MISRA-C:2012 Rules & Directives

/* MISRA-C:2012 Directive 4.1: Run-time failures shall be minimised
   Requires: pre/post-condition checks, input validation */

Std_ReturnType Adc_Read(uint8_t channel, uint16_t *result)
{
    /* Pre-condition: valid channel index */
    if (channel >= ADC_MAX_CHANNELS) {
        return E_NOT_OK;                /* guard against invalid input */
    }
    /* Pre-condition: result pointer not NULL */
    if (result == NULL_PTR) {
        return E_NOT_OK;
    }

    *result = ADC_REGS->DR[channel] & 0x0FFFu;
    return E_OK;
}

/* MISRA-C:2012 Directive 4.7: If a function returns error information,
   that error information shall be tested
   Wrong: ignoring return value */
/* Adc_Read(0u, &val);           -- VIOLATION: return value ignored */

/* Correct: always check return value */
Std_ReturnType ret = Adc_Read(0u, &val);
if (ret != E_OK) {
    /* handle error */
    Dem_ReportErrorStatus(DEM_ADC_ERROR, DEM_EVENT_STATUS_FAILED);
}

🔬 Deep Dive — Core Concepts Expanded

This section builds on the foundational concepts covered above with additional technical depth, edge cases, and configuration nuances that separate competent engineers from experts. When working on production ECU projects, the details covered here are the ones most commonly responsible for integration delays and late-phase defects.

Key principles to reinforce:

• Configuration over coding: In AUTOSAR and automotive middleware environments, correctness is largely determined by ARXML configuration, not application code. A correctly implemented algorithm can produce wrong results due to a single misconfigured parameter.
• Traceability as a first-class concern: Every configuration decision should be traceable to a requirement, safety goal, or architecture decision. Undocumented configuration choices are a common source of regression defects when ECUs are updated.
• Cross-module dependencies: In tightly integrated automotive software stacks, changing one module's configuration often requires corresponding updates in dependent modules. Always perform a dependency impact analysis before submitting configuration changes.