From: Harold Hallikainen <harold@mai.hallikainen.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Wed, 17 Feb 2021 19:03:53 -0800
Subject: Re: [EE]:: Simple Task Scheduler written in C
Thread-Topic: [EE]:: Simple Task Scheduler written in C
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Reminds me of something I wrote a LONG time ago!

http://www.piclist.com/techref/microchip/language/c/MultiTask.c.htm

Harold


>
> oops! hit the wrong key :-)
>
> here's the code:
>
>  	.data
>
> alt_task_pc:	.dsw	1
> tmp_bl:		.dsw	1
>
> yield	.macro	arg
>
>  	movf	arg+0,w
>  	movwf	tmp_bl+0
>  	movf	arg+1,w
>  	movwf	tmp_bl+1
>
> ; <<<< 	this is the really really important trick!!!
> ;	use the assembler to generate the return address
> ;	not an instruction such as "call"
>
>  	movlw	($+8) & 0xff		; low (addr of "lab9")
>  	movwf	arg+0
>  	movlw	(($+8) >> 8) & 0xff	; high (addr of "lab9")
>  	movwf	arg+1
>
>  	movf	tmp_bl+1,w
>  	movwf	PCLATH
>  	movf	tmp_bl+0,w
>  	movwf	PCL
>
> ; lab9
>
>  	.endm
>
>
> new_task .macro	arg1, arg2
>
>  	movlw	(arg2) & 0xff		; low (addr of "task")
>  	movwf	arg1+0
>  	movlw	((arg2) >> 8) & 0xff	; high (addr of "task")
>  	movwf	arg1+1
>
>  	.endm
>
> ;=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
> ; example of use
>
>  	.code
>
> main:
>  	new_task alt_task_pc, task2
>
> lab1_1:
>
>  	; do task1 stuff
>
>  	yield	alt_task_pc
>
>  	; do more task2 stuff
>
>  	yield	alt_task_pc
>
>  	goto lab1
>
> ;=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
> task2:
>
> lab2_1
>  	; do task2 stuff
>
>  	yield	alt_task_pc
>
>  	; do more task2 stuff
>
>  	yield	alt_task_pc
>
>  	goto lab2_1
>
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>


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