[i] == baudrate) { return speed_arr[i]; } } return -1;}int serial_open(Serial *pDevice, const char *sDevice, int baudrate){ int handle = -1; SerialImpl *impl = (SerialImpl*)pDevice; if (!impl) { return -1; } if (!sDevice || sDevice[0] == '\0') { return -2; } handle = open(sDevice, O_RDWR, 0); if (-1 == handle) { perror("open"); return -3; } impl->handle = handle; snprintf(impl->sDevice, sizeof(impl->sDevice), "%s", sDevice); if (0 != serial_setting(pDevice, baudrate)) { serial_close(pDevice); return -4; } return 0;}int serial_setting(Serial *pDevice, int baudrate){ int handle = -1; int speed = 0; struct termios options; SerialImpl *impl = (SerialImpl*)pDevice; if (!impl) { return -1; } handle = impl->handle; if (handle <= 0) { return -2; } speed = serial_comspeed_get(baudrate); if (speed < 0) { return -3; } impl->baudrate = baudrate; if (tcgetattr(handle, &options) != 0) { perror("tcgetattr"); return -4; } if (cfsetispeed(&options, speed) != 0 || cfsetispeed(&options, speed) != 0) { perror("cfsetispeed"); return -5; } //no partity options.c_cflag &= ~PARENB; options.c_iflag &= ~INPCK; //8bits options.c_cflag |= CS8; //stop 1bits options.c_cflag &= ~CSTOPB; //no flow control options.c_cflag &= ~CRTSCTS; options.c_cflag &= ~CSIZE; if (tcsetattr(handle, TCSANOW, &options) != 0) { perror("tcsetattr"); return -6; } return 0;}int serial_read(Serial *pDevice, char *buf, int len){ int handle = -1; int size = 0; SerialImpl *impl = (SerialImpl*)pDevice; if (!impl) { return -1; } handle = impl->handle; if (handle <= 0) { return -2; } if (!buf || len <= 0) { return -3; } size = read(handle, buf, len); if (-1 == size) { perror("read"); return -4; } return size;}int serial_write(Serial *pDevice, const char *buf, int len){ int handle = -1; int size = 0; SerialImpl *impl = (SerialImpl*)pDevice; if (!impl) { return -1; } handle = impl->handle; if (handle <= 0) { return -2; } if (!buf || len <= 0) { return -3; } size = write(handle, buf, len); if (-1 == size) { perror("write"); return -4; } return size;}void serial_close(Serial *pDevice){ int handle = -1; SerialImpl *impl = (SerialImpl*)pDevice; if (!impl) { return; } handle = impl->handle; if (handle != -1) { close(handle); }}Serial* CreateSerialDevice(){ SerialImpl *pDevice = (SerialImpl*)malloc(sizeof(SerialImpl)); if (pDevice) { pDevice->base.Open = serial_open; pDevice->base.Close = serial_close; pDevice->base.Write = serial_write; pDevice->base.Read = serial_read; pDevice->handle = -1; pDevice->baudrate = 0; pDevice->sDevice[0] = '\0'; } return (Serial*)pDevice;}void DestroySerialDevice(Serial *pDevice){ if (pDevice) { pDevice->Close(pDevice); free(pDevice); }}

//測試文件

#include #include #include #include #include "serial.h"int main(int argc, char *argv[]){ char sbuf[128]; int count; int size; int ret; Serial *port = CreateSerialDevice(); assert(port != NULL); ret = port->Open(port, "/dev/ttyS3", 921600); assert(ret == 0); while (1) { snprintf(sbuf, sizeof(sbuf), "%d", count++); size = port->Write(port, sbuf, strlen(sbuf)); assert(size != -1); usleep(1000*1000); } port->Close(port); DestroySerialDevice(port); return 0;}

//工程文件

cmake_minimum_required(VERSION 3.0)project(serial)set(CMAKE_BUILD_TYPE "Debug")add_library(serial SHARED serial.c)add_executable(echo echo.c)target_link_libraries(echo serial)

測試結果：

X3派側echo每隔1s發送一次遞增數據，PC側putty接收并打印。