PIC 18C Microcontoller Program Flow Method

Co-routines/tasks Allows all cocalls

Bob Ammerman [rammerman at prodigy.net] of RAm Systems says

The PIC18Cxx2 chips contain quite a few nice new features. One of the neatest is programmable access to the stack. This feature allows many powerful tricks.

Notes:

1. this code has _NOT_ been tested!
2. all multi-byte values are little-endian
3. I assume the code space never exceeds 16 bits worth (which it never will on the 242, 252, 442 or 452 chips).

 Co-routines/tasks version 2
 Allows cocalls from subroutines.
 Works by allocating parts of the stack space to each coroutine/task.
Note: limits the available stack depth for each task. There is no checking
if one task overruns anothers stack!
 CBLOCK
 TASKX_SP ; STKPTR for task X
 TASKY_SP ; STKPTR for task Y
 ENDC
initialize:
 ; initialize values for all but the first task
 movlw 16 ; start tasky's stack at level 16
 movwf TASKY_SP,A
 movwf STKPTR,A
 movlw low(tasky)
 movwf TOSL,A
 movlw high(tasky)
 movwf TOSH,A
 clrf STKPTR,A ; back to first task's stack area
 ...fall thru into first task...
taskx:
 .
 .
 .
 rcall x_cocall_y
 .
 .
 rcall x_cocall_y
 .
 bra taskx
x_cocall_y:
 movff STKPTR,TASKX_SP
 movff TASKY_SP,STKPTR
 return
tasky:
 .
 .
 .
 rcall y_cocall_x
 .
 .
 rcall y_cocall_x
 .
 bra tasky
y_cocall_x:
 movff STKPTR,TASKY_SP
 movff TASKX_SP,STKPTR
 return

.