Automotive Electronics & Standards

In automotive, MISRA refers to MISRA C / MISRA C++, a set of coding guidelines used to develop safe, reliable, and predictable software—especially for embedded systems like those found in vehicles.

What does MISRA stand for?

MISRA = Motor Industry Software Reliability Association

It was created by major automotive companies and suppliers to reduce software-related risks in vehicles.

Why MISRA is important in automotive

Modern cars rely heavily on embedded software for:

• Engine control units (ECUs)

• Braking systems (ABS)

• Airbags

• Steering (EPS)

• ADAS and safety systems

A software bug in these systems can be life-threatening, so MISRA focuses on preventing unsafe coding practices.

What MISRA actually does

MISRA provides rules and directives for writing code (mainly in C and C++) that:

• Avoid undefined or implementation-defined behavior

• Prevent memory corruption

• Improve readability and maintainability

• Make code easier to analyze and verify

• Reduce runtime failures

Common MISRA standards used

• MISRA C:2012 – most widely used in automotive

• MISRA C:2004 – older, still seen in legacy systems

• MISRA C++:2008 – for C++ automotive projects

Mandatory vs Advisory rules

MISRA rules are categorized as:

• Mandatory – must be followed (no exceptions)

• Required – can be violated only with justification

• Advisory – best practices

Automotive projects usually require MISRA compliance reports.

Where MISRA fits in automotive standards

MISRA works alongside:

• ISO 26262 – Functional Safety

• AUTOSAR – Automotive software architecture

• ASPICE – Process maturity model

MISRA focuses on how code is written, not system design.

Tools used to check MISRA compliance

• Polyspace

• PC-lint

• Coverity

• QAC

• Cppcheck (partial)

In one sentence

MISRA is a set of coding rules used in automotive software to ensure safety, reliability, and predictable behavior in embedded systems.

RAMS in automotive stands for Reliability, Availability, Maintainability, and Safety—a framework used to ensure vehicle systems operate dependably, are available when needed, easy to maintain, and safe throughout their lifecycle.

R – Reliability

Will the system work correctly over time?

• Probability that a system performs its intended function

• Example:

  • ECU should not fail during 10 years / 200,000 km

  • Sensor should not give false readings frequently

Metrics:

• MTBF (Mean Time Between Failures)

• Failure rate (λ)

A – Availability

Is the system operational when needed?

• Takes into account reliability and repair time

• Example:

  • ADAS system must be available whenever the vehicle is running

  • Vehicle downtime due to software failure must be minimal

Formula (simplified):

Availability = MTBF / (MTBF + MTTR)

M – Maintainability

How easily and quickly can faults be diagnosed and fixed?

• Ease of servicing, software updates, diagnostics

• Example:

  • OBD diagnostics

  • OTA (Over-the-Air) updates

  • Modular ECU replacement

Metrics:

• MTTR (Mean Time To Repair)

S – Safety

Will the system avoid causing harm, even when it fails?

• Most critical part in automotive

• Focuses on preventing hazards to people

• Example:

  • Airbag must not deploy unintentionally

  • Steering must fail safely

Standards:

• ISO 26262 (Functional Safety)

• SOTIF (ISO 21448)

Why RAMS is important in automotive

Cars are safety-critical systems. RAMS ensures:

• Fewer breakdowns

• Reduced recalls

• Compliance with regulations

• Customer trust

• Lower lifecycle cost

Where RAMS is applied

• Vehicle level (entire car)

• System level (braking, steering, powertrain)

• Software & hardware

• From concept → design → production → service