> interrupt:
>     save STATUS to primary save area
>     save PCLATH to primary save area
>     set PCLATH to zero
>     is it the high priority interrupt ?
>       YES:
>         save additional stuff, like FSR perhaps to primary area
>         handle the interrupt
>         restore state from primary save area
>         RETFIE
>       NO:
>         move saved STATUS, PCLATH to secondary save area
>         save additional stuff, like FSR perhaps to secondary area
>         determine which interrupt it is and jump to handler routine
>       END
>
> Each low priority interrupt handler routine:
>     clear the interrupt condition
>     re-enble interrupts
>     handle the interrupt
>     goto restore_low_priority_interrupt
>
> restore_low_priority_interrupt:
>     restore additional stuff like FSR from secondary save area
>     restore PCLATH and STATUS from secondary save area
>     RETURN

I just read my earlier response and realized that this is wrong.  You do
need a separate save area for each low priority interrupt, since a low
priority interrupt could be interrupted by another low priority interrupt in
this scheme.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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