portasm.s

FreeRTOS is a portable, open source, mini Real Time Kernel - a free to download and royalty free RTO

;/*
;	FreeRTOS.org V5.2.0 - Copyright (C) 2003-2009 Richard Barry.
;
;	This file is part of the FreeRTOS.org distribution.
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;	***************************************************************************
;	*                                                                         *
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;	* This is a concise, step by step, 'hands on' guide that describes both   *
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;	***************************************************************************
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;	1 tab == 4 spaces!
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;*/

	INCLUDE portmacro.inc

	IMPORT	vTaskSwitchContext
	IMPORT	vTaskIncrementTick

	EXPORT	vPortYieldProcessor
	EXPORT	vPortStartFirstTask
	EXPORT	vPreemptiveTick
	EXPORT	vPortYield


VICVECTADDR	EQU	0xFFFFF030
T0IR		EQU	0xE0004000
T0MATCHBIT	EQU	0x00000001

	ARM
	AREA	PORT_ASM, CODE, READONLY



;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Starting the first task is done by just restoring the context 
; setup by pxPortInitialiseStack
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
vPortStartFirstTask

	PRESERVE8

	portRESTORE_CONTEXT

vPortYield

	PRESERVE8

	SVC 0
	bx lr

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Interrupt service routine for the SWI interrupt.  The vector table is
; configured in the startup.s file.
;
; vPortYieldProcessor() is used to manually force a context switch.  The
; SWI interrupt is generated by a call to taskYIELD() or portYIELD().
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

vPortYieldProcessor

	PRESERVE8

	; Within an IRQ ISR the link register has an offset from the true return 
	; address, but an SWI ISR does not.  Add the offset manually so the same 
	; ISR return code can be used in both cases.
	ADD	LR, LR, #4

	; Perform the context switch.
	portSAVE_CONTEXT					; Save current task context				
	LDR R0, =vTaskSwitchContext			; Get the address of the context switch function
	MOV LR, PC							; Store the return address
	BX	R0								; Call the contedxt switch function
	portRESTORE_CONTEXT					; restore the context of the selected task	



;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Interrupt service routine for preemptive scheduler tick timer
; Only used if portUSE_PREEMPTION is set to 1 in portmacro.h
;
; Uses timer 0 of LPC21XX Family
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;	

vPreemptiveTick

	PRESERVE8

	portSAVE_CONTEXT					; Save the context of the current task.	

	LDR R0, =vTaskIncrementTick			; Increment the tick count.  
	MOV LR, PC							; This may make a delayed task ready
	BX R0								; to run.
	
	LDR R0, =vTaskSwitchContext			; Find the highest priority task that 
	MOV LR, PC							; is ready to run.
	BX R0
	
	MOV R0, #T0MATCHBIT					; Clear the timer event
	LDR R1, =T0IR
	STR R0, [R1] 

	LDR	R0, =VICVECTADDR				; Acknowledge the interrupt	
	STR	R0,[R0]

	portRESTORE_CONTEXT					; Restore the context of the highest 
										; priority task that is ready to run.
	END