APPENDIX A MIPS III INSTRUCTION SET DETAILS
Preliminary User’s Manual S15543EJ1V0UM
503
LBU
Load Byte Unsigned
LBU
base
LBU
1 0 0 1 0 0
rt
offset
31
26 25
21 20
16 15
0
6
5
5
16
Format:
LBU rt, offset (base)
Description:
The 16-bit
offset is sign-extended and added to the contents of general register base to form a virtual address.
The contents of the byte at the memory location specified by the effective address are zero-extended and loaded
into general register
rt.
Operation:
32
T:
vAddr
←
((offset
15
)
16
|| offset
15..0
) + GPR [base]
(pAddr, uncached)
←
AddressTranslation (vAddr, DATA)
pAddr
←
pAddr
PSIZE - 1..3
|| (pAddr
2..0
xor ReverseEndian
3
)
mem
←
LoadMemory (uncached, BYTE, pAddr, vAddr, DATA)
byte
←
vAddr
2..0
xor BigEndianCPU
3
GPR [rt]
←
0
24
|| mem
7 + 8* byte..8* byte
64
T:
vAddr
←
((offset
15
)
48
|| offset
15..0
) + GPR [base]
(pAddr, uncached)
←
AddressTranslation (vAddr, DATA)
pAddr
←
pAddr
PSIZE - 1..3
|| (pAddr
2..0
xor ReverseEndian
3
)
mem
←
LoadMemory (uncached, BYTE, pAddr, vAddr, DATA)
byte
←
vAddr
2..0
xor BigEndianCPU
3
GPR [rt]
←
0
56
|| mem
7 + 8* byte..8* byte
Exceptions:
TLB refill exception
TLB invalid exception
Bus error exception
Address error exception