PXN20RM Datasheet, PDF (1203/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Nexus Development Interface (NDI)
switch, the program trace message resulting from that branch indicates the previous execution state. The
new state is not signaled until the next program trace message.
In some cases, a Program Correlation Message is generated to indicate execution mode status Refer to
Program Correlation Messages on page 36-88 for more information on these cases.
Branch/Predicate Instruction History (HIST)
If DC[PTM] is set, BTM messaging uses the branch history format. The branch history (HIST) packet in
these messages provides a history of direct branch execution used for reconstructing the program flow.
This packet is implemented as a left-shifting shift register. The register is always pre-loaded with a value
of one (1). This bit acts as a stop bit so that the development tools can determine which bit is the end of
the history information. The pre-loaded bit itself is not part of the history, but is transmitted with the
packet.
A value of one (1) is shifted into the history buffer on a taken branch (condition or unconditional) and on
any instruction whose predicate condition executed as true. A value of zero (0) is shifted into the history
buffer on any instruction whose predicate condition executed as false as well as on branches not taken.
This includes indirect as well as direct branches not taken. For the evsel instruction, two bits are shifted
in, corresponding to the low element (shifted in first) and the high element (shifted in second) conditions.
Sequential Instruction Count (I-CNT)
The I-CNT packet is present in all BTM messages. For traditional branch messages, I-CNT represents the
number of sequential instructions, or non-taken branches in between direct/indirect branch messages.
For branch history messages, I-CNT represents the number of instructions executed since the last
taken/non-taken direct branch, last taken indirect branch or exception. Not taken indirect branches are
considered sequential instructions and cause the instruction count to increment. I-CNT also represents the
number of instructions executed since the last predicate instruction.
The sequential instruction counter overflows when its value reaches 255. The next BTM message is
converted to a synchronization type message.
Program Trace Queueing
Nexus3+ implements a message queue. Messages that enter the queue are transmitted via the auxiliary pins
in the order in which they are queued.
NOTE
If multiple trace messages need to be queued at the same time, Watchpoint
Messages have the highest priority (WPM  OTM  BTM  DTM).
Freescale Semiconductor
PXN20 Microcontroller Reference Manual, Rev. 1
36-53