Lpc2000

Hi
I don't know if anyone else has seen this but its driving me nuts.
I have timer1 on a 40uS interval triggering an FIQ. (All the FIQ 
does is toggle an IO pin and exit.) No other interrupts are active.

In practice the leading edge of the pulse produced on the IO pin 
jitters by around 230nS to 280nS around the 40uS interval.

The really wierd thing is if I change the main code routine, ie add 
lines or comment things out, the extent of the jitter changes. In 
fact if I pad my code out with some 'asm{nop;}' by trial and error I 
can get rid of the jitter completely.

Whilst the FIQ is active the rest of the code is in a loop. At 
present, just checking for a flag to change state.

I need this pulse to be as accurate as possible, a few nS jitter at 
most. If anyone can shed some light on this I would be very grateful.

I am using the latest Keil beta release of their compiler. The 
device is an LPC2294, cclk=60MHz and pcklk=cclk/2

many thanks
Simon