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

Assembler syntax
LDRHT , [ {, #}] Offset: Thumb only
LDRHT , [] {, #+/-} Post-indexed: ARM only
LDRHT , [], +/- Post-indexed: ARM only
where:
See Standard assembler syntax fields on page A8-7.
The destination register.
The base register. The SP can be used.
Instruction Details
+/- Is + or omitted if or the optionally shifted value of is to be added to the base
register value (add == TRUE), or – if it is to be subtracted (permitted in ARM code only,
add == FALSE).
The immediate offset applied to the value of . Any value in the range 0-255 is permitted.
can be omitted, meaning an offset of 0.
Contains the offset that is applied to the value of to form the address.
Operation
if ConditionPassed() then
EncodingSpecificOperations(); NullCheckIfThumbEE(n);
offset = if register_form then R[m] else imm32;
offset_addr = if add then (R[n] + offset) else (R[n] - offset);
address = if postindex then R[n] else offset_addr;
data = MemU_unpriv[address,2];
if postindex then R[n] = offset_addr;
if UnalignedSupport() || address = ‘0’ then
R[t] = ZeroExtend(data, 32);
else // Can only apply before ARMv7
R[t] = bits(32) UNKNOWN;
Exceptions
Data Abort.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. A8-159