Battery voltage measurement

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.

uint16_t battery_mv(void)
{
    gpio_write(VBAT_EN, 1);
    uint32_t raw = adc_read(CH_VBAT);
    gpio_write(VBAT_EN, 0);
    return raw * 3300 / 4095 * 2;   /* 1:1 divider */
}

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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