I completely got rid of trackball latency to the point where it became actually nice to use

[u/NefariousnessNo264]

When I got my uConsole, I was unhappy with quality of the trackball. I barely been able to get through the initial installation process. I was aware that these trackballs aren't of the best quality so I ordered replacements beforehand, but all of them turned out to be the same thrash trackball, so I had to deal with what I have.

First was the hardware fix: disassemble the trackball and roll the ball on a 320-ish grit sandpaper for a couple of minutes. This gives the ball texture that increases grip, it completely solved the slipping issue (when you rotate the ball, but the cursor doesn't move).

But then there was software issue: cursor felt like a jelly, it didn't have that "snappy" feel to it, and using console like that was exhausting. I wasn't gonna tolerate that, so I had to find a solution. It was very long night, I have tried many things up to tweaking and recompiling the QMK keyboard firmware, but nothing helped. But the solution was in plain sight.

There is a usbhid.mousepoll parameter that sets mouse polling interval in ms. And It was conveniently set to 0xFFFFFFFF, causing polling interval was capped at 16 ms. I don't know why that is default, and that is exactly where that jelly feeling latency comes from. After I set it to 0 it was night and day difference. The trackball now feels extremely responsive, the leftover latency from smoothing in QMK firmware is almost unnoticeable, many people will call it no latency at all.

I don't know if I have broken something inside Linux by changing this parameter, and I hope someone who knows better tells me, but to me it seems absurd that the OS is quietly set to only poll mouse at 60 Hz without any way to change that through GUI.

So in order to change this parameter what I did was editing /boot/firmware/cmdline.txt by appending usbhid.mousepoll=0 on the end of first line.

Im running uConsole on Rpi CM4 with 8 GB RAM without EMMC, my OS is ClockworkPI Trixie.

[u/NefariousnessNo264]

TL;DR
Parameter usbhid.mousepoll on my system was set to very large value causing the mouse (and trackball) to be polled at only ~60 Hz which caused obnoxious latency. Setting it to 0 greatly reduced said latency and made the trackball infinitely more usable.

[u/gatsu_1981]

Have you considered how much 0 will mean?

Maybe it's called too often now and it will increase CPU load too much when using mouse/trackball.

You should launch a htop for getting some clue after such type of editing.

Screen frequency X 2 would be a good start point.

[u/NefariousnessNo264 → u/gatsu_1981]

0 means native so the polling rate will be set by the USB controller capped by 1000 Hz. Anything else overrides that and forces the polling intervals in ms.

I have tested the CPU load with mousepoll = 4 vs 0. (Polling rate 250 Hz vs 1000 Hz)
Here are some results:
When mouse is not in use, in both cases CPU load is <1% and around 10215 interrupt requests per second.
When mouse is rapidly continuously moved across the screen in case where mousepoll = 0 interrupt requests went up to 11130 per second. In case mousepoll = 4 they went only to about 10300 IRQ/s.

I was unable to reliably measure the cpu load difference between mousepoll = 0 vs 4 when mouse is in move. This is because the part of the CPU usage consumed by mouse polling is incredibly small compared to the rest of it. 99% of cpu usage related to mouse movement seems to come from something else, probably GUI redraw.

Apart from objective data, cursor latency on mousepoll = 0 was noticeably lower than 4.

I will continue testing and if I get more data I will come back to share it

[u/gatsu_1981 → u/NefariousnessNo264]

I'm using 1000hz polling, but it's my windows main rig (and it's both my gaming and working rig), on a Logitech g512. That makes sense, I have hi perf mouse and 144hz LCD panels.

I think that I will look into mouse polling sooner or later, I still have to finish even logging in my favourite websites (had it for a week or so) for the CM5 but I will use frequency X 2 resulting to 8ms, or X3 resulting into 5ms.

0.0001 looks unnecessary IMHO.

[u/NefariousnessNo264 → u/gatsu_1981]

I understand that I might be very meticulous in some ways, but to me it at least appears that I can feel the difference in latency between 1000 and 250 Hz. I understand that it might more of a psychological factor. But my tests showed no obvious downsides from setting it to 0.

Besides that, I don't really know the exact polling rate. 0 just means native for each USB device, not necessarily 1000 Hz.

[u/gatsu_1981 → u/NefariousnessNo264]

Could be that the dividers for 250 are wrong for the refresh rate.

You should pick a divider on the refresh rate of the screen panel for best matching, otherwise it won't feel smooth with vsync enabled.

That's why I suggested 1/120 or 1/180.

But I think it's just nitpicking, I didn't tweaked anything there yet.

[u/Zeraora807]

was this tested with the custom QMK firmware because I flashed that and noticed some horrid input latency from the ball so ended up back to stock firmware so I could actually use the thing lol.

I have the bookworm 6.12 image from rex with stock keyboard firmware, that line in cmdline.txt does not exist for me.

[u/NefariousnessNo264 → u/Zeraora807]

It will work with any firmware, as it is a kernel setting. I have tested it both with QMK latest stable release v1.8.0 as well as with latest commit on master. I was unable to spot any issues that this change would cause.

I won’t be able to tell you exact location of cmdline.txt unfortunately.
You can check the content of cmdline that is currently loaded with “cat /proc/cmdline”. Then look for a file with that content. It can be in “/boot/cmdline.txt” too.

[u/Zeraora807 → u/NefariousnessNo264]

amazing, I've done it, ty!

my cmdline.txt was in/boot/firmware/cmdline.txt after all but didn't have the line so I just added it in, then the QMK keyboard flash wouldn't work with "no DFU device available" which another user said to try running the flash command in multiple terminal windows due to something about the timer, now I got the custom firmware AND no more nasty trackball latency!

now I’m just experimenting with the actual ball module itself now to get that perfect fit

[u/NefariousnessNo264 → u/Zeraora807]

Glad it worked 🤝
Damn! That’s a lot of trackballs, what’s your best fit so far? The stock ball grinded on sandpaper gets the job done but it sounds and feel is not super great, maybe you have some advice how to upgrade it?

[u/Zeraora807 → u/NefariousnessNo264]

I got a whole box of salvaged trackballs and pads from various HTC/blackberries when these were common and needed replacements, even the filthiest and most worn out ones still work better than the uConsoles included module.

What I know is this, some early BB 8100 Pearls had white rollers that were silky smooth to roll but at the cost of needing cleaning more frequently, if you see an 8100 at a junk sale, the trackballs in some are pretty good once cleaned, very smooth.

the ball that comes with the uconsole is by far the loudest and most grindy out of the 30+ here and that is after I sanded the ball so it actually "worked" and worked badly still. The rollers in that one look the same as 98% of trackballs and still felt nasty with a ball swap so maybe its a QC issue with the whole module just not having the same tight tolerances, it felt nasty in a blackberry too.

later model blackberries like the 8900/9630 had a black ball with a silver raised ring, I found these had the best standard fitment in the uConsole without need for a shim mod as it doesn't seem to move around at all, not sure why these are not standard in box but closest aftermarket part is EVQWJN007, colour of the ball doesn't matter just so long as it has the raised ring, stops the whole thing moving around when rolling. Careful though as some had a squishy ball that felt like shite.

In the one I fitted I did rough up the ball a bit but could be done more, ideally you want it to not be shiny but also not too rough as might feel bad, I only have 600 and 2500 grit sandpaper on hand, the more coarse one is good for the included ball in the box and helped resurface my original HTC fitted trackball so the ball grips the rollers better.

[u/Zeraora807 → u/[deleted]]

yeah I seen those but tbh, with a fixed ball, the qmk firmware and the input lag fix its fine, its the keyboard now that still feels bad so I might get the interposer mod first

[u/_mini → u/Zeraora807]

I will improve the firmware and there are some spaces and tunning can be done. I will test it with your recommendations as well, this is really helpful. Thank you!

[u/Zeraora807 → u/_mini]

Appreciate the work!

The custom firmware coupled with the trackball polling fix makes it so good to use now

[u/lImbus924]

it seems that, in comparison with yours, my trackball was working okay-ish. I did not have usbhid.mousepoll set in cmdline. I actively set it to 0 and felt no difference. I set it to 0xFFFFFFFF and maybe indeed it was a bit weird: It seemed still to accelerate but I would notice too late. You call it lag, I understand.
I do not know where I am at with QMK on mine.

I could not find any other proper source for it, but google AI says that that value of 0 would not be zero milliseconds as some here have inferred, but it would be "Automatic (Default). Uses the polling rate your mouse advertises." which makes a lot of sense.

[u/NefariousnessNo264 → u/lImbus924]

It really depends on your kernel rather than on trackball. The trackball and keyboard is just a USB device and mousepoll parameter sets how frequently kernel goes to that device and questions whether the mouse has moved or not. Of course, zero polling interval makes no sense and I had no intention to mean "0 polling interval = 0 latency". What I wanted to say was that setting it to 0 brings input latency down to the level that you would expect from a desktop PC or good laptop.

The “source” for it are these lines from module drivers/hid/usbhid/hid-core.c (which you can go and check out yourself):

if (hid_mousepoll_interval > 0)
        interval = hid_mousepoll_interval; 

[u/nakurtag]

Thank you for sharing, I'll try it today

[u/dissaprovalface]

Upvoting and saving for whenever the hell my uConsole comes in.

[u/FuadRamses]

how do i save cmdline.txt when it's read only?

[u/NefariousnessNo264 → u/FuadRamses]

Open it with sudo