Encoder ISR at top priority

The code

Embedded C for Cortex-M. It compiles. There are 3 real bugs in it: the kind that pass a bench test and fail in the field.

void encoder_init(void)
{
    NVIC_SetPriority(EXTI9_5_IRQn, 0);
    NVIC_EnableIRQ(EXTI9_5_IRQn);
}

void EXTI9_5_IRQHandler(void)
{
    BaseType_t woken;
    EXTI->PR1 = EXTI_PR1_PIF7;
    int32_t pos = encoder_read();
    xQueueSendFromISR(pos_q, &pos, &woken);
}

What an interviewer expects

• Point to each line you'd stop in a code review.
• Say what actually breaks: the failure mode, not just the rule it violates.
• Fix it, then defend the fix when asked the follow-up.

The bugs, reference fixes and the follow-up question are in the practice app, after you've tried it.

Companies that test this

Matched on the skills each company's embedded roles emphasise.

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