5 Part 5: V-Modell Reference Work Products

5.3 Products

5.3.9 System Specifications

5.3.9.6 External Hardware Module Specification

Responsible: Hardware Architect (when using process module Hardware Development)

Activity: Preparing External Hardware Module Specification

Participating: Hardware Developer, Logistics Developer, Ergonomics Manager, Inspector, Safety Manager

Purpose

The »External Hardware Module Specification describes all functional and non-functional requirements posed on an »External Hardware Module. In order to prepare the specification, the requirements will be derived from the specifications of higher system elements. If changes are required in the course of the following development, the applicable specification shall be adapted at first. The »Evaluation Specification System Element defines the evaluation cases required for demonstrating the requirements of interfaces and specifications.

The External Hardware Module Specification mainly describes the requirements posed on the work product External Hardware Module and specifies the connected interfaces.

The requirements tracing ensures that all requirements posed on the respective elements will be taken into account. The External Hardware Module Specification will be prepared together with the architecture design of the »Hardware Units. The »Hardware Architect is responsible for the preparation of these products, thus ensuring the consistency between specification and architecture.

Requirements of the External Hardware Module Specification may influence the Logistic Support Specification, just as logistic requirements may influence the External Hardware Module Specification.

Is generated by

Hardware Architecture, Hardware Implementation, Integration and Evaluation Concept (see product dependency 4.7)

Depends on

Make-or-Buy Decision (see product dependency 5.14)

Hardware Specification, Logistic Support Specification, External Software Module Specification, Software Specification, External Unit Specification, System Specification (see product dependency 5.23)

External Software Module Specification, External Unit Specification, Request for Proposal, Contract, Contract Addendum (see product dependency 5.53)

5.3.9.6.1 External Hardware Module Overview

The »External Hardware Module Overview provides a brief survey of the work product External Hardware Module, which is to be realized. It outlines tasks and objectives of the work product External Hardware Module, e.g., by means of a block diagram with explanatory notes. For a better understanding, the role of the element within a »Hardware Unit will be described.

5.3.9.6.2 Interface Specification

An interface represents the boundary between a a work product of the type External Hardware Module and its environment. It describes the data exchanged at the system boundary and their logic dependencies. Thus, the interface defines the services to be provided by the work product External Hardware Module. One External Hardware Module can support several interfaces.

The interface description collects all functional requirements posed on the work product External Hardware Module, specifies all interfaces and presents them in their environment. Together with the non-functional requirements, the interface description defines the information required for developing the work product External Hardware Module. The interface description describes the interfaces to other hardware elements and the interfaces to the environment, e.g. the man-machine interface or interfaces to »Enabling Systems.

The description of the functional interface is subdivided into the description of the static elements and the description of the dynamic behavior. The static behavior specifies the structure of the interface, through which the functionalities of the work product External Hardware Module can be used. The dynamic behavior determines the sequence of use and the logic dependencies of the transmitted data and signals.

Static elements of a hardware interface include, e.g., information on electrical performance parameters (power, voltage, current, frequency, polarity), information on the mechanical design (type of connector, connector assignment, type of cable), or information on the technical design (function call and parameter list, transmission device, layout of user interface). The description of the dynamic behavior includes, e.g., the determination of communication protocols and their specification, the description of synchronization mechanisms and references for the use and operation of the interface. The description of functional sequences and data flows in normal, borderline and exceptional cases is also part of the dynamic behavior. Frequent interfaces of hardware elements include the following:

External communication interfaces for operations
Test and diagnosis interfaces (e.g., JTAG, switches, LED's)
Electrical, mechanical, hydraulic or pneumatic interfaces

Ideally, the description of the communication interfaces will be based on the layers of the OSI reference model.

The interface description is based on the summary of interfaces in the architecture and on the interface realizations of the »System Specifications of higher system elements.

The interface description should consider if a re-use of already existing system elements is possible. In addtion, it should be ensured that the interface is stable, thus allowing a long use of the hardware element.

5.3.9.6.3 Non-Functional Requirements

In addition to the functional requirements, an external hardware module must fulfill several non-functional requirements. Non-functional requirements are particularly important for hardware elements. They include at least the following requirements:

Computational capability as referred to computer architecture,
memory requirements (VM, NVM),
reliability (operation and storage, e.g. avoidance of metastability of programmable logic or data retention time in case of PROMS),
safety and security,
»Logistic Requirements (reliability, availability, maintainability, replaceability, repairability, usability, operability, disposal),
efficiency (power consumption, voltages, power supply units),
EMC (electromagnetic compatibility),
CE, »VDE,
environmental conditions,
legal requirements (safety and security, hazardous substances, etc.)
technologies to be used,
specifications for component selection,
materials, screening, marking, interfaces, heat management,
confidentiality and security (e.g., no user interface, encryption for ensuring the confidentiality of fixedly coded secret system parameters).

The non-functional requirements will be described in detail and specified by the actually required values. The non-functional requirements relevant for the work product External Hardware Module will be derived from the specifications of higher system elements or hardware elements.

5.3.9.6.4 Acceptance Criteria and Receiving Evaluation Criteria

Acceptance criteria specify which criteria must be fulfilled in order to ensure that the delivered work product of the type External Hardware Module fulfills the requirements of the External Hardware Module Specification. The acceptance criteria shall be presented in a measurable way. From a contractual point of view, the acceptance criteria describe the conditions for the decision as to whether the work product of the type External Hardware Module fulfills the applicable requirements or not. Acceptance criteria refer to functional and non-functional requirements.

The acquirer shall outline structure and number of acceptance criteria. The acceptance criteria should be structured in accordance with their significant components: initial situation, action(s) and expected result. In any case, the expected acceptance results must be specified for each acceptance criterion.

The receiving evaluation determines if the acceptance criteria are fulfilled. Thus the acceptance criteria are included as requirements into the Evaluation Specification Delivery.