AMCC PPC405 - Assembler Extended Mnemonics

402 AMCC Proprietary
Revision 1.02 - September 10, 2007
PPC405 Processor
Preliminary User’s Manual
B.4 Assembler Extended Mnemonics
In the appendix “Assembler Extended Mnemonics” of the PowerPC Architecture, it is required that a PowerPC
assembler support at least a minimal set of extended mnemonics. These mnemonics encode to the opcodes of
other instructions; the only benefit of extended mnemonics is improved usability. Code using extended mnemonics
can be easier to write and to understand. Table B-5 lists the extended mnemonics required for the PPC405.
Note for every Branch Conditional mnemonic:
Bit 4 of the BO field provides a hint about the most likely outcome of a conditional branch. (Branch Prediction on
page 52 describes branch prediction). Assemblers should set BO
4
= 0 unless a specific reason exists otherwise. In
the BO field values specified in the following table, BO
4
= 0 has always been assumed. The assembler must allow
the programmer to specify branch prediction. To do this, the assembler will support a suffix to every conditional
branch mnemonic, as follows:
+ Predict branch to be taken.
– Predict branch not to be taken.
As specific examples, bc also could be coded as bc+ or bc−, and bne also could be coded bne+ or bne−. These
alternate codings set BO
4
= 1 only if the requested prediction differs from the standard prediction (see Branch
Prediction on page 52).
Table B-5. Extended Mnemonics for PPC405
Mnemonic Operands Function
Other Registers
Changed
Page
bctr Branch unconditionally to address in CTR.
Extended mnemonic for
bcctr 20,0
181
bctrl Extended mnemonic for
bcctrl 20,0
(LR) ← CIA + 4
bdnz target Decrement CTR.
Branch if CTR ≠ 0.
Extended mnemonic for
bc 16,0,target
175
bdnza Extended mnemonic for
bca 16,0,target
bdnzl Extended mnemonic for
bcl 16,0,target
(LR) ← CIA + 4.
bdnzla Extended mnemonic for
bcla 16,0,target
(LR) ← CIA + 4.
bdnzlr Decrement CTR.
Branch, if CTR ≠ 0,to address in LR.
Extended mnemonic for
bclr 16,0
175
bdnzlrl Extended mnemonic for
bclrl 16,0
(LR) ← CIA + 4.