Interrupt latency problems on MPC860

[leonp]

On Wednesday 14 November 2001 22:43, you wrote:
> We are using RTEMS 4.5.0 on a 50MHz MPC860.
Our case is MPC860 at 25MHz.

> 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.
What exactly do you call 'latency'? As far as I was able to understand from 
the following posts you include the interrupt processing time into this 
figure. Am I right?
Anyway, when we measured the time between the IRQ line change and the first 
instruction been reached in the user ISR routine with oscilloscope, it was 
14micro at our 25MHz Power Quick with instructions cache 'on' and data cache 
'off'.
Also, may be you have some kind of measurement problem?

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

-- 
Dr.Leon M.Pollak
Director
PLR Information Systems Ltd.
leonp at plris.com