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)
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