PWM duty and frequency control

The code

Embedded C for Cortex-M. It compiles. There are 5 real bugs in it: the kind that pass a bench test and fail in the field.

void set_duty(float pct)
{
    uint32_t arr = TIM3->ARR;
    TIM3->CCR1 = (uint32_t)(pct * arr / 100.0f);
}

void set_freq(uint32_t hz)
{
    uint32_t arr = (TIMER_CLK / hz) - 1;
    TIM3->ARR = arr;
}

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.

Related challenges