Using slow ROM for new games?

Discussion of hardware and software development for Super NES and Super Famicom.

Moderator: Moderators

Forum rules
  • For making cartridges of your Super NES games, see Reproduction.
User avatar
Señor Ventura
Posts: 186
Joined: Sat Aug 20, 2016 3:58 am

Re: Using slow ROM for new games?

Post by Señor Ventura » Tue Jan 05, 2021 7:23 pm

lidnariq wrote:
Tue Jan 05, 2021 5:10 pm
Uh. The amount of time to read or write a single byte can be as little as 1÷(3.6MHz), but DMA is the only thing that can sustain anything close to that.
So, something is happening here... i ialways believed that the reason why the DMA runs at 2.68 mhz was the WRAM (cause it ran supposedly at 2.68mhz).

But now the problem seems to be totally the DMA by itself. Better thought, at least maybe the cpu could read from WRAM at 3.58mhz, but writing at 2.68mhz. It has sense to me.


In this point, the DMA constraints could be a hardware problem, or a software problem?. How boots the snes?.
The rest of the areas of WRAM doesn't allow to write that Byte at 3.58mhz?, only the one marked of blue?.

lidnariq
Posts: 10548
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Using slow ROM for new games?

Post by lidnariq » Tue Jan 05, 2021 7:30 pm

Señor Ventura wrote:
Tue Jan 05, 2021 7:23 pm
In this point, the DMA constraints could be a hardware problem, or a software problem?. How boots the snes?.
Hardware. We don't really know where the timing problem comes from.

There's lots of other weird gotchas in here. We don't have obvious reasons for many of them.
The rest of the areas of WRAM doesn't allow to write that Byte at 3.58mhz?, only the one marked of blue?.
It literally says on the image you have there, on the right side.

Code: Select all

2000 - 3FFF 3.58 M PPU, etc.
0000 - 1FFF 2.68 M WRAM (8K - BYTE)
and then at the bottom

Code: Select all

RAM 1 ----Fix 2.68 MHz 8K byte
RAM 2 ----Fix 2.68 MHz 120K byte

tepples
Posts: 22361
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)
Contact:

Re: Using slow ROM for new games?

Post by tepples » Tue Jan 05, 2021 7:42 pm

Just a conjecture:

WRAM's B bus port can be written with a fast cycle because there are guaranteed not to be fast writes in consecutive CPU cycles.
WRAM's B bus port can be read with a fast cycle because there are guaranteed not to be fast reads in consecutive CPU cycles, and setting the address presumably preloads the value into a register in the DRAM's controller.

creaothceann
Posts: 314
Joined: Mon Jan 23, 2006 7:47 am
Location: Germany
Contact:

Re: Using slow ROM for new games?

Post by creaothceann » Tue Jan 05, 2021 11:27 pm

Señor Ventura wrote:
Tue Jan 05, 2021 7:23 pm
i always believed that the reason why the DMA runs at 2.68 mhz was the WRAM (cause it ran supposedly at 2.68mhz).
There also might be slow RAM/ROM chips in the cartridge.
My current setup:
Super Famicom ("2/1/3" SNS-CPU-GPM-02) → SCART → OSSC → StarTech USB3HDCAP → AmaRecTV 3.10

User avatar
Señor Ventura
Posts: 186
Joined: Sat Aug 20, 2016 3:58 am

Re: Using slow ROM for new games?

Post by Señor Ventura » Wed Jan 13, 2021 5:55 pm

I'm looking at the rom info of the snes9x, What is the difference between "30/fastrom" and "31/fastrom"?.

lidnariq
Posts: 10548
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Using slow ROM for new games?

Post by lidnariq » Wed Jan 13, 2021 5:57 pm

first digit 2 = slow
first digit 3 = fast

second digit 0 = lorom
second digit 1 = hirom

User avatar
Señor Ventura
Posts: 186
Joined: Sat Aug 20, 2016 3:58 am

Re: Using slow ROM for new games?

Post by Señor Ventura » Fri Jan 15, 2021 5:29 am

lidnariq wrote:
Wed Jan 13, 2021 5:57 pm
first digit 2 = slow
first digit 3 = fast

second digit 0 = lorom
second digit 1 = hirom
Thank you ^^

User avatar
Señor Ventura
Posts: 186
Joined: Sat Aug 20, 2016 3:58 am

Re: Using slow ROM for new games?

Post by Señor Ventura » Sat May 01, 2021 3:13 am

In snes9x the rom information shows 92/fast rom.

Is this an error?.

lidnariq
Posts: 10548
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Using slow ROM for new games?

Post by lidnariq » Sat May 01, 2021 12:07 pm

https://problemkaputt.de/fullsnes.htm#s ... eromheader
scroll down to "ROM Speed and Map Mode (FFD5h)"

psycopathicteen
Posts: 2993
Joined: Wed May 19, 2010 6:12 pm

Re: Using slow ROM for new games?

Post by psycopathicteen » Sun May 02, 2021 9:15 am

I think an SA-1 chip would've been possible in 1990. It's just that Nintendo and Ricoh didn't figure out how to make it back then.

tepples
Posts: 22361
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)
Contact:

Re: Using slow ROM for new games?

Post by tepples » Sun May 02, 2021 9:43 am

Early 65816 CPUs had problems with sep and rep at high speeds, with signals not propagating to the rest of the chip on time. It was 1992 when someone at Sanyo figured out how to make the 65816 reliable past 4 MHz.

93143
Posts: 1357
Joined: Fri Jul 04, 2014 9:31 pm

Re: Using slow ROM for new games?

Post by 93143 » Sun May 02, 2021 12:13 pm

That source just says you had to insert a NOP if your clock was higher than 4 MHz. Seems like something Ricoh could have fixed by inserting wait states. Or would it be too difficult to identify specific instructions coming in on the data lines without fiddling with the core?

tepples
Posts: 22361
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)
Contact:

Re: Using slow ROM for new games?

Post by tepples » Sun May 02, 2021 2:02 pm

Yield for 11 MHz-binned 65816 cores in fourth quarter 1990, when the console first came out, probably wouldn't have been that good anyway. It was a bit different situation by first quarter 1996 when the two big SA1 games (Super Mario RPG and Kirby Super Star) were released in Japan, as Moore's law predicts that transistor density would have quadupled over that time.

User avatar
Señor Ventura
Posts: 186
Joined: Sat Aug 20, 2016 3:58 am

Re: Using slow ROM for new games?

Post by Señor Ventura » Sun May 02, 2021 4:16 pm

Señor Ventura wrote:
Sat May 01, 2021 3:13 am
In snes9x the rom information shows 92/fast rom.

Is this an error?.
Sorry i was talking about donkey kong country. Snes9x shows rom information as 92/fast rom.

What is this?.

lidnariq
Posts: 10548
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Using slow ROM for new games?

Post by lidnariq » Sun May 02, 2021 4:20 pm

Well, what do you think, given the link I replied with?

Post Reply