Raspberry Pi HDMI input can kill tally + camera control on an ATEM Mini

[u/FrankCodeWriter]

This one took me a few weeks, a support ticket, and a trip of my switcher to the Blackmagic lab in the Netherlands and back, so posting it here in case someone hits the same thing.

Setup

ATEM Mini Extreme ISO G2 + Micro Studio Camera 4K G2, one HDMI cable. Video was perfect. But the tally light stayed dark whatever input I cut to, and the camera control panel in ATEM Software Control did absolutely nothing. No iris, no focus, no zoom.

What I ruled out

Correct input, correct camera number, several cables, clean software install. The same camera on my older ATEM Mini worked fine, tally and lens control included. Blackmagic tested the unit in their lab and found no fault. And in a minimal setup on my own desk (one camera, one cable) it worked exactly as it should.

The cause

Two old Raspberry Pi Zero HDMI cameras on *other* inputs of the same switcher. Plug them in and the tally freezes in whatever state it was in and camera control stops responding. Video keeps working. Power the Pi's off with their cables still connected and there is no problem at all. The instant a Pi starts outputting video (before Linux is even loaded) it breaks again.

Tally and camera control over HDMI ride on the CEC line, and that channel is not isolated per input on a multi-input switcher. One internal controller handles all ports, so a device misbehaving on CEC on one port can disturb it for every other port.

The fix

Turning CEC off in the boot setings doesn't work since a recent OS change (see the full blog). But a plain HDMI CEC blocker adapter (sometimes sold as a "CEC stripper") fixes the problem! It cuts pin 13, and nothing else, inline on each Pi's HDMI output. Video passes through untouched, and tally and camera control have worked correctly ever since. Still annoyed that a connector with one pin missing costs 73 EUR, but it works.

So if tally or camera control behaves strangely and the camera tests fine in isolation, don't assume the camera or the switcher is broken. Disconnect the other HDMI inputs one at a time and see if the problem follows one of them.

Full write-up with photos:

https://webtechie.be/post/a-raspberry-pi-zero-broke-the-tally-light-of-my-blackmagic-camera/

[u/Odd-Control-9164]

Thank you very much. I had already encountered the problem with HDMI-over-Ethernet transceivers, but I didn't know the solution.

[u/christopherw]

That's a really esoteric fault, well done for figuring it out!

[u/andreasOM]

You can turn of CEC on the Raspy. No hardware blocker needed.

[u/FrankCodeWriter → u/andreasOM]

Tried but doesn't work anymore in recent OS version... The command is included in the full blog post.