Encoding:

LBU32

000101

rt

base

offset

6

5

5

16

Format: 

LBU rt, offset(base)

microMIPS

Load Byte Unsigned

Purpose:

Load Byte Unsigned

To load a byte from memory as an unsigned value

Description: 

 GPR[rt] = memory[GPR[base] + offset]

The contents of the 8-bit byte at the memory location specified by the effective address are fetched, zero-extended, and placed in GPR rt. The 16-bit signed offset is added to the contents of GPR base to form the effective address.

Restrictions:

None

Operation: 

vAddr = sign_extend(offset) + GPR[base]
(pAddr, CCA) = AddressTranslation (vAddr, DATA, LOAD)
pAddr = pAddrPSIZE-1..3 || (pAddr2..0 xor ReverseEndian3)
memdoubleword = LoadMemory (CCA, BYTE, pAddr, vAddr, DATA)
byte = vAddr2..0 xor BigEndianCPU3
GPR[rt] = zero_extend(memdoubleword7+8*byte..8*byte)

Exceptions:

TLB Refill, TLB Invalid, Address Error, Watch