> #define MODEMDEVICE "/dev/ttyS1"
I believe that you are loop-backing in the right physical serial port. Now
your device file is changed to ttyS1.
termios flags are changed !
EAGAIN (Resource temporarily unavailable) is a temporary condition that
may change in the later executions.
- Jos Collin
> 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
>> _______________________________________________
>> Indian Libre User Group Cochin Mailing List
>> http://www.ilug-cochin.org/mailing-list/
>> http://mail.ilug-cochin.org/mailman/listinfo/mailinglist_ilug-cochin.org
#[email protected]
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