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March 2002 Release
585
Virtex-II Pro™ Platform FPGA Documentation
1-800-255-7778
Alphabetical Instruction Listing
R
b
Branch
Description
target
is a 32-bit operand that specifies a displacement to the branch-target address. The
assembler sets the instruction-opcode LI field to the value of
target
6:29
.
The next instruction address (NIA) is the effective address of the branch target. The NIA is
calculated by adding the displacement to a base address, which are formed as follows:
•
The displacement is obtained by concatenating two 0-bits to the right of the BD field
and sign-extending the result to 32 bits.
•
If the AA field contains 0 (relative addressing), the branch-instruction address is used
as the base address. The branch-instruction address is the current instruction address
(CIA).
•
If the AA field contains 1 (absolute addressing), the base address is 0.
Program flow is transferred to the NIA. If the LK field contains 1, then the address of the
instruction following the branch instruction (CIA + 4) is loaded into the LR.
Pseudocode
If AA
=
1
then NIA
←
EXTS(LI
||
0b00)
else
NIA
←
CIA + EXTS(LI
||
0b00)
if LK
=
1 then
(LR)
←
CIA + 4
Registers Altered
•
LR if LK
=
1.
Exceptions
•
None.
Compatibility
This instruction is defined by the PowerPC user instruction-set architecture (UISA). It is
implemented by all PowerPC processors.
b
target
(AA=0, LK=0)
ba
target
(AA=1, LK=0)
bl
target
(AA=0, LK=1)
bla
target
(AA=1, LK=1)
I Instruction Form
18
LI
AA LK
0
6
3
0
3
1
Содержание Virtex-II Pro PPC405
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