Обнаружение сигнала на Com порте

#include <stdio.h> 
#include <errno.h> 
#include <string.h> 
#include <termios.h> 
#include <fcntl.h> 
#include <unistd.h> 
#include <sys/ioctl.h> 
#include <sys/signal.h> 
#include <linux/serial.h>
#define DEVICE "/dev/ttyS0" 
#define TRUE    1
#define FALSE    0
// read the current level from RING INDICATOR pin 
// Parameters: int fd – a handle to the file descriptor of the tty.
// Returns: 
//     TRUE (1)    - if the TIOCM_RI flag is set.
//     FALSE (0)    - if the TIOCM_RI flag is not set.
//     < 0     - if an error occurred reading the flags.
int get_rng_state(int fd) 
{ 
int return_val = 0;
int serial = 0;
// Check that the file descriptor given is not rubish.
if(fd < 0)
{
fprintf(stderr, "Bad file descriptor (%d).\n", fd);
return fd;
}
// try to read the value.
if(((return_val = ioctl(fd, TIOCMGET, &serial))) < 0)
{ 
fprintf(stderr, "ioctl(TIOCMGET) failed: %d: %s\n", errno, strerror(errno)); 
return return_val; 
} 
// Success!, set the output value to TRUE or FALSE.
return (serial & TIOCM_RI) ? TRUE : FALSE; 
} 
// sample code for blocking until rng state changes 
int main(int argc, char** argv) 
{ 
int return_code = 0; 
int omode = O_RDONLY;
// This struct will hold the results of the TIOCGICOUNT ioctl call.
// The serial_icounter_struct is defined in linux/serial.h
struct serial_icounter_struct serial_counter;
// open the serial stream 
int fd = open(DEVICE, omode, 0777); 
if(fd < 0) 
{ 
fprintf(stderr, "open() failed: %d: %s\n", errno, strerror(errno)); 
return fd; 
}
if((return_code = get_rng_state(fd)) < 0) 
{
return return_code; // bug out if an error occurred.
}
else
{
printf("Device opened, intitial RI state: %s\n", (return_code ? "SET" : "UNSET")); 
}
// detect rng changes forever 
int i=0; 
int state;
int wait_on_ri;
int ring_count = 0;
while(1) 
{ 
// The flags to wait on. assigned to an int here so that it can be passed by ref.
wait_on_ri = TIOCM_RI;
// Get the current state, break out of the while loop if this fails.
if((state = get_rng_state(fd)) < 0)
{
// an error occurred reading the state.
return_code = state;
break;
}
// Print out "SET" if state != 0 or "UNSET" if state == 0.
printf("%6d rng state: %s\n", i++, (state ? "SET" : "UNSET"));
// store the current state
// block until line changes state 
if((return_code = ioctl(fd, TIOCMIWAIT, &wait_on_ri)) < 0) 
{ 
fprintf(stderr, "ioctl(TIOCMIWAIT) failed: %d: %s\n", errno, strerror(errno)); 
break; // break out of the while loop.
}
return_code = 0;
// make sure its the RI port
if ((return_code = ioctl(fd, TIOCGICOUNT, &serial_counter)) < 0)
{
fprintf(stderr, "ioctl(TIOCGICOUNT) failed: %d: %s\n", errno, strerror(errno)); 
break; // break out of the while loop.
}
return_code = 0;
// Notify that the count has changed.
if(ring_count != serial_counter.rng) 
{
printf("Ring count changed from %d to %d\n", ring_count, serial_counter.rng);
ring_count = serial_counter.rng; // update the ring count.
}
else
{
// This should not happen, but if we print it out it will be easy to see if it does
// then we need to figure out why
printf("Ring count remains unchanged at %d\n", ring_count);
}
}
// clean up
close(fd);
return return_code;
}