El primero es este y las llamadas que se le hacen desde el código fuente PERL son del tipo my $rx_clr = rx_decode($rx_msg, $key1, $key2); siendo key1 y key2 los bytes de un CRC16 (eso creo).
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- sub rx_decode
{
my $rx_msg = shift;
my $key1 = shift;
my $key2 = shift;
die "Undefined Message Bytes" unless defined $rx_msg;
# Descramble payload bytes. This is perfomed in a similar way to the
# encoder by calling the CRC routine initially with magic values
# then doing some bit shifts and logic.
my $enc1 = 0; # Defaults to 0
my $rx_clr;
# Take each message byte in turn and descramble:
foreach my $byte (split //,$rx_msg)
{
$byte = ord $byte;
# Starting with the magic init values, use the returned
# CRC16 as the init values for the next round.
$key1 = crc16($key1, 0x1021, 0xFF);
$key2 = crc16($key2, 0x8005, 0xFF);
# Now some bit shifting weirdness:
my $enc2 = ($enc1 >> 3) | ($enc1 << 5);
# And some XORing for good measure:
my $enc3 = ($byte ^ $enc2) & 0xFF;
my $enc4 = ($enc3 ^ $key1) & 0xFF;
my $enc5 = ($enc4 ^ $key2) & 0xFF;
$enc1 = ($enc2 ^ $enc5) & 0xFF;
$rx_clr .= chr $enc5;
}
return $rx_clr;
}
Dentro de este código hay una llamada a la función crc16 que es esta:
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- sub crc16
{
my $init = shift;
my $poly = shift;
my $val = shift;
die "Undefined CRC value"
unless defined $val && defined $poly && defined $init;
my $var;
for (my $i=0; $i<8; $i++)
{
$var = $val << 8;
$var ^= $init;
$init += $init;
$val <<= 1;
if ($var & 0x8000)
{
$init ^= $poly;
}
}
return $init & 0xFFFF;
}
Muchas gracias por vuestra ayuda.
