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

Assembler syntax
STR , [ {, #+/-}] Offset: index==TRUE, wback==FALSE
STR , [, #+/-]! Pre-indexed: index==TRUE, wback==TRUE
STR , [], #+/- Post-indexed: index==FALSE, wback==TRUE
where:
See Standard assembler syntax fields on page A8-7.
Instruction Details
The source register. The SP or the PC can be used. However, use of the PC is deprecated.
The base register. The SP can be used. For offset addressing only, the PC can be used.
However, use of the PC is deprecated.
+/- Is + or omitted if the immediate offset is to be added to the base register value (add == TRUE),
or – if it is to be subtracted (add == FALSE). #0 and #-0 generate different instructions.
The immediate offset used to form the address. Any value in the range 0-4095 is permitted.
For the offset addressing syntax, can be omitted, meaning an offset of 0.
Operation
if ConditionPassed() then
EncodingSpecificOperations();
offset_addr = if add then (R[n] + imm32) else (R[n] - imm32);
address = if index then offset_addr else R[n];
MemU[address,4] = if t == 15 then PCStoreValue() else R[t];
if wback then R[n] = offset_addr;
Exceptions
Data Abort.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. A8-385