UM0434 datasheet(350/390 Pages) STMICROELECTRONICS

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UM0434

Nexus3 module

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of zero indicates not taken. Certain instructions (evsel) generate a pair of predicate bits

that are both reported as consecutive bits in the history field.

e200z3 indirect branch message instructions (Book E)

Table 245 shows the types of instructions and events that cause indirect branch messages

or branch history messages to be encoded.

e200z3 direct branch message instructions (Book E)

Table 246 shows the types of instructions that cause direct branch messages or that toggle

a bit in the instruction history buffer to be messaged out in a resource full message or

branch history message.

BTM using branch history messages

Traditional BTM 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, or a not-taken indirect branch. A value of one indicates the

conditional instruction was executed or the direct branch was taken. A value of zero

indicates the conditional instruction was not executed or the direct branch was not taken.

Certain instructions (evsel) generate a pair of predicate bits that are both reported as

consecutive bits in the history field.

Branch history messaging facilitates program trace by providing the information described in

Chapter : e200z3 indirect branch message instructions (Book E) on page 351”:

Branch history messages solve predicated instruction tracking and save bandwidth because

only indirect branches cause messages to be queued.

BTM using traditional program trace messages

Program tracing can utilize either branch history messages (DC1[PTM] = 1) or traditional

direct/indirect branch messages (DC1[PTM] = 0).

Table 245.

Indirect branch message sources

Source of indirect branch message

Instructions

Taken branch relative to a register value

bcctr, bcctrl, bclr, bclrl, se_bctr,

se_bctrl, se_blr, se_blrl

System call/trap exceptions taken

sc, se_sc, tw, twi

Return from interrupts/exceptions

rfi, rfci, rfdi, se_rfi, se_rfci, se_rfdi

Table 246.

Direct branch message sources

Source of direct branch message

Instructions

Taken direct branch instructions

b, ba, bl, bla, bc, bca, bcl, bcla,

se_b. se_bc, se_bl, e_b, e_bc,

e_bl, e_bcl, isync, se_isync

Instruction synchronize

isync, se_isync

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