SNES Game genie problem

[tbfa]

Haha great!
Super Mario World is easy to work. So your SNES rev may be 93 below.

PIN 6* from picture is not a /CE real PIN?

[Fisher]

Possibly it is.
Sure it is!!
Usually it's connected to /CART.
Maybe it should be pulled low...

[tbfa]

Okay!!!

About DK2, it is one of Champions in cart protection. SRAM checks, and others. It Will be hard to do It works. I have dk3 and never works

[lidnariq]

Well, pin 6 in your picture is actually pin 22 (since the pin 1 key is at the other end). And pin 22 is /CE... so ... yeah, you're disconnecting the signal from the cart edge "/ROMSEL" and since the game is always working it must float low when not driven.

This isn't a good thing; it means that whenever the CPU is reading from RAM, PPU, or APU it'll get in a fight. (But it looks like the Game Genie has some resistors in the way causing the ROM to always lose the fight?)

[tbfa]

Sorry , with "PIN 6" i mean 6th PIN from mask ROM down side , from left to right direction.

I don't undestand much about snes hardware and logic.

[Fisher]

This isn't a good thing; it means that whenever the CPU is reading from RAM, PPU, or APU it'll get in a fight. (But it looks like the Game Genie has some resistors in the way causing the ROM to always lose the fight?)

Isn't this called sort of a race condition?
The bus arbitrer that would solve this problem just can't because of the missing control pin.
This can lead to a program crash, or an exception, if I'm rememebering my architecture classes right.

[lidnariq]

Yeah, my best guess is that leaving the ROM enabled all the time speeds things up by enough to compensate for the resistors slowing things down.

It's an answer that I'm not terribly comfortable with, but... I'm not up for tracing the SNES Game Genie PCB at the moment, so I don't have any better data to work with.

[tepples]

Try connecting /CE to ground and seeing if it still works. If it does, then lidnariq is right about what's going on: grounding /CE and using /OE for all decoding makes relatively slow ROMs respond faster at the cost of more power consumption. I've even seen games that leave /CE and /OE asserted all the time and use a separate 3-state bus transceiver for decoding, such as Holy Diver for Famicom.

Is there a separate /OE on that ROM, and if so, what's it connected to?

[Fisher]

I had put a piece of paper on the /ROMSEL pin.
No success.
But exchanging the resistors to 100 Ohms did made it boot.
Should I care for the 10K pulldowns??

Edit:
Here is the Charles McDonald's notes about the SNES GameGenie Nocash pointed me at the begining.

genie.txt

(26.79 KiB) Downloaded 154 times

It doesn't have the full schematics, but has most things explained like "this connect in there" stuff.

I'll do some more tests and see what happens!!

[creaothceann]

The pressure here is because of the kids, that really want to play Donkey Kong 2 with the codes.

In that case use an emulator.

[lidnariq]

So, if I understand Mr. MacDonald's notes correctly ... the GG passes through, or fails to pass through, the /ROMSEL signal to the cart depending on whether there's an address match. If there's a match, it drives a specific value onto the 16-bit data bus (of which only half is exposed on the SNES). If the cart (for whatever reason) ignores /ROMSEL, then the resistors ensure that the GG wins instead of the cart.

I still don't have a better working theory than "timing issues, possibly because a lot of SNES carts swapped /ROMSEL and /RD" as to why cutting pin 22 sometimes helps. Maybe differences in 68k vs 5a22 timing??

For no good reason I'm uncomfortable with the GAL.

[Fisher]

In that case use an emulator.

That was the first thing I tried.
But they just don't liked to play on the small computer screen, even with the original SNES joysticks.
Now they're very happy with DK2's invincibility code.

"timing issues

Other than swap these pins functions, maybe Nintendo did some funny stuff with Pin 57 (CPU_CLK).
If I understood correctly the GameGenie uses this pin to sync.
Does any game uses it??
Most special chip games I saw used the Pin 1's clock.

For no good reason I'm uncomfortable with the GAL.

I can try to dump it's contents as I've done before with the other PAL ICs, if needed.
Fortunatelly, you're the man who interpreted it.

[lidnariq]

Other than swap these pins functions, maybe Nintendo did some funny stuff with Pin 57 (CPU_CLK).
If I understood correctly the GameGenie uses this pin to sync.
Does any game uses it??

I don't think so. I think pin 57 is redundant with /RD and /WR; i.e. if pin 57 is high one of /RD or /WR are low.

In contrast, pin 1 is the ≈21.5MHz master clock.

I can try to dump it's contents as I've done before with the other PAL ICs, if needed.
Fortunatelly, you're the man who interpreted it.

I, uh. Gosh, I don't think there's really a good reason to bother dumping the PAL until someone's bothered to trace the PCB photos of the rev1 SNES GG.

[tepples]

But they just don't liked to play on the small computer screen, even with the original SNES joysticks.

PCs have VGA, DVI, or HDMI out, and HDTVs tend to have HDMI and often VGA in. What inputs does your TV have, and what video outputs does your PC have?

[Fisher]

I, uh. Gosh, I don't think there's really a good reason to bother dumping the PAL

Ok.
since I really can't desolder and resolder that LSI chip, I won't be able to do a nice scan either.
It was very cool to dump the PAL. Unfortunatelly, the last one was used by a GPL violator, wich threw a thread I tought was a suicide note... How fool I was!!
I tried to understand his reasons, but Zepper seemed to have got really angry!!

What inputs does your TV have

That's a really nice idea!!
Unfortunatelly the PC is a little too far from the TV.
I think I'll try to get a 15m cable. That should be enough to be nicelly installed though the attic.
Would this size give some noticable problems?
I'll try to get wireless gamepads too, so the party'll be complete!!

I'm posting a picture of the mod I made, just if someone finds necessary:

Finished modification

I just ignored the pulldowns, since I got no trouble up to now.
Again, many thanks for helping me!!
My kids also say thanks!!