Addressed Music

OK, so, I remember someone saying to me about music and sound limits, and they believed the highest value they could get their ID's up to were 80 - 7F, today I wanted to remove that limit, so I did.


Here is a disassembly of Sonic 1 that has been altered to read the location of music rather than an ID:


Download


Here's how it works, originally, if you wanted to play a music track, you would do this:

Code:

Music



		move.b	#$81,d0

		bsr	PlaySound

That ID can only be from 80 to 7F, that leaves you with 100 slots for music, sfx and control. In the one above, you would do this instead:

Code:

Music



		move.l	#Music81,d0

		bsr	PlayMusic

Here, you simply move the location of the music (no matter where it is) to d0, and call the routine, There are 4 types to use:

Code:

Music



		move.l	#Music81,d0

		bsr	PlayMusic



		move.l	#SoundA0,d0

		bsr	PlaySound



		move.l	#SoundD0,d0

		bsr	PlayAdvance



		move.l	#Sound_E0,d0

		bsr	PlayControl

PlayMusic for BGM music, PlaySound for SFX, PlayAdvance for advance SFX of ID D0 and higher, and PlayControl for the special E0 - E4 software sound manipulation (fading, stopping, speed change, SEGA sound, etc).


There are now no ID limits, only the limit of the ROM, if you wish to apply it to your disassembly rather than having to build off of the one above, search for "; MJ:" I have tagged all of the changes made.


There SHOULD be no bugs, but even the best of us make mistakes, good luck and enjoy.

 

is it okay to use this code in homebrew?

 

I can't see why not, I wouldn't have made it public otherwise.

 

I'm a bit confused. Let me see if I understood it. So with this I can add how many songs I want in the hack? It's completely unlimited just because it reads the music pointer directly?

 

Exactly my point EK, the same goes for SFX, and music control routines, the only limit is the ROM size limit.

 

What is the ROM size limit exactly? I remembered that S&K would reject a cart that would make the total larger than 4MB right? Or am I mistaken?

 

This is all I've always wanted. This is really impressive. For the most awesomeness, it's really easy to implement.. Thank you very much for this!

it's 5MB. But every SMPS rarely reaches 4KB of size, so thousands of songs and sound effects are needed to reach all the ROM space. I'm sure that no one will have courage to do this.

 

While I'm certain this is a great advantage, surely there's a few disadvantages, right?

 

There is only 1 disadvantage I can think of, and it's not one the community would consider a disadvantage, SEGA surely did seem very concerned when it came to memory usage, which explains why every data in the ROM is kept as small as possible (i.e. everything is stored as bytes and reads up through a table of the large data), it's why the PCM samples in most SEGA games are ADPCM, and why they tend to reuse certain data over and over.


The disadvantage caused by this is that you'll be moving a long-word of data to a data register instead of a byte, so the ROM will be 3 bytes bigger for every music/sound call in the ROM, I would've considered the actually routine for saving the long-word a disadvantage as it takes a little longer, but this is compensated when the sound driver doesn't need to unpack the ID like it used to, so it's about the same speed overall.

 

5MB? Isn't it 4MB?

 

Actually, yes. All the official game cartridges were limited to 4 MB of ROM size, so do most of emulators, including Regen. The only known exception is Super Street Fighter II, which was 5 MB. However, addressed ROM space was still limited to 4 MB, and the game used the mapper to overpass this limitation. Mapper allowed the game to 'map' unreachable portions of ROM (after the 4th MB) into a visible address space. Addressing space was divided into 512 KB ROM banks and the mapper allowed to map 512 KB chunks of actual ROM chip to these banks.


However, even this 4 MB limitation is cartridges' fault, not hardware's. The hardware is actually capable of addressing more than 4 MB of ROM data. It can work with 8 MB and even 10 MB ROMs. But the way cartridge board is designed doesn't allow to access addresses part 4th MB -- the processor will freeze waiting for the bus. I don't know exactly about the details of this 'design' and what exactly leads to this limitation (as I'm pretty unexperienced in how hardware works). I learned all this from HardwareMan's post -- this guy actually made a cartridge with extended adressed ROM space. Unfortunately, I can't seem to find his post now.