Umar Umar - 4 months ago 29
C Question

serial port getting stuck at read() data

I have connected an HC-05 bluetooth module to microZed board and trying to send and receive data via uart in Linux, Now the the send code is working when I send data from my board to the app it works perfectly given below is my code for sending

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#include <pthread.h> /* for threads */
#include <termios.h> /* uart */
#include <fcntl.h> /* uart */
#include <unistd.h> /* uart */
#define MODEMDEVICE "/dev/ttyPS1"
int main()
{
printf("Opening %s\n", MODEMDEVICE);
int portfd = open(MODEMDEVICE, O_RDWR | O_NOCTTY);
if (portfd < 0) {
printf("ERROR coultn't open %s\n", MODEMDEVICE);
return -1;
}
/* set terminal settings */
struct termios tty;
tcgetattr(portfd, &tty);

cfsetospeed(&tty, (speed_t)B9600);
cfsetispeed(&tty, (speed_t)B9600);
tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS8;
tty.c_iflag = IGNBRK;
tty.c_lflag = ICANON;
tty.c_oflag = 0;
tty.c_cflag |= CLOCAL | CREAD;
tty.c_cc[VTIME] = 0;
tty.c_cc[VMIN] = 1;
tty.c_iflag &= ~(IXON | IXOFF | IXANY);
tty.c_cflag &= ~(PARENB | PARODD);
tty.c_cflag |= PARENB;
tty.c_cflag &= ~CSTOPB;
tcsetattr(portfd, TCSANOW, &tty);
/* sleep a bit */
usleep(200000);
/* flush possible characters in the input buffer */
tcflush(portfd, TCIOFLUSH);
char buf;

int i;

while(1) {

buf++;
write(portfd, &buf, 1);
write(portfd, "\r\n", 2);
usleep(200000);

}
return 0;
}


Now the problem arises when I try send data from the app to the Bluetooth module , sometimes the program stops and says "random nonblocking pool initialized" or it gets stuck at
i = read(portfd, buf, 20);
in the code given below

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#include <pthread.h> /* for threads */
#include <termios.h> /* uart */
#include <fcntl.h> /* uart */
#include <unistd.h> /* uart */
#define MODEMDEVICE "/dev/ttyPS1"
int main()
{
printf("Opening %s\n", MODEMDEVICE);
int portfd = open(MODEMDEVICE, O_RDWR | O_NOCTTY);
if (portfd < 0) {
printf("ERROR coultn't open %s\n", MODEMDEVICE);
return -1;
}

printf("hello1\n\r");
/* set terminal settings */
struct termios tty;
tcgetattr(portfd, &tty);

cfsetospeed(&tty, (speed_t)B9600);
cfsetispeed(&tty, (speed_t)B9600);
tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS8;
tty.c_iflag = IGNBRK;
tty.c_lflag = ICANON;
tty.c_oflag = 0;
tty.c_cflag |= CLOCAL | CREAD;
tty.c_cc[VTIME] = 0;
tty.c_cc[VMIN] = 1;
tty.c_iflag &= ~(IXON | IXOFF | IXANY);
tty.c_cflag &= ~(PARENB | PARODD);
tty.c_cflag |= PARENB;
tty.c_cflag &= ~CSTOPB;
tcsetattr(portfd, TCSANOW, &tty);
/* sleep a bit */
printf("hello2\n\r");
usleep(200000);
/* flush possible characters in the input buffer */
tcflush(portfd, TCIOFLUSH);
char buf[20];
printf("hello3\n\r");
int i;

while(1) {
i = read(portfd, buf, 20);
printf("hello\n\r");

buf[i] = 0;
printf("%s", buf);
printf("\n\r");

}
return 0;
}


Any suggestions how can I fix this ?

Answer

I found the solution , first mistake was pointed out by this post . I should have set time to wait for character read to greater than 0 and minimum number of characters to read to zero

 tty.c_cc[VTIME] = 5;
 tty.c_cc[VMIN] = 0;

and thanks to sawdust for pointing out that I needed to set the tty.c_lflag flag to 0 to enable raw input instead of canonical, now the code is reading the data constantly