Some questions about the Cortex-M3 bit-banding feature

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(I am new to ARM microcontrollers. Pardon me if this is a naïve question. )

ARM-M3 processor provides a unique bit-banding feature which maps a bit in the first 1M address range of SRAM and peripheral regions to a 32-bit word in another alias address ranges, respectively.

My questions are:

  • Why only map the first 1M? What's so special about this first 1M range?

  • The mapped 32M alias ranges are still in the SRAM/Peripheral range, so they cannot be used for other purpose, right?

  • If I want to set a bit in the bit-banding region, should I write 0xFFFFFFFF, 0x000000FF or just 0x1 to the mapped alias word? It seems all of them can work but I am not sure which one is safe/correct.

cortex-m
cortex-m3
bit-banding
asked on Stack Overflow Oct 4, 2020 by smwikipedia • edited Oct 4, 2020 by Frant

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