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timing problem with userland driver

I ported a OS9 vendor specific usb driver to X.
The OS9 version was done on a Lombard under 9.2.2. When the driver runs
it has to do repeated communication cycles with the device. In 9.2.2. on
that Lombard this went up to 60Hz.

Now I redid this driver in X. As directed I went userland.
Which works fine - except that the iceBook with double speed has timing
problems. The best measurement is 50Hz.
This would last - but when there is other action on the machine (even
things like scrolling a window) the rates go down to low as 20Hz. This
is not acceptable for my users. This device needs at least 38Hz-44Hz
stable.

If it is reliable I could use timers to fire the communications at 0.023
seconds to get something around 42Hz.

Do I need to go to the kernel to get stable cycle rates or is there a
way to tell darwin that I need more,stable , processing time. (top shows
me less 5% cpu usage).

--
Hado Hein, Berlin, Fed.Rep. of Germany

http://HadoH.bei.t-online.de (stage lighting profession)
http://www.batchmaker.de (software authoring, including stage lighting)
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