Encoding:

Format:

LDR rt, offset(base)

Purpose:

Load Doubleword Right

To load the least-significant part of a doubleword from an unaligned memory address

Description:

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

The 16-bit signed offset is added to the contents of GPR base to form an effective address (EffAddr). EffAddr is the address of the most-significant of 8 consecutive bytes forming a doubleword (DW) in memory, starting at an arbitrary byte boundary.

A part of DW, the most-significant 1 to 8 bytes, is in the aligned doubleword containing EffAddr. This part of DW is loaded appropriately into the most-significant (left) part of GPR rt, leaving the remainder of GPR rt unchanged.

Restrictions:

Availability and Compatibility:

This instruction has been removed in Release 6.

Release 6 removes the load/store-left/right family of instructions, and requires the system to support misaligned memory accesses.

Operation:

vAddr = sign_extend(offset) + GPR[base]
(pAddr, CCA) = AddressTranslation (vAddr, DATA, LOAD)
pAddr = pAddrPSIZE-1..3 || (pAddr2..0 xor ReverseEndian3)
if BigEndianMem = 1 then
   pAddr = pAddrPSIZE-1..3 || 03
endif
byte = vAddr2..0 xor BigEndianCPU3
memdoubleword = LoadMemory (CCA, byte, pAddr, vAddr, DATA)
GPR[rt] = GPR[rt]63..64-8*byte || memdoublworde63..8*byte

Exceptions:

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