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Showing posts with the label ISO26262 Part6

How do you derive SSRs from TSR?

We recently conducted a training on Functional Safety Software. We started to discuss Software Safety requirements (SSRs), stating something like “SSRs are derived from the Technical Safety requirements (TSRs). Start by looking into those requirements in TSR that are assigned to SW”. Immediately, one of the trainees asked “oh, all we need to do is to filter out the TSRs for SW, and put them into a new document, name this document as SSR and that’s it we are done?” No marks for guessing that we shouted a loud and clear “NOOOO!!!” This is the subject of this blog. Once you have the TSR, how should you derive the SSR? We will tell you the actionable steps that you can take and also give you an example of how we have derived SSRs from TSRs. Firstly, let’s look at the actionable steps in the process of deriving the SSR: Read and understand the TSRs assigned to SW. What is the Software supposed to do? Is this clearly specified? The first step before starting the SSR is to ensure that SW Requ

A Handy Checklist for Safety Software Architecture

The ISO Standard specifies several methods on how to do Safety Software Architecture. These principles are generically stated. But most often these are not clear: - Why are these principles defined? - How do we ensure which principles we have achieved?  - Have we achieved the principle sufficiently?  For e.g., for a principle that states "restricted size of interfaces', why do I need this rule and how restricted should the size be? In this article, we first explain why these principles are needed in the context of Safety, and then propose a set of questions for each principle. These questions aim to act as a checklist to determine if the principle has been sufficiently satisfied. Assuming that most Organizations have well-defined guidelines for software architecture and the lessons learnt and best practices based on the experience from previous projects, these questions are intended to guide the architect or the reviewer of the architecture to think if all possible aspects hav

8 Steps for a best-practice Software Safety Analysis

Software Safety Analysis (SSA) is a kind-of-a verification activity that is performed on the Software to prove that it achieves all the Safety goals and provides the required Independence and freedom from interference.  Quite often we have seen that it is not clear for Software teams on how to do this analysis and which parts of the Software should they set their focus on. Also, in many cases, the activity is started towards the fag end of the project nearly when the safety software development has been completed, treating it more as a paper work to be completed.                             In this article, we present an 8-step method for performing a meaningful analysis. Before applying the method, here are some aspects to keep in mind: Basis and stage of the analysis SSA must be performed during the Architecture stage, based on the static and dynamic aspects of the Architecture. This provides the opportunity to correct weaknesses at an early stage of the software development. Stati