You Mean We

1
You Mean Were Still Working On It?

• Sustaining a Design

2
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

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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

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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

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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
• IT team
• Self-interest and common courtesy
• You dont want 18 questions per day
• Ethics Do unto others
• Example (ICB)

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Suggestions for Sustainability

• Remember the dual nature of design input
• The CAD perspective
• Schematic gt PCB layout package gt circuit board
• HDL gt Synthesizer gt Fuse file gt Programmed
  FPGA
• The human perspective
• Schematic
• Interrelationships (time, space, connection)
• Debugging tool
• Functionality description
• HDL
• Describes functions and interaction
• Renders constraints understandable
• Ensure Readability!

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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.

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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

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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)

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Suggestions for Sustainability (cont.)

• Dont

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Suggestions for Sustainability (cont.)

• Do

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Suggestions for Sustainability (cont.)

• Help!

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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 (dont 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.

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

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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