Reply To: New Koryuu test firmware 1.1-test0

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Hi newsupermarkio,

I’m using the Koryuu with a Capcom CPS changer S-video output with Street Fighter 2 Turbo PCB.

The connection is:
Capcom CPS changer S-video -> Koryuu -> Component Video -> RetroTink Comp2RGB -> PVM

With the stock Koryuu firmware, I encountered a strange issue where after 5 minutes of operation, the video starts to flicker and eventually it loses all color.

Hmm, that’s odd. Losing color usually happens because lock on the chroma subcarrier is lost and/or the chroma signal becomes weak enough that the ADC chip’s “color kill” threshold is hit. This can be due to a variety of reasons.

Given that there is initially color in the output, but the colors start to flicker and the picture eventually falls back to grayscale, there may be some sort of a process that gradually degrades the chroma signal and/or subcarrier after lock on the sync signals has initially been established.

(CPS Changer apparently uses the CXA1645 video chip for its composite and S-Video outputs. This is the same chip as in some Sega Genesis/Mega Drive models, which are known to sometimes be problematic with the Koryuu, although S-Video modded units tend to have good S-Video output, in my experience. I wonder if there is a connection here…)

A direct S-video connection into my PVM display is ok. The S-video input to a RetroTink 2x Pro to an HDMI display is ok too.
I have separately tested the RetroTink Comp2RGB -> PVM connection with a SNES -> HD retrovision cable -> RetroTink Comp2RGB -> PVM, and verified that works fine. Thus, I believe there may be an issue with how the Koryuu is handling the S-video output of the CPS Changer.

Interesting. I wonder if having multiple converters/transcoders chained might contribute to the problem.

If I understand correctly, your PVM has S-Video and RGB inputs in some form or another. As the Comp2RGB seems to have a SCART output connector, there is probably an adapter to the BNC RGsB inputs on the PVM, correct?

I have an idea for exploring this a bit further. The Koryuu is technically capable of outputting an RGsB or RsGsBs signal in addition to YPbPr, so it should be possible to simplify the video chain a bit by connecting the Koryuu directly to the PVM (modulo RCA->BNC adapters, probably). Would you be willing to try a version of the current in-development firmware with RGsB output instead of YPbPr?

I would like to make sure I have the correct understanding of the issue. If you do not mind, could you confirm or correct my understanding, please?

With the current public test firmware (1.1-test0), is the process leading to the issue roughly as follows?

  1. Initial sync is established: the picture is stable and has color.
  2. Roughly 5 minutes passes, possibly with some game activity or attract mode on-screen.
  3. The colors and/or picture start to flicker or glitch. (How? Wrong colors, image flickering between grayscale and color, image blanking out or its geometry distorting?)
  4. Color is lost. The picture shown on-screen is now in grayscale. (Apart from missing color, is the picture otherwise stable?)

Another thought that came to my mind is whether it might be possible to try the composite output of your CPS changer with the Koryuu to see if it has a similar problem as with S-Video.

I suspect there may be some issue with the field reversal and updated the Koryuu firmware to version 1.1 to see if the issue goes away. The updated firmware did seem to help the issue, but after several minutes of operation, I could see the video start to flicker again under certain scenarios/screens. It seems that the issue gets cleared out between screen transitions, but certain video input patterns seem to trigger the flickering/color issue. The start up screen/attract mode with vertical scrolling seems to be problematic, as is Chun Li’s stage for some reason. I think the field reversal solution helps, but it seems there remains some residual issue that is still not fully resolved. Do you have any theories why this might be happening?

At present, I do not have any particularly strong hypothesis about the cause of the issue you are experiencing. It could be a variety of things. The gradual nature of the degradation of color may be a sign of an ongoing physical phenomenon, such as temperature changes in some component(s) affecting the chroma subcarrier somehow, but this requires more investigation to say anything for certain.

The field reversal issue is related to interlaced NTSC modes, which should cause visible, jarring artifacts in the picture (as if every set of two consecutive lines were swapped). Not sure if that can have anything to do with color issues.

Could you perhaps record a video of the issue? Just a smartphone-quality video should be plenty to get an initial understanding of the issue.

A side note on the firmware update procedure, as it took me a while to get this working with proper driver and programmer software:

Yes, the Windows instructions in the junkerhq wiki are not very good at the moment when using the Olimex programmer (Khazama seems to be hardwired for a particular, different type of programmer). We are hoping to update the instructions soon. I have created a raw, non-narrated screencast of a relatively straight-forward process to update the Koryuu firmware in Windows using modern, free tools, but it needs to be turned into a proper tutorial.