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example-exti.md

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ExampleEXTI

Purpose

ExampleEXTI is the minimal external interrupt test.

It validates:

  • EXTI configuration on PC13
  • callback dispatch on both edges
  • interaction between EXTI and a GPIO output (PB0)

Build

./tools/build-example.sh --example exti --preset nucleo-debug --test 0

Equivalent macro selection:

  • EXAMPLE_EXTI
  • TEST_0

Hardware setup

  • Use the Nucleo user button on PC13.
  • Observe the LED connected to PB0.

Runtime behavior

  • The firmware registers an EXTI callback on PC13.
  • The trigger mode is BOTH_EDGES.
  • Every edge calls toggle_led().

That means:

  • button press toggles the LED
  • button release toggles the LED again

Expected result

  • The LED changes state on every transition of the button signal.
  • The main loop stays idle; the observable behavior comes entirely from the interrupt.

What a failure usually means

  • Nothing happens: EXTI line not configured, wrong pin mapping, or callback not firing.
  • Only one transition toggles: edge trigger configuration is wrong.
  • Repeated chatter: mechanical bounce or noisy input.

Notes

This example is intentionally simple. It is useful to verify interrupt routing before adding more complex interrupt-driven logic.