Entering and leaving STOP mode

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 enter_sleep(void)
{
    uart_puts("Sleeping\r\n");
    HAL_SuspendTick();
    HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON,
                          PWR_STOPENTRY_WFI);
    HAL_ResumeTick();
    uart_puts("Awake\r\n");
}

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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