Introducing the VeriSNES (FPGA-based SNES)

Discussion of hardware and software development for Super NES and Super Famicom.

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Revenant
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by Revenant » Mon Apr 23, 2018 3:24 pm

syboxez wrote:I think having a way to get sharper video out of a real 3CHIP console would sell quite well, especially if it was a modless solution.
If you have to use something on the expansion bus to emulate the PPUs in lieu of the original video output, you're arguably no longer getting any video out of a real 3CHIP at all. Why not just sell/buy an entire clone console at that point?

(To clarify: the only relevant signals that exist on the expansion port are the 8-bit peripheral bus and the PPU dot clock)

syboxez
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by syboxez » Mon Apr 23, 2018 3:46 pm

Revenant wrote:If you have to use something on the expansion bus to emulate the PPUs in lieu of the original video output, you're arguably no longer getting any video out of a real 3CHIP at all. Why not just sell/buy an entire clone console at that point?

(To clarify: the only relevant signals that exist on the expansion port are the 8-bit peripheral bus and the PPU dot clock)
You'd still have a real CPU and APU in there, and people tend to like the accuracy that FPGA cores could theoretically provide (given they're implemented correctly). The Turbo Chameleon 64 is seen as a top of the line product for the C64 (likely due to its accurate emulation of the 1541 in addition to its multitude of other features, but also its VGA output), so I don't see a reason why we couldn't have a comparable top of the line product for SNES, and assuming accuracy, I don't see people minding the fact that the PPUs are emulated with an FPGA.

Also a quick look at the schematics show that all the data lines connecting the CPU and PPU1 together are available through the expansion port. Whether this would be enough to be able to replace PPU1 and PPU2 with FPGA replacements using the expansion port is unknown to me, as I do not develop hardware, but if it is, this could be a viable solution.

Assuming the price is <$100 or so, it would be a cheaper alternative to the Super NT that I'm sure people would be willing to buy (similar to how people still use the NESRGB and HiDef NES instead of just buying an NT Mini). And I don't think I need to elaborate on why cheapo clone consoles aren't a proper solution.

Hell, even the fat 1CHIPs have the same expansion port, so it might be possible to replace the integrated PPU1/PPU2 with more accurate FPGA versions, although I'm not sure how many people will want it for that purpose as the 1CHIPs already output good video (after proper attenuation).
Last edited by syboxez on Mon Apr 23, 2018 3:55 pm, edited 1 time in total.

lidnariq
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by lidnariq » Mon Apr 23, 2018 3:54 pm

syboxez wrote:The older SNESs had pretty terrible RGB video output due to internal issues in PPU2's analog output.
Uh....

The original 5C78 has exactly the video bandwidth that Nintendo intended it to have. Sharp chunky pixels wouldn't have even been visible in the displays you could buy at the time.

Several SNES games explicitly took advantage of the limited bandwidth to cause color blending (e.g. Kirby's Dreamland); several Genesis games did too.
syboxez wrote:You'd still have a real CPU and APU in there
Honestly, those aren't The Hard Or Interesting Part.

Nevermind that S-CPUs seem to be what die the most readily anyway.

syboxez
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by syboxez » Mon Apr 23, 2018 4:03 pm

lidnariq wrote:Uh....

The original 5C78 has exactly the video bandwidth that Nintendo intended it to have. Sharp chunky pixels wouldn't have even been visible in the displays you could buy at the time.

Several SNES games explicitly took advantage of the limited bandwidth to cause color blending (e.g. Kirby's Dreamland); several Genesis games did too.
I don't think it's the video bandwidth that was the issue here, more the slow rise/fall times of the analog output of PPU2, which does not exist on the 1CHIPs. Color blending still doesn't happen using RGB on a 3CHIP, and I fail to see upsides to smearing the whole picture without having that. And if people want color blending, they should use composite anyway. I, for one among many others, prefer to use RGB even on games like Sonic where the developers intended the use of a composite output. This is especially the case since many developers used RGB on a PVM to develop their games, making this argument only apply to some games. Also the SNES had true transparency as a result of color math. And blending hi-res 512x224 graphics together is already possible without quality loss (see: emulators and Super NT).

I wouldn't be too sure that a blurry image was Nintendo's original intention when designing the SNES, and it is impossible to say that every game developer developed their games with the intention that the gamer would be using composite output, especially since the SNES supported S-Video and RGB.
lidnariq wrote:Honestly, those aren't The Hard Or Interesting Part.

Nevermind that S-CPUs seem to be what die the most readily anyway.
In my experience, PPU2 seems to die the most (I have a few consoles with dead PPU2s and only 1 with a dead CPU), but that's anecdotal.

lidnariq
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by lidnariq » Mon Apr 23, 2018 4:16 pm

syboxez wrote:I don't think it's the video bandwidth that was the issue here, more the slow rise/fall times of the analog output of PPU2
Those are two ways of saying the same thing.
Color blending still doesn't happen using RGB on a 3CHIP
And no significant population had displays that could use the RGB output outside of arcades. (And ... maybe SCART users in europe? How prevalent was that?)
I, for one among many others, prefer to use RGB
You're allowed to like things that are better than reality, big chunky pixels and all. But don't claim that they're authentic; they're every bit as fake as Eagle or 2xSaI.
I wouldn't be too sure that a blurry image was Nintendo's original intention when designing the SNES
They did three different revisions of PPU2 without increasing the video output bandwidth. They clearly thought it was working as intended. Given how buggy the 1CHIP is I don't think one could reasonably argue its output was the "intended" version either.
it is impossible to say that every game developer developed their games with the intention that the gamer would be using composite output, especially since the SNES supported S-Video and RGB.
I don't need to disprove anyone did. I just need to ask what did the average person have? And the answer is: composite, which is already lower video bandwidth what the 5C78 emitted as RGB.

ccovell
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by ccovell » Mon Apr 23, 2018 4:19 pm

I made a page illustrating the SNES' blurry RGB, and where it happens. It is not intentional, as the PPU can slam the R/G/B to full on or to black, but transitions to an intermediate shade take a long time to settle, hence blurriness:

http://www.chrismcovell.com/gotRGB/snesblur.html

Image

lidnariq
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by lidnariq » Mon Apr 23, 2018 4:28 pm

... yeah, ok, that's clearly a variable impedance as a function of the output voltage, i.e. a changing bandwidth as a function of the brightness, which there's really no way to justify.

Sorry.

Locutus73
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by Locutus73 » Mon Apr 23, 2018 4:39 pm

lidnariq wrote:And ... maybe SCART users in europe? How prevalent was that?
I'm from Italy and I don't remember any TV without SCART since I was a kid (look at my nickname for guessing how old I am).
My first use of SCART was with a Philips TV and my C64 in the 80s. Here a RGB SCART cable was the first mandatory accessory (ok, I know it's an oxymoron) to buy with any old console and computer.

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Zonomi
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by Zonomi » Tue Apr 24, 2018 2:03 am

lidnariq wrote:And no significant population had displays that could use the RGB output outside of arcades. (And ... maybe SCART users in europe? How prevalent was that?)
TV with SCART were mandatory in France.

calima
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by calima » Tue Apr 24, 2018 2:39 am

And Finland as well, every TV came with SCART, and consoles shipped with SCART adapters, because not every TV had composite input. Those adapters were naturally composite -> scart, not true RGB; true RGB cables were sold everywhere.

Locutus73
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by Locutus73 » Tue Apr 24, 2018 5:57 am

calima wrote:And Finland as well, every TV came with SCART, and consoles shipped with SCART adapters, because not every TV had composite input. Those adapters were naturally composite -> scart, not true RGB; true RGB cables were sold everywhere.
Yep… those little RCA to SCART adapters. They always stayed in their original unopened plastic bags here. Composite was always considered simply unwatchable.

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lidnariq
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by lidnariq » Tue Apr 24, 2018 9:34 am

Right. A while ago I'd discovered that in France, due to SECAM, their NES had to use RGB. But what I was asking was—given that SCART does, for good and ill, actually support composite—how often did the original bundled cables support RGB and/or how often did people buy the better cables.

You seem to have answered that too.

Locutus73
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by Locutus73 » Thu Apr 26, 2018 4:09 am

lidnariq wrote:Right. A while ago I'd discovered that in France, due to SECAM, their NES had to use RGB.
Same exact issue with imported NTSC consoles (popular here before the online era); RGB cable was mandatory in order to see… colours.
lidnariq wrote: But what I was asking was—given that SCART does, for good and ill, actually support composite—
I’d say for good… SCART was cool for this reason, bringing multiple connection variants on the same cable.
lidnariq wrote:how often did the original bundled cables support RGB
I never saw one.
lidnariq wrote: and/or how often did people buy the better cables.
I can’t exclude that casual users (i.e. kids with consoles coming from Santa) used the included CVBS cable. Gamers with some knowledge preferred the (few bucks) optional better RGB cable. Hardcore gamers, with import consoles, had to use the RGB cable in order to see any colour.

[EDIT]
You NA guys missed the joy of trying to blindly plug a SCART connector on the back of a TV doing contorsions…

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creaothceann
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by creaothceann » Thu Apr 26, 2018 5:08 am

Locutus73 wrote:You NA guys missed the joy of trying to blindly plug a SCART connector on the back of a TV doing contorsions…
Just pick the TV up with one hand & rotate it, grab the connector with the other hand and plug it in, then slowly put the TV down again. :mrgreen:
My current setup:
Super Famicom ("2/1/3" SNS-CPU-GPM-02) → SCART → OSSC → StarTech USB3HDCAP → AmaRecTV 3.10

Great Hierophant
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Re: Introducing the VeriSNES (FPGA-based SNES)

Post by Great Hierophant » Thu Apr 26, 2018 7:36 am

Nothing I have ever seen suggests that Japanese SCART was particularly widely adopted, even in the SNES days, and most NES and SNES era game development took place in Japan.

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