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PostPosted: Mon Feb 18, 2013 6:33 pm 
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I was checking the AOROM page and found this part very strange:

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In theory, it would be possible to implement the bank select register with a 74HC377 octal D latch, allowing up to 512 kilobytes of PRG ROM, but no Rare game used this much memory.

With 7 bits for indexing banks you could go as high as 4MBytes, so where did the 512KBytes figure came from? Is that because of the position of the mirroring bit (there's only 1 unused bit between the bank index and the mirroring bit)? That wouldn't stop you from using all 7 bits, you'd just get a strange layout for them (or you could even bump the mirroring bit to the highest bit).

Also, the mention of Rare is pretty random, and even looks like something tepples would do here in the forums, but in the Wiki it's just plain confusing. Why would Rare be the only developers that would make large games?


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PostPosted: Mon Feb 18, 2013 6:38 pm 
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Most AxROM games were developed by Rare.


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PostPosted: Wed Mar 12, 2014 3:37 am 
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Most AxROM games were developed by Rare.

There is plenty of mapper #7 games not made by Rare at all. Solstice comes to mind.

It's not like the VRC mappers for example who are exclusive to Konami.

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With 7 bits for indexing banks you could go as high as 4MBytes, so where did the 512KBytes figure came from?

It comes from the iNES mapper #7 extension that implements the 4 lower bits only for bank switching. Sure you could use the 3 upper bits as well, but it wouldn't be iNES mapper #7 any more. Check the good old (and innacurate) Firebug doccument for details.

However, mapper 2 (UNROM extention) and 3 (CNROM extention) are extended to 8-bits of bank select, as there is no mirroring select bit. This may be weird, strange and make few sense, but that's just the way it is.


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PostPosted: Wed Mar 12, 2014 6:34 am 
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It makes plenty of sense to me. Oversize extensions are defined so as not to have to extend one field past another field. With UNROM, BNROM, and CNROM, there's only one field in the written value, so the extension doesn't need to cross another field. (This excludes CNROM with protection diodes, which has been assigned to a different mapper.) With AOROM, on the other hand, the mirroring page bit is in the way.


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PostPosted: Wed Mar 12, 2014 8:14 am 
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This discussion would be better placed on the wiki itself: http://wiki.nesdev.com/w/index.php?title=Talk:AxROM

Also, just click history to find out who wrote something.

As for the statement at hand, I would agree this seems strange and out of place. BNROM is a good mention as a variant of AxROM. A theoretical octal latch variant isn't a useful digression. It doesn't exist. The size described is wrong. The mention of Rare is pointless (the point that Rare used AxROM a lot is valid, but that's already part of the lead paragraph). To top it off, I can think of 3 different sensible places to put the nametable bit, so it's not even something emulators should extend like we have with oversized BNROM. Without resolving this ambiguity this statement can't even be considered a proposal for an extended AxROM.

In contrast, a similar statement is given on the BNROM page and seems totally fine to me there for all the opposing reasons. (Oversized BNROM homebrew does exist and has emulator support, the size described is correct, Rare is not mentioned, and the extension to the existing mapper is unambiguous.)


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PostPosted: Wed Mar 12, 2014 9:32 am 
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I don't think there is any ambiguity in extending mapper #7, not is the size wrong.
Since the mirroring bit is bit 4, it allows to use unambiguously bits 0-3 for bankswitching, which allows for 2^4 = 16 banks of 32kb = 512kb.
An octal latch is only one of the ways such a mapper could be realized, there is no 5-bit latches chips, so you either have to buy 8-bit or use 2 chips of 4-bit (or do whatever you want, that isn't the point of this thread).

What is wrong, however, is the mention of Rare.


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PostPosted: Wed Mar 12, 2014 9:34 am 
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The 74377 suggestion is actually a standardized notice, which takes a reason as a parameter. It defaults to "mask ROM would have been too expensive back then", which is fine for mappers whose oversize extension would exceed 1 MB, such as BNROM, CNROM, and UNROM. But for oversize extensions producing sizes that were plausible in the later NES era, I had to come up with a better excuse for why Nintendo didn't implement the suggestion. For example, later Dragon Warrior games use 512 KiB of PRG ROM on the SUROM board, and Mega Man 4 and Mega Man 6 use 512 KiB of PRG ROM on the TGROM board.

Rare AOROM games: 21
Non-Rare AOROM games: 13, including 5 developed by someone else but ported to NES by Rare.
So that makes 26 games developed or ported by Rare and 8 other.


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PostPosted: Wed Mar 12, 2014 9:36 am 
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Seriously what is that http://wiki.nesdev.com/w/index.php/INES_Mapper_007 ?!
WTF ?

Such pages should be deleted, mapper 7 should redirect to AxROM page instead (and etc... for other mappers as well)


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PostPosted: Wed Mar 12, 2014 11:16 am 
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tepples wrote:
So that makes 26 games developed or ported by Rare and 8 other.

No doubt about that, but the fact that they were the ones to release the largest number of AOROM games doesn't automatically make them the only ones able to release a 512KB game on that board. Nowadays, any user in this board has higher chances of releasing such a game than Rare.


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PostPosted: Wed Mar 12, 2014 11:21 am 
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So what should I put down as the most likely reason why the oversize extension wasn't used during the NES's commercial era (which I take to mean pre-1997)?


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PostPosted: Wed Mar 12, 2014 12:24 pm 
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Uhhh... The games they had to make fit nicely in 256KB? The developers were told they only had 256KB to work with because the purchased boards had 4-bit latches?

I honestly don't see why speculating on this is relevant in a page should be stating facts. Also, considering that "Rare" is an english word commonly used by game collectors, people not familiar with the company might get unnecessarily confused.


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PostPosted: Wed Mar 12, 2014 3:24 pm 
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Here's a few guesses:
- ROMs cost enough (at the time) that the incremental cost for a 512KiB ROM meant one may as well use an ASIC.
- By the time games had enough assets to warrant a 512 KiB ROM, everyone was using ASIC mappers anyway.
- 512 KiB of data is awkward to manage with only 32KiB at-a-time banking and only 2 KiB of internal RAM.
- There were only 25ish games released by Nintendo with 512 KiB ROMs, out of approximately 1400. In a purely statistical sense, the odds of any given mapper instantiated with 512KiB ROM is fairly low.


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PostPosted: Wed Mar 12, 2014 3:37 pm 
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lidnariq wrote:
- By the time games had enough assets to warrant a 512 KiB ROM, everyone was using ASIC mappers anyway.

There were some pretty late AOROM games though, like The Lion King and Aladdin, both released in 1995 (both are also pretty bad, specially when compared to their pirate counterparts).


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PostPosted: Wed Mar 12, 2014 9:12 pm 
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tepples wrote:
So what should I put down as the most likely reason why the oversize extension wasn't used during the NES's commercial era (which I take to mean pre-1997)?

I don't think it's very useful to speculate about the past in this way on the wiki. It's fun to offer guesses here on the board, but the wiki is reference material. Irrelevant material impedes understanding, after a point.

At most it's worth mentioning the theoretical oversize variant using an octal latch. You could even link this forum discussion about it, if you want to give someone a handle to the speculation stuff, but I don't think it belongs on the article page. (It's not much more relevant than any of the infinity of other possible other ideas that could have been implemented in a similar board.)


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PostPosted: Thu Mar 13, 2014 12:34 am 
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I agree with rainwarrior, the speculation has no place in the wiki.

As if I were to tell why 512k mapper 7 was never made, I'd rather ask : which game HAD to use 512k mapper 7 ? None of course. So that's why it has never been done. Nobody outside of this forum would ever develop an entire game JUST for using a particular hardware configuration (yes, StarFox was made on the sole purpose to test the Super FX, but here we're not talking about a super new chip or technology, just an additional latch bit). End of story.

Quote:
- 512 KiB of data is awkward to manage with only 32KiB at-a-time banking and only 2 KiB of internal RAM.

I don't think it's awkward to manage, once you made up the tranpoline zone that is repeated in each bank. 32k banks also means less banks, so easier to manage.
Also the size of PRG banks has no relationship ever with RAM size.


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