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Waiting for Device::Serialport

by wjw (Priest)
on May 17, 2018 at 16:39 UTC ( #1214759=perlquestion: print w/replies, xml ) Need Help??

wjw has asked for the wisdom of the Perl Monks concerning the following question:

I am working on a RPi<->Arduino project and noticed that my Perl script boosts my load average to 127. The rough Perl code is below and runs just fine, as does the Arduino code. What I would like is to find a way to 'sleep' that Perl script for the 14 seconds between reads from the Arduino.

This is not hugely important right now, but might take on more importance as I add more projects to the RPi3. I have looked at sleep, delay, and several of the XXXX.Sleep.XXX modules on CPAN, but was wondering if someone with more experience with long running Perl scripts (mine have been exclusively run-once-and-done scripts) might have some advice.

My goal is to let the RPI run off and do other things while I wait for the next Arduino message, and thus reducing system resource usage during that (currently 15 second) wait. Any input/experience appreciated.

#!/usr/bin/perl -w use Modern::Perl; use Device::SerialPort::Arduino; use DBI; #use Proc::Daemon; use DateTime; use JSON; #use Data::Dumper; my $dbfile = "/home/wjw/weather_data"; my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile" ,"",""); my ($key,$val, %rx, $q, $cnt, %last, %hash, $sth, $char_cnt, $rec_cnt, + $char, $timeout, $buffer, $timestamp, $json); #################################### # Set up the serial port my $dev = Device::SerialPort->new("/dev/ttyUSB0") || warn "Can't open +/dev/ttyUSB0 $!"; my $debug = 0; #set to 1 if debug print statements +are to be displayed my $profile = 0; # set to '1' when running NYTProfile. + Limits run length... $dev->baudrate(115200); # you may change this value $dev->databits(8); # but not this and the two following $dev->parity("none"); $dev->stopbits(1); $dev->read_char_time( 0 ); # don't wait for each character $dev->read_const_time( 1000 ); # 1 second per unfulfilled "read" call #################################### while (1) { #Proc::Daemon::Init; #my $continue = 1; #$SIG{TERM} = sub { $continue = 0 }; #while ($continue) { # Poll to see if any data is coming in my $char = $dev->lookfor(); $cnt++; if ($char) { # if ($debug == 1) { # say "Raw input is -> $char"; # } $rec_cnt ++; next if $rec_cnt == 1; # The first line incoming tends to b +e two lines combined, skip it. $timestamp = uts_to_iso(time()); my $line = $char; chomp($line); if ($debug == 1) { say $line; } $json = decode_json($line); # print Dumper($json); if ( (exists($json->{'bbl'})) and (not exists($json->{'ra'}))) + { $q = "insert into weather_data values (?, ?, ?, ?, ?, ?, ? +, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"; my $sth = $dbh->prepare($q); $sth->execute(undef, $timestamp, dt('date'), dt('time'), $ +json->{'wd'}, $json->{'wv'}, $json->{'tF'}, $json->{'tC'}, $json->{'b +p'}, $json->{'rh'}, $json->{'li'}, $json->{'ov'}, $json->{'lux'}, $js +on->{'bbl'}, $json->{'irl'}, 'null', 'null' ); } elsif ( (exists($json->{'ra'})) and (exists($json->{'bbl'})) +) { $q = "insert into weather_data values (?, ?, ?, ?, ?, ?, ? +, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"; $sth = $dbh->prepare($q); $sth->execute(undef,$timestamp, dt('date'), dt('time'), $j +son->{'wd'}, $json->{'wv'}, $json->{'tF'}, $json->{'tC'}, $json->{'bp +'}, $json->{'rh'}, $json->{'li'}, $json->{'ov'}, $json->{'lux'}, $jso +n->{'bbl'}. $json->{'irl'}, $json->{'ra'}, $json->{'rr'} ); } elsif ( (exists($json->{'ra'})) and (not exists($json->{'bbl +'}))) { $q = "insert into weather_data values (?, ?, ?, ?, ?, ?, ? +, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"; $sth = $dbh->prepare($q); $sth->execute(undef,$timestamp, dt('date'), dt('time'), $j +son->{'wd'}, $json->{'wv'}, $json->{'tF'}, $json->{'tC'}, $json->{'bp +'}, $json->{'rh'}, $json->{'li'}, $json->{'ov'}, 'null', 'null', 'nul +l', $json->{'ra'}, $json->{'rr'} ); } elsif ( (not exists($json->{'ra'})) and (not exists($json->{ +'bbl'}))) { $q = "insert into weather_data values (?, ?, ?, ?, ?, ?, ? +, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"; $sth = $dbh->prepare($q); $sth->execute(undef,$timestamp, dt('date'), dt('time'), $j +son->{'wd'}, $json->{'wv'}, $json->{'tF'}, $json->{'tC'}, $json->{'bp +'}, $json->{'rh'}, $json->{'li'}, $json->{'ov'}, 'null', 'null', 'nul +l', 'null', 'null' ); } sleep(1); } } ################################ sub uts_to_iso { my $uts = shift; my $date = DateTime->from_epoch(epoch => $uts, time_zone => 'Ameri +ca/Chicago'); return $date->ymd().'T'.$date->hms().'Z'; } ################################ sub sayq { my $qs = shift @_; if (length($qs) > 0) { say $qs; } } ################################# sub dt { my $request = shift(@_); my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localti +me(); if ($request =~ /date/) { $year = $year + 1900; return "$year" . "-" . "$mon" . "-" . "$mday"; } if ($request =~ /time/) { return "$hour" . ":" . "$min" . ":" . "$sec"; } }

...the majority is always wrong, and always the last to know about it...

A solution is nothing more than a clearly stated problem...

Replies are listed 'Best First'.
Re: Waiting for Device::Serialport
by huck (Parson) on May 17, 2018 at 17:57 UTC

    I do something similar but its a pic 16f877 i read from that polls Dallas One-wire 18s20 temp sensors. i use the following

    $ob->read_char_time(5); # avg time between read char $ob->read_const_time(500); # timeout after 500 milliseconds = +0.5 seconds
    I also am looking for complete lines so i use
    my $ob = tie (*FH, 'Device::SerialPort', $cfgfile) || die "Can't tie: $!\n"; ## TIEHANDLE ##
    and to read in all available lines i use
    @gotits=<FH> ;
    This seems to work well for me, but i can get a bunch of lines all at once for while i too only cycle every 15 seconds a cycle reads about 50 18s20 sensors 6 at a time and there may not be much time between the lines for each sensor.

    One thing that may be affecting you is that

    $timestamp = uts_to_iso(time());
    runs even if you do not want to insert the lines.

    Another thing i noticed is repeated calls to dt(). saying

    my $dtdate=dt('date'); my $dttime=dt('time');
    and then using the variables in the execute may speed things up.

    and a last observation is that each insert cycle you run the $dbh->prepare($q); pulling these out of the while loop such that

    $q = "insert into weather_data values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ? +, ?, ?, ?, ?, ?, ?)"; my $sth = $dbh->prepare($q);
    is only run once, nd the loop code just uses $sth->execute(...); may speed things up a whole lot.

      Good advice. I will incorporate those suggestions. Thank you!

      UPDATE: Thanks again for the feedback! I did run through to check on those things you noticed. As IFAIK, the repeated statements all only happen once the $dev->lookfor() completes. That said, looking again made me realize that the sleep(1) which I ignored even after looking at how sleep worked( could not determine if it reduced allocated resourced on the system or not), could be changed to 14 seconds as long as the timeout for reading character was increased a bit. I also moved all the processing of getting things into the DB into its own sub. The result is that the increase in sleep time reduced cpu system resources from the aforementioned 1.27 down to less between .23 to .37 on a 1 minute average and 0.4 on a 10 minute average, and that is with htop running and two ssh sessions going. So thanks again! /huck for taking the time!

      Update 1: Figured I would repost the code that I ended up here for posterity sake, and maybe helpful to someone else...

      ...the majority is always wrong, and always the last to know about it...

      A solution is nothing more than a clearly stated problem...

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