Changing it up a bit here. I'm doing some prototype code that will eventually be translated into C/XS, but I'm having some brain fart moments here trying to sort out whether my logic is, actually logical.

Because the distribution isn't available yet, it's not test-worthy. What I'm looking for is eyes on the logic itself, not whether it works or not. What's supposed to happen is this:

caller sends in a start data marker ([), an end data marker (]), a digit that represents the number of times the start/end markers should be seen before identifying we have data (3), and finally, a test "reset" identifier (!) for the transmitter to say "wait, reset that crap, let's start over"

I've got it working in basic test cases, but I'm wondering if some keen-eyed Monks can have a glance at the situation (I've left everything as simple-to-understand if() statements for this review) to see how I could expand on the assurance aspect of ensuring the receiver only gets good data, and continues to work if not.

Receiver (rx):

use warnings;
use strict;

use RPi::Serial;

my $s = RPi::Serial->new('/dev/ttyUSB0', 9600);

my $data;
my ($rx_started, $rx_ended) = (0, 0);

while (1){
    if ($s->avail){
        my $data_populated = rx('[', ']', 3, '!');

        if ($data_populated){
            print "$data\n";
            rx_reset();
        }
    }
}

sub rx {
    my ($start, $end, $delim_count, $rx_reset) = @_;

    my $c = chr($s->getc); # getc() returns the ord() val on a char* p
+erl-wise

    if ($c ne $start && ! $rx_started == $delim_count){
        rx_reset();
        return;
    }
    if ($c eq $rx_reset){
        rx_reset();
        return;
    }
    if ($c eq $start){
        $rx_started++;
        return;
    }
    if ($c eq $end){
        $rx_ended++;
    }
    if ($rx_started == $delim_count && ! $rx_ended){
        $data .= $c;
    }
    if ($rx_started == $delim_count && $rx_ended == $delim_count){
        return 1;
    }
}
sub rx_reset {
    $rx_started = 0;
    $rx_ended = 0;
    $data = '';
}

[download]

Sender (tx):

use warnings;
use strict;

use RPi::Serial;

my $s = RPi::Serial->new('/dev/ttyS0', 9600);

for (qw(x [[[hello]]] ! [[[world]]] a b)){
    # x     = no start marker seen yet, reset
    # [[[   = start data ok
    # hello = data
    # ]]]   = end data ok
    # !     = RX reset command
    # [[[   = start data ok
    # world = data
    # ]]]   = end data ok
    # a     = no start marker set, reset
    # b     = no start marker set, reset

    $s->puts($_);
}

[download]

Works fine in such a situation, here's the output after starting rx in one window, and running tx in another window after that:

$ perl examples/rx.pl
hello
world

[download]

I apologize for the lack of a testable example, but this is a thought-process-only kind of post I'm trying to get ideas from by eye at this time.

Thanks all,

-stevieb

In reply to Code review: Start and End markers to ensure Serial data is valid by stevieb

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