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492
March 2002 Release
1-800-255-7778
Virtex-II Pro™ Platform FPGA Documentation
Chapter 7:
Exceptions and Interrupts
R
Critical and Noncritical Exceptions
The PPC405 supports critical and noncritical exceptions. Generally, the processor responds
to critical exceptions before noncritical exceptions (certain debug exceptions are handled at
a lower priority). Four exceptions and their associated interrupts are critical:
•
Critical-input exception.
•
Machine-check exception.
•
Watchdog-timer exception.
•
Debug exception.
Critical interrupts use a different save/restore register pair (SRR2 and SRR3) than is used
by noncritical interrupts (SRR0 and SRR1). This enables a critical interrupt to interrupt a
noncritical-interrupt handler. The state saved by the noncritical interrupt is not
overwritten by the critical interrupt.
Because a different register pair is used for saving processor state, a different instruction is
used to return from critical interrupt handlers—
rfci
.
Transferring Control to Interrupt Handlers
shows how the components of the PPC405 exception mechanism interact when
transferring program control to an interrupt handler.
Alignment
0x0600
Noncritical
Synchronous
Precise
Unaligned operand of
dcread
,
lwarx
,
stwcx.
dcbz
to non-cacheable or write-
through memory.
Program
0x0700
Noncritical
Synchronous
Precise
Improper or illegal instruction
execution.
Execution of trap instructions.
FPU Unavailable
0x0800
Noncritical
Synchronous
Precise
Attempt to execute an FPU
instruction when FPU is disabled.
System Call
0x0C00
Noncritical
Synchronous
Precise
Execution of
sc
instruction.
APU Unavailable
0x0F20
Noncritical
Synchronous
Precise
Attempt to execute an APU
instruction when APU is disabled.
Programmable-Interval
Timer
0x1000
Noncritical
Asynchronous
Precise
Time-out on the programmable-
interval timer.
Fixed-Interval Timer
0x1010
Noncritical
Asynchronous
Precise
Time-out on the fixed-interval
timer.
Watchdog Timer
0x1020
Critical
Asynchronous
Precise
Time-out on the watchdog timer.
Data TLB Miss
0x1100
Noncritical
Synchronous
Precise
No data-page translation found.
Instruction TLB Miss
0x1200
Noncritical
Synchronous
Precise
No instruction-page translation
found.
Debug
0x2000
Critical
Asynchronous
and synchronous
Precise
Occurrence of a debug event.
Table 7-1:
Exceptions Supported by the PPC405D5
(Continued)
Exception
Vector
Offset
Classification
Cause
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