[Nut-upsuser] APC Modbus support is finally here!

[d tbsky]

Jim Klimov <jimklimov+nut at gmail.com>
> Regarding shutdowns triggered due to calibration - the `CAL` state should be specially handled with regard to `OB`/`LB` in `upsmon` since recently. However this driver seems to use `TEST` here? Raised a question in https://github.com/networkupstools/nut/pull/2184 discussion (also referenced your replies there). Actually, now I wonder (did not test) how `upsmon` interacts with `upssched` in case of calibrations, if this is suppressed or not...

Hi:
    I attached load to SMT2200RM and tested "calibrate.start".  I
compare the behavior with "Back-UPS 1100VA" (driver "usbhid-ups").
results below:

1. The first thing I noticed: there is no beeper status attribute
"ups.beeper.status" with driver apc_modbus. and there is no beeper
control command like "beeper.disable/beeper.enable". normally I will
disable beeper before starting calibration since many ups will beep.
SMT2200RM also beeps when calibration. so I can only use "upscmd
beeper.mute" to mute the beep. BTW, apcupsd modbus also didn't have
beeper attribute and commands. I don't know if it is a restriction of
modbus?

2. when testing
   SMT2200RM "ups.status" is  "OB TEST CAL". "ups.test.result" is
"Passed, Source: Protocol " (seems not correct) .
   Back-UPS "ups.status" will change to "OB" for a few seconds and
then change to "OL DISCHRG".  "ups.test.result" is "In progress".

3. After one minute I stop testing with "calibrate.stop".
("test.battery.stop" for Back-UPS)
   SMT2200RM "ups.status" is  "OL". "ups.test.result" is "Passed,
Source: Protocol " (seems not correct).
   Back-UPS "ups.status" is "OL CHRG". "ups.test.result"  is "Aborted".

4. when ups recharge to 100%
   SMT2200RM: ups.status is  "OL" and  ups.test.result is "Passed,
Source: Protocol "
   Back-UPS: ups.status is "OL" and ups.test.result is "No test initiated"

5. I notice that beeper is re-enabled automatically for SMT2200RM (it
will beep if I restart calibration). It is a good thing since
currently there is no command to unmute the beeper.

as the observation above, maybe Back-UPS with usbhid-ups behavior
could be a reference.