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8.8.1
Local Fault Call
When the selected fault handler entry in the fault table is an entry type 000
processor operates as described in
•
A new frame is created on the stack that the processor is currently using. The stack can be the
user stack, supervisor stack or interrupt stack.
•
The fault record is copied into the area allocated for it in the stack
•
The processor gets the IP for the first instruction in the called fault handling procedure from
the fault table.
•
The processor stores the fault return code (001
If the fault handling procedure is not able to perform a recovery action, it performs one of the
actions described in
section 8.7.2, "Program Resumption Following a Fault" (pg.
If the handler action results in recovery from the fault, a
procedure allows processor control to return to the program that was executing when the fault
occurred. Upon return, the processor performs the action described in
Operation" (pg.
7-7), except that the arithmetic controls field from the fault record is copied into
the AC register. If the processor is in user mode before execution of the return, the process controls
field from the fault record is not copied back to the PC register.
8.8.2
System-Local Fault Call
When the fault handler selects an entry for a local procedure in the system procedure table (entry
type 10
), the processor performs the same action as is described in the previous section for a local
2
fault call or return. The only difference is that the processor gets the fault handling procedure's
address from the system procedure table rather than from the fault table.
8.8.3
System-Supervisor Fault Call
When the fault handler selects an entry for a supervisor procedure in the system procedure table,
the processor performs the same action described in
with the following exceptions:
•
If the fault occurs while in user mode, the processor switches to supervisor mode, reads the
supervisor stack pointer from the system procedure table and switches to the supervisor stack.
A new frame is then created on the supervisor stack.
•
If the fault occurs while in supervisor mode, the processor creates a new frame on the current
stack. If the processor is executing a supervisor procedure when the fault occurred, the current
stack is the supervisor stack; if it is executing an interrupt handler procedure, the current stack
is the interrupt stack. (The processor switches to supervisor mode when handling interrupts.)
section 7.1.3.1, "Call Operation" (pg.
) in the PFP return type field.
2
section 7.1.3.1, "Call Operation" (pg.
(a local procedure), the
2
7-6), with the following exceptions:
(Figure
8-4), beginning at NFP-1.
8-13).
ret
instruction in the fault handling
section 7.1.3.2, "Return
FAULTS
8
7-6),
8-17
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