536
March 2002 Release
1-800-255-7778
Virtex-II Pro™ Platform FPGA Documentation
R
Debug Modes
The PPC405 supports the following four debug modes:
•
Internal-debug mode for use by software debuggers.
•
External-debug mode for use by JTAG debuggers.
•
Debug-wait mode for interrupt servicing when a JTAG debugger is in
use.
•
Real-time trace mode for use by instruction-trace tools.
The internal-debug and external-debug modes can be enabled simultaneously.
Debug-wait mode and real-time trace mode are available only when both the
internal-debug and external-debug modes are disabled.
Internal-Debug Mode
Internal-debug mode is used during normal program execution and provides
an effective means for debugging system software and application programs.
The mode supports setting breakpoints and monitoring processor status. In
this mode, debug events can cause debug interrupts. The debug-interrupt
handler is used to collect status information and to alter software-visible
resources.
Internal-debug mode is enabled by setting the internal-debug mode bit in
debug-control register 0, DBCR0[IDM]
=
1. Debug interrupts are enabled by
setting MSR[DE]
=
1. An internal debug event can cause a debug interrupt only
when both DBCR0[IDM]
=
1 and MSR[DE]
=
1.
External-Debug Mode
External-debug mode can be used to alter normal program execution. It
provides the ability to debug system hardware as well as software. The mode
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.
Instructions stuffed into the processor can provide access to a variety of
system resources, including DCRs and system memory. However, memory-
protection mechanisms continue to operate in external-debug mode. Debug
software can modify the MSR or TLB entries as necessary to enable access into
protected memory locations.
External-debug mode is enabled by setting the external-debug mode bit in
debug-control register 0, DBCR0[EDM]
=
1.
Debug events in external-debug mode can cause debug interrupts if internal-
debug mode is also enabled. Here, the processor stops with a debug-interrupt
pending. The external debugger can perform debug operations and restart the
processor. When the processor is restarted the debug interrupt occurs,
transferring control to the debug-interrupt handler. The handler can be used
to collect processor-status information and to alter software-visible resources.
An external debug event can cause a debug interrupt only when both
DBCR0[IDM]
=
1 and MSR[DE]
=
1.
Содержание Virtex-II Pro PPC405
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