Interrupt latency problems on MPC860

[Phil Torre]

We are using RTEMS 4.5.0 on a 50MHz MPC860.  Our application relies
on a particular periodic interrupt being serviced with no more
than 78 microseconds of latency.  We keep having problems because
that interrupt isn't being serviced on time.

There's not much else going on in the system currently.  Several
tasks are asleep or blocking on I/O, but none of them should be
waking up and causing a context switch.  (We've got things really
stripped down trying to pin down the latency problem, so practically
everything but our critical interrupt is commented out.)

Is 78us of latency for maskable interrupts a reasonable goal, or is
that outside of RTEMS' performance envelope?  Any comments are welcome.

Thanks,
-Phil

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Phil Torre                               phone: 425-820-6363 x234
Design Engineer                          email: ptorre at zetron.com
Switching Systems Group                    fax: 425-820-7031
Zetron, Inc.                               web: http://www.zetron.com