
MOTOROLA
8-10
DEVELOPMENT SUPPORT
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RCPU
REFERENCE MANUAL
The second method is not as precise as the first method because of the delay be-
tween the assertion of the watchpoint pins and the assertion or negation of VSYNC
using the development port serial interface. It has the advantage, however, of al-
lowing the program to run in quasi-real time (slowed only by show cycles on the
external bus), instead of stopping execution at the starting and ending events.
8.1.4.4 Detecting the Trace Window Starting Address
For a back trace, the value of the status pins (VF[0:2] and VFLS[0:1]) and the ad-
dress of the cycles marked with the indirect change-of-flow attribute should be
latched starting immediately after the negation of reset. The starting address is the
first address in the program trace cycle buffer.
For a window trace, the value of the status pins and the address of the cycles
marked with the indirect change-of-flow attribute should be latched beginning im-
mediately after the first VSYNC is reported on the VF pins. The starting address of
the trace window should be calculated according to the first two VF pin reports.
Assume VF1 and VF2 are the two first VF pin reports and T1 and T2 are the ad-
dresses of the first two cycles marked with the indirect change-of-flow attribute that
were latched in the trace buffer. Use
Table 8-7
to calculate the trace window start-
ing address.
8.1.4.5 Detecting the Assertion or Negation of VSYNC
Since the VF pins are used for reporting both instruction type information and
queue flush information, the external hardware must take special care when trying
to detect the assertion or negation of VSYNC. A VF[0:2] encoding of 011 indicates
the assertion or negation of VSYNC only if the previous VF[0:2] pin values were
000, 001, or 010.
8.1.4.6 Detecting the Trace Window Ending Address
The information on the VF and VFLS status pins changes every clock. Cycles
marked with the indirect change-of-flow are generated on the external bus only
when possible (when the SIU wins the arbitration over the external bus). Therefore,
Table 8-7 Detecting the Trace Buffer Starting Point
VF1
VF2
Starting Point
Description
011
VSYNC
001
Sequential
T1
VSYNC asserted followed by a sequential
instruction. The starting address is T1.
011
VSYNC
110
Branch direct
taken
T1 – 4 +
offset(T1 – 4)
VSYNC asserted followed by a taken direct branch.
The starting address is the target of the direct
branch.
011
VSYNC
101
Branch indirect
taken
T2
VSYNC asserted followed by a taken indirect
branch. The starting address is the target of the
indirect branch.
F
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