串口处理代码

许多流行的linux串口编程的版本中都没对c_iflag（termios成员变量）这个变量进行有效的设置，这样传送ASCII码时没什么问题，但传送二进制数据时遇到0x0d,0x11和0x13却会被丢掉。不用说也知道，这几个肯定是特殊字符，被用作特殊控制了。关掉ICRNL和IXON选项即可解决。

c_iflag &= ~(ICRNL | IXON);

0x0d 回车符CR

0x11 ^Q VSTART字符

0x13 ^S VSTOP字符

ICRNL 将输入的CR转换为NL  

IXON 使起动/停止输出控制流起作用

#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <stdio.h>

#include <pthread.h>
#include <sys/times.h>
#include <sys/select.h>
#include <assert.h>
#include <sys/types.h>
#include <cutils/atomic.h>
#include <hardware/hardware.h>

#include "serial.h"


//串口相关
struct termios serial_oldtio;
struct termios serial_newtio;
fd_set read_fds;


 static int set_serial_opts(int fd, int nSpeed, int nBits, char nEvent, int nStop)
 {
    int ret = -1;

    if (fd < 0)
        return -1;

    //将目前终端机参数保存到结构体变量serial_oldtio中
    if (tcgetattr(fd, &serial_oldtio) != 0)
    {
        goto fail;
    }

    //结构体serial_newtio清0
    memset(&serial_newtio, 0, sizeof(serial_newtio));

    //设置串口参数
    serial_newtio.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
    serial_newtio.c_oflag &= ~OPOST;
    serial_newtio.c_iflag &= ~(ICRNL | IXON | IGNCR);
    serial_newtio.c_cflag |= CLOCAL | CREAD; //启动接收器
    serial_newtio.c_cflag &= ~CSIZE;

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

    serial_newtio.c_cc[VINTR] = 0;
    serial_newtio.c_cc[VQUIT] = 0;
    serial_newtio.c_cc[VERASE] = 0;
    serial_newtio.c_cc[VKILL] = 0;
    serial_newtio.c_cc[VEOF] = 0;
    serial_newtio.c_cc[VTIME] = 1;
    serial_newtio.c_cc[VMIN] = 0;
    serial_newtio.c_cc[VSWTC] = 0;
    serial_newtio.c_cc[VSTART] = 0;
    serial_newtio.c_cc[VSTOP] = 0;
    serial_newtio.c_cc[VSUSP] = 0;
    serial_newtio.c_cc[VEOL] = 0;
    serial_newtio.c_cc[VREPRINT] = 0;
    serial_newtio.c_cc[VDISCARD] = 0;
    serial_newtio.c_cc[VWERASE] = 0;
    serial_newtio.c_cc[VLNEXT] = 0;
    serial_newtio.c_cc[VEOL2] = 0;



    switch (nBits)
    {
        case 7: serial_newtio.c_cflag |= CS7;break;
        case 8: serial_newtio.c_cflag |= CS8;break;
        default:
            serial_newtio.c_cflag |= CS8;break;
    }


    switch (nEvent)
    {
        case 'O':
            serial_newtio.c_cflag |= PARENB;
            serial_newtio.c_cflag |= PARODD;
            serial_newtio.c_iflag |= (INPCK|ISTRIP);
            break;

        case 'E':
            serial_newtio.c_cflag |= PARENB;
            serial_newtio.c_cflag &= ~PARODD;
            serial_newtio.c_iflag |= (INPCK|ISTRIP);
            break;

        case 'N':
            serial_newtio.c_cflag &= ~PARENB;
            break;

        default:
            serial_newtio.c_cflag &= ~PARENB;
            break;
    }

    switch (nSpeed)
    {
        case 9600:
            cfsetispeed(&serial_newtio, B9600);
            cfsetospeed(&serial_newtio, B9600);
            break;

        case 19200:
            cfsetispeed(&serial_newtio, B19200);
            cfsetospeed(&serial_newtio, B19200);
            break;

        case 38400:
            cfsetispeed(&serial_newtio, B38400);
            cfsetospeed(&serial_newtio, B38400);
            break;

        case 57600:
            cfsetispeed(&serial_newtio, B57600);
            cfsetospeed(&serial_newtio, B57600);
            break;

        case 115200:
            cfsetispeed(&serial_newtio, B115200);
            cfsetospeed(&serial_newtio, B115200);
            break;

        default:
            cfsetispeed(&serial_newtio, B9600);
            cfsetospeed(&serial_newtio, B9600);
            break;
    }

    if (nStop == 1)
        serial_newtio.c_cflag &= ~CSTOPB;
    else if (nStop == 2)
        serial_newtio.c_cflag = CSTOPB;

    //刷新在串口中的输入输出数据
    tcflush(fd, TCIFLUSH);

    //设置当前的的串口参数为flydvd_newtio
    if (tcsetattr(fd, TCSANOW, &serial_newtio) != 0)
    {
        goto fail;
    }

    ret = 0;

    fail:
        return ret;
 }

 int serial_write(int fd, unsigned char *buf, int len)
 {
    int ret = -1;

    if (fd < 0)
        return ret;

    //写入数据
    ret = write(fd, buf, len);

    return ret;
 }

 long serial_read(int fd, unsigned char *buf, int len)
 {
    long ret = -1;
    struct timeval tv_timeout;

    FD_ZERO(&read_fds);
    FD_SET(fd, &read_fds);
    tv_timeout.tv_sec = 1;
    tv_timeout.tv_usec = 0;

    switch (select(fd+1, &read_fds, NULL, NULL, &tv_timeout))
    {
        case -1:
            printf("select error");
            break;

        case 0:
            printf("select timeout");
            break;

        default:
            if (1)
            //if (FD_ISSET(fd, &read_fds))
            {
                //读取数据
                ret = read(fd, buf, len);
            }
            break;
        }

    return ret;
 }

int serial_open(char* serialName,int nSpeed)
{
    int fd = -1;
    int res = 0;
    pthread_t thread_id;

    fd = open(serialName,O_RDWR | O_NOCTTY | O_NDELAY);

    if (fd > 0)
    {
        if (set_serial_opts(fd, nSpeed, 8, 'N', 1) == -1)
        {
            return -1;
        }

        FD_ZERO(&read_fds);
    }

    return fd;
}

int serial_close(int fd)
{
    if (fd < 0)
        return -1;

    //恢复旧的端口参数
// tcsetattr(fd, TCSANOW, &serial_oldtio);

    //关闭串口
    if (!close(fd))
    {
        return 0;
    }

    return -1;
}