DExx-vd_isl – horizontal jitter in scaling mode

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My DExx-vd isl experiences significant horizontal jitter when in scaling mode. In general the higher the output resolution, the worse the jitter, 480p and 720p are unstable, 1080p and above being generally unusable. This manifests itself in frequently dropped signal over HDMI, and flickering horizontal shifts to the right, which get worse towards the bottom of the frame.

Tweaking the sync Vth can sometimes make a difference, but it isn’t really possible to bring this under control.

Line multiplier mode by comparison is much steadier, able to provide a near-stable sync at 2560×1440 most of the time, depending on the source, with Pure being slightly more stable than Adaptive.

I’ve tried firmware 0.59 and 0.60 (https://github.com/marqs85/DExx-vd_isl/commit/9e331e8cf281465fb8c72a9d71176c5e77d81a4d), with 0.59 slightly more stable, although there isn’t much in it. I’m using a Mega Drive, and a GameCube with the original component cable, and both have had this same issue.

I’m using a Meanwell 5V 4A PSU rather than the original DE10-Nano PSU, as I read elsewhere the idea that the stock PSU may not provide enough power – it hasn’t seemed to have affected the jitter problem either way though.

I’ve seen reference in other threads here to a noisy ground connection between the DE10-Nano and the DExx-vd isl, which may cause this jitter problem. My DE10-Nano is new, and cleaning the contacts hasn’t made a noticeable difference. If ground noise is the cause, is there a recommended way to improve the ground connection between the DE10-Nano and the DExx-vd_isl?

[marqs]

We have been looking into the issue which seems to manifest in some setups and is related to (external) clock generation and noise caused by it. If you are capable of soldering, there is at least one hack you can try which should significantly improve signal integrity. That involves connecting GPIO pin 2 to GND on DExx board as shown below:

Scratching some solder mask off the GND plane

Solder blob added between the pin and exposed GND plane

If you perform the hack, please remove DExx from DE10-Nano when not using the DExx firmware/SD card to avoid the situation where any other firmware would drive 1 into that pin while it is connected to GND.

For those who are unable to solder, I’ve been thinking about a backup solution which would generate clock internally on FPGA. Unfortunately that could be only applied to non-framelock mode and limited number of fixed output modes (e.g. 1080p@60).

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Thanks, that change has made scaling mode just as stable as line multiplier mode for me now.

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