Event sampling for JoyWarrior24F8

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muttley
Posts: 1
Joined: Tue May 31, 2011 11:30 pm

Event sampling for JoyWarrior24F8

Post by muttley »

Hello everybody,
I'm writing a small GTK+ application to visualize traces in real time using a JW24F8 sensor on Linux.
Searching in previous posts and on internet I found different solution to interface the sensor (joystick.h, allegro...), and they all seem to work pretty fine (I can calibrate, get raw data etc....).
I notice, however, some problem regarding specific issues:
1) In blocking mode, the sensor provides samples with very irregular sampling, with lower bound of 125Hz. Why is it not fixed at 125Hz?
2) It is also not clear how the channels are multiplexed on the USB output. If I do a bufferized read, the channels sequence is pretty random.

Does someone of you guys have any clue about these?

Thanks and sorry for stressing! :)
Guido Körber
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Re: Event sampling for JoyWarrior24F8

Post by Guido Körber »

The rate at which data is read from a USB device is controlled by the host. I don't know how precise Linux is with the timing for the interrupt endpoint polling, on MacOS and Windows it is pretty accurate. Possibly there is some latency in the USB host stack involved.
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