Component Technologies for Embedded Systems Johan Eker

Ptolemy II A Software Laboratory Ptolemy II – Actor based models – Implemented in Java – Graphical modeling and simulation environment – Multiple “models of computation” – Hierarchical & heterogeneous models – Code generation

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).

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

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

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

Hierarchical, Heterogeneous Modeling and Design in Ptolemy II sensors leader Br Acc Ba bang-bang PID follower controller actuators S Models of computation

Actor Interaction Semantics Are actors active? passive? How is the flow of control determined? Are communications timed? synchronized? buffered? How is the communications mediated?

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 producer actor consumer actor Ports

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

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

Caltrop Actor Language Imperative, but with a functional flavor Ports, states, parameters & actions Operates on token streams A:[1,2,3,...], B: [1,2,3,...] C: [2,4,6,...] Embedded in a host language actor Add () double A, double B  double C: action [a], [b]  [c]: c := a + b; end Input port Output port Input patternOutput expression Action body

States actor B () Double Input ==> Double Output: Integer n := 0; Double sum := 0; action [a] ==> [sum / n] : n := n + 1; sum := sum + a; end

Multiple actions, action conditions actor C () Double Input ==> Double Output: action [a] ==> [a] where a >= 0 end action [a] ==> [-a] where a < 0 end end actor D () Double Input ==> Double Output: action [a] ==> [abs(a)] end end

Port patterns actor PairwiseSwap [T] () T Input ==> T Output: action [a, b] ==> [b, a] end end examples –[a, b, c] –[a, b, c | s] –[| s]

Channel selectors actor Switch [T] () multi T Data, Integer Select ==> T Output: action [a] at i, [i] ==> [a] end end

Action tags, action selectors actor FairMerge [T] () T Input1, T Input2 ==> T Output: A: action [a], [] ==> [a] end B: action [], [a] ==> [a] end selector (A B)* end other selectors are conceivable, e.g. (A B)* | (B A)* ( (A B) | (B A) )*

Caltrop implementation —the big picture. Caltrop CalCore Caltrop (0) Caltrop (n) parsing Caltrop (1) transformation, annotation code generation source text Caltrop AST target platform Ptolemy IIMosesKoala OSMatlab/PålsjöDSP/FPGA split-phase CalCore 

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

Summary “Don’t 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 “What’s Ahead for Embedded Computing?”, IEEE Computer, Sept – –