一个串口通信程序，适用于3g模块发送简单AT指令

源码如下：

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

int tty_fd;

int max(int a,int b)
{
    return a>b?a:b;
}

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‘:                     //奇校验
            newtio.c_cflag |= PARENB;
            newtio.c_cflag |= PARODD;
            newtio.c_iflag |= (INPCK | ISTRIP);
            break;
        case ‘E‘:                     //偶校验
            newtio.c_iflag |= (INPCK | ISTRIP);
            newtio.c_cflag |= PARENB;
            newtio.c_cflag &= ~PARODD;
            break;
        case ‘N‘:                    //无校验
            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;
        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]  = 0;
    newtio.c_cc[VMIN] = 0;
    tcflush(fd,TCIFLUSH);
    if((tcsetattr(fd,TCSANOW,&newtio))!=0)
    {
        perror("com set error");
        return -1;
    }
//  printf("set done!\n");
    return 0;
}

int open_port(int fd,int comport)
{
    //    char *dev[]={"/dev/ttyS0","/dev/ttyS1","/dev/ttyS2"};
    //    long  vdisable;
    if (comport==0)
    {
        //printf("open /dev/ttyUSB0");
        fd = open( "/dev/ttyUSB0", O_RDWR|O_NOCTTY|O_NDELAY);
        if (-1 == fd)
        {
            perror("Can‘t Open Serial Port");
            return(-1);
        }
        else
        {
        //  printf("open ttyUSB0 .....\n");
        }
    }
    else if(comport==1)
    {    fd = open( "/dev/ttyUSB1", O_RDWR|O_NOCTTY|O_NDELAY);
        if (-1 == fd)
        {
            perror("Can‘t Open Serial Port");
            return(-1);
        }
        else
        {
        //  printf("open ttyUSB1 .....\n");
        }
    }
    else if (comport==2)
    {
        fd = open( "/dev/ttyUSB2", O_RDWR|O_NOCTTY|O_NDELAY);
        if (-1 == fd)
        {
            perror("Can‘t Open Serial Port");
            return(-1);
        }
        else
        {
        //  printf("open ttyUSB2 .....\n");
        }
    }
    if(fcntl(fd, F_SETFL, 0)<0)
    {
        printf("fcntl failed!\n");
    }
    else
    {
        //printf("fcntl=%d\n",fcntl(fd, F_SETFL,0));
    }
    if(isatty(STDIN_FILENO)==0)
    {
        printf("standard input is not a terminal device\n");
    }
    else
    {
    //  printf("isatty success!\n");
    }
//  printf("fd-open=%d\n",fd);
    return fd;
}
int main(int argc, char *argv[])
{
    int maxfd;
    fd_set rd;
    int nread,i;
    char tmp_buff[8];
    char buff[1024];
    char send_buf[1024];
    int offset;
    char recvbuf[1024];

    struct timeval timeout={0,50000};
    int timeout_flg = 0;
    int recv_flg = 0;

    //  pthread_t check_ack_thread;
    //   pthread_attr_t check_ack_thread_attr;

    if((tty_fd=open_port(tty_fd,1))<0)
    {
        perror("open_port error");
        return 0;
    }
    if((i=set_opt(tty_fd,115200,8,‘N‘,1))<0)
    {
        perror("set_opt error");
        return 0;
    }
//  printf("fd=%d\n",tty_fd);

    FD_ZERO(&rd);

    strcpy(send_buf,argv[1]);
//  printf("uart >> ");
    send_buf[strlen(send_buf)] = ‘\r‘;
    send_buf[strlen(send_buf) + 1] = ‘\n‘;
    send_buf[strlen(send_buf) + 2] = 0;
    write(tty_fd, send_buf, strlen(send_buf));
    memset(send_buf,0,sizeof(send_buf));

    FD_SET(tty_fd, &rd);
    FD_SET(fileno(stdin), &rd);

    maxfd = max(fileno(stdin), tty_fd) + 1;

    if(select(maxfd, &rd, NULL,NULL,NULL) < 0)  {
        perror("select error\n");
    }
    if(FD_ISSET(tty_fd, &rd)){
        while((nread = read(tty_fd, buff, sizeof(buff))) > 0)
        {
            printf("%s", buff);
            memset(buff, 1 , sizeof(buff));
        }
        exit(1);
    }

    close (tty_fd);
    return 0;  

}

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