min/max and actual values on absolute axes

min/max and actual values on absolute axes

[Peter Hutterer]

Hi guys,

A question regarding min/max values on absolute axes of input devices. I
have a few bugreports related to the synaptics driver and the trigger for
the bug are coordinates outside the min/max range.

Example evtest output: http://bugs.freedesktop.org/attachment.cgi?id=27229

 Event type 3 (Absolute)
    Event code 0 (X)
      Value   6044
      Min     1472
      Max     5472
    Event code 1 (Y)
      Value   1261
      Min     1408
      Max     4448


>From Documentation/input/input-programming:
"This setting would be appropriate for a joystick X axis, with the minimum of
0, maximum of 255 (which the joystick *must* be able to reach, no problem if
it sometimes reports more, but it must be able to always reach the min and
max values), [...]"

Do I read this correct that min/max is intended as guideline only and cannot
be relied on for actual coordinate boundaries?

Cheers,
  Peter

Re: min/max and actual values on absolute axes

[Dmitry Torokhov]

Hi Peter,

On Tue, Jun 30, 2009 at 09:42:58AM +1000, Peter Hutterer wrote:
> Hi guys,
> 
> A question regarding min/max values on absolute axes of input devices. I
> have a few bugreports related to the synaptics driver and the trigger for
> the bug are coordinates outside the min/max range.
> 
> Example evtest output: http://bugs.freedesktop.org/attachment.cgi?id=27229
> 
>  Event type 3 (Absolute)
>     Event code 0 (X)
>       Value   6044
>       Min     1472
>       Max     5472
>     Event code 1 (Y)
>       Value   1261
>       Min     1408
>       Max     4448
> 
> 
> From Documentation/input/input-programming:
> "This setting would be appropriate for a joystick X axis, with the minimum of
> 0, maximum of 255 (which the joystick *must* be able to reach, no problem if
> it sometimes reports more, but it must be able to always reach the min and
> max values), [...]"
> 
> Do I read this correct that min/max is intended as guideline only and cannot
> be relied on for actual coordinate boundaries?
> 

That is correct. Input core does not perform any "snapping" of the
reported coordinates to the min/max boundaries, these values are
advisory only.

-- 
Dmitry