> >> @@ -98,6 +99,9 @@ struct mt_device {
> >> bool serial_maybe; /* need to check for serial protocol */
> >> bool curvalid; /* is the current contact valid? */
> >> unsigned mt_flags; /* flags to pass to input-mt */
> >> + __s32 dev_time; /* the scan time provided by the device */
> >> + unsigned long jiffies; /* the frame's jiffies */
> >> + unsigned timestamp; /* the timestamp to be sent */
> >
> > Why not just dev_time here?
>
> because max dev_time is at least 65535 according to the norm, and the
> win 8 device I have has his max value of 65535.
> Which means that every 6 seconds and a half the counter resets, and
> the value is not properly reset in the way I understand the
> specification. The device just forwards an internal clock that is
> never reset.
Ok, I though it was a 32-bit value, and that it would wrap with a
longer period. It does not change the essence of the definition,
though. If we say "seconds" instead of "hours", we should still be
fine, no?
> So if you wait 653500 us + 8ms, everything happens as if the device
> sent this frame right after the previous one (you get the same value).
Yes, but we have this effect on a 32-bit counter as well.
> I think that it's the job of the kernel to provide clean and coherent
> values through evdev, which won't be the case if the jiffies thing is
> not in place: every devices will have a different behavior, leading to
> complicate things in the user-space.
The whole point is to provide the device clock to userland when it
exists, isn't it? Thus, the jiffies would never be used. If a future
device needs additions to work conformly, we just have to deal with it
at that point in time.
To conclude, we obviously have devices with a rather short wrap-around
time. However, since the normal inter-frame time is in the millisecond
range, it should not be overly restrictive to change the definition of
the minimum wraparound time from hours to seconds.
Thanks,
Henrik
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