Actor Oriented Programming with CAL designing embedded system components

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Actor Oriented Programming with CAL-designing
embedded system components

• Johan Eker
• Department of Automatic Control, Lund University
• Chris Chang, Jörn Janneck, Yang Zhao
• EECS, University of California at Berkeley
• LUCAS Seminar, October 22, 2002

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Multipurpose tools

• Express almost anything, guarantee
  almost nothing
• You only need to know one programming
  language!
• Easy to get started, harder to finish
• 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
• Combine several dedicated tools
• Dont get it right, keep it right

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Component Technologya component is a component
is a component

• Examples Java beans, VB-components, etc
• Rationale
• Encapsulation Reuse
• Successful in many areas
• Embedded components
• Problems with concurrency
• Threads do not compose well
• Difficult to encapsulate properties such as
  priorities, deadlines, execution times, etc.
• Static interfaces not good enough
• State-of-the art technology does not suffice

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Enter actor oriented programming

• Actors and models
• An application (or a model) is expressed as a
  network of actors
• Actors communicate via token passing
• When an actor is fired it consumes tokens and
  produces token
• The actor itself is agnostic about when and how
  it is scheduled and how and with whom it is
  communicating

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What's an actor
parameters
input ports
output ports
99
12
\
3
1
N
Actor
tokens
tokens
L
A
C
Data
state
Actors decouple data and control
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What's an application
B
D
A schedule Fire A Fire A Fire B Fire A Fire
C Fire D
A
C

• A Model of Computation governs the actor
  interaction, i.e.
• Sheduling
• Communication

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Hierarchical, heterogeneous modeling and design
in Ptolemy II
Slide courtesy of Edward Lee
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Components

• Actor Component
• A network of actors can be transformed into a
  single actor

MoC
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Enter CALCal Actor Language

• A domain-specific language for writing dataflow
  actors
• Ports, states, parameters
• Produces consumes tokens

A
actor A() Double input Double output
mutable Integer n 0 mutable Double sum
0 action a sum / n do n n
1 sum sum a end end
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Multiple actions and tags

• An actors defines a set of input-output relation

• Port pattern example
• in11,2,3, in21 matches all
• in11, in22 matches a2 a4
• in11,2,3, in2 matches a1

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Parameters Guards
actor A(Double max) Double input Double
output mutable Integer n 0 mutable
Double sum 0 action a guard sum
max do end action a sum / n do
n n 1 sum sum a end end
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Action schedules, priorities type parameters
actor FairMergeT() T Input1, T Input2 T
Output A action a, a do end
B action , a a do end schedule (A
B) end end

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

actor AnotherMergeT() T Input1, T Input2 T
Output A action a, a do end
B action a, b a do end priority B
A end end
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A CAL Application
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Analysis of a CAL Application
input
input
output
output

• Map the network into a petri net
• Compute firing vectors
• Find legal firing sequences
• Select a schedule
• Calculate buffer sizes
• Fold the CAL actor descriptions for A, B C

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Source level transformation
Assume we found the following schedule

• fire A, action a2
• fire B, action b1
• fire C, action c1

What are the benefits?

• Removes external buffers
• No need for a scheduler
• Source level components
• CAL provides an dynamic
• component interface

Components are refined upon composition!
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Some Cal Buzzwords

• Control flow analysis
• Token production/consumption rates
• Side effect free expressions
• Lambda and procedural closures
• First class of course
• Type parametric
• Immutable varibles as default
• No aliasing

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Key Concept Orthogonal Concerns
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Summary

• Embedded system components
• Java code for Ptolemy II/Grafchart frameworks
• C-code
• Compiler is being developed at UCB and Thales
  Research Ltd, UK.
• More information
• Eker et al Taming heterogeneity-the Ptolemy
  Approach, IEEE Proceedings
• http//www.gigascale.org/caltrop
• http//ptolemy.eecs.berkeley.edu