On Thu, 2007-03-08 at 11:20 +0100, Steven Scholz wrote:
> Philippe Gerum wrote:
> > On Thu, 2007-03-08 at 11:08 +0100, Steven Scholz wrote:
> >> Philippe,
> >>>> using an oscilloscope I found that the AT91RM9200 spends up to 300µs in
> >>>> the
> >>>> interrupt handler for ethernet controller.
> >>>> Now I wonder if this interrupt handler will be preempted by Xenomai if
> >>>> there
> >>>> is a high priority, periodic real time task?
> >>> Hw interrupts are forcibly enabled before entering any Linux IRQ
> >>> handler, exactely to prevent the issue you described (e.g. fiddling with
> >>> an IDE controller in PIO mode also gives funky latency results unless
> >>> the latter is true), so the answer is yes.
> >> Thanks.
> >>>> Thus will the duration of the
> >>>> ethernet interrupt handler add the the worst case latency?
> >>> Not from Linux IRQ handlers; you may want to check this using the
> >>> tracer. If hw interrupts are masked there, then it's a blatant bug.
> >> How could I check this using the tracer? Small hint please?
> > http://www.xenomai.org/index.php/I-pipe:Tracer
> I know this. But I was asking how I could use it to check the above problem.
> Is "Trace IRQs-off times CONFIG_IPIPE_TRACE_IRQSOFF ... Instrument each
> disable and re-enable of hardware IRQs. This allows to identify the longest
> path in a system with IRQs disabled." the important stuff?
Yes. If the "IRQ off" marker appears when running the Linux ethernet IRQ
handler, then we have a problem.
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