Is this 'impossible ST tune' possible on CPC?

[tastefulmrship]

gwEm of The Psycho Hacking Force (Atari-ST) has written a pretty impressive 128 byte music demo. My question is; is it possible to convert the ST code into CPC Z80-speak?

Here's the link & a YouTube video.
http://dhs.nu/news.php


128 Byte Choonage by gwEm / PHF (Atari ST music demo)

[arnoldemu]

gwEm of The Psycho Hacking Force (Atari-ST) has written a pretty impressive 128 byte music demo. My question is; is it possible to convert the ST code into CPC Z80-speak?

Here's the link & a YouTube video.
http://dhs.nu/news.php


128 Byte Choonage by gwEm / PHF (Atari ST music demo)

yes, I've done it before.

[Gryzor]

yes, I've done it before.

Share! Enlighten us!

[arnoldemu]

Share! Enlighten us!

Using my friend's Atari ST, I used his "hacker cartridge" to view the memory, identify the music player and save out the memory.
I then transferred this to cpc, using my own disc reader tool (long lost now ).
Then I used a basic program on the cpc, to dissassemble the code, and generate the dissassembled 68000 assembly code.
Then I printed this out, and instruction by instruction, converted it into 1 or more z80 instructions.
The end result was I had converted the music driver and I could play atari st music on the cpc.

So I would do the same for this one, *if I had the time*, and hope that it doesn't generate a load of data that is too big for the cpc's ram.

[SyX]

The sourcecode is included, it's short and very easy to understand, but i don't know if it's possible to convert at cpc, because it's using the Timer D to alter the wave to sound more "sid".

[ralferoo]

From memory (I had a quick look at the source at lunch time, and I used to have an Amiga not an ST so the use of the timer is all guesswork):

* the "algorithmic note generation" is reading the ROM a byte at a time, using the bottom 3 bits of each to choose one of 8 notes
* the timer is used to stop the sound early (maybe this is the "more sidlike" thing, certainly it's done in the interrupt function called sid) - seems to be set to the same frequency as the note, so presumably so it plays exactly 1 complete wave
* that timer *might* change the way the AY works, I don't know enough about ST hardware.
* the note is played every 4th vblank
* a digidrum (which the CPC doesn't have) is played alternates 1 beat or 2 beats behind the note

Probably wouldn't fit in 128 bytes on the CPC, but I'm sure you could get a similar sounding effect in not much more...