Subject: Re: uhid and UPS's
To: Lennart Augustsson <>
From: Wolfgang S. Rupprecht <>
List: tech-userlevel
Date: 11/15/2004 13:23:52
Lennart Augustsson writes:
> This is a rather unusual device.  Is this really the way power
> devices are supposed to work?

The only usb power-control info I've been able to find is an old 1997
pdf from intel at, . It shows
several report-ids (id 1 to id 11, see pdf pages 51-58), but it
appears that the intention was to offer related bundles of

I'm inclined to think APC misunderstood the intention of the report
id's.  On the other hand, APC is a very common brand of UPS in the US,
so this is going to come up more frequently as time goes on.

> Anyway, perhaps there should be a way not to make a separate
> uhid device for each report id.  This is the way it used to
> be (but that doesn't work for devices where only the report
> id distinguishes a mouse from a keyboard).
> I suggest using 'flag 1' on the uhidev device.

Ok.  I'll play around. I might try to turn off the multi-uhid logic
for power devices (eg. hid page 0x84 and 0x85) or perhaps just for APC
power-control devices.

Martin Husemann writes:
> On Mon, Nov 15, 2004 at 09:24:03PM +0100, Lennart Augustsson wrote:
> > This is a rather unusual device.  Is this really the way power
> > devices are supposed to work?
> I wonder what logic made the manufacturer declare it as uhid anyway.
> It does have a button and some LEDs, but so does my CD drive.

I've been scratching my head over that one too.  Maybe they intended
the UPS to be a keyboard-like device that would type "shutdown -h +1
'power is gone and you are screwed.'"

In any case, it is tempting to tie it into the apm logic a bit tighter
and have the kernel and UPS coordinate the power-off event a bit
better than they now do.  The current apcupsd power-off logic uses a
timer in the UPS and if the shutdown is a bit slow the UPS could cut
power before the kernel unmounted everything.