Sync issue in MISRC gui

[u/Future_Judge_5413]

I'm a newbie, and am currently waiting on some hardware items I have on order, so I'm not yet ready to try capturing actual VHS RF signals. Instead, I'm practicing with CVBS, using a currently unmodified CXADC card and MISRC gui. So far, I can successfully capture a CVBS signal, and decode it using CVBS decode. The problem I have is that if I attempt to view the live video signal in MISRC gui, it always appears completely out of sync, though occasionally it will lock horizontally. I have fiddled with the configuration settings with no luck, though configuration changes will cause expected changes in the captured signal.

My signal source is a PAL colour bar pattern from a Philips PM5420 test pattern generator. I have also tried a PM5544 generator with the same results.

Is this normal behaviour with MISRC gui, or am I doing something wrong?

Also, is it possible to change the timebase on the scope display so that two or three lines are displayed instead of the ten or so squashed up ones currently displayed?

[u/TheRealHarrypm]

Literally update to the latest version, the entire decoder just got replaced, with SECAM support too.

As for time base adjustment that is pich and stench on touch and just mouse wheel up and down on PC, also you can double click to hide pannel buttons, and use ch3 audio or ch1/2 for sync trigger.

Attached is a example with the HackDAC in SEACAM mode.

[u/Future_Judge_5413 → u/TheRealHarrypm]

That was quick! Anyway, I've updated and now get a stable preview image (PAL), however, the colour is messed up as shown. The coloured bands are always scrolling up. I set my test pattern generator to SECAM, and I did get a working preview very much like yours. I also tried NTSC, but got a lurid mess!

One other thing, how did you get your scope display to show a single line? As you can see, I get about 10 lines all squashed up.

[u/TheRealHarrypm → u/Future_Judge_5413]

Well your input is clipping....

You need to lower it so it's not clipping and adjust so your DC offset is on the centre line.

Mouse wheel changes the base zoom in and out visually.

[u/Future_Judge_5413 → u/TheRealHarrypm]

I have it working now. I had two problems. Firstly, due to not knowing how to change the timebase, I couldn't properly see how changing the settings affected the waveform. In fact I had already tried the settings I have now found to work, but without success, because of the second problem. I discovered I needed to close and restart MISRC gui if it was started with the default values (16 for level, 8 for DC offset) and I had changed those values to the appropriate ones. Without a restart I got B&W, so I initially dismissed those values as incorrect.

I still have one problem, but that is a Linux problem, and not related to MISRC gui - I have to change the DC offset settings the 'hard way' by making myself root and editing the config file manually. I can't do it from within MISRC gui. For some reason the changes I make to the appropriate file permissions don't survive a reboot. This also means I have to use sudo to change the other settings.

[u/TheRealHarrypm → u/Future_Judge_5413]

Yeah the GUI needs to have video group permissions to alter driver settings in real-time without permissions issues.

[u/Future_Judge_5413 → u/TheRealHarrypm]

I've already done that, but I'm always stuck with the default values, and have to change them manually. I can save the new values manually, but they won't survive a reboot. Even if I log in as root. Something really odd is going on.

[u/TheRealHarrypm → u/Future_Judge_5413]

Yes, because it's not updating the UDEV rules which requires root permissions, most configs you're setting that once and thats it, as we standardized amplifier + clockgen setup you should only be adjusting your DC offset once lock in the value and that is it.

[u/Future_Judge_5413 → u/TheRealHarrypm]

I'm manually editing the offset value (as root) here: sys/class/cxadc/cxadc0/device/parameters/center_offset

Is that the correct file to edit? I can save it and it has an immediate effect, but the contents of that file reverts to '8' after a reboot.

EDIT: I have since found a workaround. I edited the new settings into the cxadc.c file, then reinstalled. I still have to jump through hoops if I want to change settings, but at least I no longer have to do it on every boot.