206
MicroBlaze Processor Reference Guide
UG081 (v14.7)
Chapter 5:
MicroBlaze Instruction Set Architecture
lbui
Load Byte Unsigned Immediate
Description
Loads a byte (8 bits) from the memory location that results from adding the contents of register rA
with the value in IMM, sign-extended to 32 bits. The data is placed in the least significant byte of
register rD and the other three bytes in rD are cleared.
A data TLB miss exception occurs if virtual protected mode is enabled, and a valid translation entry
corresponding to the address is not found in the TLB.
A data storage exception occurs if access is prevented by a no-access-allowed zone protection. This
only applies to accesses with user mode and virtual protected mode enabled.
Pseudocode
Addr
← (
rA) + sext(IMM)
if TLB_Miss(Addr) and MSR[VM] = 1 then
ESR[EC]
←
10010;ESR[S]
←
0
MSR[UMS]
←
MSR[UM]; MSR[VMS]
←
MSR[VM]; MSR[UM]
←
0; MSR[VM]
←
0
else if Access_Protected(Addr) and MSR[UM] = 1 and MSR[VM] = 1 then
ESR[EC]
←
10000;ESR[S]
←
0; ESR[DIZ]
←
1
MSR[UMS]
←
MSR[UM]; MSR[VMS]
←
MSR[VM]; MSR[UM]
←
0; MSR[VM]
←
0
else
(rD)[24:31]
←
Mem(Addr)
(rD)[0:23]
←
0
Registers Altered
•
rD, unless an exception is generated, in which case the register is unchanged
•
MSR[UM], MSR[VM], MSR[UMS], MSR[VMS], if an exception is generated
•
ESR[EC], ESR[S], if an exception is generated
•
ESR[DIZ], if a data storage exception is generated
Latency
•
1 cycle with
C_AREA_OPTIMIZED=0
•
2 cycles with
C_AREA_OPTIMIZED=1
Note
By default, Type B Instructions will take the 16-bit IMM field value and sign extend it 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 instruction
for details on using 32-bit immediate
values.
lbui
rD, rA, IMM
1 1 1 0 0 0
rD
rA
IMM
0
6
11
16
31
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