GB: MBC30 or MBC3 with 4MB support

[roytam1]

Please fill out this form:

Expected behavior

All blocks should have a tick.

Actual behavior

blocks starting from block 7F get a F(ail) mark.

Steps to reproduce the behavior

-Load ROM
-Start emulation

Crash bugs

it doesn't crash emulator.

ROM details

Which games are affected by the issue (please state if GBA or GB game):
https://github.com/EricKirschenmann/MBC3-Tester-gb

Which games, if any, are NOT affected by the issue (please state if GBA or GB game):

Include screenshots of ROM Information (File > ROM Information):

If you are using a BIOS file, please say which one.
Not using BIOS ROM.

Option details

Video driver (simple, opengl):
simple

Sound driver (directsound, xaudio, openal, SDL):
SDL

Build details

Operating System (Windows, Mac, Linux (state distribution), etc.):
Win7 SP1 x64

If using Linux, specify if using xorg or Wayland:
Nil.

Version of code (pre-built binary version, or commit ref, or just "master"):
2.1.4-eecde424

cross-reference:
mgba-emu/mgba#1713

[roytam1]

for hackfixing this issue, changing from 0x7f to 0xff will make mbctest.gb pass the test.
https://github.com/visualboyadvance-m/visualboyadvance-m/blob/master/src/gb/gbMemory.cpp#L365

[rkitover]

@roytam1 According to this informal spec I found:

https://gist.github.com/drhelius/3745961

MBC3 rom bank select actually is supposed to accept values up to 0x7f, if you are sure that this is wrong then we should fix it, but please give me a technical explanation, I am actually clueless about the hardware emulation and we need to be very careful about things like this and document everything properly.

[roytam1]

MBC3 rom bank select actually is supposed to accept values up to 0x7f

because it is actually MBC30, but with MBC3 in ROM type byte.

but please give me a technical explanation

https://gekkio.fi/files/gb-docs/gbctr.pdf (search MBC30)

[rkitover]

@roytam1 as I admitted, I'm clueless about these things, thank you for the info.

What in your opinion is the best way to distinguish this MBC30 variant, would rom size be sufficient?

[roytam1]

would rom size be sufficient?

yeah it should work.

[FredrIQ]

MBC30 cartridges should be possible to distinguish by the rom and sram sizes, yes. E.g. Japanese Crystal uses a MBC30, but (as per above) identifies as a MBC3 with added SRAM, since MBC30 don't have their own MBC identifier but uses the same as MBC3.

[rkitover]

Any hints where I can find the right crystal rom, the one I tried was a 2M rom size, please email me at rkitover@gmail.com.

[roytam1]

Any hints where I can find the right crystal rom, the one I tried was a 2M rom size, please email me at rkitover@gmail.com.

retail cart of Pokemon Crystal JP is 2MB in size, and there are custom projects make use of MBC30 with 4MB ROM with success.

[roytam1]

and by the way, there is also a project make use of normal MBC3 and 4MB ROM. https://shop.insidegadgets.com/product/gameboy-4mb-32kb-fram-mbc3-with-rtc-flash-cart/