Memory Formats; Figure 2-1 Byte-Invariant Big-Endian (Be-8) Format; Figure 2-2 Little-Endian Format - ARM Cortex r1p3 Technical Reference Manual

2.5

Memory formats

2.5.1 Byte-invariant big-endian format
2.5.2 Little-endian format
ARM DDI 0363E
ID013010
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.
The processor can treat words of data in memory as being stored in either:
• Byte-invariant big-endian format
• Little-endian format.
Additionally, the processor supports mixed-endian and unaligned data accesses. For more
information, see the ARM Architecture Reference Manual.
In byte-invariant big-endian (BE-8) format, the processor stores the most significant byte of a
word at the lowest-numbered byte, and the least significant byte at the highest-numbered byte.
Figure 2-1 shows byte-invariant big-endian (BE-8) format.
Address
A[31:0]
In little-endian format, the lowest-numbered byte in a word is the least significant byte of the
word and the highest-numbered byte is the most significant. Figure 2-2 shows little-endian
format.
Address
A[31:0]
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Memory
7 0
31
B0 msbyte
+1 B1
+2 B2
+3 B3 lsbyte

Figure 2-1 Byte-invariant big-endian (BE-8) format

Memory
7 0
31
b0 lsbyte
+1 b1
+2 b2
+3 b3 msbyte
Programmer's Model
Register
24 23 16 15 8 7
B0 B1 B2
Register
24 23 16 15 8 7
b3 b2 b1

Figure 2-2 Little-endian format

0
B3
0
b0
2-6