watch-pps

#!/usr/bin/perl

use strict;
use Time::HiRes qw(gettimeofday usleep);
use Math::BigFloat;

$| = 1;

# reads a file, returns a string
sub r {
  my($filename) = @_;
  open(F,"<",$filename); 
  my $r = <F>;
  close(F);
  chomp($r);
  return $r;
}
# reads a file, returns a BigFloat (which can handle a full timestamp with ns precision)
sub f {
  my($filename) = @_;
  return Math::BigFloat->new(r($filename));
}

if(not -f "count_at_interrupt") {
  die("run me from the /sys/devices/ocp.3/pps_gmtimer.* directory\n");
}

my $seconds = 0;
my $format = "%d";
if($ARGV[0] > 1) { # optional argument: seconds to wait between updates, default 1
  $seconds = $ARGV[0] - 1;
  $format = "%0.2f";
}

my $last = 0;
while(1) {
  my $cap = r("capture"); 
  my $cac = r("count_at_interrupt"); 
  my $pps = f("pps_ts");
  my $i_d = r("interrupt_delta");

  my $delay = $pps - $pps->as_int();
  if($delay > 0.9) { # is the local clock ahead of the PPS?
    $delay -= 1;
  }

  my $diff = $cap - $last;
  if($diff < 0) { # on counter wrap
    $diff += 2**32;
  }
  if($seconds > 0) { # average out the counter difference when it's measured for more than 1 second
    $diff = $diff / ($seconds + 1);
  }

  # columns: pps timestamp, capture counter difference, cycles between capture and interrupt, interrupt delay, raw capture value, clock offset
  printf("%1.3f $format %d %1.9f %d %1.9f",$pps, $diff, $cac-$cap,$i_d,$cap,$delay);
  if($seconds > 0) {
    # if we're measuring more than one second: print ppm
    printf(" %1.3f\n",($diff-24000000)/24);
  } else {
    print "\n";
  }
  $last = $cap;
 
  # calculate when the next PPS should happen
  my(@now) = gettimeofday();
  my $next = 1000000 - $now[1];
  if($pps =~ /\.([0-9]{6})/) {
    $next = $1 - $now[1];
    if($next < 0) {
      $next += 1000000;
    }
  }
  if($seconds > 0) {
    $next += $seconds * 1000000;
  }

  # sleep till ~20ms after when the PPS should happen
  usleep($next + 20000); 
}