MicroBlaze Processor Reference Guide
207
UG081 (v14.7)
Instructions
lhu
Load Halfword Unsigned
Description
Loads a halfword (16 bits) from the halfword aligned memory location that results from adding the
contents of registers rA and rB. The data is placed in the least significant halfword of register rD and
the most significant halfword in rD is cleared.
If the R bit is set, a halfword reversed memory location is used and the two bytes in the halfword are
reversed, loading data with the opposite endianness of the endianness defined by
C_ENDIANNESS
and the E bit (if virtual protected mode is enabled).
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.
An unaligned data access exception occurs if the least significant bit in the address is not zero.
Pseudocode
Addr
←
(rA) + (rB)
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 if Addr[31]
≠
0 then
ESR[EC]
←
00001; ESR[W]
←
0; ESR[S]
←
0; ESR[Rx]
←
rD
else
(rD)[16:31]
←
Mem(Addr); (rD)[0:15]
←
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
•
ESR[W], ESR[Rx], if an unaligned data access exception is generated
Latency
•
1 cycle with
C_AREA_OPTIMIZED=0
•
2 cycles with
C_AREA_OPTIMIZED=1
Note
The halfword reversed instruction is only valid if MicroBlaze is configured to use reorder
instructions (
C_USE_REORDER_INSTR = 1
).
lhu
rD, rA, rB
lhur
rD, rA, rB
1 1 0 0 0 1
rD
rA
rB
0 R 0 0 0 0 0 0 0 0 0
0
6
11
16
21
31