Transcript VHDL Synthesis for High

You Mean We’re Still Working
On It?
Sustaining a Design
2005 MAPLD
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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
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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
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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
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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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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)*
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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!
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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?
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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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Design Integrity Concepts
Suggestions for Sustainability (cont.)
• Record the Design Process (cont.)
– Describe (cont.)
• What?
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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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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
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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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Design Integrity Concepts
Suggestions for Sustainability (cont.)
• Don’t:
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Design Integrity Concepts
Suggestions for Sustainability (cont.)
• Do:
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Design Integrity Concepts
Suggestions for Sustainability (cont.)
• Help!
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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
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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.
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Design Integrity Concepts
Suggestions for Sustainability (cont.)
Comments?
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Design Integrity Concepts
Suggestions for Sustainability (cont.)
Header from same design!
(After the fact documentation)
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Design Integrity Concepts
Suggestions for Sustainability (cont.)
• Post process documentation
– Theory of Operation / Users Manual
• Generate One
• Include
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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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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
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Design Integrity Concepts