question about preemption

Joel Sherrill <> joel.sherrill at
Thu Sep 16 12:49:48 UTC 2004

Eugeny S. Mints wrote:
> Hi Manuel,
> Manuel Pedro Coutinho wrote:
>> Hi
>> I would like to know if a task which is in a system call (like an 
>> device driver call) can be preempted
>> in the RTEMS
> RTMES in not Linux:)) First of all there are no "kernel"
> and "user" mode in RTEMS. Thus there is no such concept as
> "system call" similar to Linux.  RTEMS  uses preempting scheduling based 
> on priorites
> what means that if a task gets ready and it's priority is higher than 
> priority of currently running task, current
> task is preempted (the only exception is if preemption is explicitly 
> disabled).

Nice description.  It is permissible and commonly required for
drivers to temporarily disable preemption or interrupts to
perform some task atomically.  The rule of thumb is keep the
disable period as short as possible and always restore things
to their prior state.

>         Eugeny
>> thanks
>> _________________________________________________________________
>> MSN Hotmail, o maior webmail do Brasil.

Joel Sherrill, Ph.D.             Director of Research & Development
joel at                 On-Line Applications Research
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