Logging over UART with 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.

void log_send(const char *fmt, ...)
{
    char buf[128];
    va_list ap;
    va_start(ap, fmt);
    vsnprintf(buf, sizeof buf, fmt, ap);
    va_end(ap);
    HAL_UART_Transmit_DMA(&huart2, (uint8_t *)buf, strlen(buf));
}

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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