[Nut-upsdev] USB comms dropout not detected

Daniel O'Connor doconnor at gsoft.com.au
Mon Jun 1 02:15:30 UTC 2009

I have an MGE Ellipse 1000 connected to a FreeBSD 7.1 system and it 
works well except that if I yank the cable it doesn't detect a 
problem.. It seems to quite merrily read the old data (upsc reports the 
same values).

There is nothing logged by NUT to indicate comms is lost (usbhid-ups is 
still running).

In the attached log I yanked the able at the 28 second mark and plugged 
it back in at the 48 second mark.

It seems that usbhid-ups should know the UPS is no longer present but 
upsd doesn't seem to DTRT and mark the data stale (or perhaps 
usbhid-ups is re-sending the old data structure to upsd?).

Also, I think that usbhid-ups should either try reconnecting to the UPS 
(ie search for a suitable device like it does when starting) or exit 
after several failed attempts.

I found when I was using libusb I could not detect if a device went away 
directly, in the end I settled for trying to read a string descriptor - 
since this is a mandatory operation a device always supports if it 
fails it indicates a catastrophic problem. (The lack of decent error 
codes in libusb [or maybe the FreeBSD version] is rather irritating).

I guess really if usbhid-ups exits on error then it should really just 
be started by some system specific daemon on UPS connection (eg devd in 

Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
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