Hello,
I need to use an UART to communicate between beaglebone and the device. I
have written the C code, but it has a few problems within it. I can't
identify the cause of the problem or to be more precise don't know how fix
it.
The problem is of
reading in the information and displaying it on a shell. I can easily write
any information data set that I wish, but when I try to read in response it
either doesn't read in, with the perror being displayed as (erno = EINTR
[Interrupted
function call]) meaning read () function returned negative number.
#include <iostream>
#include <termios.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <errno.h>
#define BAUDRATE B19200
#define PORT "/dev/ttyO4"
#define _POSIX_SOURCE 1
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
void signal_handler_IO(int status);
int wait_flag = TRUE;
int main ()
{
int fd=0, res=0;
int check=0;
char SYNC [] = {0x55};
char PID [] = {0x6A};
struct termios oldtio, newtio;
struct sigaction saio;
char buff[255];
fd = open(PORT, O_RDWR | O_NOCTTY | O_NONBLOCK);
if (fd<0) {perror(PORT); exit(-1);}
saio.sa_handler=signal_handler_IO;
saio.sa_flags=0;
saio.sa_restorer = NULL;
sigaction(SIGIO, &saio,NULL);
fcntl(fd, F_SETFL, FASYNC);
check = tcgetattr(fd, &oldtio);
if (check<0){perror("tcgetattr");}
check = newtio.c_cflag = BAUDRATE | CS8 | CLOCAL | CREAD ; if (check<0){
perror("c_cflag");}
check = newtio.c_iflag = IGNPAR | IXON; if (check<0){perror("c_iflag");}
check = newtio.c_oflag = 0; if (check<0){perror("c_oflag");}
//check = newtio.c_lflag = ICANON | ISIG;
check = newtio.c_lflag = 0; if (check<0){perror("c_lflag ");}
/* c_cc is responsible for an erno error */
check = newtio.c_cc[VMIN]=1; if (check<0){perror("c_cc[VMIN]");}
check = newtio.c_cc[VTIME]=0; if (check<0){perror("c_cc[VTIME]");}
tcflush(fd, TCIFLUSH);
check = tcsetattr(fd, TCSANOW, &newtio); if (check<0){perror("tcsetattr"
);}
for(;;)
{
ioctl(fd, TIOCSBRK);
usleep(1300);
ioctl(fd,TIOCCBRK);
usleep(200);
/* send request to actuator to receive the current setting and setup */
check = write(fd, SYNC, sizeof(SYNC)); if (check<0){perror("SYNC");}
check = write(fd,PID, sizeof(PID)); if (check<0){perror("PID");}
/* read response*/
res = read(fd, buff,255);
if (res < 0)
{
perror("read");
//if(errno ==EINTR) continue;
}
printf(": :%d :%d\n", res,buff);
usleep(10000);
}
close (fd);
}
void signal_handler_IO(int status)
{
wait_flag=FALSE;
e}
erno EINTR error is displayed only when i'm setting any non-zero values to
c_cc[VTIME] or c_cc[VMIN]. but still even if i set the both to zero, I
cannot read anything from the port, it's just blank.
I'm confident that i'm receiving response from the device, I have checked
it with oscilloscope.
Any assistance would be appreciated. if possible with the code examples for
me to see what should I modify.
Thank you very much for the help.
--
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