Nexus Development Interface (NDI)
Freescale Semiconductor
31-41
PXR40 Microcontroller Reference Manual, Rev. 1
31.13.1.2 e200z7 Direct Branch Message Instructions
(Power Architecture Book E)
shows the instruction types that cause direct branch messages, or toggle a bit in the instruction
history buffer in a resource full message or branch history message before it is sent out.
31.13.1.3 BTM Using Branch History Messages
Traditional BTM messaging can accurately track the number of sequential instructions between branches,
but cannot accurately indicate which instructions were conditionally executed, and which were not.
Branch history messaging solves this problem by providing a predicated instruction history field in each
indirect branch message. Each bit in the history represents a predicated instruction or direct branch. A
value of one (1) indicates the conditional instruction was executed or the direct branch was taken. A value
of zero (0) indicates the conditional instruction was not executed or the direct branch was not taken.
Certain instructions (
evsel
) generate a pair of predicate bits which are both reported as consecutive bits in
the history field.
Branch history messages solve predicated instruction tracking and save bandwidth since only indirect
branches cause messages to be queued.
31.13.1.4
BTM Using Traditional Program Trace Messages
Based on the PTM bit in the DC register (DC[PTM]), program tracing can use:
•
Branch history messages (DC[PTM] = 1); or
•
Traditional direct and indirect branch messages (DC[PTM] = 0)
Branch history saves bandwidth and keeps consistency between methods of program trace, yet can lose
temporal order between BTM messages and other types of messages. Since direct branches are not
messaged, but are instead included in the history field of the indirect branch history message, other types
of messages can enter the FIFO between branch history messages. The development tool cannot determine
the order of “events” that occurred for direct branches by the order in which messages are sent out.
System call / trap exceptions taken
sc, tw, twi
Return from interrupts / exceptions
rfi, rfci, rfdi
Table 31-25. Direct Branch Message Sources
Source of Direct Branch Message
Instructions
Taken direct branch instructions
b, ba, bl, bla, bc, bca, bcl, bcla
Instruction synchronize
isync
Table 31-24. Indirect Branch Message Sources (continued)
Source of Indirect Branch Message
Instructions
Summary of Contents for PXR4030
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