
RCPU
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MOTOROLA
8-5
8.1.3 Program Flow-Tracking Pins
The following sets of pins are used in program flow tracking:
Instruction queue status pins (VF[0:2]) denote the type of the last fetched in-
struction or how many instructions were flushed from the instruction queue.
History buffer flushes status pins (VFLS [0:1]) denote how many instructions
were flushed from the history buffer during the current clock cycle.
Address type pin 1 (AT1) indicates whether the cycle is transferring an instruc-
tion or data.
The write/read pin (WR), when asserted during an instruction fetch show cy-
cle, indicates the current cycle results from an indirect change-of-flow.
Cycle type pins (CT[0:3]) indicate the type of bus cycle and are used to deter-
mine the address of an internal memory or register that is being accessed.
8.1.3.1 Instruction Queue Status Pins
Instruction queue status pins VF[0:2] indicate the type of the last fetched instruction
or how many instructions were flushed from the instruction queue. These status
pins are used for both functions because queue flushes occur only during clock cy-
cles in which there is no fetch type information to be reported.
Table 8-3
shows the possible instruction types.
Table 8-4
shows VF[0:2] encodings for instruction queue flush information.
Table 8-3 VF Pins Instruction Encodings
VF[0:2]
Instruction Type
VF Next Clock Will Hold
000
None
More instruction type information
001
Sequential
More instruction type information
010
Branch (direct or indirect)
not
taken
More instruction type information
011
VSYNC was asserted/negated and therefore the
next instruction will be marked with the indirect
change-of-flow attribute
More instruction type information
100
Exception taken — the target will be marked with
the program trace cycle attribute
Queue flush information
1
NOTES:
1. Unless next clock VF=111. See below.
2. The sequential instructions listed here affect the machine in a manner similar to indirect branch instructions.
Refer to
8.1.1.2 Sequential Instructions with the Indirect Change-of-Flow Attribute
.
101
Branch indirect taken,
rfi
,
mtmsr
,
isync
and in
some cases
mtspr
to CMPA-F, ICTRL, ECR, or
DER — the target will be marked with the indirect
change-of-flow attribute
2
Queue flush information
1
110
Branch direct taken
Queue flush information
1
111
Branch (direct or indirect)
not
taken
Queue flush information
1
F
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