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daniel5151 / surface-dial-linux

A Linux userspace controller for the Microsoft Surface Dial. Requires Linux Kernel 4.19 or higher.
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Events lag behind when using evdev_rs::ReadFlag::NORMAL #4

Closed mutwilligekartoffel closed 3 years ago

mutwilligekartoffel commented 3 years ago

Almost immediately after starting the service, input from the dial starts lagging behind.

Events are processed immediately whenever I turn the dial, but they do not match my inputs. Instead they are delayed, so rotating the dial 90° cw, then inverting direction will continue to output clockwise rotation values for a short while.

Still events will only be thrown as long as I keep turning in either direction. So there is no time delay but rather some kind of event flow impediment.

The delay is strongly noticable on a Raspberry Pi 4 and slightly less pronounced on my desktop machine.

This issue is fixed when fetching events using evdev_rs::ReadFlag::BLOCKING instead of evdev_rs::ReadFlag::NORMAL in dial_device/events.rs.

I would like to propose switching to evdev_rs::ReadFlag::BLOCKING but I have no knowledge of evdev and do not know whether the change may break stuff elsewhere.

First encountered on Raspberry Pi 4:

Less pronounced reproducable on Zen3 Desktop:

Edit: I almost forgot: You are absolutely awesome! Thank you for creating this!

daniel5151 commented 3 years ago

Thanks for the detailed report!

I just tested out evdev_rs::ReadFlag::BLOCKING on my machine, and it seems to be working fine. Personally, I can't tell the difference between the two, but then again, I've never actually tested this code on any "underpowered" devices (such as a Raspi).

... I have no knowledge of evdev and do not know whether the change may break stuff elsewhere.

Me and you both! I kinda just hacked this code together over the course of a week or two, so my knowledge of evdev (and surrounding libraries) is pretty surface-level (pardon the pun).

That said, I did quick once-over through the code that would be impacted by this change, and it looks like there shouldn't be any problems by switching to BLOCKING. I'll push up the change and close this issue.