How to clear buffer before call libevdev_next_event

[Knoppix]

Mr. Hutterer
Thank you for your kindness. (Execuse me for my english I am not native)

Indeed, the problem is I cannot figure out which data is calibration and how
much lines it will take. Sometimes when I do calibration the device gives me
20 lines garbage data but sometimes much more.
If I use 10 second sleep everything is okey but this is not good solution.

Lastly, do you know is there any way to clear device buffer with kernel's
call? I mean
I am not asking for libevdev but I am asking for different way, may you
advice me anything please? (I tried fsync, fflush, ioctl(fd, I_FLUSH,
FLUSHRW),
tcflush(fd, TCIOFLUSH) but not worked.)

Best Regards.

On Tue, Jan 15, 2019 at 1:53 AM Peter Hutterer <peter.hutterer at who-t.net>
wrote:

> On Fri, Jan 11, 2019 at 11:52:35AM +0300, Knoppix wrote:
> > Hi,
> >
> > I set some calibration/settings on input device (*turn device wheel to
> > left. I did this with write() function*) while this happens input system
> > gathers data. So when I first call libevdev_next_event it gives me old
> > garbage data. But I dont want those.
> >
> > How can I flush/clear buffered data with libevdev? Is there any way?
>
> If the device continuously sends data at a high frequency, it'll be hard
> to
> figure out exactly when the new data represents whatever you set the device
> to, so you'll need some guessed delay anyway. But the easiest way is to
> just
> discard the data coming out of libevdev until you're convinced it's within
> the new calibration range.
>
> libevdev doesn't do anything other than update a few internal states with
> the data, so if you take the libevdev_next_event() and not do anything with
> it, that event is discarded.
>
> Cheers,
>    Peter
>
>
>