Sonic 1 "Mega PCM" driver

I had a quick go on implementing Mega PCM in Sonic 1: Project 28, and it all worked out perfectly, like in the other disassemblies. I didn't have enough time and will to also apply a HQ playback guide yet, but the fact the main one worked means all the rest will do. Here's disassembly for the reference:
https://www.dropbox.com/s/l6jzn3l9wf3isru/Sonic_1_28_with_MegaPCM.7z?dl=0

I tested it in Kega, Gens and Regen, tried to locate samples at different offsets in ROM, both ran GHZ 3 from Level Select and got to it through the normal game play -- I couldn't reproduce the weird bug you're talking about. I even have no idea how a thing like this could happen, because the Mega PCM code is quite steady for this sort of things: it ensures offsets are correct before reading data and there is no way you could corrupt Z80 RAM or Mega PCM's variables by playing a broken sample.

Could you PM me that buggy ROM? I'm quite interested to see what could wrong here.

 

So, I figured out GT Koopa's problem. Since two or more people had it, I think this should be highlighted.

The bug described above occurs when you forgot to follow this part of guide in the first post:

Basically, the old driver was hardcoded to play sample $83 with different pitches for samples ($88-$8B), in order to do this, loc_71CAC routine modified drivers code in Z80 RAM. This fix essentially was for the old driver's code as you see, for Mega PCM, it just breaks its code in a random place.

So, by playing samples $88-$8B, the unwanted fix works and the Mega PCM code gets corrupted, which causes playback bugs.

Yes, it's totally clean. In fact, the disassembly I posted earlier was a modified one used in S1 Hacking Studio 2, hence Jump Dash, Spin Dash and a lot of other changes. The program isn't released here yet.

 

Bump.

SSRG user 'Mike B Berry' reported me he had issues with SEGA PCM playback using Puto's custom code, which most of hacks actually use (http://info.sonicretro.org/SCHG_How-to:Fix_the_SEGA_Sound). It turned out that the problem occurred if you apply Mega PCM HQ playback guide, the SEGA PCM wasn't played in various emulators and on real hardware. Apparently, it was working in Kega, which is why I missed that. Although I did run tests in different emulators, even on hardware, my test ROM had a debug screen replacing SEGA logo, so just I couldn't see the problem.

The fix is simple. I've added it into the guide already.

Don't apply this if you didn't use this guide: http://forums.sonicretro.org/index.php?showtopic=29057&view=findpost&p=715140

 

Getting it work in Sonic 2 will require a lot of work, because it uses SMPS Z80 driver.

The fact is, with sound engine working on the M68K side (SMPS 68k), the Z80 is completely free to process digital sound samples in a continuous loop, which means, you can utilize all the processor's resources as you like, there's nothing besides you and your code. In case of SMPS Z80, the whole sound engine is also running on the Z80 along with the DAC driver. They have to share the same memory space, which is limited to 8 KB in Z80, and, of course, the execution time. Furthermore, hardware limitations make things even harder. The Z80 can only view the game ROM through a small 32 KB window, and with sound engine in the works, it often comes that the sound engine needs to access one part of ROM to read music data, at the same time the DAC driver needs another to read samples data. They have to share bank window as well, which, of course, needs some more resources and performance.

I'm not trying to say this is something impossible. A lot of sound engines on the Z80 could also playback DAC with no issues. But implementing a new and quite a complex DAC driver into Sonic 2 may require a lot of work.

I have plans to attempt an SMPS Z80 port of it, not sure if this happens any soon. I'm not too familiar with SMPS Z80, as my experience with it was little. The last time I had some issues on implementing another bank switching mechanism into it (not for Mega PCM, just to have multiple banks for music and SFX). But why not try it at least, this is gonna be challenging

 

Ehh, frankly, I totally forgot about Clone Driver =P

I've heard of it, but never used it myself, because I'm not hacking Sonic 2 per se. But considering it's 68K nature, this is definitely what I should be looking for. Thanks mentioning it. But that said, I'm still interested in pulling this thing with the original Sonic 2's sound driver.

EDIT: Quoted due to new page

 

Here you go: https://dl.dropbox.com/u/44757401/Sonic_1_with_MegaPCM_HQ.7z
This example features Mega PCM playing a digital song on the title screen and replaces some DAC samples in game.

Actually, I've already showed two Sonic 1 disassemblies with Mega PCM in this topic. Both of them also have already compiled ROM for your convenience, see s1built.bin file.

Also, compiling a disassembly is pretty easy, just run build.bat file. If everything is successful, assembler will generate a ROM file for you. It's usually named s1built.bin in case of a Sonic 1 disassembly.

 

This is intentional. As well as different music in GHZ 2 and 3 and somewhere else.

Because this isn't exactly a clean Hivebrain's disassembly, secretly, this is S1 Hacking Studio 2.0 version of disassembly, so I quickly did some music swaps and game tweaks because I was bored. A bit modified disassembly doesn't affect the way you apply Mega PCM guides at all.

 

Good job, PsychoSk8r!

I'm planning do a Clone Driver port as well and write a full guide, but I don't know when I can start, because now I have few other things I should finish first. Hope to get on it this month, eventually.

As for the garbled DACs issue you had, hearing how it sounds in the ROM you've provided, it looks like Mega PCM is trying to play compressed DPCM samples as uncompressed PCM. Ensure you've changed 'pcm' to 'dpcm' in playback flags for the compressed samples.