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 Post subject: AVS for NES dev?
PostPosted: Fri Jan 06, 2017 2:07 pm 
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Does anyone know if the RetroUSB AVS reproduces the NES's hardware quirks, e.g. the DMC/gamepad conflict? I'm looking into purchasing a hardware NES for dev-testing purposes, and the AVS seems like a more dependable option than an eBay-sourced original, assuming it can do what I need it to do.


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 Post subject: Re: AVS for NES dev?
PostPosted: Fri Jan 06, 2017 2:34 pm 
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It contains a FPGA programmed to replicate behaviour. I don't know how exact the FPGA in the AVS replicates everything, so i'm just saying this: there are probably some obscure behaviours in the original which aren't even fully charted yet. This is a theoretical and (to be fair) small problem which you nevertheless can avoid by getting original hardware.


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 Post subject: Re: AVS for NES dev?
PostPosted: Fri Jan 06, 2017 2:38 pm 
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If you know of a 100% reliable way to test for such quirks, either in a game or a test ROM, let me know and I'll be happy to try it on my AVS.


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 Post subject: Re: AVS for NES dev?
PostPosted: Fri Jan 06, 2017 3:27 pm 
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People are still discovering quirks in the original hardware every once in a while, so I think it's safe to say that the AVS can't possibly work 100% like the original console. Until someone decides to replicate CPU and PPU dies at the lowest level, copying their exact transistor layouts, we're stuck with "close-but-not-quite" replications of the original logic.

If the software you're developing doesn't make use of intricate raster effects or pushes the boundaries of the console's design too much, it should be safe to use accurate emulators and/or an AVS during development, and have someone else test the final build on original hardware for you just to be sure everything is OK. But if you're doing complex effects that rely on very precise timing and/or manipulation of hardware registers at sensitive times, you definitely should be using the original console for testing.


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 Post subject: Re: AVS for NES dev?
PostPosted: Fri Jan 06, 2017 3:51 pm 
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WheelInventor wrote:
I don't know how exact the FPGA in the AVS replicates everything, so i'm just saying this: there are probably some obscure behaviours in the original which aren't even fully charted yet. This is a theoretical and (to be fair) small problem which you nevertheless can avoid by getting original hardware.

tokumaru wrote:
If the software you're developing doesn't make use of intricate raster effects or pushes the boundaries of the console's design too much, it should be safe to use accurate emulators and/or an AVS during development, and have someone else test the final build on original hardware for you just to be sure everything is OK. But if you're doing complex effects that rely on very precise timing and/or manipulation of hardware registers at sensitive times, you definitely should be using the original console for testing.

Looks like I'll have to stick with the real deal to ensure flexibility and compatibility, then. I'd kind of suspected as much, but I'm glad (though also slightly disappointed) to have it confirmed. Thanks for your help!


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 Post subject: Re: AVS for NES dev?
PostPosted: Fri Jan 06, 2017 4:00 pm 
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The other thing to think about is what % of the people you want to sell this to will still be using an original NES to play the game vs some other clone (retron, AVS, etc).


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 Post subject: Re: AVS for NES dev?
PostPosted: Fri Jan 06, 2017 4:30 pm 
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hackfresh wrote:
The other thing to think about is what % of the people you want to sell this to will still be using an original NES to play the game vs some other clone (retron, AVS, etc).

The original console is always the common ground though, since all others are modeled after it. Even if all original Nintendo units fail, the original design is still the reference for all other implementations. If different developers start to cater to the inaccuracies of this or that clone, the standard is lost.


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 Post subject: Re: AVS for NES dev?
PostPosted: Fri Jan 06, 2017 4:46 pm 
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Given how many emulators don't implement the DPCM glitch without compatibility problems, and that the PAL revision doesn't have the glitch, it might have been a sensible idea for the RetroAVS not to implement it (depending on point of view / implementation details).

As far as test ROMs, maybe these ones will do?
http://forums.nesdev.com/viewtopic.php?p=63998#p63998


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 Post subject: Re: AVS for NES dev?
PostPosted: Fri Jan 06, 2017 6:58 pm 
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I can understand why one might choose not to implement the DPCM glitch, but if programmers suddenly started ignoring this glitch while still marketing their products as "NES games", that could be a problem for anyone still using the original console.

Not that this kind of problem is unheard of, even back in the commercial days of the NES. For example, there are a few games reading from $2004 for timing reasons, but IIRC, early PPUs didn't support $2004 reads. The Master System port of Earthworm Jim apparently has problems with its status bar, because not all consoles support scaled sprites, unlike the Game Gear, where the original game's status bar worked fine.


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 Post subject: Re: AVS for NES dev?
PostPosted: Fri Jan 06, 2017 8:09 pm 
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koitsu wrote:
If you know of a 100% reliable way to test for such quirks, either in a game or a test ROM, let me know and I'll be happy to try it on my AVS.


In addition to the glitch test that rainwarrior linked, this OAM-synchronized controller read test looks like it could be a good way to see how cycle-accurate the AVS is:
viewtopic.php?f=2&t=14319&start=15#p172188


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