NewRisingSun wrote:The fact that a ROM image has more than 512 KiB of PRG-ROM already unambiguously indicates that the MMC3 chip/clone must support it, so adding a new mapper or a submapper to convey that information is redundant.
The entire point of wanting a separate mapper is to denote that the MMC3 ASIC (and its contemporary clones) can't handle more than 512K of PRG. My objective is specifically signaling to people making ROM hacks that "no, you can't just casually get that". Historically we've had serious problems with people testing against emulators, not against hardware, and making things that couldn't be put on, let alone run on, hardware.
Even worse are the people who denied this reasoning, and patched the emulator to remove the size limitation to support their ROM hack.
If we insisted that Mapper 4 be strictly limited to a maximum of 512 KiB of PRG-ROM because the original MMC3 had that limitation, then we would also have to insist that Mapper 3 be strictly limited to a maximum of 32 KiB of CHR-ROM because the original CNROM board had that limitation.
The difference is that oversize CNROM has a trivially-implementable definition; for up to 128K CHR, it's literally just "connect more wires".
Historically, MMC3 is not as trivial.
Now, of course, INL is offering to make that hardware, and the objection largely is bypassed. I'm having a hard time weighing the historical reasons for why emulators had to enforce these constraints with this offer.
This has, of course, come up before a bunch. https://forums.nesdev.com/viewtopic.php?t=10474 https://forums.nesdev.com/viewtopic.php?t=12866 https://forums.nesdev.com/viewtopic.php ... 04#p180204