Instruction Model
PowerPC e500 Core Family Reference Manual, Rev. 1
Freescale Semiconductor
3-23
The load/store multiple instructions are listed in
Table 3-14
.
3.3.1.3
Branch and Flow Control Instructions
Some branch instructions can redirect instruction execution conditionally based on the value of
bits in the CR. Information about branch instruction address calculation is provided in the EREF.
3.3.1.3.1
Conditional Branch Control
For branch conditional instructions, the BO operand specifies the conditions under which the
branch is taken. The first four bits of the BO operand specify how the branch is affected by or
affects the condition and count registers. The fifth bit, shown in
Table 3-16
as having the value y,
is used by some implementations for branch prediction as described below.
NOTE
The e500 does not implement the static branch prediction defined in
Book E and described here. In the e500, the BO operand is ignored for
branch prediction. The e500 instead implements dynamic branch
prediction as part of the branch table buffer (BTB), described in
Section 4.4.1, “Branch Unit Execution.”
The encodings for the BO operands are shown in
Table 3-16
.
Table 3-14. Integer Load and Store Multiple Instructions
Name Mnemonic
Syntax
Load Multiple Word
lmw
r
D
,d(r
A
)
Store Multiple Word
stmw
r
S
,d(r
A
)
Table 3-15. BO Bit Descriptions
BO Bits
Description
0
Setting this bit causes the CR bit to be ignored.
1
Bit value to test against
2
Setting this causes the decrement to not be decremented.
3
Setting this bit reverses the sense of the CTR test.
4
Used for the
y bit, which provides a hint about whether a conditional branch is likely to be
taken (static branch prediction) and may be used by some implementations to improve
performance. The e500 does not use static branch prediction and ignores this bit.
Table 3-16. BO Operand Encodings
BO
Description
0000
y
Decrement the CTR, then branch if the decremented CTR
≠
0 and the condition is FALSE.
0001
y
Decrement the CTR, then branch if the decremented CTR = 0 and the condition is FALSE.
Summary of Contents for PowerPC e500 Core
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Page 38: ...PowerPC e500 Core Family Reference Manual Rev 1 Part I 2 Freescale Semiconductor...
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