Floating Point Support - Motorola MVME167 Series Installation Manual

Using the 167Bug Debugger
5

Floating Point Support

5-18
It may turn out that your program uses one or more of the exception
vectors that are required for debugger operation. Debugger
facilities may still be used, however, if your exception handler can
determine when to handle the exception itself and when to pass the
exception to the debugger.
When an exception occurs which you want to pass on to the
debugger; i.e., ABORT, your exception handler must read the
vector offset from the format word of the exception stack frame.
This offset is added to the address of the 167Bug target program
vector table (which your program saved), yielding the address of
the 167Bug exception vector. The program then jumps to the
address stored at this vector location, which is the address of the
167Bug exception handler.
Your program must make sure that there is an exception stack
frame in the stack and that it is exactly the same as the processor
would have created for the particular exception before jumping to
the address of the exception handler.
The floating point unit (FPU) of the MC68040 microprocessor chip
is supported in 167Bug. For MVME167Bug, the commands MD,
MM, RM, and RS have been extended to allow display and
modification of floating point data in registers and in memory.
Floating point instructions can be assembled and disassembled
with the DI option of the MD and MM commands.