[systemd-bugs] [Bug 87435] hwdb: Logitech, Inc. RX 250 Optical Mouse DPI data (older model)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87435

--- Comment #7 from Peter Hutterer <peter.hutterer at who-t.net> ---
(In reply to Thomas H.P. Andersen from comment #6)
> That sounds reasonable. I was working on a patch for mouse-dpi-tool to show
> the frequencies in a histogram. If we only really need the max frequency
> then current code is fine. In my testing the mouse would use 142.9Hz ~90% of
> the time. I could not find any specific steps to trigger the higher or lower
> frequencies. I guess the user just has to move the mouse for a while and
> hope we have found the max?

pretty much. I don't know what the devices employ for frequency scaling - is it
lots of little movements, lots of large movements? I honestly don't know. You
can still do the frequency patch if you want though, it may be useful.

> For all the mice I tested I was able to find an advertised dpi on the
> internet. I just tested that I could get reasonably close to that dpi with
> your tool and then used the advertised value. Does that make sense?

definitely. with high enough dpis a slight erratic movement or measurement
error can quickly result in odd numbers, so if the manufacturer says 1000dpi
and you measure in the 900-1100 range then I'd say go with the advertised one.
There's other factors involved too, if the surface isn't perfect you may not
get the exact reading even if you move the right distance, etc.


> Nitpick: the tool truncates the frequency when creating the hwdb entry. So
> for 142.9Hz it will use xxx at 142.

I didn't think we needed floating point frequencies tbh and I'm still not
convinced that we do. Rounding otoh would be useful I guess.

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