> Only high priority interrupts are in use, so from what I've read that
> means that the appropriate registers get backed up automatically. The

If things hasn't changed, the compiler only saves "a basic context"
(see section 3.4 of the compiler's manual for a complete list), but
for some weird reason it does not consider some registers as PROD,
TBLPTR,...,  part of the "basic ones", although it uses them at its
wild as temporally variables. So you end catched by corrupting them
inadvertely.

If my memory doesn't leak, the < save = section ("MATH_DATA") > option
will instruct the compiler to save all them.

> Another related question.... is it safe to modify variables from an
> interrupt that are being used in the mainline? Is there any point at
> which an undesired value could exist in the register? My interrupt runs

It depends ...

> a matrix keyboard/LED scanning routine on a timer so that the LEDs are
> multiplexed properly. The keyboard data is read in the interrupt and
> processed (for debouncing, etc.) in the mainline. But this sometimes
> causes erroneous behaviour.

 ... how you implement it.


Oscar

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