ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Examples
ARMv4 and ARMv5 Differences
The distinction between BE and BE-32 is not visible if all agents use the same endian format, because a
given memory address always accesses the same location in memory. However, if there are two agents with
different endianness the effect is as shown in Example H-1 and Example H-2.
Example H-1 Distinction between BE and BE-32 word stores observed by an LE agent
In this example:
Agent1 is big endian, R1=0x1000, R2=0x11223344
Agent2 is little endian, R1=0x1000.
Agent1:
Agent2:
STR R2, [R1]
LDR R2, [R1] // If Agent1 uses BE-32 endian format: R2 = 0x11223344
// If Agent1 uses BE endian format: R2 = 0x44332211
Example H-2 Distinction between BE and BE-32 byte stores observed by an LE agent
In this example:
Agent1 is big endian, R1=0x1000, R2=0x44, R3=0x11
Agent2 is little endian, R1=0x1000.
Agent1:
Agent2:
STRB R2, [R1]
STRB R3, [R1, #3]
H.3.3 Semaphore support
LDRB R2, [R1] // If Agent1 uses BE-32 endian format: R2 = 0x11
// If Agent1 uses BE endian format: R2 = 0x44
The only semaphore support in ARMv4 and ARMv5 is provided by the SWP and SWPB ARM instructions. Use
of these instructions is deprecated in ARMv6 and ARMv7 in favour of the exclusive access mechanism
provided by LDREX, STREX, and related instructions.
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