My guess is your at close to the expected rate; based on those numbers.
100 Hz, 133 Hz, and 200 Hz are some common sample rates used by
digitizers. If I recall correctly, Microsoft established 133 Hz as minimum.
The alternating 8/12ms is throwing me so I'm not sure if your HW is trying
for 100 Hz or 133 Hz. Googling "thinkpad tablet 133 pps" turns up more
hits than value of 100 so I assume it probably should be 8ms consistently.
So you might be able to find 2-3ms savings on kernel side somewhere. I
don't have any guesses were that'd come from.
If I recall correctly, the Intuous tablets can be set to 100, 133, or 200
sample rates and then send at that fixed rate; with all other tablets
sending at 1 fixed sample rate in that 133 Hz range.
If your window drags really feel off then I suspect there are improvements
to be made outside kernel.
Chris
On Sun, Jan 13, 2013 at 1:38 AM, Bobby Powers <bobbypow...@gmail.com> wrote:
> Hi folks,
>
> I've recently acquired a Thinkpad x230t, which has a Wacom touchscreen
> (vendor/product: 056a:00e6).
>
> When moving my finger around quickly on the screen (especially evident
> when dragging a window around in X) there is a noticeable lag. I
> added some debugging statements in wacom_wac.c:wacom_tpc_mt_touch()
> and verified that the lag is visible at the kernel level, rather than
> being some X vsync artifact or something.
>
> I then noticed that my debugging printk's were being called every 8 or
> 12 milliseconds, alternating:
> [14265.968153 < 0.011958>] wacom 2-1.5:1.1: wacom_tpc_mt_touch: x:
> 1580, y: 783
> [14265.976128 < 0.007975>] wacom 2-1.5:1.1: wacom_tpc_mt_touch: x:
> 1589, y: 790
> [14265.988148 < 0.012020>] wacom 2-1.5:1.1: wacom_tpc_mt_touch: x:
> 1599, y: 798
> [14265.996128 < 0.007980>] wacom 2-1.5:1.1: wacom_tpc_mt_touch: x:
> 1610, y: 806
> [14266.008023 < 0.011895>] wacom 2-1.5:1.1: wacom_tpc_mt_touch: x:
> 1622, y: 814
> [14266.016000 < 0.007977>] wacom 2-1.5:1.1: wacom_tpc_mt_touch: x:
> 1633, y: 822
> [14266.027994 < 0.011994>] wacom 2-1.5:1.1: wacom_tpc_mt_touch: x:
> 1645, y: 831
>
> (`dmesg -d` is what reports the delta)
>
> It seems like others have reported similar[1]. The endpoint interval
> for the Finger interface is 5 frames, which I believe translates to 5
> ms (I'm new to the USB stack, please correct any errors I have!):
>
> [13496.745718] wacom: endpoint interval: 7
> [13496.745784] input: Wacom ISDv4 E6 Pen
> /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.5/2-1.5:1.0/input/input38
> [13496.750724] wacom: endpoint interval: 5
> [13496.750815] input: Wacom ISDv4 E6 Finger as
> /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.5/2-1.5:1.1/input/input39
>
>
> And I see the wacom driver initializes a single URB, which re-submits
> itself at the end of it's callback, which seems to be the common
> idiom.
>
> I guess I'm looking to see if there is anything I can do to try to get
> data faster/with less lag from the device (can I try manually
> decreasing endpoint->bInterval, or will that just cause
> instability/Bad Things?), or how I would debug this in a better way.
> Let me know what additional data I can provide as well.
>
> thanks!
>
> yours,
> Bobby
>
>
> 1 -
> http://old.nabble.com/Pen-Cursor-lag-on-Wacom-on-Asus-Slate-ep121-to32360422.html
>
>
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