Terdistribusi @2012,Eko Didik Sistem Embedded Jaringan ...didik.blog.undip.ac.id/files/2012/...Sistem_Embedded-Terdistribusi.pdf · dari kebutuhan sampai pengujian sistem I Kasus:

Jaringan dalam SistemEmbeddedTerdistribusi

@2012,Eko DidikWidianto

Sistem EmbeddedTerdistribusi

Event- &Time-TriggeredSystem

Evolusi KomputingTerdistribusi

Why Distributed MightBe Better

Lisensi

Jaringan dalam Sistem EmbeddedTerdistribusi

Kuliah#5 TSK-612 Sistem Embedded Terdistribusi - TA2011/2012

Eko Didik Widianto

Teknik Sistem Komputer - Universitas Diponegoro







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Review Kuliah Sebelumnya

I Pemodelan sistem embedded terdistribusi menggunakan UMLI Keterkaitan antara UML dengan metodologi desain yang diambilI Tipe diagram UML:

I Struktur: component diagram, deployment diagram, classdiagram

I Perilaku: use-case diagram, activity diagram, state diagramI Prinsip kerja sistem elevator: prinsip dasar, profil dan unjuk kerja,

arsitektur kontrol, sistem keselamatan, antarmuka pengguna danpertimbangan desain

I Implementasi UML untuk desain sistem elevatorI Mendesain sistem embedded terdistribusi secara komprehensif, mulai

dari kebutuhan sampai pengujian sistemI Kasus: mesin penjual soda otomatis (soda vending machine,

automated retail kiosk)







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Tentang Kuliah #5

I Pendekatan komunikasi/jaringan dalam sistem embedded terdistribusiI Event-triggered: transfer message asinkronI Time-triggered: transfer message sinkron

I Teknik sistem terdistribusi:I Sumber daya listrik terdistribusi (power switch)I Sinyal kontrol termultipleksI Komputasi terdistribusiI “Smart nodes” – kasus ekstrim dari terdistribusi

I Pengembangan sistem dari elektromekanikan menjadi distributedI Link

I Website: http://didik.blog.undip.ac.id/2012/03/06/kuliah-tsk-612-sistem-embedded-terdistribusi-2011/

I Email: [email protected] Acknowledgement:

I Beberapa gambar yang ada di slide ini diambil darihttp://www.ece.cmu.edu/~ece649/[ECE649]

http://didik.blog.undip.ac.id/2012/03/06/kuliah-tsk-612-sistem-embedded-terdistribusi-2011/


mailto:[email protected]

http://www.ece.cmu.edu/~ece649/







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Bahasan

Sistem Embedded Terdistribusi

Event- & Time-Triggered SystemPengiriman Message di Sistem TerdistribusiPendekatan Event-TriggeredPendekatan Time-Triggered

Evolusi Komputing TerdistribusiMenambah MikrokomputerRemote Power Switched SystemUse Multiple ComputersFully Distributed Control Network

Why Distributed Might Be BetterKelebihan Sistem TersentralModularitas Dalam Sistem TerdistribusiDiagnosabilitas dalam Sistem TerdistribusiKelebihan Sistem Terdistribusi Lainnya

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Multi-system Autonomous TerhubungNetwork







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Sistem Caterpillar 797

I Caterpillar Inc. produsesn peralatan/mesin berat (http://www.caterpillar.com/)







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Sistem Caterpillar Braking/Cooling Control







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X-By-Wire dalam Otomotif

I X-By-Wire (Drive-by_Wire) merupakan teknologi kuncidalam kontrol komputer dalam otomotif menggantikankontrol mekanik

I Mempunyai requirement yang ketat (Safety-RelatedFault-Tolerant)




Event- &Time-TriggeredSystemPengiriman Message diSistem Terdistribusi

PendekatanEvent-Triggered

Pendekatan Time-Triggered



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BahasanSistem Embedded Terdistribusi




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Contoh Sistem: Tombol Pemanggil Elevator

I Up ButtonI Button press

I Up Button LightI Light onI Light off

I Down ButtonI Button press

I Down Button LightI Light onI Light off









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Elevator Call Button: Event-Based MessagesI Button Press

I Turn on button lightI Send a “button pressed” message every time button

pressedI Keep button light turned on for 500 msec after button

pressedI Then turn button light off unless an acknowledgement

message is received

I Turn button light off when told to by hallway computer

I Hallway computer (hall controller, one for all floors)I When button is pressed, send acknowledgement to keep

light onI When button is pressed, notify dispatching computer to

send elevator carI When car doors open, send “turn button light off” message

I For dependable systems, need handshake messagesat every step

I Might be at application layerI Might be at network protocol layer









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Elevator Call Button: Time-TriggeredMessages

I Send “button” and “button light” messages every 150msec

I Each message has current state of “on” or “off”I Button Press

I Set “button state” variable to “pressed” (gets copied tohallway computer)

I Turn on button light and force on for 500 msec; then followmessage value

I Whenever you can, check the button light state and set lightaccordingly (perhaps every 150 msec)

I Hallway computer (one for all floors)I While button is pressed, notify dispatching computer to

send elevator carI Set button light state to “on”

I When car doors open, set button light state to “off” & buttonstate to “off”

I Message acknowledgements often not requiredI Missed button light state messages are self-correctingI User must correct a completely missed “button press”

message by pressing again









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Event-based vs Time-Triggered Message

I Event-based messages (“events”)I Send messages in response to an event

I Similar to event-triggered systemsI Think “asynchronous” state machine transitions

I Can have high message frequency with an “event shower”

I Time-Triggered messages (“state variables”)I Message sending is invisible to application programmer

I Send messages periodically with the latest informationI Think “synchronous” state machine transitions

I Reduces problems with missed messagesI Matches communication & computing load to system control

loop speeds rather than external environmentI Have to infer that an event happened based on observing a

value changeI Might be easy to miss a sequence of quick events









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Sistem Event-TriggeredI Sensors feed computers

I But their values arrive asynchronously – whenever valuesare available

I So, sensor values mustbe queuedI Computers are demand driven

I They process values from queues when availableI Network messages are queued for transmission

I Network is demand drivenI Transmission queues release messages according to some

network protocolI Actuators are demand driven

I Actuator outputs occur in response to event messages









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Problem - Coordinating EventAutomatic Transmission Car

I http://en.wikipedia.org/wiki/Automatic_transmissionI Car example: transmission unlocks to shift out of park if:

I (Engine is running) ANDI (Parking brake is OFF) ANDI (Brake is ON)









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Salah Satu Urutan Event

I But, this is too simplistic!I There are many arrival orders









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Problem di State Machine Asinkron

I Asynchronous state machines have trouble withcomplex condition

I Need to use states to keep track of which events have beenseen if order is flexible

I (This is also a problem with UML sequence diagrams)









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I Computers poll sensorsI Sensors queried periodicallyI Sampled whether or not there has been a change

I Computers are time triggeredI Sensors are sampled when it is time perform a computationI State variables are placed in buffers for later transmission on

networkI Network is periodic

I Copies of buffers are sent to all nodes periodicallyI Receiving nodes store most recent values, even if previous value

unusedI The “blackboard architecture?

I The receive buffers are that node’s locally stored copy of thecurrent blackboard contents

I Actuators are periodically drivenI Actuators outputs asserted periodically regardless of change/no

change









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Time-triggering MenyederhanakanKoordinasi Event

I Example: transmission unlocks to shift out of park if:I (Engine is running) ANDI (Parking brake is OFF) ANDI (Brake is ON)









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Updating Isi Buffer

I Design based on periodically updated state variablesI Every compute/communication block has a state variable

bufferI Buffer contents are updated whenever source sends an

updateI Buffer values are read whenever consuming functional block

needs them









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Perbedaan Desain: Event vs Time-Triggered

I Event triggered:I State machine only changes states when event occurs

I Actions within state are executed exactly once, when state is enteredI Each arc can have ONLY ONE incoming event/message

I Instantaneous state changesI Events arrive via network message or are serialized in some other wayI Requirements statements can depend on exactly ONE message

I In many cases these are simpler to understand & designI But, they are easily confused by dropped, duplicated, or out-of-order

messagesI Coordinating multiple messages requires messy temporary variables

I Time triggered:I State machine changes periodically based on variables and most recent

inputsI State machine has to infer events by noting state changesI Can change state based on multiple messages and/or local

variable valuesI Actions within each state are executed continually

I Tend to be more robust to dropped or out-of-order messages





Evolusi KomputingTerdistribusiMenambah Mikrokomputer

Remote Power SwitchedSystem

Use Multiple Computers

Fully Distributed ControlNetwork


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Step By Step Evolution

I how systems evolve from electromechanical to distributed?

1. Add a microcomputer2. Remote Power Switched System3. Use Multiple Computers

I Mostly-Distributed Control Network

4. Fully-Distributed Control Network










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No Computer at All

I You don’t need a computer at all to operate light bulbs withswitches!

I Non-computer control is possibleI RLC circuits, analog transistors, etc.










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Why Add A Computer?I Permits optimization

I Using a many-to-many relationship for actuators to controlsensors requires relays or other signal isolation (isolationrelays would also be “computation” )

I Can change control loop behavior depending on systemoperating modes

I Enables adding sophisticated features in softwareI Safety interlocks

I Require brake pedal to be depressed before shiftinginto gear

I Active safety operationsI Car locks doors once shifted into gear

I Timers, counters, conditional logicI Variable interval wipers that adapt to rain intensity

I Enables context-sensitive operationI Switches can be momentary closure “soft switches”I Permits controller to set value even when switch isn’t

pressedI Example: rear view window heaters off after timeout or

if outside temp is hot










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Sistem Tersentral

I Central computerI Reads input sensorsI Provides motive power to actuatorsI Common ground (e.g., metal vehicle frame) used as

electrical return path










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Wiring










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Wiring










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Apa yang Bisa Ditingkatkan Berikutnya?

I Computer has to switch power to actuatorsI Power switching components can be much larger than

microcontrollerI Power-carrying wires can form a thick, heavy wire bundle –

every conductor has to carry activation power, not just asignal

I So, let’s move power switching out to periphery ofsystem










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Remote Power Switched System

I Actuator outputs from computer are control signalsI Power is fed to remote switching modules that obey control

signals from CPUI No computational power in power switches – can be just

power transistorsI Blue lines are low-current logic signals, not high-current

switched power










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Mengapa Menggunakan Remote PowerSwitching?

I Thinner, lighter centralized cable bundlesI Pure centralized approach requires all power to touch CPU,

causing congestionI Control signal wires can be thinner, lighter, and more

flexible than power-controlled actuator wiresI Remote switched power can be run from power supply

directly to switching nodesI Cable can daisy-chain from region to regionI Yes, the power cable needs to be thicker since it handles all

power loads, but not as thick as a bundle of switched powerlines

I This sets the stage for networking in the nextevolutionary step

I Remote power switching isn’t a convincing win on wiring,but is a good start

I What if we replace all the analog control wires with anetwork?










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Use Multiple ComputersI It doesn’t take much more to put a CPU at each remote

power switchI We already have housing, circuit board, power distributionI Compared to that, a $1 microcontroller can be an

acceptable additional cost

I But, analog signals from central CPU to remote CPUs isinefficient

I So, let’s change multiple analog signals to serial digitalcommunications










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Menambah CPU di Blok Sensor - Aktuator

I Many sensors are near actuatorsI Sensor/actuator pairs are used to close control loopsI Many embedded systems aren’t that big, so it’s hard to be

too far from a CPU

I Add CPUs so that all sensors & actuators connect to aremote CPU

I This changes to a fully distributed approachI “Central” CPU might not really exist, just “big” and “small”

distributed CPUsI While we’re at it, switch to a network instead of

point-to-point wiring










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Jaringan Kontrol Terdistribusi

I Both power and control signals flow across a sharedwire

I Remote power switch nodes have a small computer fornetworking










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Contoh: Central Control + 4 CornerControllers










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Fully Distributed Control Network

I Main difference is no central CPUI No “Brain” node calling the shots – all the computation is

distributedI If all the remote CPUs can handle functionality, do you need

a central CPU?I (answer depends mostly on the software architecture)










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Tradeoff Kontrol Embedded TerdistribusiI Multiplexing control wires saves weight, wire cost,

cable thicknessI One digital wire replaces multiple analog wiresI Network must be fast enough to keep control loops closedI Can use one wire per distribution node if network bandwidth

is a concernI Network interface computer added to remote

switching nodesI Interfacing to even a simple network requires computer-like

capabilityI In simplest case, computer just “muxes” wires

I Local computer’s job is to translate control signals andswitch power locally

I More complicated computers permit functions tomigrate

I Once we have a remote computers, why not do computationthere beyond just network interface?

I Carried to its logical conclusion, don’t even need the centralcomputer anymore

I But, doing this requires a significant rethinking of softwarearchitecture










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Fine Grain Distributed System

I Each sensor and actuator also has CPU, power switching,network connection






Why Distributed MightBe BetterKelebihan Sistem Tersentral

Modularitas Dalam SistemTerdistribusi

Diagnosabilitas dalamSistem Terdistribusi

Kelebihan SistemTerdistribusi Lainnya

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Why Distributed Might Be Better

I Lots of little things can be better than one big thingI Extensibility / Flexibility / Task Partitioning










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Evolusi Elektronika OtomotifSource: [Kassakian96])

I Currently 12V DC power; 800 WattsI Old style: centralized power fed to actuators via

electromechanical switchesI Wiring harnesses with point-to-point connections

I New style: distributed computers each with severalsensors/actuators

I Local wiring from sensors/actuators to each ECU (ElectronicControl Unit)

I Global wiring/bus among ECUsI Power switched within ECU for light loads, with relays for

heavy loads

I Future: perhaps 42V DC power; 2.5 KW average / 12KW peak

I Higher voltage is more efficient for motors and distributionI Use local switching at sensors/actuators to reduce wiring

I Also put a CPU at every sensor/actuator

I Maybe an AC distribution bus so transformers can be used










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Kelebihan Sistem TersentralA Centralized System Justification

I Simple programming modelI Ability to think about distributed architectures is an

uncommon skill

I Powerful CPU(s)I Can use CPU for any needed function (can use desktop PC

sometimes)I Can adapt CPU loading to operating mode

I Better operating environment for digital electronicsI Put machine in sheltered area away from combustion,

environment

I Arguably simpler software configurationI All changes are made in one place in the system










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Kapan Sistem Tersentral Perlu“Dipertimbangkan”

I Total system cost/weightI Housing + cooling costs may outweigh wiring savingsI Distributed system has components in harsher environment

than central systems

I System expandabilityI Central system has limit on I/O connectorsI Distributed system has limit on bus fanout (typically 32

nodes)I But, arguably easier to install repeaters/bridges

I Distributed system has limited communication bandwidth(compared to backplane)

I Inventory costsI Distributed systems have cheaper components, potentially










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Modularitas Dalam Sistem TerdistribusiI Modular system development, support, and evolution

I A different team designing each nodeI Well-defined, tightly enforced interface (system message

formats)I Can upgrade individual models and limit effect of changes

on rest of system

I Limits competition for resources among differentfeatures

I Can add compute+I/O power incrementallyI But, wastes resources on a node that might be inactive

most of the timeI Difficult to share compute resources

I Reduces interactionsI Easier to make worst-case guarantees on a per-module

basisI Can re-certify only modules that have changedI Can have “critical” and “non-critical” modules, reducing

certification effort










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Contoh: Subsistem Mobil

I Different subsystems oftenprovided by different vendors

I Engine, transmission, anti-lockbrakes, power windows, etc.

I Different CPU for eachsubsystem means:

I Each vendor has a CPU all toitself – minimal softwareintegration issues

I Can change any componentwithout worrying about details ofinternal software affecting othersubsystems

I Change to conveniencesubsystem (windows) can beeasily shown to have no effecton safety critical subsystem(brakes)










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Diagnosabilitas dalam Sistem Terdistribusi

I Very often this is the decisive advantageI Decreasing maintenance and repair costs can make a big

difference!

I Remote diagnosabilityI Can isolate problems based on available processors

I Especially useful on systems where cables and connectorshave high failure rates

I General ideas:I Each controller can diagnose its own sensors/actuatorsI Each controller can diagnose its local connection to the

networkI Each controller can determine which other controls seem to

be aliveI Sampling a few controllers or network segments identifies

problem areas










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Contoh Diagnosabilitas










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Kelebihan Sistem Terdistribusi Lainnya

I FlexibilityI Can modify or upgrade systems by changing components

I Robust data transmissionI Digital network lets you use error coding, controlling noise

on signals

I Simpler to build and maintainI Single bus means you can’t hook the wrong wires up –

there is only one “wire”!

I Enables fault toleranceI A single CPU is a single point of failure – multiple CPUs

support fault tolerance

I Improves safety certifiabilityI Separate CPU for critical functions means non-critical CPU

can’t cause safety faults










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Flexibility di Sistem Terdistribusi

I Can add new components more easilyI Multiple vendors can add components to a well defined

HW+SW standard interfaceI New components can have different physical size/shape as

long as they can interface to the network

I Scalable systems can be created on apay-as-you-scale basis

I More copies of components added as system growsI (But, there are limits before repeaters are needed for network)

I But, individual node packaging might be too much overheadif most systems have only 2 or 3 copies of a component

I A single module with a couple long signal wires might becheaper than a couple modules with a network wire










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Contoh: Tombol Panggilan Elevator

I Can build using two standard units:I Two-button unit for middle floorsI One-button unit for end floors (spin arrow around for top floor)

I Adding more floors involves adding more button boxes to networkI Cost of long wiring runs makes using a network worthwhile

I But, for 2 or 3 floor lifts (which are the most prevalent):I Middle floor buttons aren’t the majority of those usedI Might be cheaper just to use a single controller box with discrete wires










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Transmisi Data yang Handal

I Analog data suffers from noiseI Digital data can be noise resistant

I Error detect & retransmitI Error correcting codes

I Digital sensor/actuator data provides better tradeoffsI Lower bit rate gives better SNRI Arbitrarily high precision at cost of bit rate

I Once you have digital data transmission, you also geta distributed processor










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