Data retained across resets

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.

__attribute__((section(".noinit"))) static struct {
    uint32_t boot_count;
    uint32_t last_fault_pc;
} retained;

void boot_record(void)
{
    retained.boot_count++;
    if (RCC->CSR & RCC_CSR_IWDGRSTF) {
        log_watchdog_reset(retained.last_fault_pc);
    }
}

void HardFault_Handler(void)
{
    retained.last_fault_pc = __get_PSP();
    NVIC_SystemReset();
}

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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