Two real time tasks?

I have a question concerning running two real time tasks at once. 
I've created two such tasks, one running every 250 microseconds, and 
one every 10 millieconds. For testing purposes, I have each test turn 
a parallel port line on when the task starts to run, and off just 
before it goes back to sleep. Viewing the two outputs on a scope, 
everything looks fine.

But, if the slower task takes longer than 250 microseconds to run 
(actually the problem happens before then), it is not pre-empted to 
allow the faster task to run. Instead, once it is done, the faster 
task runs, and then the next instance of the faster task runs 
earlier, presumably so that the average execution rate remains 250 
microseconds.

Is there anything I can do to have execution of the slower task 
halted to allow the faster task to run at the correct time, and then 
return to the slower task when the faster task is finished?

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Chris Smolinski
Black Cat Systems
http://www.blackcatsystems.com
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