UM10429
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2010. All rights reserved.
User manual
Rev. 1 — 20 October 2010
185 of 258
NXP Semiconductors
UM10429
Chapter 19: Appendix LPC1102 ARM Cortex-M0 reference
Strongly-ordered —
The processor preserves transaction order relative to all other
transactions.
The different ordering requirements for Device and Strongly-ordered memory mean that
the memory system can buffer a write to Device memory, but must not buffer a write to
Strongly-ordered memory.
The additional memory attributes include.
Execute Never (XN) —
Means the processor prevents instruction accesses. A HardFault
exception is generated on executing an instruction fetched from an XN region of memory.
19.3.2.2 Memory system ordering of memory accesses
For most memory accesses caused by explicit memory access instructions, the memory
system does not guarantee that the order in which the accesses complete matches the
program order of the instructions, providing any re-ordering does not affect the behavior of
the instruction sequence. Normally, if correct program execution depends on two memory
accesses completing in program order, software must insert a memory barrier instruction
between the memory access instructions, see
However, the memory system does guarantee some ordering of accesses to Device and
Strongly-ordered memory. For two memory access instructions A1 and A2, if A1 occurs
before A2 in program order, the ordering of the memory accesses caused by two
instructions is:
Where:
- —
Means that the memory system does not guarantee the ordering of the accesses.
< —
Means that accesses are observed in program order, that is, A1 is always observed
before A2.
19.3.2.3 Behavior of memory accesses
The behavior of accesses to each region in the memory map is:
Fig 39. Memory ordering restrictions
Normal access
Device access, non-shareable
Device access, shareable
Strongly-ordered access
Normal
access
Non-shareable
Shareable
Strongly-
ordered
access
Device access
A1
A2
-
-
-
-
-
<
-
<
-
-
<
<
-
<
<
<