EmStar: An Environment for Developing Wireless Embedded Systems Software

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EmStar An Environment for Developing Wireless
Embedded Systems Software
Joint work by Busek, Cerpa, Elson, Estrin, Girod,
Stathopoulos, and many others contributions Pres
ented by Jeremy Elson jelson_at_cens.ucla.edu
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Fundamental Design Problems

• We are trying to build systems that meet global
  performance criteria
• Design evaluation must use a global view

BUT...

• The systems are inherently distributed and have a
  strictly local view.
• Systems entire purpose is to reduce and
  summarize data, where it cant all be collected
  practicably.
• The loss of this comprehensive information is
  crucial In a deployed system, we dont know if
  using the discarded information would have
  changed the outcome.

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Fundamental Design Problems

• Reuse of proven algorithms (and code) is very
  important, even for normal software
• Given the difficulty of instrumenting our fielded
  systems, reuse becomes crucial

BUT...

• Domain knowledge seems to seep in at virtually
  every layer, making reuse difficult

How do we create reusable components? How do we
verify components that we change?
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The EmStar Approach

• Allow software to be finely decomposed,
  modularized
• Provide rich forms of inter-module communication
• Toolchest of mechanism, not policy modules
• Isolate as much domain knowledge as possible
• Provide a run-time environment for deep debugging
• High visibility into the system is key
• Debug in a transparent context before the
  necessarily opaque deployment

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Modules that Isolate Domain Knowledge
Collaborative Sensor Processing Application
Domain Knowledge
3d Multi- Lateration
State Sync
Reusable Software
(Flexible Interconnects not a strict stack)
Topology Discovery
Acoustic Ranging
Neighbor Discovery
Reliable Unicast
Leader Election
Time Sync
Radio
Sensors
Audio
Hardware
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A Slow Descent into Reality

• EmStar allows the same Linux code to be used
• In a pure (low-fidelity) simulation
• Mostly simulated, but using a real wireless
  channel
• In a real testbed, small-scale but
  high-visibility
• Deployed, in-situ, at scale -- but low
  visibility
• Advantage over traditional simulators the
  debugged code itself, not just the high-level
  concepts, flow from simulation into the real
  world
• To maintain high visibility, we trade scale for
  reality

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EmStar Run-Time Environments
The spectrum allows high-visibility
debugging before jumping into low-visibility
deployment
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The Ceiling Array A Real Wireless Channel
Motes used to transmit and receive packets -- A
real-world augmentation to a virtual simulation
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Portable Array In-Situ, so Smaller Scale
Cables (green, invisible) attach to in-situ motes
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Real Deployment Stargates running Linux
Stargate (Intel, Crossbow) X-Scale based,
400MHz 32MB RAM, Flash runs Linux
Possible Network Interfaces
Mote Low-power, link to stand-alone motes
802.11 Higher power, faster back-channel
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EmView Visualization in All Modes
Base Station
Dynamic Construction Routes around faults Time,
control flow out Data, status return
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Deployments

• Seismic testbed
• Time distribution, control and monitoring
• James Reserve/ESS
• Diffusion, Tiered Architectures
• Sensorware Integration
• EmSim ran with existing (pre-EmStar) software
• Other CENS Projects
• Reusable toolbox will speed development