Timeout with fgets()?

[KenHorse]

I have a USB to serial convertor (/etc/ttyUSB0) that I read from, using fgets.

I'm looking for a way, that if nothing is received with a few seconds, the script terminates. As in  a "serial timeout"

Of course, fgets seems to hang forever if it never sees a EOL and I need a way around that

[gw1500se]

The manual explains stream_set_timeout.

[KenHorse]

Doesn't that require that /dev/ttyUSB0 is opened as a socket? I don't know how to do that

[gw1500se]

'fgets' reads until it finds an EOF, newline or reaches a specified number of bytes. You didn't show any code so if none of those conditions occurs in your case it will hang forever. I am guessing what you are trying to accomplish but I suspect you are using the wrong read for a ttyUSB device. You might try minicom instead.

[KenHorse]

Here's the code I'm using, which works just fine as long as serial data is returned:

 

//***NEW SERIAL FUNCTION***
function serial($cmd) {		
	$port = "/dev/ttyUSB0";	
	$c = exec('stty -F '. $port .' cs8 -parenb -cstopb -echo raw speed 57600');

	if(!file_exists($port)) {
		echo "I am not blocked!";
	} else {
		$f = fopen($port, "w+");
		fwrite($f, $cmd."\r");		

		while(1) {			
			$read = fgets($f);			
			if(strlen($read) >5) {
			//	echo $read;
				$x = $read;
				fclose($f);		
				break;
			} else {
				fwrite($f, $cmd."\r");
			//	echo "[Error Resend]\n";
			}		
	}	
		}
	
	$substring = substr($read,0,1);
	if($substring =="-"){			
		print"<CENTER><H2>We encountered an error when sending $read". "Please close window and try again</H2></CENTER>";	
		//$noDataToSend ="False";	
		exit();		
	}
return $x;
}

BUT, if the communicated-with device doesn't respond, obviously fgets hangs. Normally I'd refer to that circumstance as a serial timeout. That's what I'm trying to get around.

 

And I do know minicom but that's not a help in this case

Edited September 5, 2021 by KenHorse

[gw1500se]

I don't think there is a way to do what you want with fgets. I don't know why you think mincom won't work. I haven't tried it but perhaps, as you suggested earlier, using sockets might work.

[KenHorse]

Are you saying it's possible to call minicom from a script, pass it an argument and have it return data?

[gw1500se]

Yes, by using exec.