[Nut-upsuser] UPS Requiring URB_INTERRUPT with Megatec Protocol

Simon fooba9r at gmail.com
Tue Mar 5 03:33:11 GMT 2019


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

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.

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

The UPS is cheap and cheerful, details can be found here
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.

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