Doorbell

A button is connected to PA0. Use an EXTI interrupt to mirror the button state to PA5, just like Challenge 03 but interrupt-driven instead of polling.

Your firmware should:

  1. Configure PA0 as input, PA5 as output
  2. Configure EXTI0 for both rising and falling edge on PA0
  3. Enable EXTI0 in NVIC (IRQ 6)
  4. In EXTI0_IRQHandler: clear the pending bit, read PA0 (IDR),

and mirror its state to PA5 using BSRR

The main loop should just spin. Let the ISR do all the work.

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