March 2002 Release
499
Virtex-II Pro™ Platform FPGA Documentation
1-800-255-7778
Interrupt-Handling Registers
R
During a noncritical interrupt, SRR0 is loaded by the processor with the effective address
of the interrupted instruction (bits 30:31 are always 0, because instruction addresses are
word aligned). An
rfi
instruction is used to return from the noncritical-interrupt handler to
the instruction address stored in SRR0. Depending on the exception, this effective address
represents either:
•
The instruction that caused the exception.
•
The instruction that would have executed had no exception occurred. For example,
when an
sc
instruction is executed SRR0 is loaded with the instruction effective
address following the
sc
.
See the specific instruction for details.
SRR1 is loaded with a copy of the MSR when a noncritical interrupt occurs. An
rfi
instruction restores the machine state by copying the contents of SRR0 into the MSR
(defined and reserved MSR fields are updated).
SRR0 is a privileged SPR with an address of 26 (0x01A) and SRR1 is a privileged SPR with
an address of 27 (0x01B). Both registers are read and written using the
mfspr
and
mtspr
instructions.
Save/Restore Registers 2 and 3
The save/restore registers 2 and 3 (SRR2 and SRR3) are 32-bit registers used to save
machine state when a critical interrupt occurs. Interrupts defined as critical are:
•
Critical-Input Interrupt.
•
Machine-Check Interrupt.
•
Watchdog-Timer Interrupt.
•
Debug Interrupt.
The format of each register is shown in
During a critical interrupt, SRR2 is loaded by the processor with the effective address of the
interrupted instruction (bits 30:31 are always 0, because instruction addresses are word
aligned). An
rfci
instruction is used to return from the critical-interrupt handler to the
instruction address stored in SRR2. Depending on the exception, this effective address
represents either:
•
The instruction that caused the exception.
•
The instruction that would have executed had no exception occurred. For example,
when a watchdog-timer interrupt occurs SRR2 is loaded with the effective address of
the next-sequential instruction.
0
31
Copy of Machine-State Register
SRR1
Figure 7-2:
Save/Restore Registers 0 and 1
0
30 31
Interrupted-Instruction Effective Address
0
0
SRR2
0
31
Copy of Machine-State Register
SRR3
Figure 7-3:
Save/Restore Registers 2 and 3
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