Development Capabilities and Interface
MOTOROLA
MPC823 USER’S MANUAL
20-7
DEVELOPMENT
20
CAPABILITIES
&
INTERFACE
20.2.1.2.4 Detecting the Trace Window Start Address. When using back trace, latching
VF, VFLS, and the address of the cycles marked program trace cycle should all start
immediately after reset is negated. The start address is the first address in the program trace
cycle buffer. When using window trace, latching of VF, VFLS, and the address of the cycles
marked as program trace cycle should all start immediately after the first VSYNC is
recognized on the VF pins. The start address of the trace window should be calculated
according to the first two VF pin reports. Assume VF1 and VF2 are the first two VF pin
reports and T1 and T2 are the two addresses of the first two cycles marked with the program
trace cycle attribute that were latched in the trace buffer. Use the following table to calculate
the trace window start address.
20.2.1.2.5 Detecting VSYNC Assertion/Negation. Because the VF pins are used to
report both instruction type and queue flush information, the external hardware must take
special care when trying to detect the assertion/negation of VSYNC. When VF = 011, it is a
VSYNC assertion/negation report only if the prior value of VF was 000, 001, or 010.
20.2.1.2.6 Detecting the Trace Window End Address. The information on the status
pins that describes the last fetched instruction and last queue/history buffer flush changes
every clock. Cycles marked as program trace cycle are generated on the external bus only
when the system interface unit arbitrates over the external bus. Therefore, there is a delay
between the report that a cycle marked as program trace cycle is performed and the actual
time that this cycle can be detected on the external bus.
When you negate VSYNC using the serial interface of the development port, the core delays
reporting that VSYNC occurred on the VF pins until all addresses marked with the program
trace cycle attribute are externally visible. Therefore, the external hardware should stop
sampling VF, VFLS, and the address of the cycles marked as program trace cycle
immediately after VF = VSYNC. The last two instructions reported on the VF pins are not
always valid. Therefore, at the last stage of the reconstruction software, the last two
instructions should be ignored.
Table 20-2. Detecting the Trace Buffer Starting Point
VF1
VF2
STARTING POINT
DESCRIPTION
011
VSYNC
001
Sequential
T1
VSYNC is asserted and followed by a sequential
instruction. the start address is T1.
011
VSYNC
110
Branch Direct Taken
T1 - 4 +
Offset(T1 - 4)
VSYNC is asserted and followed by a taken direct branch.
the start address is the target of the direct branch.
011
VSYNC
101
Branch Indirect Taken
T2
VSYNC is asserted and followed by a taken indirect
branch. the start address is the target of the indirect
branch.