UM10462
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User manual
Rev. 5.5 — 21 December 2016
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NXP Semiconductors
UM10462
Chapter 24: LPC11U3x/2x/1x Appendix ARM Cortex-M0
Vector table —
If the program changes an entry in the vector table, and then enables the
corresponding exception, use a
DMB
instruction between the operations. This ensures that
if the exception is taken immediately after being enabled the processor uses the new
exception vector.
Self-modifying code —
If a program contains self-modifying code, use an
ISB
instruction
immediately after the code modification in the program. This ensures subsequent
instruction execution uses the updated program.
Memory map switching —
If the system contains a memory map switching mechanism,
use a
DSB
instruction after switching the memory map. This ensures subsequent
instruction execution uses the updated memory map.
Memory accesses to Strongly-ordered memory, such as the System Control Block, do not
require the use of
DMB
instructions.
The processor preserves transaction order relative to all other transactions.
24.3.2.5 Memory endianness
The processor views memory as a linear collection of bytes numbered in ascending order
from zero. For example, bytes 0-3 hold the first stored word, and bytes 4-7 hold the
second stored word.
describes how words of data are stored in
memory.
24.3.2.5.1
Little-endian format
In little-endian format, the processor stores the
least significant byte
(lsbyte) of a word at
the lowest-numbered byte, and the
most significant byte
(msbyte) at the
highest-numbered byte. For example:
24.3.3 Exception model
This section describes the exception model.
24.3.3.1 Exception states
Each exception is in one of the following states:
Inactive —
The exception is not active and not pending.
Pending —
The exception is waiting to be serviced by the processor.
Fig 79. Little-endian format
5HJLVWHU
$
OVE\WH
PVE\WH
$
$
%
%
%
%
%
%
%
%
0HPRU\
$
$GGUHVV