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From: sansom@trwrb.UUCP (Richard Sansom)
Newsgroups: net.micro.atari16
Subject: Re: Supervisor mode
Message-ID: <1385@trwrb.UUCP>
Date: Mon, 27-Oct-86 16:40:56 EST
Article-I.D.: trwrb.1385
Posted: Mon Oct 27 16:40:56 1986
Date-Received: Tue, 28-Oct-86 06:30:38 EST
References: <660@chinet.UUCP>
Reply-To: sansom@trwrb.UUCP (Richard Sansom)
Distribution: net
Organization: TRW EDS, Redondo Beach, CA
Lines: 50
Keywords: Hardware tweaking

In article <660@chinet.UUCP> cabbie@chinet.UUCP (Richard Andrews) writes:
>
>	I want to do some hardware tweaking and mave been attempting
>to enter supervisor mode but am still getting bus errors?  Does
>anyone have some general purpose source code to do this?
>

Gemdos function 0x20 is the one you want:

Call:	Super(stack);	- or -	    gemdos(0x20, stack);

where "stack" is a pointer to your supervisor stack or NULL (0L) if you
want to use the user stack as supervisor stack.  The function returns a
pointer to the old supervisor stack.  You MUST restore the stack to this
value when you exit supervisor mode or else the machine  will crash.

C code example:

    long    old_ssp;		/* old supervisor stack pointer */

    old_ssp = Super(0L);	/* enter supervisor mode, use the user stack*/

    /* your super code goes here */

    Super(old_ssp);		/* exit supervisor mode, restore stack */

Assembly example:

    clr.l   -(sp)		; pass a long zero (use user stack)
    move.w  #$20,-(sp)		; pass gemdos function 0x20
    trap    #1			; enter supervisor mode
    add.l   #6,sp		; clean up the stack
    move.l  d0,old_ssp		; save old stack pointer

; your super code goes here

    move.l  old_ssp,-(sp)	; pass the old stack pointer
    move.w  #$20,-(sp)		; pass gemdos function 0x20
    trap    #1			; exit supervisor mode
    add.l   #6,sp		; clean up the stack

-Rich

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