***********************************************************************

***

***     BusErrTest

***     

***     Build commands:

***

***     asm BusErrTest.a

***     link BusErrTest.a.o -o BusErrTest

***

***********************************************************************

                    STRING  ASIS

                    PRINT   OFF

                    INCLUDE 'Traps.a'

                    INCLUDE 'QuickEqu.a'

                    INCLUDE 'SysEqu.a'

                    PRINT   ON

                    machine mc68030

***********************************************************************

UnImpTrap       EQU     $A89F

HWPriv          EQU     $A198

***********************************************************************

InstallVector   PROC    EXPORT

        IMPORT  OldGuy

        IMPORT  BusErrProc

        move.l      a0,-(sp)            ;preserve reg

        lea         OldGuy,a0           ;OldGuy is a place to keep the original bus error vector

        move.l      8,(a0)              ;so fill it up with the vector, victor

        lea         BusErrProc,a0       ;get the address of our bus error handler

        move.l      a0,8                ;and install it

        move.l      (sp)+,a0            ;restore reg

outtahere

        rts

        ENDP

***********************************************************************

CauseBusErr     PROC    EXPORT      

        movem.l     a0/d0,-(sp)         ;preserve the register we use

        move.l      #$FFFFFFFF,a0       ;this address looks pretty dangerous...

        move.b      (a0),d0

        movem.l     (sp)+,a0/d0         ;restore the registers we use

        rts                             ;it's Miller time

        ENDP

***********************************************************************

ReplaceVector   PROC    EXPORT

        IMPORT  OldGuy

        move.l      a0,-(sp)            ;preserve reg

        lea         8,a0                ;point to the 680x0 bus error vector

        move.l      OldGuy,(a0)         ;and fill it full of the original

        move.l      (sp)+,a0            ;restore reg

        rts                             ;system handler vector

        ENDP

***********************************************************************

BusErrProc      PROC    EXPORT          ;THIS CODE ASSUMES THE BUS ERROR

                                        ;EXCEPTION STACK FRAME FOR THE 

                                        ;68030!!! (REF MOTOROLA 68030 USER'S

                                        ;MANUAL PAGE 8-25)

        IMPORT  OldGuy

RegOffset   EQU     4*2

        movem.l     a1/d0,-(sp)         ;take only pictures, leave only footprints

        move.b      6+RegOffset(sp),d0  ;get the id nibble for the stack frame

        andi.b      #$F0,d0             ;don't care 'bout the lower nibble...

        cmpi.b      #$B0,d0             ;make sure it's the one we like

        bne.s       NotOurs             ;if not, pass it on to system handler

        bclr.b      #0,$A+RegOffset(sp) ;clear DF bit of Special Status Reg

                                        ;so that the instruction will not be re-tried

        move.l      scrnbase,a1         ;let the user know we arrived by inverting

        move.w      #$2ff,d0            ;a hunk o' screen

Loop

        eori.l      #$ffffffff,(a1)+    ;we do a long word at a time

        dbra        d0,Loop             ;till d0 goes negative

        movem.l     (sp)+,a1/d0         ;clean up after ourselves

ret     rte                             ;and return from the exception

NotOurs

        movem.l     (sp)+,a1/d0         ;restore battered registers

        move.l      OldGuy,-(sp)        ;and pass control onto the system

        rts                             ;bus error handler

        ENDP

***********************************************************************

OldGuy  PROC    EXPORT

        DC.L    0                       ;a long word for storage

        ENDP

theEnd  PROC    EXPORT

        ENDP

        END