12005 MAPLD Design Integrity Concepts

You Mean We’re Still Working On It?

Sustaining a Design

22005 MAPLD Design Integrity Concepts

Agenda – Design Sustainability

• Definitions– Sustainable – Capable of being supported (AH)– Sustainability – The characteristic of an item

that allows it to be supported

• Why is this important?

• Suggestions for sustainability

• Summary

32005 MAPLD Design Integrity Concepts

Why Sustainability?

• Missions may be multiple decades long– Flight systems may develop anomalous behavior– Ground equivalents may need repair– An understanding of the design is necessary to ensure

mission success– Original designers will not be available for debugging

• Other critical assignments• Working in telecon• Cruising the Pacific

– Sustainable designs allow analysis and correction without the access to the original designers

42005 MAPLD Design Integrity Concepts

Why Sustainability? (cont.)• Many designs are derivative

– Reuse of unmodified circuits essential for similar performance in modified designs

– Acceptable modification depends on creative incorporation of what IS• Derivation may take many years

– Example – Alice UVS• Design 1 – Rosetta (1997-2001)• Design 2 – New Horizons (2002-2005)• Design 3 – LRO (2005-2008)• Design 4 – Juno (2006 - ???)

– Staffing will not be constant– Human memory will not be precise

• Sustainability ensures an ability to efficiently build on past successes

52005 MAPLD Design Integrity Concepts

Why Sustainability (cont.)• You may not be the person who has to make it work

– Staffing is dynamic• You may quit• You may get re-assigned• Somebody with more clout may be needed to satisfy the customer

– Teams produce a product and share debugging• Test technician• S/W designer• I&T team

– Self-interest and common courtesy • You don’t want 18 questions per day• Ethics – Do unto others

– Example (ICB)*

62005 MAPLD Design Integrity Concepts

Suggestions for Sustainability• Remember the dual nature of design input

– The CAD perspective• Schematic => PCB layout package => circuit board• HDL => Synthesizer => Fuse file => Programmed FPGA

– The human perspective• Schematic

– Interrelationships (time, space, connection)– Debugging tool– Functionality description

• HDL– Describes functions and interaction– Renders constraints understandable

– Ensure Readability!

72005 MAPLD Design Integrity Concepts

Suggestions for Sustainability (cont.)

• Record the design process– Keep a notebook (type not vital)– Describe everything of importance

• Why? – Is this bus used for this function? – Is this function implemented like this? – Etc.

• How?– Do these things talk to one another?– Does this sequential logic work (state diagrams)?– Is the address map decoded?– Are errors handled?– Etc.

82005 MAPLD Design Integrity Concepts

Suggestions for Sustainability (cont.)

• Record the Design Process (cont.)– Describe (cont.)

• What?– Signals are needed to perform this function?– Do the waveforms look like?– Timing do I expect to observe?– Changes have I made?– Etc.

• When? – Record chronology– Provide a way to reproduce what was done– Make part of permanent project record– Example – Radarsat 1 Notebook

92005 MAPLD Design Integrity Concepts

Suggestions for Sustainability (cont.)

• Schematics– Provide an overview of the design

• Schematic table of contents• Block diagram (hierarchical design if available)

– Provide consistent naming scheme• Descriptive of signal direction / function / polarity• Consistent across logic gates and within various blocks

– Cluster sub-circuits on contiguous pages– Make connections between components explicit– Add comments where necessary for clarification– Remove unused circuitry (for FPGA schematics)

102005 MAPLD Design Integrity Concepts

Suggestions for Sustainability (cont.)• Don’t:

112005 MAPLD Design Integrity Concepts

Suggestions for Sustainability (cont.)

• Do:

122005 MAPLD Design Integrity Concepts

Suggestions for Sustainability (cont.)• Help!

132005 MAPLD Design Integrity Concepts

Suggestions for Sustainability (cont.)• HDL (Must be done from beginning!)

– Provide overall orientation to design– Provide top-level comments on

• Level of use (top, intermediate, etc.)• Overall purpose of function / block / module• Signal function and origination (external and internal)

– Provide operational comments on• State machine purpose and configuration (how? why?)• Transition logic (theory and reasoning)• Function of particular sequences• State to control signal translation

– Clarify obscure references• Remove superseded code (don’t comment out) and explain uncommon

structures– Improve readability

• Create logical file names• Minimize file, logic block, function sizes• Include related functions together (error generation, data interface, basic

function, etc.

142005 MAPLD Design Integrity Concepts

Suggestions for Sustainability (cont.)

Comments?

152005 MAPLD Design Integrity Concepts

Suggestions for Sustainability (cont.)Header from same design!(After the fact documentation)

162005 MAPLD Design Integrity Concepts

Suggestions for Sustainability (cont.)

• Post process documentation– Theory of Operation / Users Manual

• Generate One• Include

– Design concept / features– Operational Constraints– Appropriate Uses– Complete Engineering Documentation

• Update, release and correct as necessary– Create design archive

• Self-consistent and complete• Place under revision control• Control changes

172005 MAPLD Design Integrity Concepts

Summary• Useful designs will be corrected, modified and

evaluated – FOR A LONG TIME!– By people besides you

• Sustainability measure must be implemented to make this happen efficiently

• Sustainability requires– Adequate conceptual documentation and records– Clear and readable implementation records– Finalized and controlled configuration records

• Ensuring sustainability will preserve your legacy