Nexus Development Interface (NDI)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 36-93
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
Nexus2+ 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).
36.7.9.3.4 Program Trace Timing Diagrams
Figure 36-72. Program Trace (MDO = 12)—Indirect Branch Message (Traditional)
MCKO
MSEO[1:0]
TCODE = 4
Source Processor = 0b0000
Number of Sequence Instructions = 128
Relative Address = 0xA5
01
11
00
MDO[11:0] 0000 0010 0000
0000 1010 0101
0000 0000 0100
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