What is DIA (Development Interface Agreement) for ISO 26262?

As well as the HARA analysis for identifying the ASIL Level, DIA is defined in the early stages of the lifecycle according to ISO 26262. A DIA is precisely the agreement between customer and supplier in which are specified the responsibilities for activities to be performed, evidence to be reviewed, or work products to be exchanged by each party related to the development of items or elements.

The DIA specifically applies to the development phase, the supply agreement instead applies to production.

The DIA is so important because in the automotive sector, there is strong cooperation between suppliers and the manufacturer. The interface between the two parties is therefore fundamental in order to develop complex systems in accordance with all the requirements of functional safety.

The relationship between supplier and manufacturer has to be defined for elements or components within specific projects. It is not applied for devices sold off the shelf for which the application of use is not known.

In particular, what is outside the DIA is not binding for the suppliers. It is therefore so essential that these steps are taken at the early stages to properly define the safety characteristics of the project.

Supplier Selection Criteria

The supplier selection criteria include an assessment of the supplier’s ability to develop and, if applicable, produce items and elements of comparable complexity and ASIL according to the ISO 26262.

Supplier selection criteria include:

• Evidence that the supplier’s quality management system is adequate
• The supplier’s track record and quality
• Confirmation of the supplier’s functional safety capability within the supplier’s offer
• Results of previous functional safety assessments
• Recommendations from the vehicle manufacturer’s development, production, quality and logistics departments to the extent that they have an impact on functional safety

Already in the request for quotation (RFQ) a whole series of requirements concerning functional safety must be indicated:

• Formal request for compliance with ISO 26262
• Indications of the scope of supply, such as battery functions, properties and limits
• The safety targets or set of relevant safety requirements, including their assigned ASIL (or a conservative value if not available)
• The target values of the elements for failure rates and diagnostic coverage, if already available

The content of a DIA

A DIA should specify all the information prior to the development of a supply project, starting from its planning.

So, first of all, from manufacturer’ side a DIA shall include:

• The Safety Lifecycle activities to be performed by the customer and the Safety Lifecycle activities to be performed by the supplier
• The responsibility assigned to each party for each activity
• The communication or confirmation of target values
• The interface methods and tools required for collaboration between customer and supplier
• The functional safety assessment activities, according to ISO 26262-2, including the specification of which organization performs the functional safety assessment
• Any other relevant information to perform the supply

The provider is obliged to discuss the DIA and comment on it if anything is unclear or insufficiently consistent. Hence his direct responsibility in defining the plan and the activities to be carried out also becomes evident.

Customer Documentation

To make the project work, the supplier must provide evidence to the customer that the capability of the production process is met and maintained.

It is recommended to provide to customers with preliminary information to be choose as a supplier, including:

• Offer and Conditions
• Properly completed qualification questionnaires
• Selected project resources and their capability assessment, i.e. safety team members’ skills, competencies and qualification
• Organization-specific rules and processes, incl. tools, libraries
• Preliminary Plans, i.e. safety plans
• Iterative revisions addressing customer concerns
• Comments about DIA

Along project initiation and execution, it is a good practice to keep the documentation always updated, in regard to:

• Safety Plan
• HARA
• Hardware component behavior models, fault metrics
• Proven in use assessment (if applicable), with independent assessment of fitness for the project
• Change Management
• Specifications; Hardware, Software, integration.
• Implementation Constraints
• Verification Plan
• Hardware, Software and Integration Verification
• Review and Audits
• Series Production
• Post-SOP (Start of Production) Reports for Operation and Maintenace