[嵌入式]linux 串口调试（UART serial ttyS）

一、设备树下开启串口

路径：kernel\arch\arm\boot\dts下的对应dts文件
例如：

&uart4{
    pinctrl-names = "default";
  pinctrl-0 = <&uart4m1_xfer>;
  status = "okay";
};

二、查看嵌入式设备是否成功挂载串口

/dev/ 路径下有：ttyS*

三、交叉编译 测试程序 uart_comm.c

执行 arm-linux-gnueabihf-gcc uart_comm.c -o uart_comm

四、拷贝uart_comm到嵌入式设备，然后执行 ./uart_comm

五、嵌入式设备通过USB转串口接到电脑，打开串口调试工具测试

直接上代码：

//示例代码 文件名：uart_comm.c
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <errno.h>

int set_opt(int, int, int, char, int);
void main()
{
	int fd, nByte, flag = 1;
	char *uart4 = "/dev/ttyS4";
	char buffer[512];
	char *uart_out = "Please input,waiting....\r\n";
	char *uart_demo = "Linux uart demo\r\n";
	int i;

	memset(buffer, 0, sizeof(buffer));
	//if((fd = open(uart4, O_RDWR|O_NOCTTY))<0)//默认为阻塞读方式
	if ((fd = open(uart4, O_RDWR | O_NONBLOCK)) < 0) //非阻塞读方式
		printf("open %s is failed", uart4);
	else
	{
		set_opt(fd, 115200, 8, 'N', 1);
		write(fd, uart_demo, strlen(uart_demo));
		write(fd, uart_out, strlen(uart_out));
		while (1)
		{
			write(fd, uart_demo, strlen(uart_demo));
			write(fd, uart_out, strlen(uart_out));
			memset(buffer, 0, sizeof(buffer));
			while ((nByte = read(fd, buffer, 512)) > 0)
			{
				buffer[nByte + 1] = '\0';
				printf("%s\r\n", buffer);
				write(fd, buffer, strlen(buffer));
				memset(buffer, 0, strlen(buffer));
				nByte = 0;
			}
			sleep(1);
			printf("send date.\r\n");
		}
	}
}

int set_opt(int fd, int nSpeed, int nBits, char nEvent, int nStop)
{
	struct termios newtio, oldtio;
	if (tcgetattr(fd, &oldtio) != 0)
	{
		perror("SetupSerial 1");
		return -1;
	}
	bzero(&newtio, sizeof(newtio));
	newtio.c_cflag |= CLOCAL | CREAD;
	newtio.c_cflag &= ~CSIZE;

	switch (nBits)
	{
	case 7:
		newtio.c_cflag |= CS7;
		break;
	case 8:
		newtio.c_cflag |= CS8;
		break;
	}

	switch (nEvent)
	{
	case 'O':
		newtio.c_cflag |= PARENB;
		newtio.c_cflag |= PARODD;
		newtio.c_iflag |= (INPCK | ISTRIP);
		break;
	case 'E':
		newtio.c_iflag |= (INPCK | ISTRIP);
		newtio.c_cflag |= PARENB;
		newtio.c_cflag &= ~PARODD;
		break;
	case 'N':
		newtio.c_cflag &= ~PARENB;
		break;
	}

	switch (nSpeed)
	{
	case 2400:
		cfsetispeed(&newtio, B2400);
		cfsetospeed(&newtio, B2400);
		break;
	case 4800:
		cfsetispeed(&newtio, B4800);
		cfsetospeed(&newtio, B4800);
		break;
	case 9600:
		cfsetispeed(&newtio, B9600);
		cfsetospeed(&newtio, B9600);
		break;
	case 115200:
		cfsetispeed(&newtio, B115200);
		cfsetospeed(&newtio, B115200);
		break;
	case 460800:
		cfsetispeed(&newtio, B460800);
		cfsetospeed(&newtio, B460800);
		break;
	default:
		cfsetispeed(&newtio, B9600);
		cfsetospeed(&newtio, B9600);
		break;
	}
	if (nStop == 1)
		newtio.c_cflag &= ~CSTOPB;
	else if (nStop == 2)
		newtio.c_cflag |= CSTOPB;
	newtio.c_cc[VTIME] = 100; ///* 设置超时10 seconds*/
	newtio.c_cc[VMIN] = 0;
	tcflush(fd, TCIFLUSH);
	if ((tcsetattr(fd, TCSANOW, &newtio)) != 0)
	{
		perror("com set error");
		return -1;
	}

	//	printf("set done!\n\r");
	return 0;
}