RTC wake-up from STOP 2

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 rtc_wakeup_every(uint16_t seconds)
{
    RTC->CR &= ~RTC_CR_WUTE;
    RTC->WUTR = seconds - 1u;
    RTC->CR |= RTC_CR_WUCKSEL_2 | RTC_CR_WUTIE | RTC_CR_WUTE;   /* ck_spre, 1 Hz */
    NVIC_EnableIRQ(RTC_WKUP_IRQn);
}

void RTC_WKUP_IRQHandler(void)
{
    RTC->ISR &= ~RTC_ISR_WUTF;
    sample_flag = true;
}

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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