Sleep until there's work

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.

static volatile bool work_pending;

void USART1_IRQHandler(void)
{
    rx_push(USART1->RDR);
    work_pending = true;
}

void main_loop(void)
{
    for (;;) {
        if (!work_pending) {
            __WFI();
        }
        work_pending = false;
        process_rx();
    }
}

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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