_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_
THIS DON'T IN ANY WAY REPLACE THE ORIGINAL OVERSCAN RELEASE. PLEASE-_
READ THE ORIGINAL BEFORE THIS!!!_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_
_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_

This version of the Overscan software, is written by Klaus Pedersen
(micro@imada.ou.dk). Thanks to 

       Bernd Gebauer and Karsten Isakovic, Berlin

for the original. I don't in any way take any credit or blame for
this (but bug reports are welcome). If the original writers are 
pissed, I will do mine to make it good again...


What then have been fixed?
   o a bug that ment that some programs wrote one pixel outside
     the screen, have been fixed.
   o the software is 68010/20/30/40 clean. (see techincal bits)
   o the software works on TOS 1.4 and __later__! (it don't use
     undocumented system variables to enlarge the screen memory
     any more!)
   o it is now possible to disable Overscan, from within a bad
     program (last resort, as it is not possible to tell accs
     and the AES about the new screen size).
   o it is also possible to enable/disable Overscan form the
     desktop (general, because it is possible to init. AES and
     accs).
   o the driver is now 3700 bytes, of which 3000 stays in memory,
     (not counting the larger screen (68Kb)).


I have added a new menu to the the Setup menu. Press UNDO and the
software asks you to filp the overscan switch. When you have done
that, the software makes the nesseary changes and returns.
It is possible to call the Setup menu from the Set Pref. menu and
change back to Overscan! (this might not work on new TOSes as it
depends on a strange feature in the Desktop!)


The CLEANUP switch (ALT-[R-SHIFT]-HELP) now checks if the Overscan
switch is active or not, and make the nessary changes! This is a 
last resort to run bad programs, because it is not possible to tell
accs and the AES about the new screen size.
 

TECHINCAL BITS
- move SR,Dx - have been removed, the instruction was used to 
  check if the CPU was in USER or SUPER mode!!! The instruction
  can be used to that on all 680x0 cpus, but cpu's later than
  the 68000 tells you with a PRIVILEGE VIALTION exception, if
  the CPU was in USER mode.
  
- the offsets to parameters from within the TOS dispatchers have
  been fixed so that it works on all 680x0 CPUs. This is how you
  should link into the GEMDOS trap:

- remember that GEMDOS, XBIOS, BIOS is documented to change
  D0-D2/A0-A2, this means that you should be able to use them too,
  If is wasn't for TurboC and many other applications, that consider
  A2 safe! (use as few registers as possible and don't use D3-D7/
  A2-A7)!
  AES and the VDI are special! Here you can't even A0 and A1 and
  D0 and D1 is used to pass parameters! (Save all registers!)

   LINK INTO GEMDOS
=====================  
longframe       EQU $059E

                DC.B "XBRAnnnn" ; This is all XBRA is about
OldDos:         DC.L 0          ; place the old address here!
MyDos:          move    USP,A0
                btst    #5,(SP)      ; called from Supervisor- or User-mode?
                beq.s   tst_funcs    ; Parameter is on USER stack
                lea     6(SP),A0     ; Old (small) stack frame.
                tst.w   longframe.w  ; Is this running on a CPU
                beq.s   tst_funcs    ; with a long stackframe?
                addq.w  #2,A0        ;    -then add 2 more bytes.
tst_funcs:      cmpi.w  #Pterm0,(A0) ; Check the FUNCTION numbers!
                bne.s   notmine

... here do the stuff you need to do ...
                
notmine:        movea.l OldDos(PC),A0 ; Now return to the original!
                jmp     (A0)


   LINK INTO VDI/AES
======================
magicAES        EQU  200
magicVDI        EQU  115

                DC.B "XBRAnnnn"
OldVec:         DC.L 0
MyGem:          cmpi.w  #magicVDI,D0    ; Is it a [VDI]-call ?
                bne.s   NotMyGem1       ;   no -> continue
                movem.l A0-A1,-(SP)     ; preserve all A-Regs!
                movea.l D1,A1           ; Address of VDI-Parameters
                movea.l (A1)+,A0        ; Control[0] = function number
                cmpi.w  #func,(A0)      ; Check the FUNCTION numbers!
                bne.s   NotMyGem        ;    not mine -> next; 

... here do the stuff you need to do ...

NotMyGem:       movem.l (SP)+,A0-A1
NotMyGem1:      move.l  OldVec(PC),-(SP) ; call Orginal GEM-dispatcher
                rts                     ; ... call