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trap_a.asm
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Assembly Source File
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1992-09-03
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2KB
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52 lines
* trap_a.asm - Example trap handling code (leaves D0 intact). Entered
* in supervisor mode with the following on the supervisor stack:
* 0(sp).l = trap#
* 4(sp) Processor dependent exception frame
*
*
* Copyright (c) 1992 Commodore-Amiga, Inc.
*
* This example is provided in electronic form by Commodore-Amiga, Inc. for
* use with the "Amiga ROM Kernel Reference Manual: Libraries", 3rd Edition,
* published by Addison-Wesley (ISBN 0-201-56774-1).
*
* The "Amiga ROM Kernel Reference Manual: Libraries" contains additional
* information on the correct usage of the techniques and operating system
* functions presented in these examples. The source and executable code
* of these examples may only be distributed in free electronic form, via
* bulletin board or as part of a fully non-commercial and freely
* redistributable diskette. Both the source and executable code (including
* comments) must be included, without modification, in any copy. This
* example may not be published in printed form or distributed with any
* commercial product. However, the programming techniques and support
* routines set forth in these examples may be used in the development
* of original executable software products for Commodore Amiga computers.
*
* All other rights reserved.
*
* This example is provided "as-is" and is subject to change; no
* warranties are made. All use is at your own risk. No liability or
* responsibility is assumed.
INCLUDE "exec/types.i"
INCLUDE "libraries/dos.i"
XDEF _trapa
XREF _countdiv0
XREF _oldTrapCode
CODE
_trapa: ; our trap handler entry
CMPI.L #5,(SP) ; is this a divide by zero ?
BNE.S notdiv0 ; no
ADD.L #1,_countdiv0 ; yes, increment our div0 count
endtrap:
ADDQ #4,SP ; remove exception number from SSP
RTE ; return from exception
notdiv0:
TST.L _oldTrapCode ; is there another trap handler ?
BEQ.S endtrap ; no, so we'll exit
MOVE.L _oldTrapCode,-(SP) ; yes, go on to old TrapCode
RTS ; jumps to old TrapCode
END