Component Technologies for Embedded Systems

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Component Technologies for Embedded Systems

• Johan Eker

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Ptolemy IIA Software Laboratory

• Ptolemy II
• Actor based models
• Implemented in Java
• Graphical modeling and simulation environment
• Multiple models of computation
• Hierarchical heterogeneous models
• Code generation

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The Caltrop Actor Language

• a language for writing dataflow actors.
• It is designed as a domain-specific language.
• It compiles against the Ptolemy API (Pt/Java).

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Component Technology

• Examples Java beans, VB-components, etc
• Rationale
• Encapsulation
• Reuse
• Divide complexity
• Successful in many areas
• Problems with concurrent components
• Threads are not components
• Priorities are global parameters
• Difficult to design embedded systems component
  with state-of-the art technology

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Multipurpose tools

• Express almost anything, guarantee almost nothing
• You only need to know one programming language
• Quick starts, but sometimes slower endings
• Programmerslanguage, a lifelong marriage
• Examples
• Java
• C/C with RTOS, ADA, Modula-2
• RMA EDF scheduling

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Sharpen your tools

• Use problem specific tools
• Constrain the solutions
• Choice of tools, a major design decision
• Combine several tools

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Hierarchical, Heterogeneous Modeling and Design
in Ptolemy II
Models of computation
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Actor Interaction Semantics
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Ptolemy II Basics

• A model is a a set of interconnected actors and
  one director
• Actor
• Input output ports, states, parameters
• Atomic or composite
• Communicates using tokens
• When it is fired it produces and consumes tokens

Ports
consumer
producer
actor
actor
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Ptolemy II Basics

• Director
• Manages the data flow and the scheduling of the
  actors
• The director fires the actors
• Receiver
• Defines the semantics of the port buffers
• Models of Computation
• Define the interaction semantics
• Implemented in Ptolemy II by a domain
• Director Receiver

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Key Orthogonalizing the Concerns

• Write your actors so that communication and
  scheduling can be factored out
• Requires stylized Java and many informal
  contracts
• Solution generate Java actors from a more
  abstract description such as Caltrop

Communication
Scheduling
Algorithm
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Caltrop Actor Language

• Imperative, but with a functional flavor
• Ports, states, parameters actions
• Operates on token streams
• A1,2,3,..., B 1,2,3,... ÞC 2,4,6,...
• Embedded in a host language

actor Add () double A, double B ? double C
action a, b ? c c a b end end

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States
actor B () Double Input gt Double Output
Integer n 0 Double sum 0
action a gt sum / n n n 1
sum sum a end end
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Multiple actions, action conditions
actor C () Double Input gt Double Output
action a gt a where a gt 0 end action a
gt -a where a lt 0 end end
actor D () Double Input gt Double Output
action a gt abs(a) end end
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Port patterns
actor PairwiseSwap T () T Input gt T
Output action a, b gt b, a end end

• examples
• a, b, c
• a, b, c s
• s

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Channel selectors
actor Switch T () multi T Data, Integer
Select gt T Output action a at i, i
gt a end end
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Action tags, action selectors
actor FairMerge T () T Input1, T Input2
gt T Output A action a, gt a
end B action , a gt a end
selector (A B) end end

• other selectors are conceivable, e.g.
• (A B) (B A)
• ( (A B) (B A) )

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Caltrop implementationthe big picture.
parsing
source text
Caltrop
transformation,annotation
Caltrop AST
Caltrop(0)
code generation
target platform
Caltrop(1)
Caltrop(n)
split-phase CalCore
Ì
CalCore
Ptolemy II
Moses
Koala OS
Matlab/Pålsjö
DSP/FPGA
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The Rest of Caltrop

• Expressions are side effect free
• Lambda, block and actor closures
• Statements
• foreach, while, if-then-else
• Few built-in types list, map, set
• Immutable variable no aliasing
• Allows analysis
• Deadlock, schedulability, memory consumption

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Summary

• Dont get it right, keep it right
• Embedded system components
• Realized in the Ptolemy II framework
• Compiler is being developed at UCB
• More information
• Edward Lee Whats Ahead for Embedded
  Computing?, IEEE Computer, Sept. 2000
• http//ptolemy.eecs.berkeley.edu
• http//www.gigascale.org/caltrop