ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Instruction Details
The label of the literal data item that is to be loaded into . The assembler calculates the
required value of the offset from the Align(PC,4) value of this instruction to the label.
Permitted values of the offset are:
Encoding T1 multiples of four in the range -1020 to 1020
Encoding T2 or A1 any value in the range -4095 to 4095.
If the offset is zero or positive, imm32 is equal to the offset and add == TRUE.
If the offset is negative, imm32 is equal to minus the offset and add == FALSE. Negative offset
is not available in encoding T1.
Note
In code examples in this manual, the syntax = is used for the label of a memory word
whose contents are constant and equal to . The actual syntax for such a label is
assembler-dependent.
The alternative syntax permits the addition or subtraction of the offset and the immediate offset to be
specified separately, including permitting a subtraction of 0 that cannot be specified using the normal
syntax. For more information, see Use of labels in UAL instruction syntax on page A4-5.
Operation
if ConditionPassed() then
EncodingSpecificOperations(); NullCheckIfThumbEE(15);
base = Align(PC,4);
address = if add then (base + imm32) else (base - imm32);
data = MemU[address,4];
if t == 15 then
if address == ‘00’ then LoadWritePC(data); else UNPREDICTABLE;
elsif UnalignedSupport() || address = ‘00’ then
R[t] = data;
else // Can only apply before ARMv7
if CurrentInstrSet() == InstrSet_ARM then
R[t] = ROR(data, 8*UInt(address));
else
R[t] = bits(32) UNKNOWN;
Exceptions
Data Abort.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. A8-123