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PIC 18C Microcontoller Program Flow Method

Co-routines/cooperative tasks mainline cocalls only

Bob Ammerman [rammerman at] 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.


  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/cooperative tasks version 1

Note: assumes that all cocalls are from mainline code (ie: the subroutine
stack is empty)

   TASKX_PC:2 ; Address of next instruction to run in task X
   TASKY_PC:2 ; Address of next instruction to run in task Y

  ; initialize values for all but the first task
   movlw low(tasky)
   movwf TASKY_PC,A
   movlw high(tasky)
   movwf TASKY_PC+1,A

   ...fall thru into first task...
   rcall x_cocall_y
   rcall x_cocall_y
   bra  taskx

   movff TOSL,TASKX_PC
   movff TOSH,TASKX_PC+1
   movf     TASKY_PC,W,A
   movwf  TOSL
   movf     TASKY_PC+1,W,A
   movwf   TOSH

   rcall y_cocall_x
   rcall y_cocall_x
   bra  tasky

   movff TOSL,TASKY_PC
   movff TOSH,TASKY_PC+1
   movf    TASKX_PC,W,A
   movwf TOSL
   movf    TASKX_PC+1,W,A
   movwf TOSH

file: /Techref/microchip/18c/multitask-coop1-ba.htm, 1KB, , updated: 2000/10/12 12:14, local time: 2024/7/15 04:09,

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