Lpc2000

Guillermo,

This is pretty much what we do - see message 12622.

I can confirm that (a) it works! and (b) it's pretty messy to get 
exactly right, and (c) it consumes a fair amount of MIPS in what's a 
MIPS-hungry system (it's fine if you're not doing much else). You 
have to be careful to have the 1st timer fire with enough time to 
take into account the worst-case interrupt latency (which is quite 
long).

By the way, I'd be curious to know how the instigator of this thread 
is getting on with these various suggestions.

Brendan

--- In lpc2000@yahoogroups.com, "Guillermo Prandi" 
<yahoo.messenger@m...> wrote:
>
> Perhaps a combination of IRQ/FIQ can be used?
> 
> Let's say FIQs are enabled inside IRQs. Then, one could set TIMER1 
> with two match registers: "some time before" (e.g. at 80 µS for 11 
> KHz) and "exactly" (at 90.9µS). Then, when the first interrupt is 
> caught, make TIMER1 generate FIQs instead of IRQs and enter idle 
> mode. Switch to IRQ afterwards. This way one can ensure that the 
FIQ 
> is always served from idle mode. Of course this too uses too much 
CPU 
> resources. A hardware solution is preferable.
> 
> Guille
> 
> --- In lpc2000@yahoogroups.com, "Rob Jansen" <rob@m...> wrote:
> >
> > Brendan,
> > 
> > > I've pointed this out to Philips in the past: hopefully, they'll
> > > recognise from this that others have the same issue.
> > >
> > > None of the work-arounds presented are ideal: a h/w fix is much 
> more
> > > preferable.
> > 
> > Just thought of this when I saw "h/w fix" ...
> > That is the easy solution, use a sample&hold replaces the variable
> > software latencies with a fixed HW one.
> > Have an interrupt and a match output generated by the timer. On a 
> match
> > trigger the S&H and write to the DAC from the interrupt routine.
> > This will introduce a delay of 1 sample time but I don't think 
> that's a
> > big problem in this case.
> > 
> > A S&H can be easy: one gate of a CD4066 and a capacitor do the 
> trick.
> > Use the other 3 and some more caps to create a switched capacitor 
> filter :o)
> > 
> > Regards,
> > 
> >       Rob
> >
>