System Development and Debugging
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
53-5
If TECR[VSYNC] is set or cleared while the core is in debug mode, this information is reported when the
first VF pins report as the core returns to regular mode. If VSYNC was not changed while in debug mode,
the first VF pins report will be encoded as VF = 0b101 (indirect branch) due to the rfi instruction that is
being issued. In both cases, the first instruction fetch after debug mode is marked with the program trace
cycle attribute and is externally visible.
53.1.4.3
Sequential Instructions Marked as Indirect Branch
There are instances where non-branch (sequential) instructions can affect the machine in a manner similar
to indirect branch instructions. These instructions include rfi, mtmsr, isync, and mtspr to registers
CMPA–CMPF, ICTRL, ICR, and DER.
The core marks these instructions are marked as indirect branch instructions (VF = 0b101). The next
instruction address is marked with the program trace cycle attribute, as if it were an indirect branch target.
Therefore, when one of these special instructions is detected in the core, the address of the next instruction
is externally visible. The reconstructing software can now correctly evaluate the effect of these
instructions.
53.1.5
Reconstructing Program Trace
When program trace is needed, external hardware must sample the status pins (VF and VFLS) of every
clock and mark the address of all cycles with the program trace cycle attribute. Although program trace
can be used in various ways, the following describes only back trace and window trace.
53.1.5.1
Back Trace
Back trace is useful when a record of the program trace before an event occurred is needed. An example
of such an event is a system failure. If back trace is needed, external hardware should start sampling VF
and VFLS and the address of all cycles marked with the program trace cycle attribute immediately after
reset is negated.
At reset, cycles marked with the program trace cycle attribute are visible on the external bus (that is, the
instruction fetch show cycle/core serialize control field (ICTRL[ISCT_SER]) is cleared at reset). To avoid
this slower default mode, it is recommended that the user enters VSYNC state as described in
Section 53.1.1, “Program Trace Functional Description.”
To exit VSYNC state after a particular event,
either trap in debug mode and trigger the freeze indication or follow the method described in
Section 53.1.1, “Program Trace Functional Description.”
After exiting VSYNC state, the trace buffer
holds the trace of the program executed before the pertinent event occurred.
53.1.5.2
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.
53.1.5.2.1
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
Summary of Contents for PowerQUICC MPC870
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