Dear Monks,

This little perl program uses GPS::NMEA to read data from a generic USB GPS dongle and continuously print out the results. It works great, when it works, which is most of the time, and I've never seen it stop. But sometimes when the program is first run:

  1. nothing happens, nothing. rerun program and it's fine.
  2. one line output (may or may not have altitude). then, more nothing.
The altitude is sometimes missing from the first or second line of output, but once (in many of test runs) I saw it spit this thing out as the altitude: x???x??x???f3Y??c??fF? which I think may be undecoded GPS data from my experiments with Serial Communication in Perl.

Anyway I need this thing to run no matter what and was wondering what's the best technique to achieve total fault tolerance. I tried to catch errors by checking the object and using eval on the hanging method (get_position has this until loop waiting to parse) to no avail. Would it be wise to fork the program and somehow monitor it for activity from the parent so a hanging child process could be restarted or something? How would that be done? Thank you! 

#!/usr/bin/perl

use strict; 
use warnings; 
use GPS::NMEA;
use Time::Piece;

my $gps = GPS::NMEA->new(
  Port => '/dev/tty.usbserial-110', # ls -l /dev | grep usb | grep tty
  Baud => 4800 # can't connect this old unit at 9600
);

STDOUT->autoflush(1);

while () {
  # https://metacpan.org/dist/perl-GPS/source/NMEA.pm#L70
  if (my ($ns, $lat, $ew, $lon) = $gps->get_position) { # hangs right 
+here

    my $ddmmyy     = $gps->{NMEADATA}->{ddmmyy}     || '???';
    my $time_utc   = $gps->{NMEADATA}->{time_utc}   || '???';
    my $alt_meters = $gps->{NMEADATA}->{alt_meters} || '???';
    
    $time_utc =~ s/\.\d+$//;
    
    if (my $t = Time::Piece->strptime("$ddmmyy $time_utc","%d%m%y %H:%
+M:%S")){
      $time_utc = $t->strftime
    }

    print join ' ', $ns, $lat, $ew, $lon, 'A', $alt_meters, $time_utc,
+ "\n"
  }
}

__END__
Output, once per second:
N 12.345678 W 123.456789 A 123.4 Mon, 29 Apr 2024 12:34:01 UTC
N 12.345678 W 123.456789 A 123.4 Mon, 29 Apr 2024 12:34:02 UTC
N 12.345678 W 123.456789 A 123.4 Mon, 29 Apr 2024 12:34:03 UTC

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In reply to Total fault tolerance for perl GPS program by Anonymous Monk

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