544
March 2002 Release
1-800-255-7778
Virtex-II Pro™ Platform FPGA Documentation
R
•
In internal-debug mode, a debug event is synonymous with debug
exception. A debug event can cause a debug interrupt if debug interrupts
are enabled (MSR[DE]
=
1). If debug interrupts are disabled, a debug event
results in a
pending
debug interrupt. A debug interrupt occurs when a
debug interrupt is pending and software sets MSR[DE] to 1.
•
In external-debug mode, a debug event stops the processor. An external
debugger connected to the processor through the JTAG port can restart
the processor. A debug event can also cause a debug interrupt if both
internal-debug mode and debug exceptions are enabled.
•
If debug interrupts are enabled and both internal-debug and external-
debug mode are enabled, a debug event stops the processor and the
debug interrupt is pending.
•
In debug-wait mode, a debug event stops the processor. A critical or
noncritical external interrupt can restart the processor to handle the
interrupt. The processor stops again when the interrupt handler is exited.
An external debugger connected to the processor through the JTAG port
can restart the processor.
•
In real-time trace mode, a debug event can cause an external trigger
event. Trigger events are used by external tools to collect instruction-trace
information.
Debug status is recorded in the debug-status register (DBSR). A debug event
can set debug-status bits even if all debug modes and debug exceptions are
disabled. System software can use this capability to periodically poll the DBSR
rather than use debug exceptions. Three events do not operate in this manner:
•
Instruction-complete (IC).
•
Branch-taken (BT).
•
Instruction address-compare (IAC) when toggling is used.
The corresponding sections for these debug events describe the conditions
under which debug status is not updated.
When debug interrupts are disabled (MSR[DE]
=
0), debug events are often
recorded imprecisely. The occurrence of a debug event is reported by the
debug status register, but the processor continues to operate normally and the
debug interrupt is pending. When debug interrupts are later enabled, the
pending interrupt causes a debug interrupt to immediately occur. See
for more information.
Debug events are not caused by speculatively executed instructions. The
processor only reports events for resolved instructions that reflect the normal
operation of the sequential-execution model.
summarizes the debug resources used by each debug event.
Table 9-4:
Debug Resources Used by Debug Events
Debug Event
DBCR0
DBCR1
DBSR
IAC
DAC
DVC
IC
Instruction Complete
IC
IC
BT
Branch Taken
BT
BT
EDE
Exception Taken
EDE
EDE
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