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

Discuss hardware-related topics, such as development cartridges, CopyNES, PowerPak, EPROMs, or whatever.

Moderator: Moderators

User avatar
rainwarrior
Posts: 8732
Joined: Sun Jan 22, 2012 12:03 pm
Location: Canada
Contact:

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

Post 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.
Last edited by rainwarrior on Wed Mar 11, 2015 3:40 pm, edited 1 time in total.
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

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

Post 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.
Drag
Posts: 1615
Joined: Mon Sep 27, 2004 2:57 pm
Contact:

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

Post 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?
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

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

Post 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.
Drag
Posts: 1615
Joined: Mon Sep 27, 2004 2:57 pm
Contact:

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

Post by Drag »

...and then comes the game that uses it. :P
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

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

Post 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.
User avatar
l_oliveira
Posts: 409
Joined: Wed Jul 13, 2011 6:51 am
Location: Brasilia, Brazil

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

Post 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.
tepples
Posts: 22708
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)
Contact:

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

Post 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.
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

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

Post 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.
User avatar
l_oliveira
Posts: 409
Joined: Wed Jul 13, 2011 6:51 am
Location: Brasilia, Brazil

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

Post 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.
tepples
Posts: 22708
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)
Contact:

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

Post by tepples »

Can someone with an EverDrive N8 bother krikzz about this?
FHorse
Posts: 232
Joined: Sat May 08, 2010 9:31 am

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

Post by FHorse »

Fixed in puNES 0.93 WIP.
User avatar
aquasnake
Posts: 515
Joined: Fri Sep 13, 2019 11:22 pm

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

Post 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.

User avatar
krzysiobal
Posts: 1037
Joined: Sun Jun 12, 2011 12:06 pm
Location: Poland
Contact:

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

Post 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..
User avatar
Quietust
Posts: 1920
Joined: Sun Sep 19, 2004 10:59 pm
Contact:

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

Post 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.
Quietust, QMT Productions
P.S. If you don't get this note, let me know and I'll write you another.
Post Reply