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Why is the WFI instruction preferred over a busy-wait loop for power saving in ARM processors?

hard📝 Conceptual Q10 of 15
ARM Architecture - Power Modes
Why is the WFI instruction preferred over a busy-wait loop for power saving in ARM processors?
AWFI executes instructions faster than busy-wait loops
BWFI reduces power by stopping CPU clock until interrupt, unlike busy-wait which keeps CPU active
CBusy-wait loops disable interrupts, WFI does not
DWFI resets CPU registers to save power
Step-by-Step Solution
Solution:

  1. Step 1: Compare WFI and busy-wait

    Busy-wait loops keep CPU running, consuming full power; WFI stops CPU clock to save power.

  2. Step 2: Understand power saving mechanism

    WFI puts CPU in low-power sleep until interrupt, making it more efficient.

  3. Final Answer:

    WFI reduces power by stopping CPU clock until interrupt, unlike busy-wait which keeps CPU active -> Option B

  4. Quick Check:

    WFI saves power by sleeping CPU, busy-wait does not [OK]
Quick Trick: WFI sleeps CPU; busy-wait wastes power [OK]
Common Mistakes:
  • Thinking WFI speeds execution
  • Confusing interrupt disabling
  • Believing WFI resets CPU

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