ADC with circular DMA

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 uint16_t adc_buf[64];
uint16_t g_avg;   /* read by the main loop */

void start_sampling(void)
{
    HAL_ADC_Start_DMA(&hadc1, (uint32_t *)adc_buf, 64);
}

void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef *h)
{
    uint32_t sum = 0;
    for (int i = 0; i < 64; i++) sum += adc_buf[i];
    g_avg = sum / 64;
}

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

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