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PowerPC 604e RISC Microprocessor Technical Summary
29
The 604e’s exceptions, and conditions that cause them, are listed in Table 2.
Table 2. Exceptions and Conditions
Exception
Type
Vector Offset
(hex)
Causing Conditions
Reserved
00000
—
System reset
00100
A system reset is caused by the assertion of either the soft or hard reset signal.
Machine
check
00200
A machine check exception is signaled by the assertion of a qualified TEA
indication on the 604e bus, or the machine check input (MCP) signal. If the
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 the TEA signal is determined by load and store operations
initiated by the processor; however, it is expected that the TEA 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 exception is imprecise with respect to the
instruction that originated the bus operation.
DSI
00300
The cause of a DSI exception can be determined by the bit settings in the
DSISR, listed as follows:
0 Set if a load or store instruction results in a direct-store exception;
otherwise cleared.
1 Set if the translation of an attempted access is not found in the primary
table entry group (PTEG), or in the rehashed secondary PTEG, or in the
range of a BAT register; otherwise cleared.
4 Set if a memory access is not permitted by the page or DBAT protection
mechanism; otherwise cleared.
5 If SR[T] = 1, set by an
eciwx
,
ecowx
,
lwarx
, or
stwcx
. instruction;
otherwise cleared. Set by an
eciwx
or
ecowx
instruction if the access is to
an address that is marked as write-through.
6 Set for a store operation and cleared for a load operation.
9 Set if an EA matches the address in the DABR while in one of the three
compare modes.
10 Set if the segment table search fails to find a translation for the effective
address; otherwise cleared.
11 Set if
eciwx
or
ecowx
is used and EAR[E] is cleared.
ISI
00400
An ISI exception is caused when an instruction fetch cannot be performed for
any of the following reasons:
The effective address cannot be translated. That is, a page fault occurred for
this part of the translation, so an ISI exception must be taken to retrieve the
translation from a storage device such as a hard disk drive.
The fetch access is to a direct-store segment.
The fetch access violates memory protection. If the key bits (Ks and Kp) in
the segment register and the PP bits in the PTE or IBAT are set to prohibit
read access, instructions cannot be fetched from this location.
An attempt is made to fetch an instruction from a segment configured as no-
execute; that is, SR[N] = 1.
An attempt is made to fetch an instruction from a block or page configured
as guarded, that is the G bit is set and translation is enabled, MSR[IR] = 1.