From Richard's C64 blog!
5th October 2017
I really should have back dated this Friday+Saturday last week, as nothing had been done today. I’ve been running late. Anyway, last week, I was doing some brain storming, and slight of hand updating of the game code.
Originally Cruiser X-79 used a 3xIRQ interrupt, but since that was just UNECESSARY, I decided to reduce it to a 2xinterrupt instead. Reason being fixing the smooth scrolling, so that it could scroll smoothly.
Other implementations which had taken place last week was related to access to levels. The size of the game map 320 blocks in height. That is way too much for one file – even compressed. Now imaging having to pack 16 levels and try to cram that into a single file? Not really possible, due to the memory restrictions.
In order to solve this problem, I decided to implement a disk load subroutine, along with the Exomizer level decruncher. Each file to decrunch has to be a game character set, tile set and also a map. To make the level packing more simpler, I decided to create a project in Endurion’s excellent C64Studio suite, and call Exomizer to compress each level file, and then import the files on to a .D64.Then I set up the file names, low + hi-byte of the END address of the program for Exomizer to decrunch. At first I had crashes, probably due to some silly mistakes I made into the code. After several attempts the code worked, and a working game / preview was in place. Brilliant.
This may sound as if the game is turning out to be disk only? Well, not necessary. I had a bash at making a 2-sided tape version of the game with TapeToolBuildV2, and my modified version of Martin’s source. Where after loading the game with picture and music. The front end comes on, then a message on screen should prompt the user to flip tape to side 2 and rewind (Or in .tap form, simply eject side 1 or the tap file, and then start side 2 – Since I use 1541Ultimate more than a tape – in order to reduce loading programs and finding load errors 😀 ).
Although this felt like a great idea. I had to disect Martin Piper’s turbo loader system, through his source. So I created a second source, which made two loads for each file. Basically, the idea is to load a test pilot $0200-$0240, then load in the selected charset/tile/map file. After each file has loaded, the loader should point the end low/byte address to the decrunch address. Then call the loader again, another two times, then after the last decrunch. Run the game. Sadly this didn’t work for me. The turbo did load the data to the correct end address, and the low/hi byte of the end address, did get stored to the correct self-mod decrunch from address of Exomizer. However, instead of actually running the decruncher, after loading (Where I added an RTS at the end of the loader (The loader is mean’t to be a subroutine), the program crashed completely with a CPU JAM. I will need to investigate further into this issue. The test disk version loads fine. I’ll let you know how I progress through making a .tap version of my game.