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FAULTS
In
Table
8-1:
•
The first (left-most) column contains the fault type numbers in hexadecimal.
•
The second column shows the fault type name.
•
The third column gives the fault subtype number as either: (1) a hexadecimal number or (2) as
a bit position in the fault record's 8-bit fault subtype field. The bit position method of
indicating a fault subtype is used for certain faults (such as trace faults) in which two or more
fault subtypes may occur simultaneously.
•
The fourth column gives the fault subtype name. For convenience, individual faults are
referenced by their fault-subtype names. Thus an OPERATION.INVALID_OPERAND fault
is referred to as an INVALID_OPERAND fault; an ARITHMETIC.INTEGER_OVERFLOW
fault is referred to as an INTEGER_OVERFLOW fault.
•
The fifth column shows the encoding of the word in the fault record that contains the fault
type and fault subtype numbers.
Other i960 processor family members may provide extensions that recognize additional fault
conditions. Fault type and subtype encoding allows all faults to be included in the fault table: those
that are common to all i960 processors and those that are specific to one or more family members.
The fault types are used consistently for all family members. For example, Fault Type 4H is
reserved for floating point faults. Any i960 processor with floating point operations uses Entry 4H
to store the pointer to the floating point fault handling procedure.
8.3
FAULT TABLE
The fault table
(Figure
8-2) is the processor's pathway to the fault handling procedures. It can be
located anywhere in the address space. From the process control block, the processor obtains a
pointer to the fault table during initialization.
The fault table contains one entry for each fault type. When a fault occurs, the processor uses the
fault type to select an entry in the fault table. From this entry, the processor obtains a pointer to the
fault handling procedure for the type of fault that occurred. Once called, a fault handling procedure
has the option of reading the fault subtype or subtypes from the fault record when determining the
appropriate fault recovery action.
8-4
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