[Nut-upsdev] USB HID - interrupt reports

Arnaud Quette aquette.dev at gmail.com
Wed Jan 9 09:33:30 UTC 2008

2008/1/2, Arjen de Korte <nut+devel at de-korte.org>:
> >> I'm strongly opposed to that changes for *MGE* devices.
> >> We would end up in missing some setting changes that are only reported
> >> through the interrupt pipe (like when muting the beeper) and overload
> >> some old low end units (resulting in temporary DOS when OB).
> >
> > There may be some merit in your first argument, although so far I have
> > never seen an input report that didn't also have a matching feature
> > report. Not having that, would mean that if one missed the input report
> > (for whatever reason), you'd never know about the change in state and also
> > could not poll for the actual status at will (there is no way to tell if
> > and when an input report will be sent).
> In addition to the above, 'usbhid-ups' doesn't (and neither has it's
> predecessor 'newhidups') been able to use variables that *only* have an
> input report, but not a matching feature report. The HID-to-NUT mapping
> has always explicitly looked for the ITEM_FEATURE flag on the HIDData
> elements to map them to NUT variables. And if there is no mapping, the
> variable can't be used either. So technically, this isn't a change.

This is absolutely true!
But the problem there is not to manage variable change through the
input pipe, but to see the real change that only happen through the
input pipe.
The beeper is a good example. The change are not visible through
feature/output (so polled) requests but only through the

Moreover, the biggest advantage of notification (obviously when the
hardware works) is to limit the computer usage. Having a full
asynchronous chain would allow me to launch the green nut project one
day (I'd like to audit this and check what can be improved to reduce
nut footprints in general, and its impact on the energy consumption in
particular. Check Green Linux, PowerTop and the like)

btw, I've not seen your change to usbhid-ups.c to limit this to non MGE units...

Linux / Unix Expert R&D - MGE Office Protection Systems - http://www.mgeops.com
Network UPS Tools (NUT) Project Leader - http://www.networkupstools.org/
Debian Developer - http://people.debian.org/~aquette/
Free Software Developer - http://arnaud.quette.free.fr/

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