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March 2002 Release
Virtex-II Pro™ Platform FPGA Documentation
1-800-255-7778
R
Debug-Wait Mode
Debug-wait mode causes the processor to enter a state in which interrupts can
be handled when the processor appears to be stopped. The mode operates in a
fashion similar to external-debug mode. It supports starting and stopping the
processor, single-stepping instruction execution, setting breakpoints, and
monitoring processor status. Access to processor resources is provided
through the JTAG port.
External-debug events stop the processor, halting instruction execution.
External-bus activity continues when the processor is stopped. Processor
resources are accessed through the JTAG port when the processor is stopped.
External-debug mode also enables instructions to be stuffed (inserted) into the
processor through the JTAG port and executed. This capability does not cause
privileged (program) exceptions, so privileged instructions can be stuffed
when the processor is in user mode.
Unlike external-debug mode, debug-wait mode enables external devices to
interrupt the processor when it is stopped. The processor transfers control to
the critical-input interrupt handler (0x0100) or the external-interrupt handler
(0x0500), as appropriate. After the interrupt handler completes and executes a
return-from-interrupt instruction, the processor re-enters the stopped state.
Debug-wait mode is enabled by setting the debug-wait mode bit in the MSR,
MSR[DWE]
=
1. Internal-debug mode and external debug mode must both be
disabled (DBCR0[IDM]
=
0 and DBCR0[EDM]
=
0).
Real-Time Trace-Debug Mode
Real-time trace-debug mode supports real-time tracing of the instruction
stream executed by the processor. In this mode, debug events are used to cause
external trigger events. An external trace tool uses the trigger events to control
the collection of trace information. The broadcast of trace information occurs
independently of external trigger events (trace information is always supplied
by the processor). Real-time trace-debug does not affect processor
performance.
Real-time trace-debug mode is always enabled. However, the trigger events
occur only when both internal-debug mode and external debug mode are
disabled (DBCR0[IDM]=0 and DBCR0[EDM]=0). Most trigger events are
blocked when either of those two debug modes are enabled.
Information on the trace-debug capabilities, how trace-debug works, and how
to connect an external trace tool is available in the
RISCWatch Debugger User’s
Guide
.
Debug Registers
The PPC405 debug resources include the following registers:
•
Debug-control registers (DBCR0 and DBCR1).
•
Debug-status register (DBSR).
•
Instruction address-compare registers (IAC1–IAC4).
•
Data address-compare registers (DAC1–DAC2).
•
Data value-compare registers (DVC1–DVC2).
A description of each register is provided in the following sections.
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