Development Capabilities and Interface
20-6
MPC823 USER’S MANUAL
MOTOROLA
DEVELOPMENT
20
CAPABILITIES
&
INTERFACE
20.2.1.2.1 Back Trace. This is useful when a record of the program trace is needed before
an event occurs, such as system failure. If back trace is needed, the external hardware
should start sampling VF and VFLS pins and the addresses of all cycles marked with the
program trace cycle attribute immediately after reset is negated. Since the instruction show
cycles programming defaults to show all out of reset, all cycles marked with the program
trace cycle attribute are visible on the external bus. VSYNC should be asserted sometime
after reset and negated when the actual event occurs. If show all is not the preferred mode
for the instruction show cycles before the event actually occurs, VSYNC must be asserted
before exiting show all mode. If the timing of the event in question is unknown, it is possible
to use cyclic buffers. After the VSYNC signal is negated, the trace buffer contains the
program flow trace of the program executed before the event in question occurred.
20.2.1.2.2 Window Trace. This is useful when a record of the program trace between two
events is required. The VSYNC pin should be asserted between these two events. After
VSYNC is negated, the trace buffer will contain information describing the program trace of
the program executed between the two events.
20.2.1.2.3 Synchronizing the Trace Window to the Internal Core Events. The
VSYNC signal is asserted or negated using the serial interface implemented in the
development port. To synchronize the assertion or negation to an internal core event, the
internal breakpoint hardware should be used with debug mode. This method is available
only when debug mode is enabled. For more information on debug mode, refer to
To synchronize the trace window to the internal core events, follow these steps:
1. Enter debug mode either straight from reset or when using a debug mode request.
2. Program the hardware to break on the event that marks the start of the trace window
3. Enable debug mode entry for the programmed breakpoint in the debug enable
4. Return to the regular code run. The hardware generates a breakpoint when the event
in question is detected and the machine enters debug mode.
5. Program the hardware to break on the event that marks the end of the trace window.
6. Assert the VSYNC signal.
7. Return to the regular code run. The first report on the VF pins is VSYNC, where
VF = 011. The external hardware starts sampling the program trace information after
the VF pins indicate VSYNC. The hardware generates a breakpoint when the event in
question is detected and the machine enters debug mode.
8. Negate the VSYNC signal.
9. Return to the regular code run and issue an rfi instruction. The first encoding on the
VF pins is VSYNC, where VF = 011. The external hardware stops sampling the
program trace information after recognizing VSYNC on the VF pins.