Lpc2000

At 08:10 AM 2/27/06 +0000, gvnn77 wrote:
>--- In lpc2000@yahoogroups.com, Robert Adsett <subscriptions@...>
>wrote:
> >
> > At 08:05 AM 2/23/06 +0000, gvnn77 wrote:
> > >--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@> wrote:
> > > >
> > > > > I am not able to understand why
> > > > >
> > > > > T0MR0 += L_COMPAREMATCH;
> > > > >
> >
> > Have you verified your interrupt latency yet? See my earlier post
>if not.
> >
> > Like Joel I'm using similar code w/o any issues.  I really think
>you need
> > to verify that your interrupt latency is reasonable.  If you
>latency is
> >
>
>Hi,
>about interrupt latency, I tried to set L_COMPAREMATCH as big as my
>tick will be greater than 1 millisecond without interesting result.
>And I think that my interrupt latency is smaller than 1 millsecond...
>What do you think?

I think you need to measure it if possible.  It's quite possible to get 
latencies all the way up to infinity.  You can get an infinite latency by 
ending up in an infinite loop with interrupts disabled or by turning off 
the interrupt source.  I can certainly imagine errors that could give you a 
latency > 1mS. Even if you end up not having an latency issue knowing what 
your latency is and how it varies is useful.  A few minutes looking at the 
waveforms from such a measurement can yield a lot of insight into what's 
going on.

In the really hard cases tracking this sort of thing down you want to use 
the waveforms used to measure latency to trigger a trace unit of some sort 
so that you can look at the last ms or so worth on instructions.  Hopefully 
you don't need that kind of horsepower.

Latency might not be the issue but without doing some sort of measurement 
of it you just don't know.

BTW a simple check in your interrupt to raise a flag if the timer is beyond 
your match point would give you some check on this as well.  It's not 
foolproof but it's something.

Robert

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