Hi Gabor,
[EMAIL PROTECTED] wrote:
>
>
> Personally I think the concept of "interrupt routines are pseudo-threads
> with random priority" is not fortunate enough.
>
> Did I misunderstand something? AFAIK when an interrupt occurs
> its handler is started as an implicit thread inheriting its priority
> from the interrupted thread. The most possible interrupted thread is
> the the Linux itself which has minus infinite priority. That means
> that an ISR will run probably the lowest priority.
>
No, this is not a good assumption. Classically, an interrupt handler has
a *hardware* priority, this is unrelated to the concept of the priority
of threads. Usually, when an interrupt occurs, it interrrupts whatever
is running provided that a) interrupts are enabled, b) if currently in
an ISR, the hardware priority of the new interrupt is higher than the
current interrupt priority (implementation is architecture dependant).
This is why you should picture interrupts in a separate way to thread
priority. Thread priority is implemented purely by the software
scheduler (it decides which thread should run based on data in a
per-thread structure).
Regards, Stuart
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