Re: A89: supervisor vs usermode...


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Re: A89: supervisor vs usermode...




both excerpts taking from jimmy mardel's '68kguide'

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excerpt1:

Bit 13: S - Supervisor bit. When this bit is set, you have more "access" to
        some instructions and also to the systembyte. The reason for this is
        that it prevents programs to disturb the OS with some instructions
        that you shouldn't use if you're not writing an OS. Is enabled
        when interruptions are generated.
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excerpt2:

SYSTEMCONTROL
-------------
These instructions changes the state of the 68000 processor. They require
that the supervisor bit (in the system byte) is set. I haven't used these,
so don't blame me if I've written something wrong.

MOVE USP    Gives a program in supervisor mode access to the stackpointer in
            user mode
RESET       Restores the peripheral units.
RTE         Returns from an interrupt.
STOP        Stops the execution until a given interrupt occurs.
CHK, TRAPV  Finds fatal program errors.
TRAP        16 instructions that give a program in usermode the possibility
            to call antoher program in supervisor mode.
...well i guess i probably answered my own questions...but anyone feel like 
elaborating???


In a message dated 99-07-26 15:07:21 EDT, you rudely write:

> what are you talking about?
>  
>  S43R80@aol.com wrote:
>  
>  > I'm just curious about the difference between supervisor and
>  > usermode...Actually why does there even have to be 2 different
>  > modes...wouldn't everything be just as easy (easier) w/ 1 mode which has
>  > access to all components....ie: interrupts...???  Could someone possibly
>  > explain the main differences betweeen these 2 modes and perhaps why it is
>  > even necessary???
>  >
>  > -Steven
>