nesdev.com
http://forums.nesdev.com/

Big RAM on FME-7: I have a test ROM
http://forums.nesdev.com/viewtopic.php?f=9&t=12467
Page 2 of 2

Author:  rainwarrior [ Wed Mar 11, 2015 3:14 pm ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

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.

Author:  lidnariq [ Wed Mar 11, 2015 3:33 pm ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

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.

Author:  Drag [ Wed Mar 11, 2015 8:21 pm ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

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?

Author:  lidnariq [ Wed Mar 11, 2015 8:40 pm ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

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.

Author:  Drag [ Wed Mar 11, 2015 9:00 pm ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

...and then comes the game that uses it. :P

Author:  lidnariq [ Wed Mar 11, 2015 9:07 pm ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

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.

Author:  l_oliveira [ Wed Mar 11, 2015 9:12 pm ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

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.

Author:  tepples [ Wed Mar 11, 2015 9:33 pm ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

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.

Author:  lidnariq [ Wed Mar 11, 2015 10:17 pm ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

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.

Author:  l_oliveira [ Thu Mar 12, 2015 6:46 am ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

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.

Author:  tepples [ Sat Mar 14, 2015 8:08 pm ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

Can someone with an EverDrive N8 bother krikzz about this?

Author:  FHorse [ Mon Mar 16, 2015 4:00 am ]
Post subject:  Re: Big RAM on FME-7: I have a test ROM

Fixed in puNES 0.93 WIP.

Page 2 of 2 All times are UTC - 7 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/