atari/jaguar.cpp: broken EEPROM support

[angelosa]

Atari Jaguar games uses an EEPROM to save games. A game that needs it is Cannon Fodder (cfodder), where it will display "ERROR" on top of the squad screen.

A bunch of things that I'm not sure about:

1. is the EEPROM on console or on cart? If former, how the console really handles formatting/managing of memory?
2. the EEPROM itself, is it really a 93C46? Did the handling ever worked?

Originally posted in https://mametesters.org/view.php?id=9342

[FoxhackDN]

The Jaguar itself doesn't have any save data capabilities, all the saves were on cart.

Jaguar CD games used a separate cart called the "Memory Track" which seems to function like the Sega CD Backup RAM cart.

https://forums.atariage.com/topic/102737-memory-track-carts/

[Gurudumps]

There are cart PCB pics online. Jaguar carts contain only 3 parts.
2x 42 pin mask ROMs, 1x 93C46 EEPROM.

[angelosa]

Does all games have that, or only some of them?

[Gurudumps]

I'd say probably all of them. There isn't much info showing the insides of Jaguar carts as they are generally expensive prized elitist collector possessions (like a lot of retro stuff now).
For now just assume that's how they all are. i.e. do the normal MAME thing.... make an educated guess based on what we know about uncommon items, which is often almost nothing ;-)

[Gurudumps]

Here's a better pic of the pcb...
https://gurudumps.otenko.com/temp/jaguar-cart-pcb.jpg
This appears to be a 1:1 chinese copy. Here's a quick reverse of the connections.
On the 93C46 EEPROM...
CS (chip select) tied to cart pin 43B (GPI01)
SK (serial data clock) tied to cart pin 42B (GPI00)
DO (serial data output) tied to cart pin 40B (E2DATA)
DI (serial data input) tied to cart pin 23A (ED0)

[angelosa]

https://www.retrosix.wiki/schematics-atari-jaguar

This claims "some" carts, I guess it needs verification about what could possibly save data ...

[Gurudumps]

If you were to monitor the cart pins tied to the EEPROM then when GPI01 (CS) is low, capture the data on D0 (D zero: data bit 0 not DO data out)and you'll see the data that is written to the EEPROM by the console. If GPI01 doesn't go low for that game then the EEPROM is not used for that game.

[cuavas]

There could be “trap” cartridges, like the ones for Sega and Nintendo consoles that attempt to write to cartridge save memory and won’t run properly if they detect that it’s present (protection against cart copiers and multi-game cartridges).

[angelosa]

6c0b546 takes care of the base interface, it now obviously needs to be moved into a cart bus.