Register access macros

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.

#define GPIOB_ODR (*(uint32_t *)0x48000414u)

void pulse_pin(void)
{
    GPIOB_ODR |= (1u << 3);
    GPIOB_ODR &= ~(1u << 3);
}

uint32_t * volatile adc_dr = (uint32_t *)&ADC1->DR;

uint16_t adc_sample(void)
{
    return *adc_dr;
}

void short_delay(void)
{
    for (int i = 0; i < 1000; i++) { }
}

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.

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