45 lines
1.6 KiB
Plaintext
45 lines
1.6 KiB
Plaintext
My motivation was to really push the MAME AY8910 emu code, as the Apple
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Mockingboard music (Skyfox, Ultima) wasn't really exercising it that
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hard.
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So as a little R&D proj, I thought I'd convert Dave Rogers' Spectrum
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128 Cybernoid routine (written in 1988).
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Here's a summary of how I did it:
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. I got cybernoid.ay from
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http://www.worldofspectrum.org/projectay/gdmusic.htm
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. Split it into bin's with AYSplitR
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. Disassembled with Inkland's dz80w (www.inkland.org)
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. I wrote 6502 macros to replace the z80 opcodes
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. For cybernoid, I hand converted the z80 code to 6502 (using the
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macros)
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. I added a few extension to AppleWin's debugger to help debug the 6502
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code (ACME symbol loading & ZP pointer support).
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I use Skyfox's MB detection routine.
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The Z80 regs are emulated with zero-page memory locations $F0..$F8
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The playback routine is very inefficient, as it:
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. saves the ZP memory
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. restores the Z80 regs
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. runs the IRQ handler
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. saves the Z80 regs
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. restores the ZP memory
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This allows playback to work simultaneously with Applesoft & ProDOS. If
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DOS3.3 doesn't disable IRQs around disk I/O, then it won't work on a
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real Apple (under DOS3.3), but it'll still work on an emulator :-)
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I profiled the IRQ handler and IIRC, it takes about 20% of the frame on
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average. This is poor, but the code can easily be optimised. Remember
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this was really just a proof of concept.
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After this, I wrote a python script to do the Z80->6502, and quickly
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converted Cybernoid-II.
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Currently playback on real h/w produces noisy renditions of the tunes. I
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have replaced my AY-register update routine with the slower one used by Skyfox
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which gives better but not perfect results.
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Tom
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25 March 2006 |