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 Post subject: Re: Dogyuun, Batsugun, Fixeight, V-V incompatible with OSSC
PostPosted: Sat Oct 17, 2020 5:02 pm 


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Joined: 14 Aug 2019
Posts: 444
Location: BW, Germany
XtraSmiley wrote:
6t8k wrote:
I'm still interested in learning more about the chip's inner workings, however. What is the root cause of the sync anomaly? How does that initialization vector work that gets written to the 0x0e register when the game boots? How do two GP9001 chips interact with each other?

In case a patch for Batsugun/Dogyuun becomes feasible, you'll be able to read about it here, but all further poking is only tangentially related to this thread, so I'll leave it open for now if or how much of that I'll post here myself.


So, I just got a cool new game. Dogyuun. I excitedly opened the box and hooked up my OSSC to my new LG C9 OLED TV... nothing.

THEN, I remembered this thread. I was so focused on Fixeight and Knucklebash, I forgot the game that started this thread...DOGYUUN!!!!!!!

Damn. OK, so I can't even get a simple sync, even with a h.samplerate moved up.

A. Any progress on a patch?
B. So OSSC Pro will definitely fix this problem, right?

Good choice. ;)


> A. Any progress on a patch?

No update so far.

> B. So OSSC Pro will definitely fix this problem, right?

You can expect a perfectly clear, stable and skew-free picture, but it will not be as good as a game without the sync anomaly, a patched game, or the cps2_digiav solution. There will be a very small amount of stutter due to a dropped/duplicated frame every now and then. This is to synchronize the output frame rate to the game's refresh rate, because the OSSC Pro will generate its own input sampling and output pixel clock signals instead of deriving them from the game's sync signal. In this manner, the anomaly contained in the latter is bypassed, but the clock signals cannot be exactly matched to the game's refresh rate.


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 Post subject: Re: Dogyuun, Batsugun, Fixeight, V-V incompatible with OSSC
PostPosted: Sat Oct 17, 2020 5:52 pm 


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Joined: 06 Mar 2006
Posts: 12451
Location: Germany
You make it sound worse than it really is. A "correction" frame every how many seconds are we talking about? It should be far from an unlocked refresh rate with an intentional framerate conversion (which is what M.2 utilized in their more recent arcade ports on PS4).


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 Post subject: Re: Dogyuun, Batsugun, Fixeight, V-V incompatible with OSSC
PostPosted: Sat Oct 17, 2020 6:00 pm 


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Joined: 14 Aug 2019
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Location: BW, Germany
Not my intention, I just wanted to state the circumstance. It's a workaround that doesn't definitely fix the problem – which wasn't the expectation anyway: I think this prospect is the best one could've hoped for. I'd expect the effect to be basically unnoticeable during normal gameplay, when you aren't explicitly paying attention to it.


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 Post subject: Re: Dogyuun, Batsugun, Fixeight, V-V incompatible with OSSC
PostPosted: Sat Oct 17, 2020 9:51 pm 



Joined: 20 Apr 2018
Posts: 225
Location: St Louis, IL, USA
6t8k wrote:
Not my intention, I just wanted to state the circumstance. It's a workaround that doesn't definitely fix the problem – which wasn't the expectation anyway: I think this prospect is the best one could've hoped for. I'd expect the effect to be basically unnoticeable during normal gameplay, when you aren't explicitly paying attention to it.


Thank you, the precise answer I was looking for.

For me It think it will be fine as I will also be taking advantage of the rotate feature, so it won't be 100% accurate anyway. When I actually get good enough to get to the 3rd level, well, maybe then I'll get serous and swap it into a tate cabinet for further play!

That being said, why can't the same workaround in the cps2_digiav solution be applied to the OSSC? Is it because the former is physically modifying the PCB?


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 Post subject: Re: Dogyuun, Batsugun, Fixeight, V-V incompatible with OSSC
PostPosted: Sat Oct 17, 2020 10:45 pm 


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Location: BW, Germany
Then it was good that Fudoh was there :)

XtraSmiley wrote:
That being said, why can't the same workaround in the cps2_digiav solution be applied to the OSSC? Is it because the former is physically modifying the PCB?

.. sort of. From the game PCB's perspective, it's just wires that are soldered onto the appropriate hookup points, the components on the PCB are not actually modified.

The reason why the cps2_digiav is not affected by the sync anomaly is that it directly taps into the pixel clock signal, which you cannot obtain from the signals that are normally accessible through JAMMA or console's A/V connectors, like RGBS, S-Video, Composite Video, and so on. In the case of the ToaplanV2 hardware, the anomaly in the sync signal has no bearing on the pixel clock signal, and the cps2_digiav can keep its lock with its help.

To try something like that with the OSSC, one would have to solder a wire from a suitable point on the respective game PCB where the pixel clock can be picked up, onto one pin of the OSSC's video digitizer chip, and customize the OSSC's firmware accordingly. marqs once suggested that idea here.


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 Post subject: Re: Dogyuun, Batsugun, Fixeight, V-V incompatible with OSSC
PostPosted: Sat Oct 17, 2020 11:54 pm 



Joined: 20 Apr 2018
Posts: 225
Location: St Louis, IL, USA
As always, you are BOTH most helpful, so I thank you BOTH! :)

OK, I meant to put OSSC Pro in my question, but your answer applies to it as well, since it's a signal through the JAMMA edge issue.

OK, so crazy idea, can the OSSC Pro have an input that has an alligator type clip where one could clip into certain game PCBs to tap into the signal directly, not needing a permanent mode or solder spot?

OK, OK, this is not realistic, I understand.

For my purposes, I will stand by and use the OSSC Pro in tate mode and ignore the small differences from an arcade CRT!

Now if only someone would help answer this question...


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 Post subject: Re: Dogyuun, Batsugun, Fixeight, V-V incompatible with OSSC
PostPosted: Mon Oct 19, 2020 6:59 am 


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Joined: 14 Aug 2019
Posts: 444
Location: BW, Germany
XtraSmiley wrote:
can the OSSC Pro have an input that has an alligator type clip where one could clip into certain game PCBs to tap into the signal directly, not needing a permanent mode or solder spot?

Given appropriate facilities in the firmware (HDL+SW), the OSSC Pro could make use of such a signal, accepting it through its expansion port, which makes connection and disconnection of this end of the wire simple. However, connecting the other end via an alligator type clip seems quite precarious. It could be displaced, touching other pins, or slip off.

Feeding the ISL51002 (the video digitizing chip the OSSC Pro uses) with the game HW's pixel clock as an external sampling clock signal, could cover a middle ground between using the cps2_digiav and going for just the standard RGBS quadruplet via the AV inputs on the OSSC Pro. The former has the added benefit that it captures the R,G,B video signals and the FM audio signal in their digital forms before the game HW converts them to analog, the latter is straightforward to use. I think it could be interesting to try, not least because you also always have perfect sampe rate and -phase this way.

Now that we have the aforementioned two other options, it might not be that worthwhile anymore to have a separate processing path in the firmware just for this use case alone – on the other hand, there may be other cases where bringing in the game HW's pixel clock signal is both feasible and lucrative, which might provide a stepping stone, perhaps something like the NES/SNES due to the jitter issue. At least marqs has labelled two pins on the expansion port as a differential clock input (while single ended clock could be input by connecting it to just one of both pins).


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