Encoding:

Format:

LHUE rt, offset(base)

Purpose:

Load Halfword Unsigned EVA

To load a halfword as an unsigned value from user mode virtual address space when executing in kernel mode.

Description:

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

The contents of the 16-bit halfword at the memory location specified by the aligned effective address are fetched, zero-extended, and placed in GPR rt. The 9-bit signed offset is added to the contents of GPR base to form the effective address.

The LHUE instruction functions the same as the LHU instruction, except that address translation is performed using the user mode virtual address space mapping in the TLB when accessing an address within a memory segment configured to use the MUSUK access mode. Memory segments using UUSK or MUSK access modes are also accessible.

Refer to Volume III, Enhanced Virtual Addressing section for additional information.

Implementation of this instruction is specified by the Config5_EVA field being set to one.

Restrictions:

Only usable when access to Coprocessor0 is enabled and accessing an address within a segment configured using

UUSK, MUSK or MUSUK access mode.

Pre-Release 6: The effective address must be naturally-aligned. If the least-significant bit of the address is non-zero, an Address Error exception occurs.

Release 6 allows hardware to provide address misalignment support in lieu of requiring natural alignment.

Note: The pseudocode is not completely adapted for Release 6 misalignment support as the handling is implementation dependent.

Operation:

vAddr = sign_extend(offset) + GPR[base]
(pAddr, CCA) = AddressTranslation (vAddr, DATA, LOAD)
pAddr = pAddrPSIZE-1..3 || (pAddr2..0 xor (ReverseEndian2 || 0))
memdoubleword = LoadMemory (CCA, HALFWORD, pAddr, vAddr, DATA)
byte = vAddr2..0 xor (BigEndianCPU2 || 0)
GPR[rt] = zero_extend(memdoubleword15+8*byte..8*byte)

Exceptions:

TLB Refill, TLB Invalid, Bus Error, Address Error, Watch, Reserved Instruction, Coprocessor Unusable