MAC7200 datasheet(247/976 Pages) FREESCALE

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Functional Description

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

169

11.11.2.1.3

BTM in ARM mode

Due to the conditional nature of 32-bit ARM instructions, 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.

Branch History Messages solve predicated instruction tracking and save bandwidth since only indirect

branches cause messages to be queued.

11.11.2.1.4

BTM in Thumb mode

Based on the PTM bit in the DC Register (DC[25]), Program Tracing can utilize either Branch History

Messages (DC[25]=1'b0) or traditional Direct/Indirect Branch Messages (DC[25]=1'b1).

Branch History will save bandwidth and keep consistency between methods of Program Trace in ARM

and Thumb modes, yet may lose temporal order between branch events and other types of messages. Since

direct branches are not messaged, but included in the history field of the Indirect Branch History Message,

other types of messages may enter the FIFO between Branch History Messages. The development tool

cannot determine the ordering of events that occurred with respect to direct branches simply by the order

in which messages are sent out.

Traditional BTM messages maintain their temporal ordering because each event that can cause a message

to be queued will enter the FIFO in the order it occurred and will be messaged out maintaining that order.

11.11.2.2 Branch Trace Message Formats (History and Traditional)

The A7S Nexus3 block supports three types of traditional BTM Messages: Direct, Indirect, and

Synchronization Messages. It supports two types of branch history BTM Messages: Indirect Branch

History, and Indirect Branch History with Synchronization Messages. Debug Status Messages, Program

Correlation Messages and Error Messages are also supported.

11.11.2.2.1

Indirect Branch Messages (History)

Indirect branches include all taken branches whose destination is determined at run time, interrupts and

exceptions. If DC[25] is cleared while in Thumb mode, or the ARM7 processor is in full 32-bit ARM

mode, indirect branch information is messaged out in the following format

(1–32 bits)

(1–8 bits)

(4 bits)

(6 bits)

HIST

U-ADDR

I-CNT

SRC

TCODE (011100)

Max length = 82 bits; Min length = 13 bits

Figure 11-26. Indirect Branch Message (History) Format

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