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Assurance Process for Complex Electronics

OVERVIEW

Complex Electronics Overview

Complex Electronics Assurance Process

TECHNIQUES

CHECKLISTS

Site Map

Techniques

Requirements Evaluation

Risk Analysis

Requirements Review

Interface Analysis

Traceability Analysis

Decision Tables and Trees

Fault Tree Analysis

Failure Modes and Effects Analysis

Design Evaluation

Design Review

Change Impact Analysis

Functional and Physical Configuration Audits

 

Interface Analysis

Interface analysis is a technique to verify that the inputs and outputs of the complex electronic device are consistent with the defined signals, outputs, inputs, and data of the rest of the system. In addition, the technique looks for inputs and outputs that do not connect with other elements of the system (missing items).

Interface analysis is a manual analysis, with an assurance engineer comparing the description of the complex electronics with other system documentation. If the various system and sub-system requirements and designs are included in a data repository, it may be possible to use a tool to automate the analysis. The use of a checklist or worksheet may help the assurance engineer confirm the status of all inputs and outputs.

This page describes Requirements Interface Analysis for external interfaces and Design Interface Analysis for internal interfaces.

Requirements Interface Analysis

Interface analysis verifies that the requirements for the complex electronics interfaces with other hardware, software, users, and other systems are correct, consistent, complete, accurate, and testable. At the requirements phase, the main goal is to ensure that the system-level data and communication paths are consistent and complete. At the board level, the analysis should show that the complex electronics device inputs and outputs match those specified for the circuit board.

Inputs to the Requirements Interface Analysis

  • Complex Electronics specification/requirements
  • Circuit board and/or sub-system specifications
  • System specification
  • Interface documentation (formal or informal)
  • System and sub-system descriptions
  • Operational concepts
  • Product information (e.g. for the complex electronic device)

Process

Interface analysis is a manual analysis that compares the inputs and outputs of the complex electronic device with the corresponding connections from the system. Each input to the complex electronics is traced to the part of the system that provides that input, and the characteristics of the input (e.g., voltage level, type of signal, acceptable range) are checked against the description of what the system will provide. The same is done for the outputs of the complex electronics. In addition, the process of comparing the inputs and outputs should identify any signals that are orphans (do not come from or go to another part of the system) or undefined.

When performing an interface analysis for a complex electronic device, you want to focus on these areas:

  • Physical. Check the number of pins on the device, and ensure that it matches the number on the circuit board drawing. If pin assignments are defined, verify that they are consistent between the circuit board and the complex electronics specification. Also check for pins that are undefined or floating.
  • Power. Are the correct voltages applied to power pins? Is the correct type of power (A/C, D/C) provided? Are the ground pins connected? What voltage levels (range) are acceptable for the input or output? What voltage is considered a “high” or a “low” for logic values? Are fan-in and fan-out requirements met?
  • Signals. Verify that input signals match the output signals of other devices. Verify that every input signal comes from somewhere, and that every output signal is used by some other device. Verify that the types of signals are correct and consistent. Check timing requirements for the signals.
  • Communications. If the complex electronics will implement any communication schema, verify that the specification is correct for that schema, and consistent with other elements of the system. Check any defined messages or data for consistency across the interface.
  • System-level. Take a step back from the details and consider how the complex electronics works within the system. Look at the functions the device has to implement and consider whether the correct inputs are provided to the device. Will the device have enough information to perform its expected functions? Also look at the broader data and communications paths. Are there any bottlenecks that could affect the timing of data coming into the complex electronics, or slow down any outputs on the way to other devices? How would failure of one part of the communication path affect the complex electronic device?

Outputs of the Requirements Interface Analysis

  • Analysis Report
  • Identified issues, inconsistencies, or errors

The primary output of an interface analysis is a report detailing the process followed, the documents used, and the final results. The formality of the report will vary with the complexity of the project, and with any contractual requirements. For small projects, the information can be provided in an e-mail or one-page report. For large and complex projects, a multi-page report will often be necessary, with review and signature by the analyst, the project manager, and perhaps others.

If the interface analysis identifies problems or inconsistencies, these should be provided to the project using their problem reporting method. The assurance engineer should follow-up on the issues, to assure that the problems are resolved and the documentation is updated.

Design Interface Analysis

While the requirements interface analysis verified the external interfaces for the complex electronics, the design interface analysis looks at the internal interfaces. Signals come in to the device, are processed, and an output is generated. The internal connections along the way need to be consistent (e.g., digital ground to digital ground) and correct.

At the design stage, the external interfaces should be re-verified. The Design Interface Analysis should be performed first on the behavioral model (to verify that the signals are handled consistently) and then on the detailed design.

Inputs to the Design Interface Analysis

  • Complex Electronics design, including HDL models and written documents
  • The worksheets (or other documents) from the Requirements Interface Analysis

The following documents may be useful as references:

  • Complex Electronics specification/requirements
  • Circuit board and/or sub-system specifications
  • System specification
  • Interface documentation (formal or informal)

Process

At the design stage, interface analysis traces the input signals through the design and verifies that the signal type, range, voltage, and other factors are consistent. Output signals are traced back into the design to verify the same characteristics. This is a manual analysis that compares the inputs and outputs of the signal at each connection within the design.

When performing an interface analysis for a complex electronic device, you want to focus on these areas:

  • Logical. Logical blocks take inputs, process them, and provide outputs. Check the description of the logical block and verify that the correct types of inputs are provided. Make sure that no inputs are undefined or floating.
  • Power. At each internal connection, verify that the voltage levels (range) are consistent. For example, if the signal is +/- 5V, it should not suddenly become+/-10V somewhere in the design. Check for consistency in the “high” and “low” voltages for logic values.
  • Signals. At each internal connection, verify that input signals match the output signals of other devices/blocks. Verify that every input signal comes from somewhere, and that every output signal is used by some other element. Verify that the types of signals are correct and consistent. Check timing requirements for the signals.

Outputs of the Design Interface Analysis

  • Analysis Report
  • Identified issues, inconsistencies, or errors

As with the requirements interface analysis, the report should indicate the inputs used, methods followed, and final results. Problems and issues should be worked through the appropriate project channels.

 

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Curator: Richard Plastow
NASA Official: Cynthia Calhoun
Last Updated: 02/23/2006