> Just browing around the piclist.com site a little.. According to
> http://www.sxlist.com/techref/microchip/multitasking.htm pre-emptive
> multitasking on a p16 core is not likely possible.
> 
> However, I think that it should be able to be done, because, if I were
> to setup an interrupt to be every X cycles, and have a state variables
> for each task, in the interrupt I would be able to save the state of
> status and w, and goto to the next routine. Say the tasks are 1,2,3..
> step 0: Begin running routine 1
> step 1: Interrupt routine 1, goto routine 2,
> step 2: Interrupt routine 2, goto routine 3,
> step 3: Interrupt routine 3, goto routine 1,
> step 4: Interrupt routine 1, return to routine 3,
> step 5: Interrupt routine 3, return to routine 2,
> step 6: Interrupt routine 2, return to routine 1,
> step 7: repeat from step 1.
> 
> Granted, this limits the call depth, but it should work nonetheless. 
> The routines would receive equal amounts of time per second, but not
> the same position in time.. Like this: 123 132 123 132, they are out
> of sequence, for lack of a better explanation.

Nice idea, but it still has some problems: 
- when in step 1 you 'goto routine 2' in all but the first cycle, how do
you know where in the code you must start?
- how do you deal with routine 2 calling other routines and being
interrupted when such a called routine was executing?

If you go for the easy approach: each routine must run up to a fixed
point (so you know it was not executing a subroutine, and you know where
it was) you have reduced your multitasking to a set of finite-state
machines, which can indeed be done on a 14-bit core. Google 'pic
pumpkin'.

Wouter van Ooijen

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