Retropie: how frequently a USB joystick is polled? Developing new encoder

[robca]

I just started writing a usb joystick/spinner encoder using a Blue Pill STM32 board. The board will present itself to the system as a composite USB device, with a joystick and a mouse profile. The joystick profile will take care of scanning the joystick and buttons, and the mouse profile will send position changes based on an optical encoder output.

I'm trying to figure out what's the ideal cycle to send USB updates to the system. With an oscilloscope I looked at the debouncing requirements for the switches, and I saw that good Happ style buttons with a decent microswitch only bounce for 2-3 msec, while cheap, crappy Sanwa style buttons sold as kits from China can easily have bounces for 50+ msec (yeas, I was really surprised by how bad those were).

So the longer I can debounce, the better, but I also want to introduce minimal delay. I know that the commonly available DragonRise zero delay usb encoder says "zero delay", but I'm assuming it will still send data via USB at a max data rate. Ideally I'd like to get to the same level of short latency and high data rate.

Does anyone know what data rates are common for USB joysticks and various retroarch cores?

[mitu]

(not an expert on these things) This wiki page might be useful to understand how the polling works for mice and how you can measure the device speed (via evhz). The page talks how the mouse polling rate can be tuned, via themousepoll module parameter, and a similar parameter exists for joypads - jspoll - , so some of the methods used to tune/measure could apply to joysticks also.

[robca]

Thanks! I did a lot of searches, but didn't think about looking for "polling", which seems to be the keyword for searches related to my issue.

I'll look into this some more and see if I find anything worth sharing.

[robca]

I just confirmed that evhz https://gitlab.com/iankelling/evhz also shows polling rates for joystick, no just mouse and keyboard. And, as expected, the RPi4 in default configuration is polling every 8msec, i.e. 125Hz.

That gives me a good starting point to shoot for (pun intended)

[robca]

Actually it turns out that evhz gets seriously confused with a HID composite device mouse+joystick sending data at high rates. sometimes I read actual values, sometimes very slow updates

I can find many mouse rate tester apps, but nothing for USB joysticks. Does anyone know of a utility for joysticks similar to mouserate?