I actually didn't do anything (meaning I didn't send James my cart -- nobody actually told me to, nor gave me an address, thus I did nothing. :-) ).
Nice find. Now the problem -- and it is a problem -- of documenting this behaviour comes into play.
- Needs to have its Hardware section updated (states there is no difference in the Acclaim chip (we now know that's wrong), and the paragraph after that is also wrong WRT that chip)
- I'm not sure what should go here. Something
probably should. I really do not like how the mapper documentation is "spread all over the place" like this, i.e. MMC3 wiki page has some info, INES_Mapper_004 page has other info, etc..***
- Probably needs reinvestigation to see what its timing behaviour is like
- Be sure to see the "IRQ counter operation" section, note the "blah blah 5 pixels later" part -- like I said, needs investigation
- Same situation as RAMBO-1 and INES_Mapper_064
And no need for Mapper 206 stuff to get updated, as supposedly those chips (Tengen MIMIC-1 and Namcot 118) lack IRQ.
I have not the slightest idea how to solve this from an emulator perspective. I imagine a ROM hash database and so on is really the only way, similar to how people differentiate between MMC3A and MMC3B and other chips. If you ask me, this warrants a separate mapper number; ex. "for the Acclaim MC-ACC chip, the behaviour is almost identical to that of a real MMC3, except for the following: * scanline IRQ generation happens on the falling edge of A12 (real MMC3 keys off rising edge), so IRQ generation happens 4 cycles later than on a real MMC3".
*** -- I imagine this confuses the hell out of a lot of people. People update one but not the other, blah blah blah. All the Disch mapper docs stuff should really just be put into a single page and section-ised, where notes can be added within each section (outside of the <pre> content). Likewise I should probably spend some time looking at the Infobox wiki template so that each chip could have an Infobox that lists off the relevant iNES mapper numbers that use the chip. (If you don't know what an Infobox is, it's the little box on the right side of pages that lists off some summarised info; example
(Developer, Publisher, Designer, etc.)).