Functional Safety in embedded systems

Have you ever thought of scenario where the brakes in your car fail? Have your thought the failure of a heavy lifting cranes and suddenly collapsing? All these scenarios are life threatening. These are the scenarios where safety is the major criteria. Following all the safety related design procedures in these systems is very important. In fact, there is something called functional safety that your system have to be complied before used in such scenarios. So, our electronics inside these systems should comply to functional safety. So, an embedded certification engineer need to know the basic criteria of functional safety.

Every system has an output and an input. The input also called excitation when applied need to provide output which is within a predetermined criteria. In this context, assessing the risks involved in the system and avoiding them is very important. Functional safety revolves around this idea. Any unacceptable risk that arises in the system should not cause physical injury to the humans.

For a designer engineer when he initially thinks of functional safety he will always to confused where to start with.  We have to segregate the functional safety process into 3 domain levels.

1. Hardware
2. software
3. Documentation

Here are the few pointers that will help the design engineer where to start with.
1. Functional safety though requires some concentration on the hardware front, it is more of a software related. It can be said that it is more of a system level thing.
2. The main expectation under the functional safety is that there should not be any risk to humans even when system fails. So, from a hardware engineer perspective, it is redundancy, continuous monitoring of on-board circuitry, shutting down the system under safe condition in case of critical failures which are important under functional safety.
3. The project has phases like requirements framing, system design, verification and validation. Functional safety should be chekced at each stage of design.
4. After functional safety analysis done at each stage as mentioned in the above point, designer go back to the previous step and implement the same if he faces any risks.
5. A functional safety engineer has to divide his system into number of sub-systems and then perform a risk analysis at each sub-system level.
6. During coding standards are to be followed
7. Standard test reports are to be prepared
8. Requirements need to be tracked at each point of the design cycle.
9. Functional safety engineer job is to identify the risks in the system and come up with meaures to mitigate those risks.

What is safety intergity level?
SIL short form for safety integrity level defines the relative level of risk-reduction provided by a safety function. To understand it more, the more the risks are reduced in your system, the higher the SIL rating we can achieve. SIL has 4 levels - SIL1, SIL2, SIL3, SIL4. When it comes to Automotive we talk about ASIL and in industrial domain we talk about SIL.

What are all the safety standards?
IEC 62304
IEC 61511
IEC 61508
IEC 60730
ISO 26262
IEC 62061
DO-178
EN 50128
IEC 61513
IEC 60335
IEC 61508 is more of an industrial standard (Examples: PLCs, drives and motors)
IEC 61513 is for the nuclear environment
ISO 26262 applies to automotive
DO-178 is for the Avionics industry
IEC 60730 is for appliances
EN 50128 is for the railways
IEC 61511 is for process industry
IEC 62061 is for machinary
IEC 62304 is for medical industry
IEC 60335 is for product manufacturing

The domains to which Functional safety is critical are
Automotive
Avionics
Industrial
Medical

Tools for functional safety
IAR used for code development is among the certified tools for functional safety

What are the various vendors that help us to achieve functional safety in our products?
1. The Hercules family from Texas Instruments where their micro controllers are ISO 26262 and IEC 61508 certified. TI provides Safe TI software frame work which helps ease your design efforts on functional safety requirements.
2. Infineon has the XMC and TLE series which helps users to achieve functional safety. Part of Infineon´s PRO-SIL parts, it is easy to achieve functional safety.
3. Safe Assure by NXP

What is expected in micro controllers/processor in functional safety?
1. The respective vendors of the micro controllers must provide functional safety software packages
2. Memory inside the micro controller with error detection and correction option. Here memory is both RAM and Flash
3. Internal clocking must have back up mechanisms
4. External error reporting by microcontroller
5. BIST - Built-in self test after power-on
6. Fault detections within the core