Motorola 700/800-Series User Manual

4-16

Using the 162Bug Debugger

Your program may create a separate vector table in memory to 
contain its exception vectors. If this is done, the program must 
change the value of the VBR to point at the new vector table. In 
order to use the debugger facilities you can copy the proper vectors 
from the 162Bug vector table into the corresponding vector 
locations in your program vector table. 

The vector for the 162Bug generalized exception handler may be 
copied from offset $08 (bus error vector) in the target vector table to 
all locations in your program vector table where a separate 
exception handler is not used. This provides diagnostic support in 
the event that your program is stopped by an unexpected 
exception. The generalized exception handler gives a formatted 
display of the target registers and identifies the type of the 
exception. 

The following is an example of a routine which builds a separate 
vector table and then moves the VBR to point at it: 

*

***  BUILDX - Build exception vector table ****

*

BUILDX  MOVEC.L  VBR,A0            Get copy of VBR.

        LEA      $10000,A1         New vectors at $10000.

        MOVE.L   $80(A0),D0        Get generalized exception vector.

        MOVE.W   $3FC,D1           Load count (all vectors).

LOOP    MOVE.L   D0,(A1,D1)        Store generalized exception vector.

        SUBQ.W   #4,D1

        BNE.B    LOOP              Initialize entire vector table.

        MOVE.L   $10(A0),$10(A1)   Copy breakpoints vector.

        MOVE.L   $24(A0),$24(A1)   Copy trace vector.

        MOVE.L   $BC(A0),$BC(A1)   Copy system call vector.

        LEA.L    COPROCC(PC),A2    Get your exception vector.

        MOVE.L   A2,$2C(A1)        Install as F-Line handler.

        MOVEC.L  A1,VBR            Change VBR to new table.

        RTS

        END