openwrt (linux）串口通信

openwrt (linux）串口通信

1. 基本的串口通信程序。先讀取內容，再將內容寫回串口。

#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>

main()
{
    int fd;
    int i;
    int len;
    int n = 0;
    char read_buf[256];
    char write_buf[256];
    struct termios opt;

    fd = open("/dev/ttyATH0", O_RDWR|O_NOCTTY|O_NDELAY);
    if(fd == -1)
    {
        perror("open serial 0\n");
        exit(0);
    }

    tcgetattr(fd, &opt);
    bzero(&opt, sizeof(opt));

    tcflush(fd, TCIOFLUSH);

    cfsetispeed(&opt, B115200);
    cfsetospeed(&opt, B115200);

    opt.c_cflag &= ~CSIZE;
    opt.c_cflag |= CS8;
    opt.c_cflag &= ~CSTOPB;
    opt.c_cflag &= ~PARENB;
    opt.c_cflag &= ~CRTSCTS;
    opt.c_cflag |= (CLOCAL | CREAD);

    opt.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);

    opt.c_oflag &= ~OPOST;

    opt.c_cc[VTIME] = 0;
    opt.c_cc[VMIN] = 0;

    tcflush(fd, TCIOFLUSH);

    printf("configure complete\n");

    if(tcsetattr(fd, TCSANOW, &opt) != 0)
    {
        perror("serial error");
        return -1;
    }

    printf("start send and receive data\n");

    while(1)
    {
        n = 0;
        len = 0;
        bzero(read_buf, sizeof(read_buf));
        bzero(write_buf, sizeof(write_buf));

        while( (n = read(fd, read_buf, sizeof(read_buf))) > 0 )
        {
            for(i = len; i < (len + n); i++)
            {
                write_buf[i] = read_buf[i - len];
            }
            len += n;
        }
        write_buf[len] = '\0';

        printf("Len %d \n", len);
        printf("%s \n", write_buf);

        n = write(fd, write_buf, len);
        printf("write %d chars\n",n);

        sleep(2);
    }

}

2. 注意

opt.c_cc[VTIME] = 0;
opt.c_cc[VMIN] = 0;

在這兩個值均爲0 的情況下，read不管有沒有數據都會立即返回。詳細情況在linux下man tcsetattr.

如果不設定這兩個值，那麼read只有收到回車後纔會讀取緩存中的數據。

異常處理：

如果串口被系統佔用，只能SSH，必須如下操作

一、修改 /etc/inittab 
####ttyS0::askfirst:/bin/ash --login
####ttyS1::askfirst:/bin/ash --login
把最下面的兩行註釋掉即可

二、

釋放ttyS0作爲通信串口

#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <termios.h>
#include <errno.h>
void CloseConsole(void) {

int fp;
struct termios options;
printf("change1\n");
fp = open("/dev/tty1",O_RDONLY); // 改變console
ioctl(fp,TIOCCONS);
close(fp);

fp = open("/dev/tts/0",O_RDWR|O_NOCTTY|O_NDELAY); //打開串口0讀寫
if(fp == -1) exit(0);
tcgetattr(fp,&options);
cfsetispeed(&options,B115200);
cfsetospeed(&options,B115200);
options.c_cflag |= (CLOCAL|CREAD);
tcsetattr(fp,TCSANOW,&options);
write(fp,"hello world!\n123",15);
close(fp);                       //關閉串口0

fp = open("/dev/tty0",O_RDONLY); //恢復console 到串口0
ioctl(fp,TIOCCONS);
close(fp);
printf("change2\n");
}

關於關閉SHELL對串口的佔用，使之能做普通的串口通信和撥號

1、步驟：
在內核編譯過程中執行make menuconfig
Character devices --->
Serial drivers --->

S3C2410 serial port support
[ ] Console on S3C2410 serial port 【注】去掉這項即可，不必修改busybox/init.c了 
< > 8250/16550 and compatible serial support (EXPERIMENTAL)
2、備註：
這樣就不能用ttyS0口來登錄ARM開發板了，你可以選擇用TELNET的方式來登錄。
做法：telnet 192.168.0.12(你的開發板的IP地址)
         輸入：“root”用戶名就可以進入你的開發板了
3、OK..

該文章轉至http://blog.csdn.net/wonengxing/article/details/9719739
                    http://blog.csdn.net/neiloid/article/details/7585876