atari2600land's Blog

You can shave off a few cycles by inverting the code:

 

wait: LDA #$FF

loop: CMP $D012

BNE loop

RTS

 

Edit: Perhaps $F0 would work as well, which would let you use BCC instead of BNE and leave the routine as soon as the raster line is at $F0 or higher, instead of hitting exactly $FF which I believe you might miss every now and then.

 

Something else you might be interested in is setting up an entire raster interrupt routine, which would be useful for things like scrolling part of the screen at a given line, change background colour etc. Often you can prepare data in the main program and once you're ready for the interrupt, set a flag that the raster interrupt routine would check and perform its magic. I'm not sure how much it would help you, but it would allow bullets to move perfectly smooth, trigger collisions by setting flags which the main program then can act upon and so on. It is not trivial to get a such routine running, but there are code examples on the net (or I could provide you some example code) if you think you would benefit from this.

Edited July 3, 2023 by carlsson

This is what I have so far. I would like to put some sound effects in the game. I believe I'm not using channel 2 in the game. How would I "trigger" a sound to be played only once? And would it have to be stored at $3000, $3400, etc.? How far can I go up if I keep doing that? Because this is where the sounds are so far:

   org $3000 
music: 
#incbin "song6f.bin"

   org $3400 
music1: 
#incbin "burgerslevel1.bin"

 

I think I'm going to get the Kung Fu cartridge for my Commodore 64 so I can test this out. And I'll try your code tomorrow.

burger_2023_07_03.zip

You can place routines almost anywhere in memory, though most music programs assemble the routine at an even page so $3000 and $3400 would be good if each routine/song is 1K or less. Actually if you're using the same player routine, you could include it once and submit a parameter through the accumulator to select which sub-song to play. Then it is up to the player if it is looping or ending when the music has ended.

 

For other, simpler sound effects you would do something similar but you probably don't need a full player routine for those.

 

I'll have a look at your code later in the week (Thursday - Friday at earliest).