Topic       : TOS - The Operating System
Author      : 
Version     : tos.hyp (December 19, 2008)
Subject     : Programmieren/Atari
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Index Size  : 93790
HCP-Version : 5
Compiled on : Atari
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View Ref-File3.3  Hooking into the reset vector                                 TOS

The recipe for hooking your own routines into the reset-vector runs as 
follows:

   . Set the system variable resvalid to the value 0x31415926, as 
     therwise resvector will be completely ignored by the BIOS ignore.

   . Write the address of your own function in the resvector vector.

   . Jump back from the function via jmp(a6).

Important: A jump back from the installed function via rts is not 
possible, since no stack has been initialised yet at this time. In 
practice one could proceed as follows, for instance:

RESMAGIC    equ       $31415926
_resvalid   equ       $426
_resvector  equ       $42a
            .text
install:    move.l    _resvalid,oldvalid
            move.l    #RESMAGIC,resvalid
            move.l    _resvector,oldreset
            move.l    #newreset,_resvector
            rts

            dc.b      "XBRARESV"
oldreset:   dc.l      0

newreset:   move.l    oldreset,_resvector
            move.l    oldvalid,_resvalid
            jmp       (a6)

            .bss
oldvalid:   .ds.l     1

Warning: So that multiple programs may install themselves, a clean 
de-installation must follow the handling of the function.

See Also: System variables   System vectors   XBRA procedure