Planet Bob - More Garbage!

RSS Bot · September 19, 2006

Hi there!

Another Park Patrol riddle has been solved! Remember me reporting that the "used" half of the first bank of the game mostly contained alternating $FF and $00 pages?

Believe it or not, but after all the fuss of getting those 4K extracted from the cartridge, some lines of code further down the road - it get's just completely overwritten with zeros! :-o

Kinda disturbing. There you have a commercially released game of 1984 coming on a 32K cartridge with 4 8K banks, one of which is completely unused by the game! :ponder:

I have source and binary attached. For a proof of concept just launch the shrinked-by-another-4K PRG into VICE and run it with SYS 24563.

I've also been analysing some of the "init" code of the game. It does mostly rearrange and zero out things. The C64 has then a memory layout for Park Patrol like this:

$0xxx-$3xxx => competely zeroed RAM

$4xxx-$7xxx => competely zeroed RAM (This is the area VIC gets to see!)

$8xxx-$9xxx => Bank 3 contents

$Axxx-$Bxxx => Bank 4 contents

$Cxxx => competely zeroed RAM

$Dxxx => I/O area. Most registers (SID/VIC) have been zeroed

$Exxx-$Fxxx => Bank 2 contents (Don't ask. No clue why it got moved there :ponder: )

If you're reading the source, I also ID'd some IRQ/NMI routines already:

pprev.zip

Fascinating things going on here. Almost forgot about that stuff during all the VCS coding years :lol:

Hm... does my memory still partially work? IRQs are event driven and NMIs timer driven, or? Hm... :twisted:

BTW: If you came here because you were hoping to find something about "Garbage" the band, you shall not go home without some Trivia bit: When Garbage did a song called "Alien Sex Fiend" on one of their singles, Alien Sex Fiend did a song called "Garbage" on their next album :lolblue: