This is a demonstration article for the initial site framework. It shows the intended editorial structure and is not presented as a historical archive.

Define the event before measuring it

An input edge, core exception entry, the first ISR instruction, and completion of useful work are four different events. Draw the timeline first; otherwise optimization becomes guesswork.

Build a minimal measurement loop

Toggle a GPIO at ISR entry and capture it beside the external trigger on an oscilloscope. Record clocking, compiler optimization, cache state, RTOS critical sections, and the load model.

cEMBEDDED NOTES / TERMINAL
void EXTI_IRQHandler(void) {
    GPIO_DEBUG->BSRR = DEBUG_PIN;
    handle_event();
    GPIO_DEBUG->BRR = DEBUG_PIN;
}

Study the distribution

A good average does not prove a reliable system. For hard real-time paths, P99, maximum latency, and the context behind the tail matter far more.