IBM PowerPC 604 User Manual page 61

• Imprecise nonrecoverable mode (FEO
=
0; FEl
=
1 ).
In
this mode, when a
floating-point insttuction causes a floating point exception, the save restore
register 0 (SRRO) may point
to
an insttuction following the insttuction that caused
the
exception.
The 604 exception classes are shown in Table 1-1.
Table 1-1. Exception Classlflcatlons
Type
Exception
Asynchronouslnonmaskable Machine check
System reset
Asynchronouslmaskable External lnterNpt
Decrementer
System management interNpl (not defined by the PowerPC architecture)
Synchronous/precise Instruction-caused exceplions
Synchronouslimprecise Floating-point exceptions (imprecise nonrecoverable mode)
The 604's exceptions, and a general description of conditions that cause them, are listed in
Table 1-2.
Table 1-2. Overview of Exceptions and Conditions
Exception Vector Offset
Causing Conditions
Type
(hex)
Reserved 00000
-
System reset
00100
A system reset is caused by the assertion of either the soft reset or hard reset
signal.
Machine check 00200 A machine check exception is signaled by the assertion of a qualified m
Indication on the 604 bus, or the machine check interrupt
~
signal. H
MSR[ME] Is cleared, the processor enters the checkstop state when one of
these signals is asserted. Note that MSR(ME] is cleared when an exception is
taken. The machine check exception Is also caused by parity errors on the
address or data bus or in the instruction or data caches.
The assertion of them signal Is determined by load and store operations
initiated by the processor; however, it is expected that them signal would be
used by a memory controller to Indicate that a memory parity error or an
uncorrectable memory ECC error has occurred.
Note that the machine check exceplion Is imprecise with respect to the
instruction that originated the bus operation.
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PowerPC 604 RISC Microproc8880r User's Manual