rs232 read pgm is not working when i connect in loopback but write is
wroking plz help...
pgm
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#define _POSIX_SOURCE 1
#define BAUDRATE B9600
#define MODEMDEVICE "/dev/ttyS1"
int main(void)
{
int ret, fd;
struct termios tio;
char buf[255];
/* Open device for reading and writing */
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NDELAY);
if (fd < 0) {
fprintf(stderr, "Error opening device %s\n", MODEMDEVICE);
goto done;
}
/* get current port attributes */
ret = tcgetattr(fd, &tio);
if (ret < 0) {
fprintf(stderr, "Error retreiving attributes, ret=%d\n", ret);
goto done;
}
tcflush(fd, TCIFLUSH);
/* set port input speed */
ret = cfsetispeed(&tio, BAUDRATE);
if (ret) {
fprintf(stderr, "Error setting input Baud rate, ret=%d\n", ret);
goto done;
}
/* set port output speed */
ret = cfsetospeed(&tio, BAUDRATE);
if (ret) {
fprintf(stderr, "Error setting output Baud rate, ret=%d\n", ret);
goto done;
}
tio.c_cflag &= ~CRTSCTS; /* HW flow ctl OFF */
tio.c_cflag &= ~PARENB; /* no parity */
tio.c_cflag &= ~CSTOPB; /* 1 stop bit */
tio.c_cflag &= ~CSIZE; /* 1 stop bit */
tio.c_cflag |= CS8; /* char size; 8N1 */
tio.c_cflag |= CREAD; /* enable receiver */
/* set port attributes */
ret = tcsetattr(fd, TCSANOW, &tio);
if (ret < 0) {
fprintf(stderr, "Error setting attributes, ret=%d\n", ret);
goto done;
}
fcntl(fd, F_SETFL, FNDELAY);
ret = write(fd, "ab\r", 3);
if (ret < 0)
fprintf(stderr, "write() of 3 bytes failed!, ret=%d\n", ret);
printf("no of data written = %d\n",ret);
usleep(5000);
while (1) {
ret = read(fd, buf, sizeof(char));
if (ret > 0) {
printf("%c",buf[0]);
}
}
done:
close(fd);
return 0;
}
##############################
####
output../a.out
no of data written = 3
########################
strace ./a.out
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
read(3, 0xbfa8d5dd, 1) = -1 EAGAIN (Resource temporarily
unavailable)
On Tue, Nov 15, 2011 at 7:52 PM, Jos Collin <[email protected]> wrote:
> > bzero(&newtio, sizeof(newtio)); /* clear struct for new port settings */
> needs #include <string.h> to suppress the warning.
>
> > int w = write(fd,"hello world\n",12);
> I think you can wait for a few milliseconds before read.
>
> >res = read(fd,buf,255);
> I don't know what you are getting after executing the code. You can try
> making your serial read non blocking to know what is happening.
>
> fcntl(fd, F_SETFL, FNDELAY);
>
> //......
> res = read(fd,buf,255);
> //.....
> if (read_ret < 0)
> {
> if (EAGAIN == errno)
> {
> printf("no data, read again.\n");
> }
> else
> {
> printf("read error.\n");
> }
> }
>
> FYI, I haven't tested your code with serial loop-back.
>
> Happy Hacking,
> Jos Collin
>
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> _______________________________________________
> Indian Libre User Group Cochin Mailing List
> http://www.ilug-cochin.org/mailing-list/
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> #[email protected]
>
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