Star Fox 2

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qwertymodo
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Star Fox 2

Post by qwertymodo » Sat Mar 21, 2015 3:37 pm

Finally got around to finishing my Star Fox 2 repro. Thought I'd come show off. No label yet, but it's the PCB work I wanted to show off anyway.

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And saving works too, so the battery is still good.

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Also, info for anybody wanting to make their own repro, there's a lot of misinformation out there about the differences between the SuperFX-1 and SuperFX-2 chips. Star Fox 2 does NOT need the SuperFX-2, it runs fine on the SuperFX-1, as the only real difference between the two is that the SuperFX-2 can map 16Mbit ROM, and the SuperFX-1 can only map 8Mbit (however, the MARIO-CHIP version used in Star Fox has a couple other issues so it doesn't work for Star Fox 2, you need a GSU-1 chip).

Anyway, if anybody's wondering, here's a list of all of the SuperFX games and their suitability as a Star Fox 2 donor (SNES Central doesn't have any info on Winter Gold, so I'm not sure on that one)

Code: Select all

______Game______|_______PCB_______|__Rev__|_RAM_|_Battery__|_Conclusion_
Dirt Racer      | SHVC-1CA0N5S-01 | GSU-1 | 256K |   No    | No
Dirt Trax FX    | SHVC-1CA0N6S-01 | GSU-1 | 512K |   No    | Yes [1]
Doom            | SHVC-1CB0N7S-01 | GSU-2 | 512K |   No    | Yes [1]
Star Fox        | SHVC-1C0N5S-01  | MARIO | 256K |   No    | No
Stunt Race FX   | SHVC-1CA6B-01   | GSU-1 | 512K |   Yes   | Yes
Vortex          | SHVC-1CA0N5S-01 | GSU-1 | 256K |   No    | No
Wild Trax       | SHVC-1CA6B-01   | GSU-1 | 512K |   Yes   | Yes
Winter Gold     |       ???       | GSU-2 |  ??? |   ???   | ???  (I've heard it works, but it's expensive)
Yoshi's Island  | SHVC-1CB5B-01   | GSU-2 | 256K |   Yes   | No

[1] Game is playable, but it won't save high scores or Pepper coins
Also, upgrading 256K PCB's to 512K isn't hard, and it does make the game playable

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Drew Sebastino
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Re: Star Fox 2

Post by Drew Sebastino » Sat Mar 21, 2015 3:46 pm

Good lord, If I hadn't known any better, I would have said you just took a picture of a normal Star Fox PCB it looks so good! How did you get the rom to look so perfect? Normally, I see people just cut the pins on the pre existing one and rewiring the connections to a rom on top of the older one, which is fine, but it doesn't look "professional". :wink:

qwertymodo
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Re: Star Fox 2

Post by qwertymodo » Sat Mar 21, 2015 3:57 pm

I made a custom adapter PCB for the new ROM to mount onto. Here's what it looked like with the adapter board installed prior to soldering on the ROM.

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Not only does this look way nicer, it allows me to use brand new, in production flash ROMs from Micron, rather than old-stock EEPROMs from who knows where, and no wires means no rattling around and potentially breaking a solder joint. It's been over two years in the making (though only a few hours worth of actual work), due to having way too many projects on my plate and work/school/life getting in the way. I may mess around with an overclock mod soon, just to see how I like it, but other than that, I'm ready to call this one finished.

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MottZilla
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Re: Star Fox 2

Post by MottZilla » Sat Mar 21, 2015 4:03 pm

That looks awesome. Very clean.

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B00daW
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Re: Star Fox 2

Post by B00daW » Mon Mar 23, 2015 9:12 am

You gonna overclock it any? The SFX in Star Fox seems to overclock pretty well to add some additional smoothness.

qwertymodo
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Re: Star Fox 2

Post by qwertymodo » Mon Mar 23, 2015 1:49 pm

Yeah, I'll probably play around with overclocking. Nothing too extreme, but I have noticed some slowdowns in certain areas, so it'll be worth playing around with as soon as I can get my hands on a few various oscillators. I suppose I could also take it to the EE lab on campus and use a signal generator too...

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l_oliveira
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Re: Star Fox 2

Post by l_oliveira » Mon Mar 30, 2015 6:14 am

I believe one of these GSU chips also have a setting to change (reduce, which doubles the clock frequency at the chip core) the clock divider, while the original Mario chip did not.

So I believe the clock divider could be the reason for your slow downs.

I made my Star Fox2 repro from a Yoshi's Island cartridge (I know, that one had only 32KB SRAM, not 64KB. I had to rectify that. It's GSU2, not GSU1 as Yoshi's Island was a 16MBIT game) and it doesn't slow down at all.

Edit: Quoting Wikipedia article:
The first version of the chip, commonly referred to as simply "Super FX", is clocked with a 21 MHz signal, but an internal clock speed divider halves it to 10.5 MHz. Later on, the design was revised to become the Super FX GSU-2 (Graphics Support Unit 2); this, unlike the first Super FX chip revision, is able to reach 21 MHz.

qwertymodo
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Re: Star Fox 2

Post by qwertymodo » Mon Mar 30, 2015 9:31 pm

l_oliveira wrote:I believe one of these GSU chips also have a setting to change (reduce, which doubles the clock frequency at the chip core) the clock divider, while the original Mario chip did not.
The original MARIO chip was only used in the original Star Fox cart, and is not the same as the GSU-1 chip on this board
The first version of the chip, commonly referred to as simply "Super FX", is clocked with a 21 MHz signal, but an internal clock speed divider halves it to 10.5 MHz. Later on, the design was revised to become the Super FX GSU-2 (Graphics Support Unit 2); this, unlike the first Super FX chip revision, is able to reach 21 MHz.
This is a bit of half-true misinformation I see all the time. The GSU-1 can run at 21MHz just fine, it's only the MARIO chip (i.e. the actual first revision of the SuperFX, not the entire GSU-1 line, there were more than 2 revisions of the chip) that can't do full-speed.

The slowdowns I've noticed were all very slight and only under certain circumstances where there were a lot of polygons rendering at the same time. They were hardly even noticeable, I was just nitpicking.

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whicker
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Re: Star Fox 2

Post by whicker » Wed Apr 01, 2015 9:53 pm

Seriously, go edit that article on Wikipedia if you're more of an expert on it.

tepples
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Re: Star Fox 2

Post by tepples » Thu Apr 02, 2015 6:38 am

The "problem" with correcting long-standing misconceptions about tech specs of closed hardware is that Wikipedia requires a previously published reliable source for every fact, not original research. If these sources are wrong, Wikipedia is wrong by design. Look up Philip Roth Wikipedia for what might go wrong.

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MaarioS
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Re: Star Fox 2

Post by MaarioS » Thu Apr 02, 2015 6:51 am

whicker wrote:Seriously, go edit that article on Wikipedia if you're more of an expert on it.
Hahahah that is so true. This would be VERY HARD to convince people that the fact they were believing in for about 10-15 years or so is actually wrong. This fact is like God, GSU-1 runs in 10,5Mhz, GSU-2 runs in 21Mhz, it is on wikipedia, everyone believes it, this was confirmed since SNES existed, everyone says that even though nobody wanted to verify that, case closed (lol)

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l_oliveira
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Re: Star Fox 2

Post by l_oliveira » Thu Apr 02, 2015 7:08 am

I'm not saying it runs at a fixed rate. I just mentioned that some chips can bypass the internal clock divider while others can't.

But anyway, by the time Starfox2 were developed it's pretty obvious it was intended to run on GSU2 even if it was going to use only 1MB of ROM space.

If anyone willing to take this to "the next level" how about someone make a test rom for this ?

qwertymodo
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Re: Star Fox 2

Post by qwertymodo » Thu Apr 02, 2015 11:17 am

To be fair, the only authoritative documentation I know of regarding the SuperFX chip is the SNES Dev Manual Book 2 which states:

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However, I can't find anywhere that it specifies which version is the "current version" as of the publication of that document.

Edit: Then there's this later in the same manual...

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So if they're documenting the clock select register, one would assume it was functional... Can't find a definitive publication date, but the copyrights on the document are 1993, 1994, 1995.

¯\_(ツ)_/¯
Last edited by qwertymodo on Thu Apr 02, 2015 11:25 am, edited 1 time in total.

tepples
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Re: Star Fox 2

Post by tepples » Thu Apr 02, 2015 11:23 am

Regarding GSU1's double speed capability or lack thereof:
Perhaps the GSU2 had some changes that made double-speed operation more reliable. Nintendo tended to design its products to be Tonka Tough with plenty of safety margin, with only a few big failures (e.g. DS and DS Lite shoulder buttons, DS Lite hinge, and Wii fan).

Regarding the "High speed clock operation" paragraph:
One-sixth of 10.74 MHz is one-twelfth of the master clock rate, which is 1.79 MHz, or the half-speed that the S-CPU uses for bit-banging the controller ports (and for no other addresses). Is the manual assuming that the GSU does twice as much work per clock as the S-CPU?

qwertymodo
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Re: Star Fox 2

Post by qwertymodo » Thu Apr 02, 2015 11:29 am

I think koitsu might not like me linking directly to the manual I'm referring to here, but a quick Google-fu for "SNES Developer Manual" should get you there. The Super FX is covered in book 2.

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