uart 超声波传感器数据读取

• 传感器选择

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• 读取数据的代码如下：

    // include/aplex_tty.h
    #ifndef _APLEX_TTY_H__
    #define _APLEX_TTY_H__                                                          

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

    int set_opt(int fd, int nSpeed, int nBits, char nEvent, int nStop);
    float read_dis(void);                                                           

    #endif        

    // src/aplex_tty.c
    #include "../include/aplex_tty.h"                                               

    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;   //CLOCAL:忽略modem控制线  CREAD：打开接受者
        newtio.c_cflag &= ~CSIZE;           //字符长度掩码。取值为：CS5，CS6，CS7或CS8

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

        switch( nEvent )
        {
        case 'O':
            newtio.c_cflag |= PARENB;           //允许输出产生奇偶信息以及输入到奇偶校验
            newtio.c_cflag |= PARODD;           //输入和输出是奇及校验
            newtio.c_iflag |= (INPCK | ISTRIP); // INPACK:启用输入奇偶检测；ISTRIP：去掉第八位
            break;
        case 'E':
            newtio.c_iflag |= (INPCK | ISTRIP);
            newtio.c_cflag |= PARENB;
            newtio.c_cflag &= ~PARODD;
            break;
        case 'N':
            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;
        case 460800:
            cfsetispeed(&newtio, B460800);
            cfsetospeed(&newtio, B460800);
            break;
        default:
            cfsetispeed(&newtio, B9600);
            cfsetospeed(&newtio, B9600);
            break;
        }                                                                           

        if( nStop == 1 )
            newtio.c_cflag &=  ~CSTOPB;     //CSTOPB:设置两个停止位，而不是一个
        else if ( nStop == 2 )
            newtio.c_cflag |=  CSTOPB;                                              

        newtio.c_cc[VTIME]  = 0;            //VTIME:非cannoical模式读时的延时，以十分之一秒位单位
        newtio.c_cc[VMIN] = 0;              //VMIN:非canonical模式读到最小字符数
        tcflush(fd,TCIFLUSH);               // 改变在所有写入 fd 引用的对象的输出都被传输后生效，所有已接受但未读入的输入都在改变发生前丢弃。
        if((tcsetattr(fd,TCSANOW,&newtio))!=0) //TCSANOW:改变立即发生
        {
            perror("com set error");
            return -1;
        }
        printf("set done!\n\r");
        return 0;
    }                                                                               

    float read_dis(void)
    {
        float distant = 0;
        int tty_fd, retval;
        int write_val = 0x55;
        char read_val[2];                                                           

        tty_fd = open("/dev/ttyO0", O_RDWR | O_NOCTTY | O_NDELAY);
        if (tty_fd < 0)
        {
            perror("open tty error ");
            return -1;
        }                                                                           

        retval = set_opt(tty_fd, 9600, 8, 'N', 1);
        if (retval < 0)
        {
            perror("set error");
            return -1;
        }                                                                           

        retval = write(tty_fd, &write_val, sizeof(int));
        if (retval < 0)
        {
            perror("write error");
            return -1;
        }      

        usleep(100000);                                                             

       retval = read(tty_fd, read_val, 2);
        if (retval < 0)
        {
            perror("read errno");
            return -1;
        }                                                                           

        distant = read_val[0] * 256 + read_val[1] ;                                 

        close(tty_fd);                                                              

        return distant;
    }      

    // main/main.c
    #include "../include/aplex_tty.h"                                               

    int main(void)
    {
        float read_dis_num = 0;                                                     

        read_dis_num = read_dis();                                                  

        printf(" distant : %f\n", read_dis_num / 1000);                             

        return 0;
    }