[Nut-upsuser] UPS Requiring URB_INTERRUPT with Megatec Protocol

[Daniele Pezzini]

> I have a UPS unit with a USB Interface that appears to work with the blazer_usb and nutdrv_qx drivers.  I have tried all combinations of subdriver and protocol and the result is always the same.  The values returned are all zero's.
>
> The issue seems to be the same as https://github.com/networkupstools/nut/issues/307
>
> Attempts to send a command to silence the beeper or trigger a battery test also fail.
>
> One interesting observation was when using the UPSmart program provided (Guangdong IDKG) in Oracle VirtualBox (Win7VM) on my Fedora laptop was that the nut drivers would show values.  As soon as the UPSmart was stopped, the values returned would stay the same and wouldn't update.

hmm... this sounds familiar.
You're not related to GitHub issue #674
(https://github.com/networkupstools/nut/issues/674), right?

> Observing the usb chatter in wireshark showed that the UPSmart program received and sent an URB_INTERRUPT to 0x81 EP.  This was happening in a pattern of receive/send URB_INTERRUPT followed by 5 GET_DESCRIPTOR request/respond.

This was the same thing I got to, the last time I looked into that
(after #307, there have been some other topics on the lists or on
GitHub, I can't remember exactly now).

> The UPS is cheap and cheerful, details can be found here
> https://www.jaycar.com.au/650va-390w-line-interactive-ups-with-lcd-and-usb/p/MP5205
> The badge on the front says 'DIGITECH Computer', model MP5205
>
> I opened the case up and removed the comms board, but there's nothing much to go on.  I was able to get details off the only IC on the board, but it's a generic microcontroller.
>
> I'm keen to get this to work but I'm a bit green on the hardware programming side of things.  So if there's grunt work to do, let me know what the next steps are.

I don't expect this to work, but could you please test
https://github.com/networkupstools/nut/pull/638 ?

Also, if you're open to (building and) testing what I throw at you, I
can try to implement something to mimic what's in #307 / #674.