// If you're guaranteed a response, try this with different VTIME and VMIN
settings. I usually use VMIN, VTIME = 0 and use select() to determine if
data is available.
do {
res = read(fd, buff, 255);
perror("read");
} while (res < 0 && errno == EINTR);
On Tuesday, 6 May 2014 14:42:34 UTC-4, Andrey wrote:
>
> 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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