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THE ACTOR MODEL APPLIED TO THE RASPBERRY PI AND THE EMBEDDED DOMAIN - - PowerPoint PPT Presentation

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THE ACTOR MODEL APPLIED TO THE RASPBERRY PI AND THE EMBEDDED DOMAIN Omer Kilic || @OmerK Erlang Solutions Ltd. 1 Agenda Current state of Embedded Systems Overview of the Actor Model Erlang Embedded Project Modelling and

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THE ACTOR MODEL APPLIED TO THE RASPBERRY PI AND THE EMBEDDED DOMAIN

Omer Kilic || @OmerK

Erlang Solutions Ltd.

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Agenda

  • Current state of Embedded Systems
  • Overview of the Actor Model
  • Erlang Embedded Project
  • Modelling and developing systems using Erlang
  • Experiments with the Raspberry Pi
  • Future Explorations
  • Q & A

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Embedded Systems

An embedded system is a computer system designed for specific control functions within a larger system, often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal computer (PC), is designed to be flexible and to meet a wide range of end-user needs

– Infinite Wisdom of Wikipedia

“

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#include “stats.h”

Source: http://embedded.com/electronics-blogs/programming-pointers/4372180/Unexpected-trends 4

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Current Challenges

  • Complex SoC platforms
  • “Internet of Things”
  • Connected and distributed systems
  • Multicore and/or heterogeneous devices
  • Time to market constraints

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Embedded Systems

  • Bare Metal
  • No underlying OS or high level abstractions
  • RTOS
  • Minimal interrupt and thread switching latency,

scheduling guarantees, minimal jitter

  • Embedded Linux
  • Slimmed down Linux, with hardware interfaces

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Embedded Systems

  • Bare Metal
  • No underlying OS or high level abstractions
  • RTOS
  • Minimal interrupt and thread switching latency,

scheduling guarantees, minimal jitter

  • Embedded Linux
  • Slimmed down Linux, with hardware interfaces

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RTOS Concepts

  • Notion of “tasks”
  • OS-supervised interprocess messaging
  • Shared memory
  • Mutexes/Semaphores/Locks
  • Scheduling
  • Pre-emptive: event driven
  • Round-robin: time multiplexed

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Embedded Linux

  • Not a new concept, increased popularity due to

abundant supply of cheap boards

  • Raspberry Pi, Beagleboard/Beaglebone, Gumstix et al.
  • Familiar set of tools for software developers,

new territory for embedded engineers

  • No direct mapping for RTOS concepts, expecially

tasks

  • Complex device driver framework
  • Here be dragons

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Actor Model

  • Proposed in 1973 by Hewitt, Bishop, and Steiger
  • “Universal primitives of concurrent computation”
  • Building blocks for modular, distributed and

concurrent systems

  • No shared-state, self-contained and atomic
  • Implemented in a variety of programming

languages

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Actor Model

  • Asynchronous message passing
  • Messages kept in a mailbox and processes in the
  • rder they are received in
  • Upon receiving a message, actors can:
  • Make local decisions and change internal state
  • Spawn new actors
  • Send messages to other actors

functionality mailbox state

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Actor Model

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Actor Model

number_cruncher

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Actor Model

number_cruncher

{calc, Values}

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Actor Model

number_cruncher worker_a worker_b worker_c

{calc, Values}

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Actor Model

number_cruncher worker_a worker_b worker_c

{calc, ValSubsetA} {calc, ValSubsetB} {calc, ValSubsetA} {calc, Values}

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Actor Model

number_cruncher worker_a worker_b worker_c

{result, ResSubsetA} {result, ResSubsetB} {result, ResSubsetC}

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Actor Model

number_cruncher worker_a worker_b worker_c

{result, ResSubsetA} {result, ResSubsetB} {result, ResSubsetC} {result, Values}

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Limitations of the Actor Model

  • No notion of inheritance or general hierarchy
  • Specific to the language and library implementation
  • Asynchronous message passing can be

problematic for certain applications

  • Ordering of messages received from multiple

processes

  • Abstract definition may lead to inconsistency in

larger systems

  • Fine/Coarse Grain

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Erlang Embedded

  • Knowledge Transfer Partnership between Erlang

Solutions and University of Kent

  • Aim of the project: Bring the benefits of concurrent

systems development using Erlang to the field of embedded systems; through investigation, analysis, software development and evaluation.

  • http://erlang-embedded.com

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Why Erlang

  • Implements the Actor model
  • Battle-tested at Ericsson and many other

companies

  • Originally designed for embedded applications
  • Support for concurrency and distributed systems
  • ut of the box
  • Easy to create robust systems
  • (...and more!)

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High Availability/Reliability

  • Simple and consistent error recovery and

supervision hierarchies

  • Built in fault-tolerance
  • Isolation of Actors
  • Support for dynamic reconfiguration
  • Hot code loading

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spawn(math, fact, [5]) Pid1

Creating an Actor

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spawn(math, fact, [5]) math:fact(5) Pid2 Pid1

Creating an Actor

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Pid2 Pid1 Pid2 ! {self(),msg}

Communication

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Pid2 Pid1 Pid2 ! {self(),msg} {Pid1,msg}

Communication

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PidB PidA link(PidB)

Bidirectional Links

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PidB PidA link(PidB)

Bidirectional Links

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Process Error Handling

  • Let it Fail!
  • Abstract error handling away from the modules
  • Leaner modules
  • Supervision hierarchies

Supervisor Worker

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PidA PidB PidC

Propagating Exit Signals

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PidA PidB PidC

Propagating Exit Signals

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PidB {'EXIT', PidA, Reason} PidC

Propagating Exit Signals

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PidB PidC

Propagating Exit Signals

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PidC {'EXIT', PidB, Reason}

Propagating Exit Signals

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Propagating Exit Signals

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PidA PidC PidB

Trapping Exits

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PidA PidC PidB

Trapping Exits

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{'EXIT', PidA, Reason} PidC PidB

Trapping Exits

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PidC PidB

Trapping Exits

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External Interfaces

  • Native Implemented Functions (NIFs) and ports

used to interface external world to the Erlang runtime.

app hw_if hw_driver.c

Erlang VM

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Erlang, the Maestro

(flickr/dereckesanches)

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Raspberry Pi

  • 700 MHz ARM11
  • 256 MB DDR2 RAM
  • 10/100Mb Ethernet
  • 2x USB 2.0
  • (HDMI, Composite

Video, 3.5mm Stereo Jack, DSI, CSI-2)

$35

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Raspberry Pi in Education

  • The Raspberry Pi Foundation is a

UK registered charity.

  • Mission statement: "...to promote

the study of computer science and related topics, especially at school level, and to put the fun back into learning computing."

  • Future Engineers/Programmers!

(flickr/lebeus)

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Raspberry Pi Peripherals

  • GPIO
  • UART
  • I2C
  • I2S
  • SPI
  • PWM
  • DSI
  • CSI-2

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The ErlBuggy!

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ErlBuggy

http://vimeo.com/48375416

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Example: GPIO

pin17 proc_a {state, high}

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Example: GPIO

pin17 proc_a {state, high} proc_b {state, low} proc_c {state, high}

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Example: GPIO

pin17 proc_a {state, high}

???

proc_b {state, low} proc_c {state, high}

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Example: GPIO

GPIO proc_a pin17 {state, 17, high} proc_b {state, 17, low} proc_c {state, 17, high}

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GPIO Proxy

  • Replaces ‘locks’ in traditional sense of

embedded design

  • Access control/mutual exclusion
  • Can be used to implement safety constraints
  • Toggling rate, sequence detection, direction

control, etc.

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Fine Grain Abstraction

  • Advantages
  • Application code becomes simpler
  • Concise and shorter modules
  • Testing becomes easier
  • Code re-use (potentially) increases
  • Disadvantage
  • Architecting fine grain systems is difficult

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Component API

Universal Peripheral/Component Modules

Peripheral API Peripheral Implementation Platform Specific Universal

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Universal Peripheral/Component Modules

An Example:

TMP102 Temperature Sensor I2C Bus Driver Linux Kernel Driver Sensor API

I2C Bus Driver Linux sysfs

TMP102 Temperature Sensor I2C Bus Driver Linux Kernel Driver

Sensor API I2C Bus Driver BSD sysctl

TMP102 Temperature Sensor I2C Bus Driver Linux Kernel Driver

Sensor API I2C Bus Driver mmap()'ed register voodoo Temperature Sensor with I2C Interface

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TI OMAP Reference System

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Ponte Prototype

(flickr/carrierdetect)

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Ponte Prototype

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Ponte Prototype

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Hardware Simulator (WIP)

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Erlang Embedded Training Stack

  • A complete package for people interested in

developing the next generation of concurrent/ distributed Embedded Systems

  • Training Modules
  • Embedded Linux Primer
  • Erlang/OTP 101
  • Erlang Embedded Framework

Erlang Embedded Framework Erlang/OTP 101 Embedded Linux Primer Hardware Platform

Get in touch if you’re interested.

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Thank you

Any sufficiently complicated concurrent program in another language contains an ad-hoc, informally- specified, bug-ridden, slow implementation of half of Erlang.

– Robert Virding

Co-Inventor of Erlang

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  • http://erlang-embedded.com
  • embedded@erlang-solutions.com
  • @ErlangEmbedded

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