
5-6
G2 PowerPC Core Reference Manual
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MOTOROLA
Exception Classes
Exceptions are roughly prioritized by exception class, as follows:
1. Nonmaskable, asynchronous exceptions have priority over all other exceptions—
system reset and machine check exceptions (although the machine check exception
condition can be disabled so the condition causes the processor to go directly into
the checkstop state). These exceptions cannot be delayed, and do not wait for the
completion of any precise exception handling.
2. Synchronous, precise exceptions are caused by instructions and are taken in strict
program order.
3. Maskable asynchronous exceptions (for example, external interrupt and
decrementer exceptions) are delayed until higher priority exceptions are taken.
System reset and machine check exceptions may occur at any time and are not delayed even
if an exception is being handled. As a result, state information for the interrupted exception
may be lost; therefore, these exceptions are typically nonrecoverable.
All other exceptions have lower priority than system reset and machine check exceptions,
and the exception may not be taken immediately when it is recognized.
5.1.1
Exception Priorities
The exceptions are listed in Table 5-3 in order of highest to lowest priority.
Instruction
address
breakpoint
01300
An instruction address breakpoint exception occurs when the address (bits 0–29)
in the IABR matches the next instruction to complete in the completion unit, and
IABR[30] is set. Note that the G2_LE core also implements IABR2, which
functions identically to IABR.
System
management
interrupt
01400
A system management interrupt is caused when MSR[EE] = 1 and the core_smi
input signal is asserted.
Reserved
01500–02FFF —
Table 5-3. Exception Priorities
Exception
Category
Priority
Exception
Cause
Asynchronous
0
System reset
core_hreset or power-on reset
1
Machine check
core_tea, core_mcp, core_ape, or core_dpe
2
System reset
core_sreset
3
Critical interrupt
core_cint (G2_LE-only)
4
System management
interrupt
core_smi
Table 5-2. Exceptions and Conditions (continued)
Exception Type
Vector Offset
(hex)
Causing Conditions
F
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