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From: d85-jmh@nada.kth.se (Jan-Olof Hendig)
Newsgroups: comp.sys.amiga.programmer
Subject: Copper mystery
Message-ID: <1991Mar27.211732.2436@kth.se>
Date: 27 Mar 91 21:17:32 GMT
Reply-To: d85-jmh@nada.kth.se (Jan-Olof Hendig)
Organization: Royal Institute of Technology, Stockholm, Sweden
Lines: 42


Here is a non amiga friendly assembler program taken from the the german
publication 'Amiga Magazin 6/90'.

	org $40000

x:
	move #4000,$dff09a ; Kill multitasking
	move.l #cop,$dff084 ; Put address of copperlist in COPADR2!!!
	
waitm:
	btst #6,$bfe001 ; wait for user to press left mb
	bne.s waitm
	rts	; the end

cop: ; copperlist starts here
	dc.w $180,$f00 ; set background to red
	dc.w $700f,-2  ; wait for line $70
	dc.w $180,$fff ; set background to white
	dc.w $e00f,-2  ; wait for line $e0
	dc.w $180,f00  ; background to red 
	dc.w $ffff,-2  ; WAIT for impossible event

This rather 'dirty' program raises some questions that the article I took the
listing from and the old Hardware manual fail to explain. Mind you, my german
is not as good as it should be.

Question number one:
Why does the program work at all ? The address to the copperlist is put
into COPADR2, but the program doesn't access COPJMP2 and neither does the
system copperlist, so how come that the list is activated at all. My version
of the hardware manual doesn't say anything about this, but maybe I didn't
read it well enough.

Question number two:
The program exits without restoring multitasking, still multitasking starts
again when the program ends. Why?
	

No flames please, just constructive answers.

Jan-Olof Hendig