Feasibility check: NES Megaman games with VRC6 sound

[phart010 | 1,779]

I thought I had asked this question on Nintendoage, but can’t seem to find it in the archives.

There is a chiptune artist named rushjet. He has done a phenomenal recreation of how all Megaman NES game soundtracks could have sounded if they were composed using Konami’s VRC6 sound chip. 

I was wondering about how feasible it would be to replace the regular Megaman soundtracks in the rom with the enhanced VRC6 soundtracks.

[TylerBarnes | 184]

You would have to port the game's assembly code to the VRC6 mapper to use that chip's sound capabilities. As far as I know the Megaman games are all UNROM, MMC1, and MMC3

Furthermore his tracks are likely going to be made in FamiTracker and exported as a NSF. The in game sound engine for Megaman need not be anything like what a tracker spits out, so you would have to do all of RushJet's work again, but would be 10x more difficult since it is at the assembly code level and not in a fancy tracker on a PC. 

Edited October 31, 2019 by TylerBarnes

[CMR | 538]

I know some of the games have hacks for using MMC5.

[Memblers | 22]

For the sound engine, the Famitracker data is almost surely going to be larger than any Megaman music.  So you need to expand the ROM, but VRC6 maxes out at 256kB PRG.  In that case, only Megaman 1 could fit extra data (as it's originally 128kB).  To know if it's feasible to replace the sound engine, you'll have to look at zero-page RAM usage. Play the NSF in an emulator while viewing RAM, then do the same with a Famitracker NSF.  If it looks close, count up the number of bytes.  The amount of RAM Famitracker uses will need to be less than the original engine.  The RAM use outside of zeropage doesn't matter, because you can easily expand that into VRC6 WRAM.

Also, VRC6 only uses CHR-ROM, not RAM.  So running it on cartridge easily might be out of the question, but I think emulators and flash carts will probably accept VRC6 CHR-RAM.

Edited November 1, 2019 by Memblers