;
;	File:		DeferredTaskMgr.a
;
;	Contains:	Deferred Task Manager
;
;	Written by:	Gary Davidian
;
;	Copyright:	© 1986-1993 by Apple Computer, Inc.  All rights reserved.
;
;	Change History (most recent first):
;
;	   <SM6>	10/14/93	pdw		Removing DTInstallHead routine - no longer needed and certainly
;									not wanted.
;	   <SM5>	 9/12/93	pdw		Added DTInstallHead routine.
;	   <SM4>	 4/11/93	chp		Modify DTInstall to run the specified task immediately if all
;									interrupts are already enabled and neither deferred tasks nor
;									VBL tasks are currently executing.
;	   <SM3>	 12/4/92	SWC		Moved InitDTQueue here from StartInit.a.
;	   <SM2>	 5/21/92	kc		Append "Trap" to the names of DTInstall,Enqueue and Dequeue to
;									avoid name conflict with the glue.
;	   <1.2>	  3/6/89	GGD		Moved DisptchTsk from InterruptHandlers.a to DeferredTaskMgr.a
;									Re-Wrote DisptchTsk to remove windows where higher priority
;									interrupts doing DTinstall might be forgotten until the next
;									interrupt. Modified DTInstall to optimize for the success path.
;

;
;	This file contains the core routines pertaining to the Deferred Task Manager.
;
;	The purpose of these routines is to allow lengthy interrupt tasks to be deferred
;	until all interrupts can be enabled. The interrupt handlers check the status of
;	the deferred task queue every time before exiting and dispatch queue tasks if the
;	interrupt mask is about to be restored to zero (all interrupts enabled).
;
;	DTINSTALL installs a routine into the deferred task queue. There is one queue
;	maintained for all interrupt levels. A low memory variable,	DTQueue, contains
;	the queue header.
;
;	Tasks are removed from the queue automatically before they are dispatched by a
;	routine in the interrupt handling code.
;
;	  written by Rich Castro	23-November-86
;	  re-written by Gary Davidian	4-March-89
;

			PRINT		PUSH, ON
			LOAD		'StandardEqu.d'
			INCLUDE		'HardwarePrivateEqu.a'
			PRINT		POP

			MACHINE		MC68020


DTCORE	 	PROC	EXPORT	

			EXPORT	InitDTQueue, DTInstallTrap, DisptchTsk, vDisptch
			IMPORT	InitQueue, ENQUEUETRAP, DEQUEUETRAP


;_______________________________________________________________________
;
; Routine:		InitDTQueue
;
; Arguments:	none
;
; Function:		called by the system init sequence in StartInit to
;				initialize the Deferred Task Manager queue
;
; Registers Used: A1
;_______________________________________________________________________

InitDTQueue	LEA		DTQueue,A1						; init deferred task queue
			BSR.L	InitQueue						; go do it
			LEA		DTInstallTrap,A1				; get ptr to deferred task install routine
			MOVE.L	A1,jDTInstall					; and init jump vector to it
			RTS


;_______________________________________________________________________
;
; Routine:		DTINSTALL
;
; Arguments:	A0 (input) :	address of deferred task queue element
;				D0 (output):	error code -	0  no error
;												-2 invalid queue element
;
; Function: 	Installs a deferred task queue element into the deferred
;				task queue pointed to by the low memory QHdr DTQueue.
;
;				Format of the deferred task queue element is:
;
;				DTLink		Link to next queue element (pointer)
;				DTType		element ID (word = DTQType)
;				DTFlags		optional flags (word)
;				DTAddr		address of deferred task routine (pointer)
;				DTParm		optional A1 parameter (long)
;				DTReservd	reserved for future use (long)
;
; Registers Used: D0,A1
;_______________________________________________________________________

DTInstallTrap
				CMP.W 	#DTQType,DTType(A0)		; is it the proper type?
				BNE.S	TypeErr				; return error if not
				LEA		DTQueue,A1				; get ptr to queue
				JSR		ENQUEUETRAP				; go add element

;	If a task is installed in the deferred task queue by non-interrupt code,				<LW2>
;	it normally just sits there until an arbitrary time later when a system
;	interrupt occurs and causes it to be executed. This patch checks to see if
;	the interrupt mask is already zero and dispatches deferred tasks immediately
;	if it can.
goToIt
				MOVE	SR,D0
				ANDI.W	#$0700,D0				; test interrupt mask
				BNE.S	@Defer					; if all interrupts are enabled:
				MOVEM.L	A0-A3/D1-D3,-(SP)		; save regs normally saved by int handler
				JSR		([jDisptch])			; dispatch deferred tasks immediately
				MOVEM.L	(SP)+,A0-A3/D1-D3
				ANDI.W	#$F8FF,SR				; reenable interrupts (disabled by dispatcher)
@Defer

				MOVEQ.L	#noErr,D0				; no errors
				RTS								; return to caller

TypeErr			MOVEQ.L	#VTypErr,D0 			; else flag the error
				RTS								; and return with error code in D0

				
;______________________________________________________________________
;
; Dispatch routine for deferred tasks. This routine checks the deferred
; task queue and removes and executes all tasks found. Regs D0-D3
; and A0-A3 are saved prior to call.
;
;______________________________________________________________________

DisptchTsk		MOVE.L	jDisptch,-(SP)			; get jump vector
				RTS								; and use it
				
vDisptch		BTST.B	#INVBL,QFLAGS+VBLQUEUE 	; doing VBL tasks?
				BNE.S	@Exit					; if so, keep deferring
				BSET.B	#InDTQ,DTQFlags			; already in dispatcher?
				BEQ.S	@DspStart				; check the queue if not
@Exit			RTS								; otherwise exit

@DspLoop		MOVEA.L	D0,A0					; else setup ptr for use
				LEA		DTQueue,A1				; get ptr to queue
				JSR		DEQUEUETRAP				; dequeue task to be executed
				MOVEA.L	DTAddr(A0),A2			; get ptr to first task
				MOVEA.L	DTParm(A0),A1			; get optional parameter
				ANDI.W	#$F8FF,SR				; enable all ints
				JSR		(A2)					; and go do task
@DspStart		ORI.W	#HiIntMask,SR			; disable all ints
				MOVE.L	DTskQHdr,D0				; get queue head
				BNE.S	@DspLoop				; loop if tasks	exist
				
				BCLR.B	#InDTQ,DTQFlags			; clear indicator
				RTS								; and exit


				END