Nut upsdev - Dec 2021 - New PR to Fix Problem with TrippLite AVR750U in usbhid-ups

Hello,

I have recently opened a small pull request for the usbhid-ups
driver to fix an issue I have had with my TrippLite AVR750U UPS.
It can be found on GitHub:
https://github.com/networkupstools/nut/pull/1228.

Back in July 2020, there was some discussion between me and a few
other users (CC'd on this mail) on the nut-upsuser list about
problems with this and similar devices. Specifically, I could not
get the UPS to turn off the load and then turn it back on once mains
power was restored. Recently, I took another look at this problem
and realized that while commands like

$ upscmd avr750u shutdown.return
OK
$ # or
$ upscmd avr750u load.on.delay30; upscmd avr750u load.off.delay 20
OK

didn't work (sometimes the UPS wouldn't turn off, sometimes it would
turn off, no matter what it didn't return after an additional 10
seconds), this command did

$ upscmd avr750u load.on.delay30; sleep 0.125; upscmd avr750u load.off.delay 20

As a result, I implemented this change to the two instcmds in the
usbhid-ups driver that result in multiple actual instcmds being
executed, and found that this fixed my problems.

Because the delay is so short, I don't think it should be an issue
for other usbhid-ups devices that don't have this problem.

I am looking forward to comments on this and am happy to work to
get it merged.

Thanks,
Scott Colby