[Nut-upsuser] Working platform with FreeBSD + USB + MGE Ellipse (usbhid-ups)

[herve-nut at mindstep.com]

Hi,

I've have had some difficulties to run NUT on freebsd, but I finally managed to
have something that work reliably enough. For those who may be interested,
here is what I did.

Os: FreeBSD 6.2-RELEASE-p7, nut: 2.2.0, libusb: 0.1.12

First, I had to patch libusb with the changes submitted by Nevil Thatcher
in the nutups forum in may 2006. Without this change, nothing works.
(http://lists.alioth.debian.org/pipermail/nut-upsuser/2006-May/000992.html)

At this point, I had something that more or less works, but the USB connection
drops occasionaly for some reasons, and won't recover. I did not trace it enough
to see what happens, but it seems that something occurs in freebsd kernel
layers that bubbles to the reading process as an "IO error" (errno=EIO=5).

The reason why it does not recover is still somehow obscurs to me, but
I'm pretty much convinced it is related to the way the libusb layer
deal with re-initialization. I'm new to this library, but it looks like
the function usb_init(); (and friends) is not designed to run more than
once in the process lifetime.

Instead of "fixing" those parts, which would have taken a lot of time,
I used another approach: I implemented a "respawn" option for the driver
process, which automatically restarts the process when it exits. I also
did a few changes in the driver code so that it exits whenever a USB
connection problem occurs.

At this point, I have something that works reliably enough. Using my
UPS (MGE ellipse 750), I see about 20 losses of connection per day,
and the system takes between 5 and 10s to recover.

I did another change which is more cosmetic than anything else. In order
to keep short reconnections silents (in my logging system), I added a
grace period that delays the COMMBAD event. If the system recovers before
this period, no event is issued.

- Hervé


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