a C Program to monitor serial port data

来源：互联网发布：java里poi是什么编辑：程序博客网时间：2024/05/22 08:20

第一步打开串口 ttyUSB0, 这部分程序放在main的前面

char *port_name = "/dev/ttyUSB0";
        int fd;

        int j;
        int nbr_writes;

        printf("\n part test of RS485: \n\n");

        fd = open(port_name, O_RDWR|O_NOCTTY|O_NDELAY);
        if (fd < 0)
        {
                printf ("error %d opening %s: %s", errno, port_name, strerror (errno));
                return 1;
        }
        printf("open %s returns %d \n", port_name, fd);

第二步初始化串口的函数         setup_com(fd);

int setup_com(int fd){
    struct termios options;
    tcgetattr(fd, &options);
    /* Set the baud rates to 9600...*/
    cfsetispeed(&options, B9600);
    cfsetospeed(&options, B9600);
    /* Enable the receiver and set local mode...*/
    options.c_cflag |= (CLOCAL | CREAD);
    /* Set c_cflag options.*/
    options.c_cflag &= ~PARENB;
    options.c_cflag &= ~PARODD;
    options.c_cflag &= ~CSTOPB;
    options.c_cflag &= ~CSIZE;
    options.c_cflag |= CS8;
    /* Set c_iflag input options */
    options.c_iflag &=~(IXON | IXOFF | IXANY);
    options.c_iflag &=~(INLCR | IGNCR | ICRNL);
    options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
    /* Set c_oflag output options */
    options.c_oflag &= ~OPOST;
    /* Set the timeout options */
    options.c_cc[VMIN] = 0;
    options.c_cc[VTIME] = 10;
    tcsetattr(fd, TCSANOW, &options);
    return 1;
}

第3步尝试写入一些数据，看是否成功

nbr_writes = write (fd, "hello!\n", 7); // send 7 character greeting
printf(" \n %d bytes written to ttyUSB0",nbr_writes);

第4步读取串口数据的函数func_485_transfer(fd)

int func_485_transfer(int fd)
{

        byte rcv_buf[1024];
        int j;
        bzero(rcv_buf,sizeof(rcv_buf));

        while(1) {

                read_datas_ttyS(fd,rcv_buf,5);
                printf("this time we have read: \n\n");
                for(j=0;j<rcv_amounts;j++)
                            printf("0x%x ",rcv_buf[j]);

                printf("\n\n");
        }

        return 0;

第5步实现具体的read函数

int read_datas_ttyS(int fd, byte *rcv_buf,int rcv_wait)
{
        int retval;
        fd_set rfds;
        struct timeval tv;

        int ret,pos;
   int j;
        tv.tv_sec = rcv_wait;
        tv.tv_usec = 0;

        pos = 0; // point to rceeive buf

        while (1)
        {
                FD_ZERO(&rfds);
                FD_SET(fd, &rfds); //关联fd与rfds

                retval = select(fd+1 , &rfds, NULL, NULL, &tv);
       switch (retval) {
       case -1:
           perror("select()");
                        return 0;
           break;
       case 0:
           printf("timed out from select()\n");
            return 0; //这里必须要return，否则屏幕会不断输出 timed out from select()
           break;
       default:
           if (FD_ISSET(fd, &rfds)) {
               ret = read(fd, rcv_buf+pos, 1024);

               pos += ret;
                rcv_amounts=pos;
           }
           break;
       }



        }

        return 1;
} // end read_datas_ttyS

最后程序用到的库和一些全局变量

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <fcntl.h>      // open() close()
#include <unistd.h>     // read() write()
#include <termios.h>    // set baud rate
#include <fcntl.h>
#include <sys/select.h>
#include <sys/time.h>
#include <sys/types.h>

typedef unsigned int byte;
int rcv_amounts;
//-----------------------

0 0