Just in case:

At 11:59 a.m. 10/10/2003, you wrote:
>Good day to all:
>
>I'm planing to work with multitasking on a PIC 16F877A, I found a lot of
>useful help in PICLIST site, I'm a attaching a code I found there, it works
>really well for two task, does anybody know how to expand it to more
>tasks??? I was trying, but I can't figure it out how... any help will be
>apreciate!!!
>
>Thanks in advance,
>
>Gonzalo

; RAM to bookmark current location in each task.
context equ 0x20
temp equ 0x77

; ``switch'' overwrites the W register.
switch   macro continuation_lable
         retlw ((continuation_lable)-task_table_start) ; return pointer to
where to continue task
         endm

power_on_setup:
         ; ...
         movlw (t1_1 - task_table_start) ; note task1_offset1 will run first
         movwf context
         movlw (t2_1 - task_table_start)

         ; task switcher
         call $+2                ; make a place for 'switch' to return to
         goto $-1                ; (i.e. here!)

         ;context_switcher:
         ; Swapping code optimized for 2 tasks.
         ; Code to handle 3 or more tasks
         ; would probably be much easier to understand.
         xorwf  context,w
         xorwf  context,f
         xorwf  context,w
         addwf  PCL,f

task_table_start:
t1_1 goto   task1_offset1
t1_2 goto   task1_offset2
t1_3 goto   task1_offset3

t2_1 goto   task2_offset1
t2_2 goto   task2_offset2
t2_3 goto   task2_offset3

task1
         NOP
         NOP
         switch task1_offset1

task1_offset1
         NOP
         NOP
         NOP

         switch task1_offset2

task1_offset2
;        fcall input_stuff
         NOP

         movwf temp
;        fcall get_mask
         NOP

         andwf temp

;       fcall output_stuff
         NOP

         switch task1_offset3

task1_offset3
         NOP
         NOP

         ; select the address at which the task
         ; will next begin executing.
         ; this is very tricky.
;        btfss condition,condition_bit
;         switch(task1_offset2)
;        switch(task1_offset3)
;task1_offset3

         goto task1


task2
         NOP
         NOP

         switch task2_offset1
task2_offset1
         NOP
         NOP
         NOP

         switch task2_offset2
task2_offset2
         NOP
         NOP
         NOP
         NOP

         switch task2_offset3
task2_offset3
         NOP
         NOP
         goto task2


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