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The PowerPC Core
MOTOROLA
MPC801 USER’S MANUAL
6-7
6
Interrupt handling is transparent to user mode code. The core uses the same mechanism to
handle all types of exceptions. When a user mode instruction experiences an exception, the
machine is placed into privileged state and control is transferred to a software exception
handler routine located at some offset within a memory-based vector table.
Each interrupt generated in the machine transfers control to a different address in the vector
table. For more information on initializing the base address of the vector table, refer to
Table 6-13 as well as the PowerPC definition of the machine state register. When the
exception has been handled, the handler can resume execution of the user program without
the knowledge that such an event ever occurred.
As specified in
precise interrupt model. An interrupt usually occurs under one of the following conditions:
PowerPC Family: The Programming Environment
, the core implements a
No instruction that logically follows the faulting instruction in the code stream has
started executing.
All instructions preceding the faulting instruction have completed with respect to the
executing processor.
The precise location (address) of the faulting instruction is known to the exception
handler.
The instruction causing the exception may not have started executing (“before
interrupt”), could be partially completed, or has completed (“after interrupt”) depending
on the interrupt and instruction types. See Table 6-2 for details.
In any case, a partially completed instruction is restartable and can be reexecuted after the
interrupt is handled. This precise exception model can simplify and speed up exception
processing because the software does not have to manually save the machine’s internal
pipeline states, unwind the pipelines, or cleanly terminate the faulting instruction stream. Nor
does it have to reverse the process to resume execution of the faulting stream.