Giotto: A TimeTriggered Language for Embedded Programming

1
GiottoA Time-Triggered Language for Embedded
Programming

• Thomas A. Henzinger Benjamin Horowitz Christopher
  Meyer Kirsch
• Presented by
• Amol Kandalgaonkar

2
Talk Overview

• Introduction
• Motivating Example
• Informal Description
• Formal definitions of Syntax
• ExampleSynchronized Robots
• Giotto Annotations
• Related work

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Introduction

• Increasing demand for high-level design
  methodologies for embedded systems
• Modifications of the embedded platform
  configuration typically require complete
  re-implementation and validation.
• The challenge is to understand the nature of the
  synthesis of real-time and concurrency and its
  operational counterparts, real-time scheduling
  and process communication

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What is Giotto ?

• Giotto is a time-triggered and platform
  independent programming language compiler
  runtime library
• Giotto aims at hard real-time control
  applications on distributed platforms
  (safety-critical applications)
• Giotto provides an abstract programming model for
  embedded control system development

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Embedded System Development

• Control Engineer Decomposes
• Designs
• Simulates
• Functionality
• Timing
• Software Engineer Decomposes
• Giotto Implements
• Tests

Application
Control Design
Giotto Program
Distributed Platform
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Motivating ExampleFly-by-wire Flight Control
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Example contd..

• Sensors,CPUs and Actuators
• Operational Modes
• Take off,cruise,landing,autopilot and degraded
• Different control laws needed in each mode
• Timing properties
• Periodic computation

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Informal Description

• Data is communicated through ports
• Port
• typed variable with a unique location in a
  globally shared namespace
• Persistent
• Input,Output,Environment and Entry
• Basic functional unit in Giotto is Task

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Contd..

• Concurrent tasks Mode
• Add/delete Tasks Switching Mode
• Task communication Drivers
• Drivers
• Code that transports and converts values between
  ports
• Synchronous,bounded code,executed logically
  instantaneously on the system level

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A Simple Task
Private ports F
Input Ports
Output Ports
Frequency
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Task Invocation
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Time line for Task Invocation
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Intertask Communication Semantics
F (10 ms)
G(5 ms)
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Intertask Communication Semantics contd..
Task
F
G
G
Time ms
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Modes

• Giotto Program is a set of Modes,each of which
  repeats the invocation of a fixed set of tasks
• At any time, a Giotto system is in a single mode
• Mode may contain modes switches,which specify
  transitions from the mode to other modes
• Mode switch can add/delete tasks
• Mode
• Parameterized set of tasks
• Period,Set of source ports,set of task
  invocations,set of actuator updates,set of mode
  switches

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A Mode
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Concrete Syntax

• Mode m ( ) period 10 ms
• taskfreq 1 do int x f ( )
• taskfreq 2 do int y g ( x , y )

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Time line for a round of Mode m
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Mode Switches

• Describes transition from one mode to another
• Specifies switch frequency,a target mode and
  driver
• Guard of the driver is called the exit condition

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Mode m
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Mode switch from m to m
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Timeline for Mode switch
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Concrete Syntax

• Start m( )
• mode m ( ) period 10 ms entryfreq 1
• taskfreq 1 do int x P ( )
• taskfreq 2 do int y Q ( x , y )
• exitfreq 2 if y 5 then m( y )
• mode m (int z ) period 10 ms entryfreq 2
• taskfreq 1 do int x P ( )
• taskfreq 4 do int u R ( x , z )

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Formal Definition of Pure Giotto

• Port Declarations ( p ,Type ,init )
• Task Declarations ( t ,In ,Out ,Priv ,f )
• Driver Declarations (d ,Src ,g , Dst, h)
• Mode Declarations
• ( m, µ,Sources,Invokes,Updates,Switches)
• Start Mode start Modes

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Giotto Annotations

• Performance constraintsTiming requirements may
  not be available on a single CPU
• Application may require proximity for tasks
• Distribute work between multiple CPUs
• Annotation with Platform constraints
• Pure Giotto is platform independent
• Annotated Giotto Directives for
  mapping,scheduling,compiling and executing a
  program on a particular platform

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Giotto Annotations contd..

• Multiple Annotation levels
• Advantages
• Permits incremental refinement
• Allows modular architecture for compiler
• Enables generation of formal models
• Hardware configurationHost and Nets
• Host CPU which can execute a Giotto task
• Nets Connects two or more hosts and can
  transport values
• Connection

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Giotto Annotations contd..

• Giotto P(P Platform) Specifies a set of
  hosts,a set of nets,worst case execution time
  information
• Giotto PM(M Map)Specifies,in addition, and
  assignment of tasks and drivers to CPUs and of
  connection to nets
• Giotto PMS(S Schedule)Specifies,in
  addition,scheduling information for each host and
  net
• Annotation is Complete if it fully determines all
  assignments at its annotation level.

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Giotto Annotations contd..

• Valid Giotto Program
• Not Overconstrained
• Consistent with the semantics of pure Giotto
• Giotto compiler(partially annotated pgm)
• Determines if it is not valid
• Produces a completely annotated valid PMS
  refinement
• Gives up and asks user for more annotations

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Schedule Constraint Graphs
Time-fixed vertices
Time-variable vertices
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Example Synchronized robots
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Two Robot Giotto Program
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Related work

• Inspired by TTA and synchronized programming
  languages
• TTA H/W architecture and communication protocol
• Giotto H/W independent,Protocol independent
  abstract layer for programming hard real time
  constraints using time triggered task invocation
  and mode switching
• Synchronized reactive languages assume zero delay
  vs Giotto unit delay value propagation

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Web Pointer

• www-cad.eecs.berkeley.edu/fresco/giotto/
• Thank you