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March 2002 Release
369
Virtex-II Pro™ Platform FPGA Documentation
1-800-255-7778
Branch and Flow-Control Instructions
R
Branch Conditional
lists the PowerPC
branch-conditional
instructions. The BO field specifies the
condition tested by the branch, as shown in
. The BI field specifies the
CR bit used in the test. These branches specify a 16-bit signed displacement to the branch-
target address by appending the 14-bit BD instruction field with 0b00. The displacement
value gives conditional branches the ability to cover an address range of ±32 KB.
Branch Conditional to Link Register
lists the PowerPC
branch-conditional to link-register
instructions. The BO field
specifies the condition tested by the branch, as shown in
. The BI field
specifies the CR bit used in the test. The branch-target address is read from the LR, with
LR[30:31] cleared to zero to form a word-aligned address. Using the 32-bit LR as a branch
target gives these branches the ability to cover the full 4 GB address range.
Table 3-6:
Branch-Unconditional Instructions
Mnemonic
Name
Operation
Operand
Syntax
b
Branch
Branch to relative address..
tgt_addr
ba
Branch Absolute
Branch to absolute address.
bl
Branch and Link
Branch to relative address. LR is updated with the
address of the instruction following the branch.
bla
Branch Absolute and Link
Branch to absolute address. LR is updated with the
address of the instruction following the branch.
Table 3-7:
Branch-Conditional Instructions
Mnemonic
Name
Operation
Operand
Syntax
bc
Branch Conditional
Branch-conditional to relative address..
BO,BI,tgt_addr
bca
Branch Conditional Absolute
Branch-conditional to absolute address.
bcl
Branch Conditional and Link
Branch-conditional to relative address. LR is
updated with the address of the instruction
following the branch.
bcla
Branch Conditional Absolute and
Link
Branch-conditional to absolute address. LR is
updated with the address of the instruction
following the branch.
Table 3-8:
Branch-Conditional to Link-Register Instructions
Mnemonic
Name
Operation
Operand
Syntax
bclr
Branch Conditional to Link Register
Branch-conditional to address in LR.
BO,BI
bclrl
Branch Conditional to Link Register
and Link
Branch-conditional to address in LR. LR is updated
with the address of the instruction following the
branch.
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