user manual

88 MicroBlaze Processor Reference Guide
1-800-255-7778 UG081 (v6.0) June 1, 2006
Chapter 4: MicroBlaze Instruction Set Architecture
Branch Immediate if Less Than
Branch if rA is less than 0, to the instruction located in the offset value of IMM. The target
of the branch will be the instruction at address PC + IMM.
Themnemonic bltidwillsettheDbit. TheDbitdetermineswhetherthereisabranch delay
slotor not. Ifthe D bitis set, itmeans that thereisa delay slotand theinstructionfollowing
the branch(i.e. inthe branchdelay slot) is allowed to complete executionbeforeexecuting
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.
If rA < 0 then
PC + sext(IMM)
PC + 4
if D = 1 then
allow following instruction to complete execution
Registers Altered
1 cycle (if branch is not taken)
2 cycles (if branch is taken and the D bit is set)
3 cycles (if branch is taken and the D bit is not set)
By default, Type BInstructionswill take the16-bit IMM fieldvalue and sign extendit to 32
bits to use as the immediate operand. This behavior can be overridden by preceding the
Type B instruction with an imm instruction. See the imm instruction for details on using
32-bit immediate values.
A delay slot must not be used by the following: IMM, branch, or break instructions. This
also applies to instructions causing recoverable exceptions (e.g. unalignement), when
hardware exceptions are enabled. Interrupts and external hardware breaks are deferred
until after the delay slot branch has been completed.
blti rA, IMM Branch Immediate if Less Than
bltid rA, IMM Branch Immediate if Less Than with Delay
1 0 1 1 1 1 D 0 0 1 0 rA IMM
0 6 11 16 31