PV Update warning

[flef]

Hello,

Thank you for all the work done in Phoebus, especially in the integration of MQTT. I believe I remember an option in DisplayBuilder/BOY to indicate that a PV has not been updated for more than X seconds (by surrounding it with a continuous pink border).

Do you know how to reproduce this functionality in Phoebus for PVs using MQTT?

Best regards,
Flef

[kasemir]

We don't care how often a PV updates. While for example a temperature readback PV might change by a little bit every second, a corresponding setpoint PV might not have been changed for months, so it sends no new data and that's just fine.

PVs can enter an INVALID state, typically because of network disconnects. Protocols like Channel Access or PV Access further include the following logic:
There's one TCP connection per server that has some of our PVs. If a PV changes, the server sends an update for that PV via the established TCP connection. When the TCP connection is closed, all those PVs which were on the connection are of course INVALID. But if there are no updates for some time, we can't be sure. Is the TCP connection really dead, or was there simply no update? That's why servers either send some periodic idle messages, or the client will eventually ask "Are you still there?", and if there's nothing from that, we also mark all the PVs on that connection as INVALID.

With MQTT, I'm not sure what the protocol offers in that regard, but we're simply using what's in the protocol; we don't add our own layer of timeouts on top of that.