Atari Jaguar Expansion Module

[kool kitty89]

This might just be a throw-away idea, but with the various (attempted and completed) expansion modules for other classic game consoles and home computers (Atari and otherwise), plus the efforts I've seen for quirky sound and/or memory expansion boards or specialized retro sound cards in the retro Sega and PC scenes, it seemed worth throwing out there. (that and the level of features SNES flash carts have reached)

 

That, and I think I've made the mistake of interjecting random mostly-off-topic ideas like that into other homebrew projects too often, back when I was an active poster.

 

Or with a single post late last year here: 

https://atariage.com/forums/topic/254003-upcoming-jaguar-game-drive-cartridge/page/125/?tab=comments#comment-4386972

 

 

I realized a more plausible and practical possible Jaguar upgrade would be a DRAM (SDRAM or PSRAM, depending on cost and availability) based SD-card style flash cart with provisions for mapping some of the RAM into use as actual expanded RAM (and not just pretending to be ROM) or at least allowing that RAM to be read and written to by an on-cart CPU or coprocessor.

 

The added CPU or MCU could be any number of things, but for folks actually interested in something remotely plausible and period-accurate to the mid 90s and the Jaguar's existing architecture, just including a faster 68000 or 68EC000 with zero wait state access to local RAM would make sense.

 

And here's the thing, it could be a basic PCB kit as well as completed boards, and include the necessary provision for flash drive interface + DRAM (potentially separate pads for DRAM and PSRAM and jumpers to select one or both) and then pads for a 68 pin PLLC socketed 68000 or 68EC000. (pads for a surface mount PLLC would probably be cheaper, but the socket seems a lot safer and a lot easier to install for those with basic soldering equipment or no equipment at all for people buying boards with sockets already installed)

 

Or if you really wanted to be safe, pads for DIP-64 68000s could be provided as well.

 

You could thus have decentralized manufacture of the boards (downloadable free plans, various people making and offering kits or just the bare PCBs, and others potentially selling completed boards in various states of completeness) and also let homebrew devs choose what features to bother supporting or requiring. (though I'd think outright requiring all features to run the game at all would be less popular)

 

Making the whole project open-source (and potentially compatible with) SaintT's SDRAM board would also make far more sense than starting from scratch.

 

 

You could do a lot of that as a single-chip FPGA too (FPGA + RAM), but with the current availability of cheap 20 MHz 68HC000s (and to some extent EC000s), mostly from China through ebay (mostly on Ebay, or potentially less reliable/safe auction/sale sites which I'd avoid) it seems like a discrete socketed 68000 would make the most sense.

 

Supplies of 16 MHz 68HC000s in 64 pin DIP packages are also relatively cheap currently and 12 MHz Hitachi 68HC000s are around at low prices intermittently as well (and HD68HC000s are very low power and quite good overclockers from what I understand)

 

And to cover the uncertain future availability of certain speed grades (and a potential flood of counterfeit/remarked chips), and to allow for overclocking, there could be jumpers or software selection for different clock rates (probably using PLLs and dividers off the native Jaguar ~13.3 MHz signal).

 

A base 13.3 MHz would be safe/conservative (and still offer a lot of advantages with a slow CPU on a separate bus, not bothering the Jaguar chipset itself, sort of like a slow PC with an all-in-one 3D accelerator + DSP sound board).

 

Then you could have 16.7 (5/4), 17.7 (x4/3), 19.9 MHz) (x3/2), and 26.6 MHz (x2). You could go higher, but 26.6 MHz seems reasonable for a virtually foolproof overclock on 20 MHz parts (and many, if not most CMOS 16 MHz parts). You could probably omit the 16.7 MHz setting, too and simplify the clock synthesizer arrangement and also only need 2-bits for selecting the clock speed (be it set in software or via jumpers or a switch block).

 

 

 

Allowing data to be streamed from the SD card (in place of a CD-ROM or hard drive) seems like it would open up a lot more opportunities for homebrew as well, plus potentially allow emulation of the Jaguar CD itself and effectively allow much more ready access to the Jaguar CD library without one of the scarce, expensive, Jaguar CD units in good working order. (and I know there's the whole piracy vs abandonware debate elsewhere, but I'd just stay out of that and focus on being free, open, and just rely on the honor system for that: ie for folks who have real copies of the game but not working CD units, plus Good Old Games style cheap license purchases and DRM-free digital downloads for any publisher/rights holder of out of print software to bring out of abandonment)

 

Well, that and I guess if Jaguar emulation software gets good enough and flexible enough, homebrew games could even be offered bundled with embedded emulators. (like GoG does with DOSBOX and ... maybe some other old home computer platforms, I'm kind of out of the loop on that) But there's obviously something special about using real hardware, and the Jaguar's quirky architecture makes it harder to capture via emulation.

 

 

 

 

 

 

[Chilly Willy]

If you're going to put another processor on an expansion card/cart, I'd say something like the 68EC020 would be better than a faster 68000. Still period authentic, but a decent boost over the original 68000 while not getting too expensive. The whole point of the EC020 was to make an 020 that was only slightly higher priced than the 68000. I'm a little surprised the Jaguar didn't use that in the first place.

 

Giving the processor local ram that isn't affected by bus contention would be a great idea as well. That's half the problem with the main 68000 - while it's running, it contends for the bus constantly, slowing everything else down.

[swapd0]

4 hours ago, Chilly Willy said:

That's half the problem with the main 68000 - while it's running, it contends for the bus constantly, slowing everything else down.

From my experience it's the other way, the 68000 has the lower priority so usually the other processors don't leave free cycles to let it run.

[Chilly Willy]

That too. ?  In any case, you'd get more processor time without either side slowing the other any with local ram for the processor. That's partly what makes the 32X faster than you would otherwise think - the 68000 and the SH2s only fight when accessing the cart rom; the rest of the time, they run full speed from their own respective local ram. When I did my 32X port of Wolf3D, I originally had the 68000 running from rom for its main loop, but moving that main loop code to work ram made things more than twice as fast as the 68000 was no longer constantly accessing the rom.

[swapd0]

I would prefer a small fpga with another GPU with cache than a 68000 or 68020 processor.

[+CyranoJ]

30 minutes ago, swapd0 said:

I would prefer a small fpga with another GPU with cache than a 68000 or 68020 processor.

So that the target audience of a couple hundred people max reduces to 3?

 

Just buy a Falcon

[Cyprian]

cool idea,

 

nice to see ANY expansion for Jag

[+Sauron]

Expansions are a complete waste of time, as they only serve to limit the target audience. You're better off coming up with a cart standard that would include bankswitched ROM + co-processor/RAM.

 

[Rick Dangerous]

OR you could save everyone a lot of time and money and go get a PS1 for $10

[Cyprian]

15 hours ago, Sauron said:

Expansions are a complete waste of time, as they only serve to limit the target audience. You're better off coming up with a cart standard that would include bankswitched ROM + co-processor/RAM.

 

Cart also would be cool.

 

Look at A8 section here on the forum, there are tons of different internal mounted expansions. Some of them sold in only couple of dozen pieces. No one treat that as waste of time

 

[+CyranoJ]

30 minutes ago, Cyprian_K said:

No one treat that as waste of time

 

Because:

1) There are many more a8 users and machines out there.

2) They all use the (mostly) same protocols so are interchangeable.

3) They are mostly used for storage, and just replace the floppy drives - they usually don't add anything, and the ones that do (VBXE) are VASTLY underutilized by anyone (See the "just get a Falcon if you want to write software for nobody" point above)

[Cyprian]

42 minutes ago, CyranoJ said:

 They are mostly used for storage, and just replace the floppy drives

CPU:  Antonia 4 MB,  Sweet 16, Turbo-816, MARS-8, Warp4, HyperSpeed XL/XE, F7, XL7, XL14, Rapidus; SOUND: Cvox, double Pokey, Quad Pokey, Pokey Max , Evie; a lot of ram expansions

More you can find there: http://atariki.krap.pl/index.php/Akcesoria_i_rozszerzenia#CPU

 

Sky is the limit

[+CyranoJ]

Just now, Cyprian_K said:

Sky is the limit

 

Yeah but it's still below the point that went straight over your head
 

Quote

and the ones that do (VBXE) are VASTLY underutilized by anyone

 

[+Sauron]

1 hour ago, Cyprian_K said:

CPU:  Antonia 4 MB,  Sweet 16, Turbo-816, MARS-8, Warp4, HyperSpeed XL/XE, F7, XL7, XL14, Rapidus; SOUND: Cvox, double Pokey, Quad Pokey, Pokey Max , Evie; a lot of ram expansions

More you can find there: http://atariki.krap.pl/index.php/Akcesoria_i_rozszerzenia#CPU

 

Sky is the limit

If you can't understand the difference between a computer and a game console, then there's no point wasting any further words on this.

 

 

[Cyprian]

1 hour ago, CyranoJ said:

 

Yeah but it's still below the point that went straight over your head
 

hehe

[Chilly Willy]

I think the idea of a processor on a cart would definitely be better. Look at the 2600 - that cart with an ARM MPU on it is so popular, it's even part of most 2600 emulators. Something like that would probably do well on the Jaguar. Given an ARM MPU with the right serial ports, it could probably emulate the CDROM as well, killing two birds with one stone.

 

[Clint Thompson]

*Unlimited amount of storage space available with direct access on an SD cart is the real expansion module.

[Zerosquare]

Yup. There's already plenty of new territory to explore using SainT's cartridge, which already exists and people have started buying. There's no point in fragmenting the market with a pie-in-the-sky project.