ARM Cortex-M4 - Behavior of Memory Accesses; Additional Memory Access Constraints for Caches and Shared Memory; Memory Region Shareability and Cache Policies

The Cortex-M4 Processor
ARM DUI 0553A Copyright © 2010 ARM. All rights reserved. 2-14
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2.2.3 Behavior of memory accesses
The behavior of accesses to each region in the memory map is:
The Code, SRAM, and external RAM regions can hold programs. However, ARM recommends
that programs always use the Code region. This is because the processor has separate buses that
enable instruction fetches and data accesses to occur simultaneously.
The optional MPU can override the default memory access behavior described in this section.
For more information, see Optional Memory Protection Unit on page 4-37.
Additional memory access constraints for caches and shared memory
When a system includes caches or shared memory, some memory regions might have additional
access constraints, and some regions are subdivided, as Table 2-12 shows:
Table 2-11 Memory access behavior
Address
range
Memory region
Memory
type
a
XN
a
Description
0x00000000 -
0x1FFFFFFF
Code Normal - Executable region for program code. You can also put data here.
0x20000000 -
0x3FFFFFFF
SRAM Normal - Executable region for data. You can also put code here. This region
includes bit band and bit band alias areas, see Table 2-13 on
page 2-16.
0x40000000 -
0x5FFFFFFF
Peripheral Device XN This region includes bit band and bit band alias areas, see
Table 2-14 on page 2-16.
0x60000000 -
0x9FFFFFFF
External RAM Normal - Executable region for data.
0xA0000000 -
0xDFFFFFFF
External device Device XN External Device memory.
0xE0000000 -
0xE00FFFFF
Private Peripheral Bus Strongly-
ordered
XN This region includes the NVIC, System timer, and system control
block.
0xE0100000 -
0xFFFFFFFF
Device Device XN Implementation-specific.
a. See Memory regions, types and attributes on page 2-12 for more information.
Table 2-12 Memory region shareability and cache policies
Address range Memory region Memory type Shareability Cache policy
0x00000000 - 0x1FFFFFFF Code
Normal
a
-
WT
b
0x20000000 - 0x3FFFFFFF SRAM
Normal
a
-
WBWA
b
0x40000000 - 0x5FFFFFFF Peripheral
Device
a
--
0x60000000 - 0x7FFFFFFF External RAM
Normal
a
-
WBWA
b
0x80000000 - 0x9FFFFFFF
WT
b