之前基于IBM deveplopworks社区的代码，做了串口初始化和发送的程序，今天在此基础上添加了读取串口数据的程序。首先是最简单的循环读取程序，第二个是通过软中断方式，使用信号signal机制读取串口，这里需要注意的是硬件中断是设备驱动层级的，而读写串口是用户级行为，只能通过信号机制模拟中断，信号机制的发生和处理其实于硬件中断无异，第三个是通过select系统调用，在没有数据时阻塞进程，串口有数据需要读时唤醒进程。第二个和第三个例子都能用来后台读取数据，值得学习。

代码一：循环读取数据

#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 0int 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("This program updates last time at %s   %s\n",__TIME__,__DATE__);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[] = "fe55aa07bc010203040506073d";write(fd,&buf,26);char buff[512];	int nread;	while(1){if((nread = read(fd, buff, 512))>0){printf("\nLen: %d\n",nread);buff[nread+1] = '\0';printf("%s",buff);}}close(fd);return 0;
}

代码清单二：通过signal机制读取数据

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<sys/signal.h>
#include<fcntl.h>
#include<termios.h>
#include<errno.h>#define FALSE -1
#define TRUE 0
#define flag 1
#define noflag 0int wait_flag = noflag;
int STOP = 0;
int res;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);
}void
signal_handler_IO (int status)
{printf ("received SIGIO signale.\n");wait_flag = noflag;
}int
main ()
{printf ("This program updates last time at %s   %s\n", __TIME__, __DATE__);printf ("STDIO COM1\n");int fd;struct sigaction saio;fd = open ("/dev/ttyUSB0", O_RDWR);if (fd == -1){perror ("serialport error\n");}else{printf ("open ");printf ("%s", ttyname (fd));printf (" succesfully\n");}saio.sa_handler = signal_handler_IO;sigemptyset (&saio.sa_mask);saio.sa_flags = 0;saio.sa_restorer = NULL;sigaction (SIGIO, &saio, NULL);//allow the process to receive SIGIOfcntl (fd, F_SETOWN, getpid ());//make the file descriptor asynchronousfcntl (fd, F_SETFL, FASYNC);set_speed (fd, 115200);if (set_Parity (fd, 8, 1, 'N') == FALSE){printf ("Set Parity Error\n");exit (0);}char buf[255];
while (STOP == 0){usleep (100000);/* after receving SIGIO ,wait_flag = FALSE,input is availabe and can be read */if (wait_flag == 0){memset (buf, 0, sizeof(buf));res = read (fd, buf, 255);printf ("nread=%d,%s\n", res, buf);
//	  if (res ==1)
//	    STOP = 1;		/*stop loop if only a CR was input */wait_flag = flag;	/*wait for new input */}}close (fd);return 0;
}

代码三：通过select系统调用进行io多路切换，实现异步读取串口数据

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<sys/signal.h>
#include<fcntl.h>
#include<termios.h>
#include<errno.h>#define FALSE -1
#define TRUE 0
#define flag 1
#define noflag 0int wait_flag = noflag;
int STOP = 0;
int res;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);
}void
signal_handler_IO (int status)
{printf ("received SIGIO signale.\n");wait_flag = noflag;
}int
main ()
{printf ("This program updates last time at %s   %s\n", __TIME__, __DATE__);printf ("STDIO COM1\n");int fd;fd = open ("/dev/ttyUSB0", 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[255];fd_set rd;int nread = 0;while(1){FD_ZERO(&rd);FD_SET(fd, &rd);while(FD_ISSET(fd, &rd)){if(select(fd+1, &rd, NULL,NULL,NULL) < 0){perror("select error\n");}else{while((nread = read(fd, buf, sizeof(buf))) > 0){printf("nread = %d,%s\n",nread, buf);printf("test\n");memset(buf, 0 , sizeof(buf));}}}}close (fd);return 0;
}