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March 2002 Release
497
Virtex-II Pro™ Platform FPGA Documentation
1-800-255-7778
Interrupt-Handling Registers
R
•
Critical input—Exception status is recorded in a device control register (DCR)
associated with the external interrupt controller. The MSR[CE] bit is used to enable
and disable the interrupt.
•
External—Exception status is recorded in a device control register (DCR) associated
with the external interrupt controller. The MSR[EE] bit is used to enable and disable
the interrupt.
•
Programmable-interval timer—Exception status is recorded in the PIT-status bit of the
timer-status register, TSR[PIS]. The MSR[EE] bit is used to enable and disable the
interrupt.
•
Fixed-interval timer—Exception status is recorded in the FIT-status bit of the timer-
status register, TSR[FIS]. The MSR[EE] bit is used to enable and disable the interrupt.
•
Debug—Imprecise exception status is recorded in the imprecise-debug exception bit
of the debug-status register, DBSR[IDE]. This indicates that a debug event occurred
while debug interrupts were disabled. Other bits in the DBSR can be set, indicating
which debug events occurred while the interrupt was disabled. The MSR[DE] bit is
used to enable and disable the interrupt.
The watchdog-timer exception is also persistent, but its persistence
prevents
further
interrupts from occurring. This function causes an interrupt to occur on a watchdog time-
out but prevents interrupts on subsequent time-outs. Exception status is recorded in the
watchdog-status bit of the timer-status register, TSR[WIS]. Once the status bit is set, further
watchdog-timer time-outs do not cause an interrupt. Clearing the bit enables time-out
interrupts to occur. The MSR[CE] bit is used to enable and disable the interrupt.
The machine-check interrupt can be disabled but the exception is not persistent. Machine-
check exception status is recorded in the machine-check interrupt status bit of the
exception-syndrome register, ESR[MCI]. However, enabling machine-check interrupts
when the status bit is set does not necessarily cause the interrupt to occur. Instead, the
interrupt occurs when the appropriate external bus-error signal is asserted. The error
signal persists only for the duration of the bus cycle that causes the error.
Interrupt-Handling Registers
When an exception occurs and an interrupt is taken, the interrupt-handling mechanism
uses the following registers:
•
Save/restore register 0
(SRR0)—Contains the return address for noncritical interrupts.
•
Save/restore register 1
(SRR1)—Contains a copy of the MSR for noncritical interrupts.
•
Save/restore register 2
(SRR2)—Contains the return address for critical interrupts.
•
Save/restore register 3
(SRR3)—Contains a copy of the MSR for critical interrupts.
•
Exception-vector prefix register
(EVPR)—Contains the base address of the interrupt-
handler table.
•
Exception-syndrome register
(ESR)—Identifies the cause of an exception. ESR is used by
five exceptions.
•
Data exception-address register
(DEAR)—Contains the memory-operand effective
address of the data-access instruction that caused the exception. DEAR is used by
three exceptions.
The machine-state register is also updated, placing the processor in privileged and real
mode. The following sections describe the effect of the interrupt-handling mechanism on
the interrupt-handling registers.
Machine-State Register Following an Interrupt
During an interrupt, the contents of the MSR (see
) are loaded into either SRR1
(noncritical interrupts) or SRR3 (critical interrupts). Depending on the interrupt, the MSR
is updated with the values shown in
.
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