B |
Debugger General Information
Creating a New Vector Table
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 to the new vector table. In order to use the debugger facilities you can copy the proper vectors from the 177Bug vector table into the corresponding vector locations in your program vector table.
The vector for the 177Bug generalized exception handler (described in detail in the 177Bug Generalized Exception Handler section in this chapter) 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:
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***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 |
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| 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 |
| MOVEC.L | A1,VBR | Change VBR to new table. |
| RTS |
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| END |
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