I got a big trouble with BeagleboneBlack Uart

Question

My beagleboneblack(let's call it "BBB") run 3.8.13-bone47, and I have been haunted by a bug for 2 weeks.

My problem is :when my BBB gets a string,my BBB will send the same string to another terminal.

For example:My laptop with a Uart2USB bridge sent a string "asd",then BBB will got "asd".But meanwhile, BBB would send "asd" to my laptop.And all of Uart module on BBB(Uart1,Uart2,Uart4) did the same thing.

By the way,I tried to avoid this bug by using two Uart(one for TX,another one for RX).Fortunately,I did it,but I still want to know the reason and the solution.

Here is my Uart.c,Uart.h and test.c:

/*====================Uart.c================*/
#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>
#include <sys/time.h>
#include <string.h>
#include "Uart.h"

#define TRUE 1
#define FALSE -1

int fd_uart;

void set_speed(void)
{
        int i;
        int status;
        int speed_arr = B38400;

        struct termios Opt;
        tcgetattr(fd_uart,&Opt);

        tcflush(fd_uart, TCIOFLUSH);

        cfsetispeed(&Opt, speed_arr);
        cfsetospeed(&Opt, speed_arr);

        status = tcsetattr(fd_uart, TCSANOW, &Opt);

        if(status != 0)
                perror("tcsetattr fd1");
}

int set_Parity(void)
{
        struct termios options;
        if( tcgetattr( fd_uart,&options)!= 0)
        {
            perror("SetupSerial 1");
            return(FALSE);
        }

        options.c_cflag &= ~CSIZE;

        options.c_cflag |= CS8;

        options.c_cflag &= ~PARENB;    /* Clear parity enable */
        options.c_iflag &= ~INPCK;     /* Enable parity checking */
        options.c_iflag &= ~(ICRNL|IGNCR);
        options.c_lflag &= ~(ICANON );

        options.c_cflag &= ~CSTOPB;

        options.c_iflag |= INPCK;

        options.c_cc[VTIME] = 150; // 15 seconds
        options.c_cc[VMIN] = 0;

        tcflush(fd_uart,TCIFLUSH); /* Update the options and do it NOW */

        if(tcsetattr(fd_uart,TCSANOW,&options) != 0)
        {
                perror("SetupSerial 3");
                return (FALSE);
        }
        return (TRUE);
}

void initUart(int argc, char **argv)
{
        char devname_head[10] = "/dev/";
        char dev_name[20];

        if(argc < 2)
        {
                printf("Please input './test_uart ttyOx'\n");
                exit(1);
        } else {

                strcpy(dev_name, devname_head);
                strcat(dev_name, argv[1]);

                fd_uart = open(dev_name, O_RDWR);
                if(fd_uart < 0)
                {
                        perror("error to open /dev/ttyOx\n");
                        exit(1);
                } else if (fd_uart == 0) {
                        printf("Can't Open Serial Port!\n");
                        exit(0);
                } else {
                        //Setup
                        set_speed();                   //baud:38400
                        if (set_Parity() == FALSE)      //8,1,n
                        {
                                printf("Set Parity Error\n");
                                exit(1);
                        }
                }
        }
}

void writeUartString(char *buf)
{
        if ( write(fd_uart,buf,strlen(buf)) < 0)
        {
                printf("write error\n");
        }
}

void writeUartMsg(char *buf,int num)
{
        if ( write(fd_uart,buf,num) < 0)
        {
                printf("write error\n");
        }
}

int readUart(char *buf)
{
        int num = 0, i = 0;
        num = read(fd_uart,buf,sizeof(buf));
        if(num < 0){
                printf("read error\n");
        }
        return num;
}

void closeUart(void)
{
        close(fd_uart);
}
/*======================================================*/

/*==================Uart.h===================*/
#ifndef UART_H
#define UART_H

void set_speed(void);
int set_Parity(void);
void initUart(int argc, char **argv);
void writeUartString(char *buf);
void writeUartMsg(char *buf,int num);
void closeUart(void);

extern int fd_uart;

#endif
/*=======================================*/

/*================test.c=================*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "Uart.h"

int main(int argc, char **argv)
{
        int i = 0,temp = 0;
        char buf[64] = {0};
        initUart(argc,argv);
        while(1){
                writeUartString("waiting\n");
                printf("waiting\n");
                memset(buf,0,64);
                temp = readUart(buf);
                printf("readUart's return value = %d\n",temp);
                if (temp > 0){
                        printf("get something\n");
                        printf("%s\n",buf);
                }
                sleep(1);
        }
        return 0;
}
/*====================================*/

Did somebody get this situation too?

Answer 1

You left echoing enableed with

options.c_lflag &= ~(ICANON );

Change it, at least, to

options.c_lflag &= ~(ICANON | ECHO );

With you are left at their original state all flags, rather then except that ICANON.