ARM Technical Support Knowledge Articles

Unexpected memory behavior at addresse ranges 0x22xxxxxx, 0x23xxxxxx, 0x42xxxxxx or 0x43xxxxxx

Applies to: Cortex-M3, Cortex-M4

Answer

Please consult the "System address map" in the processor's Technical Reference Manual.

These address ranges correspond to the "bit band alias" regions, where accesses to word-aligned addresses are converted on the fly into bit-wise accesses to the corresponding "bit band region".

Bit-banding is an implementation option for the chip designer. If bit-banding is implemented in a chip, these "bit band alias" address regions cannot be usefully populated with memory, as all word-aligned accesses will be converted into bit-band accesses.

This feature of the memory map is not mentioned in the ARMv7-M Architecture Reference Manual because bit-banding is not a feature of the architecture; it is an implementation-specific feature of these processors.

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