SNES stutter in Adaptive line mode

[SK123]

<p style=”text-align: left;”>I know there’s a sticky thread about SNES having jittery sync from 2018 has this been resolved or is my issue similar?</p>
<p style=”text-align: left;”></p>
<p style=”text-align: left;”>Using the Mister FPGA and OSSC pro for some reason on the SNES core it stutters when is adaptive line multiplier mode no matter what settings I use. Also, the picture goes black for a few seconds every minute or so. Strangely it doesn’t happen when I use pure line multiplier or scaler. This happened with the original firmware the OSSC pro came with and still with the newest 0.77.</p>

[onthewaveagain]

I remember raising this a few months back. Marqs said : “Regarding SNES core, it doesn’t have de-jitter option so Pro hardware cannot maintain framelock since the number of VCLKs per frame doesn’t remain constant. You thus have to use scaler mode with framelock off (it might remain stable even with framelock option on but under the hood the lock cannot be kept). I’ll need to look into integer scale of 224 height.”

What I found strange is that it does not stutter and go black when I use the MiSTer RGB output with Adaptive Line.

• This reply was modified 5 days, 20 hours ago by onthewaveagain.

[SK123]

Interesting. It also doesn’t stutter in Pure Line multiplier mode.

 

Marqs, is this something that can be implemented in a firmware update?

[marqs]

The root cause is SNES (clone) and for genuine one a solution (de-jitter mod) has been available for many years. A SNES core with digital output ends up constantly re-triggering frame syncing on Pro (properly enforced on upcoming fw) since its framelock is designed to operate with constant number of VCLKs per frame (that you get from any normal HDMI source or from digitized RGB). Aside from turning framelock off, there are essentially 2 other ways to solve the problem:

* addition of de-jitter option on the SNES core (which could also improve compatibility with some picky CRTs)
* re-implementing Pro’s framelock via general genlock which adjusts timing based on source vsync alone

The latter might also have some other minor benefits on Pro, but it’s currently not high priority since the existing solution works well with vast majority of sources.

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