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.
Instruction Details
The base register. The SP can be used. In the ARM instruction set, for offset addressing only,
the PC can be used. However, use of the PC is deprecated.
+/- Is + or omitted if 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).
Contains the offset that is optionally shifted and added to the value of to form the
address.
The shift to apply to the value read from . If present, encoding T1 is not permitted. If
absent, no shift is applied and all encodings are permitted. For encoding T2, can
only be omitted, encoded as imm2 = 0b00, or LSL # with = 1, 2, or 3, and
encoded in imm2. For encoding A1, see Shifts applied to a register on page A8-10.
The pre-UAL syntax STRB is equivalent to STRB.
Operation
if ConditionPassed() then
EncodingSpecificOperations(); NullCheckIfThumbEE(n);
offset = Shift(R[m], shift_t, shift_n, APSR.C);
offset_addr = if add then (R[n] + offset) else (R[n] - offset);
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. A8-393