Synchronise the MODBUS commands with the inverters's state

[s-allius]

In the proxy version 0.8 we send MODBUS commands regular by a cron job. Especially the GEN3 inverters are picky when they receive unexpected frames. Tests shows, that the inverter firmware seems to be much robuster when we send MODBUS command not in the phase when the inverter reports the data.

We want a timer in the protocol state machine, which triggers the MODBUS commands.

GEN3 inverter

For GEN3 inverters the timer should be startet/restarted when the inverter sends a new get time request. This indicates the beginning of a new reporting phase. Since the phase is about 1 minute long a timeout of 90sec should garantie that no MODBUS commands will be send during this phase.
After sending a MODBUS command the timer should be startet with a timeout of 60sec. So the cadence of the regular MODBUS request will be about 1 minute

GEN3PLUS inverter

These inverters are very robust and there are no restrictions to consider.
We can start the timer as soon as the first packet is received from the inverter and then simply start it again when sending MODBUS commands. A fixed timeout of 60sec will do.

[s-allius]

fixed by version 0.9 #112