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

Assembler syntax
STRB , [ {, #+/-}] Offset: index==TRUE, wback==FALSE
STRB , [, #+/-]! Pre-indexed: index==TRUE, wback==TRUE
STRB , [], #+/- Post-indexed: index==FALSE, wback==TRUE
where:
See Standard assembler syntax fields on page A8-7.
The source register.
The base register. The SP can be used.
Instruction Details
+/- 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. Values are:
Encoding T1 any value in the range 0-31
Encoding T2 any value in the range 0-4095
Encoding T3 any value in the range 0-255.
For the offset addressing syntax, can be omitted, meaning an offset of 0.
The pre-UAL syntax STRB is equivalent to STRB.
Operation
if ConditionPassed() then
EncodingSpecificOperations(); NullCheckIfThumbEE(n);
offset_addr = if add then (R[n] + imm32) else (R[n] - imm32);
address = if index then offset_addr else R[n];
MemU[address,1] = 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. A8-389