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Re: Big RAM on FME-7: I have a test ROM

Posted: Wed Mar 11, 2015 3:14 pm
by rainwarrior
Nestopia UE appears to use byte 8 in this way. It has no support for iNES 2, I guess. edit: apparently it does support iNES 2, and the code I found is only if not iNES 2

FCEUX and Nintendulator both support iNES 2, and don't have a fallback that uses byte 8 for RAM size.

I can't find a single ROM in my collection that doesn't have 0 in that byte, though.

Re: Big RAM on FME-7: I have a test ROM

Posted: Wed Mar 11, 2015 3:33 pm
by lidnariq
Nestopia (and UE) uses the following heuristic):

* If NES2.0, parse accordingly
* If not NES2.0, and any of the last six bytes are nonzero, clear the last nine bytes.
* If neither NES2.0 nor full of garbage, byte 8 is PRG RAM and byte 9 is PAL/not.

Re: Big RAM on FME-7: I have a test ROM

Posted: Wed Mar 11, 2015 8:21 pm
by Drag
It says it right on the MMC5 page that, lacking a valid wram size byte, you can assume 64kb wram, since no commercial MMC5 games rely on wram mirroring.

Besides, the size byte alone may not be enough for the MMC5 because, for example, there are two ways to achieve 16kb; 1 16kb chip, or 2 8kb chips, and these two methods require a mutually exclusive driving of the ram bank select register.

Edit: Nevermind, I took another look at the NES 2.0 spec; the byte actually specifies two ports of wram. I guess it doesn't matter that one chip may be considered battery backed when it isn't in reality?

Re: Big RAM on FME-7: I have a test ROM

Posted: Wed Mar 11, 2015 8:40 pm
by lidnariq
In practice, you approximately can't get 4 / 16 / 64 KiB SRAMs. (You can, but they're disproportionately more expensive). So it's reasonably safe to assume that 16=8+8 and 64=32+32.

Re: Big RAM on FME-7: I have a test ROM

Posted: Wed Mar 11, 2015 9:00 pm
by Drag
...and then comes the game that uses it. :P

Re: Big RAM on FME-7: I have a test ROM

Posted: Wed Mar 11, 2015 9:07 pm
by lidnariq
Obviously homebrewers can screw up anything, but by now? Looking through every single game we've ever seen for the NES ... they all have 2, 8, or 32 KiB SRAMs only. If they have some other value, it's made of multiple of the next smaller size.

The only 4KiB SRAM I've ever seen is the nametable memory used in the Vs. System.

Re: Big RAM on FME-7: I have a test ROM

Posted: Wed Mar 11, 2015 9:12 pm
by l_oliveira
lidnariq wrote:The only 4KiB SRAM I've ever seen is the nametable memory used in the Vs. System.
Even then, it's 2x 6116 chips.

Re: Big RAM on FME-7: I have a test ROM

Posted: Wed Mar 11, 2015 9:33 pm
by tepples
tepples wrote:This would provide ample space for a Z-machine or BASIC interpreter.
Drag wrote:...and then comes the game that uses it. :P
tpw_rules in #nesdev is working on one.

Re: Big RAM on FME-7: I have a test ROM

Posted: Wed Mar 11, 2015 10:17 pm
by lidnariq
l_oliveira wrote:
lidnariq wrote:The only 4KiB SRAM I've ever seen is the nametable memory used in the Vs. System.
Even then, it's 2x 6116 chips.
Uh...? The schematic claims it's a TC5533P-A 4 KiB SRAM. And a random picture shows a TC5533P-B 4 KiB SRAM.

To be honest, if I hadn't seen it there, I would have assumed 4 KiB SRAMs didn't exist.

Re: Big RAM on FME-7: I have a test ROM

Posted: Thu Mar 12, 2015 6:46 am
by l_oliveira
lidnariq wrote:
l_oliveira wrote:
lidnariq wrote:The only 4KiB SRAM I've ever seen is the nametable memory used in the Vs. System.
Even then, it's 2x 6116 chips.
Uh...? The schematic claims it's a TC5533P-A 4 KiB SRAM. And a random picture shows a TC5533P-B 4 KiB SRAM.

To be honest, if I hadn't seen it there, I would have assumed 4 KiB SRAMs didn't exist.
I stand corrected. Thank you ! :beer:

Sounds like that part is a major annoyance for anyone servicing these PCBs.

Re: Big RAM on FME-7: I have a test ROM

Posted: Sat Mar 14, 2015 8:08 pm
by tepples
Can someone with an EverDrive N8 bother krikzz about this?

Re: Big RAM on FME-7: I have a test ROM

Posted: Mon Mar 16, 2015 4:00 am
by FHorse
Fixed in puNES 0.93 WIP.

Re: Big RAM on FME-7: I have a test ROM

Posted: Thu Jun 10, 2021 1:46 am
by aquasnake

Code: Select all

PRG Bank 0 ($8)
7  bit  0
---- ----
ERbB BBBB
|||| ||||
||++-++++- The bank number to select at CPU $6000 - $7FFF
|+------- RAM / ROM Select Bit
|         0 = PRG ROM
|         1 = PRG RAM
+-------- RAM Enable Bit (6264 +CE line)
          0 = PRG RAM Disabled
          1 = PRG RAM Enabled

Code: Select all

ER                $6000-$7FFF
00                PRG ROM
01                Open Bus
10                Open Bus*
11                PRG RAM

*Not a recommended setting value.
**Although FME-7 has the bank switching capability of PRG RAM, no game relies on it.
***FME-7 has better bus anti-interference performance than MMC3 in the address range of $6000-$7FFF.


Re: Big RAM on FME-7: I have a test ROM

Posted: Thu Jun 10, 2021 5:03 am
by krzysiobal
aquasnake wrote: Thu Jun 10, 2021 1:46 am **Although FME-7 has the bank switching capability of PRG RAM, no game relies on it.
Why you and author of the wiki's article consider it as something special? What would you expect on the PRG lines without that "special feature" when accesing $6000 when RAM is enabled? Zeroes? Ones? Tri-state? Then it would be surprisingly special.

The mux inside FME that chooses between one of four PRG registers takes into account just CPU-A14, CPU-A13 and ROMSEL and nothing more. It does not care about the RAM/ROM bit because that would be waste of resources.

Then maybe we should also add a note that the E bit is just a general purpose output latch, that can be alternatively used as PRG-RAM-A13, PRG-ROM-A19 or something other that you wouldn't even dream of. Just no games take care of that.

MMC3, for example, outputs ones on PRG lines when accessing $6000-$7fff not because it does not have PRG banking feature, but because ROM is only enabled at $8000-$ffff, and so the mux only takes into account CPU-A14, CPU-A13 and the PRG mode bit), so it has no physical ability to distinguish $6000 from $e000..

Re: Big RAM on FME-7: I have a test ROM

Posted: Thu Jun 10, 2021 5:11 am
by Quietust
Er, just so you guys know, this thread was from over 7 years ago and got resurrected by a spambot of rather limited intelligence, so I doubt anybody's still looking to talk about this right now.