user manual

MicroBlaze Processor Reference Guide www.xilinx.com 91
UG081 (v6.0) June 1, 2006 1-800-255-7778
Instructions
R
br
Unconditional Branch
Description
Branch to the instruction located at address determined by rB.
The mnemonics brld and brald will set the L bit. If the L bit is set, linking will be
performed. The current value of PC will be stored in rD.
The mnemonics bra, brad and brald will set the A bit. If the A bit is set, it means that the
branch is to an absolute value and the target is the value in rB, otherwise, it is a relative
branch and the target will be PC + rB.
The mnemonics brd, brad, brld and brald will set the D bit. The D bit determines whether
there is a branch delay slot or not. If the D bit is set, it means that there is a delay slot and
the instruction following the branch (i.e. in the branch delay slot) is allowed to complete
execution before executing the target instruction. If the D bit is not set, it means that there
is no delay slot, so the instruction to be executed after the branch is the target instruction.
Pseudocode
if L = 1 then
(rD)
← PC
if A = 1 then
PC
← (rB)
else
PC
← PC + (rB)
if D = 1 then
allow following instruction to complete execution
Registers Altered
• rD
• PC
Latency
2 cycles (if the D bit is set)
3 cycles (if the D bit is not set)
br rB Branch
bra rB Branch Absolute
brd rB Branch with Delay
brad rB Branch Absolute with Delay
brld rD, rB Branch and Link with Delay
brald rD, rB Branch Absolute and Link with Delay
1 0 0 1 1 0 rD D A L 0 0 rB 0 0 0 0 0 0 0 0 0 0 0
0 6 11 16 21 31