ISO 26262 and functional safety
Any functional safety analysis is based on the evaluation of the hazard degree of the various failure modes that a system can generate. ISO 26262 provides several approaches in order to optimize this crucial stage.
Level of abstraction approach
This approach enables us to distinguish the roles of each level of details and therefore to focus on a single goal per level:
The level 1 is the « Item definition » that is used to define the interface of the item with the rest of the vehicle, its functionalities and to identify the potential impacts of a failure on the vehicle and thus on the people at risk.
The level 2 enables to separate the components of the item in two parts: on one hand the electronic and electric components and on the other hand the components using another technology. This stage is important because the chain of components like sensors, control units or actuators which are going to achieve the various outputs of the item can be specified.
The level 3 enables to identify which functionalities of the different parts of the item will be executed by hardware or software.
The level 4 enables to detail the different functionalities executed by the hardware and the software.
The estimation of the system hazard is only done at level 1 (HARA). This is a great step forward for the functional safety because it helps to focus the analysis only on the outputs of the item and thus limits to its bare minimum the informations to be analyzed and also allows clear consequences identification of the item failures on the vehicle and peoples.