Motorola MVME162 manual 162Bug Generalized Exception Handler

Preserving the Debugger Operating Environment

The following is an example of an exception handler which can pass an exception along to the debugger:

*

***EXCEPT - Exception handler ****

EXCEPT SUBQ.L	#4,A7	Save space in stack for a PC value.
LINK	A6,#0	Frame pointer for accessing PC space.
MOVEM.L	A0-A5/D0-D7,-(SP)	Save registers.
:

:decide here if your code handles exception, if so, branch...

MOVE.L	BUFVBR,A0	Pass exception to debugger; Get saved VBR.
MOVE.W	14(A6),D0	Get the vector offset from stack frame.
AND.W	#$0FFF,D0	Mask off the format information.
MOVE.L	(A0,D0.W),4(A6)	Store address of debugger exc handler.
MOVEM.L	(SP)+,A0-A5/D0-D7	Restore registers.
UNLK	A6
RTS		Put addr of exc handler into PC and go.

162Bug Generalized Exception Handler

The 162Bug has a generalized exception handler which it uses to handle all of the exceptions not listed in Table 4-2. For all these exceptions, the target stack pointer is left pointing to the top of the exception stack frame created. In this way, if an unexpected exception occurs during execution of your code, you are presented with the exception stack frame to help determine the cause of the exception. The following example illustrates this:

Example:	Bus error at address $F00000. It is assumed for this example
	that an access of memory location $F00000 initiates bus error
	exception processing.

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MVME162IG/D2 4-15