[knx] -control channels do NOT work

[florian-h05]

Since the recent SNAPSHOTs, *-control channels have stopped working.
I have checked when the issue first occured, and it seems that SNAPSHOT #3390 from 31st of March 2023 isn't affected by this problem. This means, that there was no change in the KNX binding that can cause this: https://github.com/openhab/openhab-addons/commits/main/bundles/org.openhab.binding.knx.

It must be a core changes, however I have no clue which one, it must be one between March 31st and April 2nd (https://github.com/openhab/openhab-core/commits/38a6d1e87bdd3fadcc2adcd4604a2bed90ab4c06), because this is the timeframe the issue first occured.

I did some debugging, and very interesting: for -control channels, the handleCommand method of the KNX Thing is never called when I send a command to Items linked to a -control channel.
This is the right behaviour when the SystemFollowProfile is applied to the channel link, and this is recommended by the KNXProfileAdvisor for -control channels.
I also wonder if it is correct to suggest follow profile for -control channels by default. Either way, this should be documented.

Manually setting system:default profile for the affected channel links should help for now, but I think there is a problem with the system:follow profile not forwarding state updates anymore.

[florian-h05]

@J-N-K @holgerfriedrich Can you reproduce?

[J-N-K]

I didn‘t check, but will have a look tomorrow. Probably openhab-core#3141 is the cause.

[florian-h05]

@J-N-K Seems like I found an error in org.openhab.core.thing.internal.CommunicationManager, I will test my fix and then open a PR.

[holgerfriedrich]

@florian-h05 sorry cannot test right now, my test system is still on M1 and has no control channels in use.
If yo need additional testing, give me some time to adapt. In contrast to @J-N-K I typically only use the text config....

[J-N-K]

I guess this only affects the follow profile, and that's why it went unnoticed.

[florian-h05]

Yeah, I agree.

-control channels broke because CommunicationManager had a wrong event subscription and did not receive ItemStateUpdateEvents. In consecuence, the follow profile broke, because it only releays state updates, which were not received.

Therefore: Will be fixed by openhab/openhab-core#3529.

@holgerfriedrich I don't think additional testing is needed here, thanks.