Linux串口编程

之前一直在纠结这个怎么做，其实就是一个读写文件的流程，需要配置下串口的参数。

不过有意思的地方更在于，一，串口是可以作为终端的，linux终端tty是很有意思的，二，串口的配置涉及缓冲区设计，这点又和C语言的缓冲区息息相关，很多公司也喜欢考这样的C语言问题。

参考文献为：http://www.ibm.com/developerworks/cn/linux/l-serials/index.html

                        http://book.51cto.com/art/200711/59766.htm#book_content

                        http://book.51cto.com/art/200711/59758.htm

其中，IBM的源码为：

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<termios.h>
#include<errno.h>

#define FALSE -1
#define TRUE 0

int speed_arr[] = { B38400, B19200, B9600, B4800, B2400, B1200, B300,B38400, B19200, B9600, B4800, B2400, B1200, B300, };
int name_arr[] = {38400,  19200,  9600,  4800,  2400,  1200,  300, 38400, 19200,  9600, 4800, 2400, 1200,  300, };
void set_speed(int fd, int speed){
  int   i; 
  int   status; 
  struct termios   Opt;
  tcgetattr(fd, &Opt); 
  for ( i= 0;  i < sizeof(speed_arr) / sizeof(int);  i++) { 
    if  (speed == name_arr[i]) {     
      tcflush(fd, TCIOFLUSH);     
      cfsetispeed(&Opt, speed_arr[i]);  
      cfsetospeed(&Opt, speed_arr[i]);   
      status = tcsetattr(fd, TCSANOW, &Opt);  
      if  (status != 0) {        
        perror("tcsetattr fd1");  
        return;     
      }    
      tcflush(fd,TCIOFLUSH);   
    }  
  }
}

int set_Parity(int fd,int databits,int stopbits,int parity)
{ 
	struct termios options; 
	if  ( tcgetattr( fd,&options)  !=  0) { 
		perror("SetupSerial 1");     
		return(FALSE);  
	}
	options.c_cflag &= ~CSIZE; 
	switch (databits) 
	{   
	case 7:		
		options.c_cflag |= CS7; 
		break;
	case 8:     
		options.c_cflag |= CS8;
		break;   
	default:    
		fprintf(stderr,"Unsupported data size\n"); return (FALSE);  
	}
	switch (parity) 
	{   
		case 'n':
		case 'N':    
			options.c_cflag &= ~PARENB;   /* Clear parity enable */
			options.c_iflag &= ~INPCK;     /* Enable parity checking */ 
			break;  
		case 'o':   
		case 'O':     
			options.c_cflag |= (PARODD | PARENB); 
			options.c_iflag |= INPCK;             /* Disnable parity checking */ 
			break;  
		case 'e':  
		case 'E':   
			options.c_cflag |= PARENB;     /* Enable parity */    
			options.c_cflag &= ~PARODD;    
			options.c_iflag |= INPCK;       /* Disnable parity checking */
			break;
		case 'S': 
		case 's':  /*as no parity*/   
		    options.c_cflag &= ~PARENB;
			options.c_cflag &= ~CSTOPB;break;  
		default:   
			fprintf(stderr,"Unsupported parity\n");    
			return (FALSE);  
		}  
	
	switch (stopbits)
	{   
		case 1:    
			options.c_cflag &= ~CSTOPB;  
			break;  
		case 2:    
			options.c_cflag |= CSTOPB;  
		   break;
		default:    
			 fprintf(stderr,"Unsupported stop bits\n");  
			 return (FALSE); 
	} 
	/* Set input parity option */ 
	if (parity != 'n')   
		options.c_iflag |= INPCK; 
	tcflush(fd,TCIFLUSH);
	options.c_cc[VTIME] = 150; 
	options.c_cc[VMIN] = 0; /* Update the options and do it NOW */
	if (tcsetattr(fd,TCSANOW,&options) != 0)   
	{ 
		perror("SetupSerial 3");   
		return (FALSE);  
	} 
	return (TRUE);  
}

int main()
{
	printf("STDIO COM1\n");
	int fd;
	fd = open("/dev/ttyS0",O_RDWR);
	if(fd == -1)
	{
		perror("serialport error\n");
	}
	else
	{
		printf("open ");
		printf("%s",ttyname(fd));
		printf(" succesfully\n");
	}

	set_speed(fd,115200);
	if (set_Parity(fd,8,1,'N') == FALSE)  {
		printf("Set Parity Error\n");
		exit (0);
	}
	char buf = 'c';
	write(fd,&buf,1);
	close(fd);
	return 0;
}

51cto的这本书讲解较为详细，对每项参数有详细解释：

#include<stdio.h>
#include<stdlib.h>
#include<fcntl.h>
#include<unistd.h>
#include<errno.h>
#include<termios.h>
#include<sys/types.h>
#include<sys/stat.h>
int main()
{
	printf("COM1 test program\n");
	int fd;
	fd = open("/dev/ttyS0",O_RDWR);
	if(fd == -1)
	{
		perror("serialport error\n");
	}
	else{
		printf("open %s succesfully\n", ttyname(fd));
	}

	struct termios Opt;
	int status;
	
	tcgetattr(fd, &Opt);
	//set speed
	cfsetispeed(&Opt, B115200);
	cfsetospeed(&Opt, B115200);
	//set databits
	Opt.c_cflag &= ~CSIZE;
	Opt.c_cflag |= CS8;
	//set parity
	Opt.c_cflag &= ~PARENB;
	Opt.c_iflag &= ~INPCK;
	//set stopbits
	Opt.c_cflag &= ~CSTOPB;
	tcsetattr(fd, TCSANOW, &Opt);
	status = tcsetattr(fd, TCSANOW, &Opt);
	if(status != 0)
	{
		perror("tcsetattr fd1");
		return;
	}

	char buf = 'd';
	write(fd, &buf, 1);
	close(fd);
	
	return 0;
}