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Memory-mapped I/O means that peripheral registers

  • A.occupy addresses in the same space as memory
  • B.are reached only by means of dedicated input and output instructions
  • C.are accessed only through the direct memory access controller
  • D.must be read twice before the value is valid

Answer: A

Any instruction that can touch memory can then touch a peripheral, which is why a memory-mapped device is so convenient in C. The cost is address space consumed and the need to mark those addresses volatile so the compiler does not optimise the accesses away.

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