Chapter 5. PowerPC Processor Core
5-29
Exception Model
Alignment
00600
An alignment exception is caused when the processor core cannot perform a
memory access for any of the reasons described below:
• •The operand of a floating-point load or store is to a direct-store segment.
• •The operand of a floating-point load or store is not word-aligned.
• •The operand of a lmw, stmw, lwarx, or stwcx. is not word-aligned.
• •The operand of an elementary, multiple or string load or store crosses a
segment boundary with a change to the direct store T bit.
• •The operand of dcbz instruction is in memory that is write-through required
• or caching inhibited, or dcbz is executed in an implementation that has
either no data cache or a write-through data cache.
• •A misaligned eciwx or ecowx instruction
• •A multiple or string access with MSR[LE] set
The processor core differs from MPC603e in that it initiates an alignment exception
when it detects a misaligned eciwx or ecowx instruction and does not initiate an
alignment exception when a little-endian access is misaligned.
Program
00700
A program exception is caused by one of the following exception conditions, which
correspond to bit settings in SRR1 and arise during execution of an instruction:
• •Illegal instruction—An illegal instruction program exception is generated when
execution of an instruction is attempted with an illegal opcode or illegal
combination of opcode and extended opcode fields (including PowerPC
instructions not implemented in the processor core), or when execution of an
optional instruction not provided in the processor core is attempted (these do
not include those optional instructions that are treated as no-ops).
• •Privileged instruction—A privileged instruction type program exception is
generated when the execution of a privileged instruction is attempted and the
MSR register user privilege bit, MSR[PR], is set. In the processor core, this
exception is generated for mtspr or mfspr with an invalid SPR field if
SPR[0] = 1 and MSR[PR] = 1. This may not be true for all PowerPC
processors.
• •Trap—A trap type program exception is generated when any of the conditions
specified in a trap instruction are met.
Floating-point
unavailable
00800
A floating-point unavailable exception is caused by an attempt to execute a
floating-point instruction (including floating-point load, store, and move instructions)
when the floating-point available bit is cleared (MSR[FP] = 0).
Decrementer
00900
The decrementer exception occurs when the most significant bit of the decrementer
(DEC) register transitions from 0 to 1. Must also be enabled with the MSR[EE] bit.
Reserved
00A00–00BFF
—
System call
00C00
A system call exception occurs when a System Call (sc) instruction is executed.
Trace
00D00
A trace exception is taken when MSR[SE] = 1 or when the currently completing
instruction is a branch and MSR[BE] = 1.
Floating-point
assist
00E00
The MPC8420 does not generate an exception to this vector. Other PowerPC
processors may use this vector for floating-point assist exceptions.
Reserved
00E10–00FFF
—
Instruction
translation
miss
01000
An instruction translation miss exception is caused when the effective address for
an instruction fetch cannot be translated by the ITLB.
Data load
translation
miss
01100
A data load translation miss exception is caused when the effective address for a
data load operation cannot be translated by the DTLB.
Table 5-8. Exceptions and Conditions (Continued)
Exception
Type
Vector Offset
(hex)
Causing Conditions
Содержание MPC8240
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