Questions about making a Star Fox 2 cartridge in a post-SNESMini era.

Ok, so a big issue in the past with making your own Star Fox 2 reproduction cart was the donor cart that would be used. Only 3 SNES games were ever released with a FX2 chip. One of them didn't support saving, and the other was PAL-only, and the last one was a very good game that few would want to destroy to turn into a Star Fox 2 cart. (Also, said PAL game due to being rare, possibly due to this, now costs more than any of the other two).

In response to this, many people said one could just use a FX1 game as a donor cart and insisted that there appeared to be absolutely zero difference whatsoever between the game running on a FX1 and FX2 chip.

However, I always wondered if this was because the only copy anyone ever had was an unfinished (even if far in production) beta. That has changed now that the SNES Mini has been released.

I tried, but couldn't find much information about someone testing this with the final version of the game. Are there any differences at all between running the final Star Fox 2 ROM on a FX1 or FX2 chip? Some people commented that the reason there is no difference is that both the FX1 and FX2 ran at the same clock speed and all the FX2 did was allow addressing of larger EEPROMs, but that seems more like a conclusion reached simply because the three currently released FX2 games were all on a 16Mb EPPROM instead of the more standard 8Mb, I don't see why Star Fox 2 would have used a FX2 if the chip only would have allowed for EPPROMs larger than 8Mb when the game itself is only 8Mb.

 

According to wiki https://en.m.wikipedia.org/wiki/List_of_Super_NES_enhancement_chips u are correct, FX1 & 2 and interchangeable in terms of instruction set, it's just the pinout, package and supported ROM size. If u can guarantee the final build satisfies the FX1 8mb maximum then it should be fine. On another note, is it possible to get these chips separately from a manufacturer so they could be used with custom pcb and avoid harvesting retail carts? I know they are custom snes chips but they were made by a 3rd party manufacturer.

 

No such thing as super fx1 or 2. Both are a super fx chip, 2 can just address a larger rom size.

 

In a word, no. Firstly, no chip fab will make a custom chip for anyone except the original customer unless authorized. Even if you could somehow convince them you did have the authority to order it, it's an about 20 year old design and would have been built using ancient process technology that nobody uses anymore.

This might not sound like a big deal, but it is, and there are lots of chips you simply can't make anymore because they were fabricated with obsolete process technologies. One example is the PS2 I/O processor, which was based on a MIPS R3000 that had been built using an LSI logic standard cell process - by the time they were making the slim PS2s, there was no fab anywhere that could run it any more, and they ended up having to build an SOC using a PowerPC core and run the IOP code using emulation. This is one of the reasons for the inferior compatibility of the slim PS2s.

 

Thank you for the explanation. I know the exact chips would not be available separately but the company may have made generic equivalents that may be still around. Looks like harvesting Super FX cartridges is the only way to go. It would be interesting to see if Star Fox 2 will work with Super FX GSU-1 cartridges.

 

It works fine on the gsu-1

 

I knew they had the same instruction set as many people have made Star Fox 2 repros using FX1 games in the past, but I wasn't aware that they had a different pinout.

Although what I wanted to know is their clock speed. From my understanding, the FX2 ran at double the clock speed of the FX1. Some people are saying this is not true and the only difference is ROM size it can address, not clock speed.

Are you sure that is the only difference? I have seen boards that allow you to use a different oscillator designed to overclock FX1 donor carts... though I don't know if it can overclock it all the way to a FX2 spec or if this won't damage the chip from extended use:

https://oshpark.com/shared_projects/5Qb0IuYp

Admittedly however, I an not that knowledgeable about electronics enough to fully understand if that is the intention of that board.

 

There is no "fx2" spec. Gsu1 and gsu2 run at the same clock speed. They are identical except for amount of rom they can address.

"Mario chip 1" ran at half the clock speed.

 

There is a lot of misinformation spread by various people about the Super FX. Everything Bad_Ad84 said is correct. Stunt Race FX is probably the typical donor game because it has battery backed SRAM.

You do not need to replace the oscillator or do any of that junk. Overclocking the Super FX will introduce potential problems.

 

Good to know. There are quite a few Stunt Race FX carts on eBay for cheap prices. There are also Winter Gold and Dirt Trax FX carts but I don't know if they have battery backup SRAM.

 

I was told about that recently.... so it's not so much that the original StarFox used a FX1... but that the FX used for Star Fox for some reason was intentionally down-clocked and that board is actually made to "over"clock StarFox 1 carts back the FX chip's standard clock?

Winter Gold is extremely expensive, far far pricier than even Mario World 2. I originally assumed it was a bad donor because it's PAL-only so many people would also have to replace the PAL chip with a NTSC one, and that's quite a bit of extra work, but now I see that it would be a bad donor because it's a somewhat rare and thus expensive cart.

EDIT: Also, I tried to look up if Dirt Trax FX also used SRAM like Stunt Race did to answer your question, and I found this:

http://nintendoage.com/forum/messageview.cfm?catid=22&threadid=135828

A SuperFX game with 512k of SRAM. Stunt Race FX, Dirt Trax FX and Doom are the only games in North America that comes with 512k stock, others you will have to upgrade the RAM.

Ok, can someone please confirm for me if Doom has SRAM or not? I see a lot of people saying yes and others no, Doom would be a perfect donor if it does indeed have SRAM, but I always assumed it did not, and I keep hearing conflicting information now.

 

Stunt race fx is a perfect donor. The rom is 8mb or under.

 

DOOM has a 512kbit (64KB) SRAM - but it doesn't have a backup battery.

 

Wait... what? So... it does actually have a SRAM chip on the PCB... but doesn't have a battery so it could be used? Why did they waste money with a board with SRAM if they weren't going to use it? And is the place to solder in a battery still there?

 

Because there are two different ways you can use the SRAM on the cartridge board - one is for saving games and the other is to expand the amount of work RAM available to the CPU from the 128KB that's installed in the console. DOOM is using it purely as expanded work RAM and not for saving data.

There is no space for the battery on the PCB, and there is also no RAM supervisor chip - which makes sense since there is no point in protecting the RAM contents if they are going to be lost anyway.

 

I see, so basically not a viable doner if you want to be able to save your game since it would be a mess of work to convert the SRAM into battery-backed storage, if it can be done at all.

Guess a copy of Stunt Race or Dirt Trax would be the way to go then.

I did want to ask though, while I would not be able to make a real SF2 cart out of Doom due to not having the ability to save (at least not keep the save after the system is powered down), since that game isn't going for too much more than Stunt Race or Dirt Trax anyway, I would still like to at least test if it runs any different on Doom than Stunt Race/Dirt Trax, if I were to desolder the EEPROM and install a socket in it's place so I can easily swap out ROMs for testing (not to mention use it as a Doom cart again by just plugging the original EEPROM back) would I be able to even close the cartridge again, or would a socket add too much bulk to put the PCB back in the cart without cutting a hole for the EEPROM?

 

It doesnt run any different. Its the same instruction set, running at the same clock speed. Use a GSU-1 (Stunt race FX)

I have even modified a doom cart to have battery backed sram - back when I didnt know about the super fx and only listened to the nonsense on the internet.

You are repeating work thats been done, its a waste of time - Stunt race FX is the donor to use, as mentioned about a million times.

 

I think some people erroneously think SRAM means "Save RAM". The 'S' means Static.

If you're wanting to put Star Fox 2 on a cartridge then it's already been said multiple times to use Stunt Race FX. The GSU-1 (Stunt Race FX) and GSU-2 (Doom) run exactly the same speed. Doom requires the GSU-2 due to having more than 8 megabits of ROM and the GSU-1 not being able to address more than 8 megabits.

 

I am not trying to be difficult or anything, It's more that I was asking if anyone had done it with the final rom, and kept getting replies of "just do this" instead of any information on what I asked.

And yes, I do plan to create one out of a Stunt Race cart (Or possibly Dirt Trax since they seem to go for about the same price), thing is this would be my first attempt so I was hoping I could use Doom or something to essentially create a cart with an eeprom I could easily swap out both for testing other FX-based games and to make sure I burned and wired it correctly before permanently soldering it onto a Stunt Race cart.

I was looking it up, and I realized that I was mistaken on how the EEPROM on Snes carts was packaged. I assumed it was just a standard DIP type IC, but it's surface-mount, so I can't just toss a socket in there (that is, if the cart's casing would even close wit a socket) and that many of them are not just drop-in but could require re-wiring due to the SNES's Mask ROMS having a custom pinout that might not match whatever blank one plans to use.

All this is why I wanted to also use Doom as a cart with a socket for the rom that I can easily swap out for testing... but now I am not sure how to even do that with the original being a surface-mounted EEPROM.

I know that it's pretty much just a small amount of RAM that is kept alive with a battery, similar to how even modern RAM in systems loses it's memory when it's power is cut, it just never occurred to me that someone could use it for actual RAM for the game instead of just saving data... mainly because it's been such a while where such small amounts of memory were actually significant that I forgot that it would have actually been a sizable amount of additional memory for the game back then.

 

Yes I have made a stunt racer based star fox 2 repo using the rom from the snes mini. It works perfectly as other have said. I used citrus3000psi's adapter board and a 5v tsop. Mine is also overclocked to 24mhz using a 2 pin crystal and some caps. You don't need to overclock it either. I did because I can.