Motorola MPC860 PowerQUICC User Manual page 956

Part VI. Debug and Test
37.1.5.2 Window Trace
Window trace is useful when a record of the program trace between two events is needed,
in which case, VSYNC state should be entered between these two events. After exiting
VSYNC state, the trace buffer holds trace information for the program executed between
the two events.
37.1.5.2.1 Synchronizing the Trace Window to Internal Core Events
The assertion/ negation of VSYNC is accomplished using the serial interface implemented
in the development port. To synchronize the assertion/negation of VSYNC to an internal
event of the core, it is possible to use the internal breakpoints hardware with the debug
mode. This method is available only when debug mode is enabled. For more information
on debug mode, see Section 37.3, ÒDevelopment System Interface.Ó
The following is a possible set of steps that enable the user to synchronize the trace window
to the internal core events:
1. Enter debug mode, either immediately out of reset or using the debug mode request.
2. Program hardware to break on the event that marks the start of the trace window
using the registers deÞned in Section 37.2, ÒWatchpoints and Breakpoints Support.Ó
3. Enable debug mode entry for the breakpoint programmed in the DER (see
Table 37-25).
4. Return to the regular code run (refer to Section 37.3.1.7, ÒExiting Debug ModeÓ).
5. The hardware generates a breakpoint when the event in question is detected and the
machine enters debug mode (refer to Section 37.3.1.2, ÒEntering Debug ModeÓ).
6. Program the hardware to break on the event that marks the end of the trace window.
7. Assert VSYNC.
8. Return to the regular code run. The Þrst report on the VF pins is VSYNC (VF =
0b011).
9. The external hardware starts sampling the program trace information after the VF
pins indicate VSYNC.
10. The hardware generates a breakpoint when the event in question is detected and the
machine enters debug mode.
11. Negate VSYNC.
12. Return to the regular code run (issue an rÞ). The Þrst encoding on the VF pins is
VSYNC (VF = 0b011).
13. External hardware stops sampling the program trace information after recognizing
VSYNC on the VF pins.
37.1.5.3 Detecting the Trace Window Start Address
When using back trace, latching of VF, VFLS, and the address of the cycles marked
program trace cycle should all start immediately after the negation of reset. The start
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