On Mar 23, 2014, at 11:12 PM, Bill S wrote:

> The output of the driver is below.   The incorrect voltage of 136 is
> shown at 0.265256.  It should match input voltage of 119 as shown at
> 0.265219 but it doesn't.  The voltages displayed on the UPS LCD panel
> information however are equal and match the input voltage provided by
> the driver.  There might be other incorrect values in the usbhid-ups
> output but that is the one that has caught my attention so far.

Unfortunately, there aren't many driver failure modes which would easily 
explain this value. Typical UPS firmware issues include using the wrong HID 
Usage code (the "Path:" in the debug output) or using the wrong combination of 
units and exponent so that the values are off by some power of ten.

We might get a little more insight with a higher debug level (please save the 
output to a file, and send it to the list as a gzip'd attachment), but that 
seems to be what the UPS is reporting for that value.

Another possibility is that when the UPS is in a passthrough mode, the driver 
should just copy the input voltage to the output voltage, and ignore the 
reported output voltage. I don't think this is how the USB HID PDC standard was 
intended to work, but it would probably make for a simpler implementation in 
the UPS. You would need to do a bit of testing to determine if, for instance, 
the ACPresent bit could be used for this purpose, or if it needs to be combined 
with other bits. (The UPS.Output.ff010043 path is non-standard, so maybe this 
would tell us something about this case, too.)

It might be helpful to test with a variac, and ramp the voltage up and down to 
see which bits change as the UPS goes from battery to boost to passthrough.

-- 
Charles Lepple
clepple@gmail




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