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Homebrew game for C64 - part 1: SID tune

It's funny how interests from your teens remain with you, how easy it is to pick them up again and how comfortable they feel.

I'll probably write more about the revival of this hobby and my collection of 8-bit computers. Let's just say for now that I've begun a C64 puzzle game based on my character Yvonne the Sheep and her friends - and enemies.

Writing for 6502 (or 6510 in this case, which makes no difference as far as the assembly language is concerned) is like putting on an old familiar comfortable jumper.

I wasn't particularly keen on doing music, I did think about just forgetting it and just going with sound effects.

But a silly tune came into my head that seemed suitable for sheep pootling around a field. I'm not a composer of any great experience but I am at home with sheet music. Notating it (in 3 voices and possibly a fourth later) was the easiest way for me to get the tune out of my head and onto 'paper'.

Before I knew it I was really hooked on this aspect of the game.
Before I started to write my code I had bought Derek Morris' book, Retro Game Dev: C64 Edition. (Most of my teen experience was ZX81, Vic20, Speccy and then Amiga, I seemed to leapfrog the C64).

It contains loads of tips and tricks, plus there's downloadable code, discussed in the book, for two simple games, a space shooter and a platformer. This includes his sound library, which I thought I might try to use because that means that I can get straight on with writing the music. It uses an execute buffer; you simply pass a pointer to a bunch of commands and data to start playing the effect / music. Writing the commands is almost like 'coding the music', which is an approach I like.

At this point, someone may be reading this and thinking "why isn't she using _____ because that would be a much easier way to enter the data and for the game to play the music".

If that's you, please tell me. I'd really like to hear. I'm coming to this fresh after a long break, and when making games in my teens I didn't add music. I've not been an active part of a retro homebrew game community (yet) and don't know the tricks or the tools that people are using (if any).

Back to the story, using DM's sound library worked well with three simultaneous voices*. But there's a snag. The voices aren't staying in sync. Maybe I've misunderstood the way that the delays work (for the length of the notes and the gaps between them). I've tried to make sure that the delay counts total the same in each bar of each voice, but maybe other commands count as cycles too. Or maybe it's the attack /decay that's throwing it out (the more notes in a bar, the more it lags). I'll have to read the code a bit more thoroughly and see what it's doing. Or maybe it's a good idea anyway to modify things so that it syncs the voices. Perhaps by writing each bar of each voice as a separate buffer so that the start of each bar for each voice can be triggered at the same time.

* I'm not a windows user, and therefore not using the IDE that Derek suggests. The tools I've gathered and like include TMPx for assembling, and so I've had to edit the syntax of Derek's code.

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