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A driver that spins waiting for a status bit should also

  • A.clear the status bit before beginning to wait
  • B.count the iterations and give up after a bound
  • C.disable interrupts for the whole of the wait
  • D.raise its own priority while waiting

Answer: B

A device that never sets the bit, because it is absent or unclocked, hangs the system for ever otherwise. A timeout turns an unbounded hang into a reported failure, which is the difference between a diagnosable product and a dead one.

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