UAV Implementation of Software Reuse

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UAV Implementation of Software Reuse

• Martin L. Gomez
• mgomez_at_aurora.aero

Aurora Flight Sciences Corporation 9950 Wakeman
Drive Manassas, VA [phone]
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Overview

• Why software reuse?
• How we did it
• What it cost us
• How we benefit

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Why Reuse?

• The traditional answer lower the DOLLAR cost of
  software development
• Other reasons
• More test opportunities means less risk of a
  crash
• Lower the opportunity costsnobody has enough
  software engineers
• Faster turnaround time

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Why Reuse (2)

• Aurora never had more than 6 or so software
  engineers at a time
• The first time we had to develop two UAVs at the
  same time, we looked for ways to do it more
  efficiently
• Over the years, this infrastructure was used to
  control
• Theseus, a 140, 7000 lbs twin-engine HALE
• AU-009, a 8, 140 lbs jet UCAV prototype
• Perseus B, a 70, 2000 lbs single-engine HALE
• Chiron, a Cessna 337 converted to a UAV testbed
• A hardware-in-the-loop simulator
• A ground control station

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How We Did It

• All UAVs have some common core of functionality
• Uplink turn buttons in GCS into actions on the
  A/V
• Downlink turn numbers in A/V into displays in
  GCS
• Lost uplink handling
• Autonavigation follow a route through space
• Autopilot wiggle the control surfaces in
  response to sensors
• Turn things on or off in response to commands or
  automatically

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How We Did It (2)

• With our traditional approach, achieving that
  functionality took 10 staff-months per UAV
• It consisted largely of software wiring, e.g.
• Read airspeed (say, an A/D reading) 3EA
• Convert binary to floating point engineering
  value 23.2 m/s
• Send it to the downlink (again turned into an
  integer)
• Send it to the autopilot (as floating point)
• Convert back to FP
• Send it to displays
• Archive it

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How We Did It (3)

• The functionality was abstracted into a few
  primitives (common to all UAVs)
• Interprocess Communication and Synchronization
• Reading and writing I/O devices
• Parsing and generating telemetry frames
• Autonavigation
• A few higher-level functions, slightly different
  for each UAV
• Mapping autopilot outputs to control surfaces
• Lost uplink handling
• Autopilot control law infrastructure
• and the rest is UAV-specific

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How We Did It (4)
Lost Uplink
Autonavigation
Autopilot
Control Mixing
Sensor Mgmt
A/D Reader
D/A Writer
Downlink process
Uplink process
Device Driver
Device Driver
Device Driver
Device Driver
Hardware
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How We Did It (5)

• The key was open-ended IPC
• We chose a RAM database to share signals between
  processes
• Generic processes, like the A/D and D/A handlers,
  or the uplink/downlink processes, are
  personalized at startup
• A big ROMd file called The Very Big List (VBL)
  tells each processes what do to on this airplane
• Each process scans the VBL when it boots

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Contents of VBL

• Logical name of process
• Signal name (OilPressure, PitchRate, etc.)
• Voltage-to-physical units calibration
• Does it get downlinked?
• In which frame?
• Field size, position, etc.
• Thus, each process knows what it has to do in
  this specific instantiation
• There may be many instantatiation of a process

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Autopilot and Control Mixing

• Autopilots are pretty generic
• Its the gains that vary dramatically from
  airplane to airplane
• The structure is pretty simple
• Surface deflection S gaini (valuei -
  commandi)
• The gains are physically separate from the
  structure
• The output of an autopilot is a virtual control
  surface
• Mapping the virtual control surface to a real one
  is a UAV-specific job

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What It Cost Us

• The cost to genericize our existing software
  was this
• Two staff-months to design the architecture and
  plan the project
• One consultant writing tools and database code
  for 3 months
• One in-house software engineer for 3 months
  adapting existing code
• Total of eight staff-months

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How We Benefit

• Being able to get basic functionality up and
  running in a few days
• Spending the time we save concentrating on the
  unique features of the UAV
• Being able to do this in 4 months with two s/w
  engineers