[Nut-upsuser] Tripplite OMNIVS1500 Woes

[Charles Lepple]

On Aug 13, 2008, at 10:14 AM, Jon Bougher wrote:

> I'm just now starting to learn how Linux handles USB devices & I  
> had another question regarding this. Is this Tripplite model  
> supposed to be a hiddev device? From what I recall reading it  
> seemed that it needed the tripplite_usb driver because it is NOT a  
> hiddev device, it uses a serial over usb connection...?

The terms "USB HID" and "hiddev" do not cover exactly the same concepts.

Most, if not all, of the USB UPSes supported by NUT use some subset  
of the USB HID specification. (USB HID devices are easier to access  
than generic USB devices in Windows.)

The serial-over-USB interface is also popular, since it does not  
involve much re-engineering of the microcontroller on the UPS.  
However, most serial-over-USB protocols do not follow the USB ACM  
serial specification, but instead present themselves as HID devices.

More advanced UPSes also present themselves as HID devices, but they  
follow the HID PDC specification, which is different from the typical  
USB-over-HID devices.

> When I plug the device in I get a /dev/hiddev0 file - and yet the  
> usbhid-ups driver will not work with this protocol. It may be a  
> missinformed shot in the dark - but is hiddev claiming the device  
> when it shouldn't be?

In general, the hiddev driver will try and claim both serial-over-USB  
and PDC HID devices, simply because their interface descriptor  
mentions the HID class. (MGE UPSes are listed in a special-case table  
since the original hiddev driver could not handle the nested report  
structure that the PDC spec requires, so they are not claimed by  
hiddev.)

One of the first things that tripplite_usb and usbhid-ups will do is  
detach the hiddev driver. At this point, if you are using devfs or  
udev, the /dev/hiddev* node should disappear. (The NUT drivers mostly  
use libusb for portable access to HID devices, and hiddev is a Linux- 
only interface.)

> And for future job's should I be looking for an MGE UPS?? It seems  
> they have been highly reccomended here.


Tripp Lite does not publish details about their proprietary USB  
protocol. APC, CyberPower and Liebert seem to follow the HID PDC  
standard, with a few non-standard extensions. MGE not only follows  
the HID PDC standard, but has provided ample development support to  
the NUT project in various forms.

I think it's important to know why MGE is recommended. There are  
certainly use cases where you don't need monitoring capability - just  
something to get you past the occasional brownout or momentary  
outage. In that case, you might not be able to justify a higher-end UPS.

-- 
Charles Lepple
clepple at gmail



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