#!/usr/bin/perl

#
# Extract the code from the 2764 used in the DECmate III.
#
# Working theory:
#   Bytes in the first 4K are simply the high nibble of the PDP-8 word,
#   duplicated to form an 8 bit byte.
#   Bytes in the second 4K are the low 8 bits of the 12 bit word.
#   

# Read in the file and assemble the words.
open(INPUT, "$ARGV[0]") || die "$ARGV[0]: $!";
while (<INPUT>) {
#               S113 0000  88000000000000000000000000000011 53
  next unless /^S113(....)(................................)..$/;
  ($addr, $data) = ($1, $2); 
#warn "$addr $data";
  $high = $addr =~ /^0/; # First 4K are high nibbles.
  @data = ();
  while ($data =~ s/^(..)//) {
    push(@data, hex($1));
  }
  $addr = hex($addr) & 07777; # Get 4K offset
  for ($b = 0; $b < 16; $b++) {
    if ($high) {
      $core[$addr+$b] = $data[$b] << 8;
    } else {
      $core[$addr+$b] += $data[$b];
      $core[$addr+$b] &= 07777; # Keep 12 bits
    }
  }
}

# TODO: Dump a BINary tape image of the reconstructed words.
$f = $ARGV[0]; $f =~ s/[.]mot$//;
$f .= ".bin";
open(OUTPUT, ">$f") || die "$f: $!"; binmode(OUTPUT);
for ($addr = 0; $addr < 100; $addr++) {
  printf OUTPUT "%c", 0200;
}
printf OUTPUT "%c%c%c", 0370, 0100, 000;
$sum = 0100; # Checksum, so far.
for ($addr = 0; $addr <= 07777; $addr++) {
  # Each word is two byetes, each added to the checksum.
  $n1 = $core[$addr] >> 6;
  $n2 = $core[$addr] & 077;
  printf OUTPUT "%c%c", $n1, $n2;
  $sum += $n1 + $n2;
}
# Output the checksum.
$sum &= 07777; # Lose all the carry-outs.
$n1 = $sum >> 6;
$n2 = $sum & 077;
printf OUTPUT "%c%c", $n1, $n2;
for ($addr = 0; $addr < 100; $addr++) {
  printf OUTPUT "%c", 0200;
}
exit 0;