Übersicht. Laufzeitumgebungen Fallstudie TinyOS

Transcription

1 Übersicht Beispielanwendungen Sensor-Hardware und Netzarchitektur Herausforderungen und Methoden MAC-Layer-Fallstudie IEEE Energieeffiziente MAC-Layer WSN-Programmierung Laufzeitumgebungen Fallstudie TinyOS 80

2 Case study embedded OS: TinyOS & nesc TinyOS developed by UC Berkeley as runtime environment for their motes nesc as adjunct programming language Goal: Small memory footprint Sacrifices made e.g. in ease of use, portability Portability somewhat improved in newer version Most important design aspects Component-based system Components interact by exchanging asynchronous events Components form a program by wiring them together (akin to VHDL hardware description language) 81

3 TinyOS components Components Frame state information Tasks normal execution program Command handlers Event handlers Handlers Form a component s interface Understand and emit commands & events Hierarchically arranged Events pass upward from hardware to higher-level components Commands are passed downward init start stop fired Command handlers TimerComponent Tasks setrate fire Frame Event handlers 82

4 Concurrency Tasks perform arbitrary, long computation Have to be run to completion since no noncooperative multi-tasking is implemented No need for stack management, tasks are atomic with respect to each other However, we need a way to handle interrupts by preemption NesC allows the definition of functions that can run preemptively (to handle interrupts) Typically such function must not execute an indeterminate amount of time Only post a regular task to perform further action 83

5 Sync and Async By default functions (i.e. commands and events) are sync (e.g. can t be preempted) Only functions labeled async can run preemptively Example: async command void led0on(); For example all interrupt handlers must be async Async functions can only call async commands and signal async events How to call a sync function from within an async one? post a task to call these functions posting a task is async; tasks themselves are always sync So why use tasks at all? Why not labeling everything async? sync functions can t lead to race conditions async can lead the system into inconsistent states E.g. concurrent access to a variable 84

6 Atomic However, concurrent access to a code fragment can be made atomic Example: command bool increment() { atomic { a++; b = a + 1; } } So why not sprinkling the code with atomic blocks? Atomic blocks have a CPU cost You should minimize how many atomic blocks you have 85

7 Split-phase programming Handler/task characteristics and separation has consequences for programming model How to implement a blocking call to another component? Example: Order another component to send a packet Blocking function calls are not an option! Split-phase programming First phase: Issue the command to another component Receiving command handler will only receive the command, post it to a task for actual execution and returns immediately Returning from a command invocation does not mean that the command has been executed! Second phase: Invoked component notifies invoker by event that command has been executed Consequences e.g. for buffer handling Buffers can only be freed when completion event is received 86

8 Structuring commands/events into interfaces Many commands/events can add up nesc solution: Structure corresponding commands/events into interface types Example: Structure timer into three interfaces StdCtrl Timer Clock Build configurations by wiring together corresponding interfaces init StdCtrl start stop fired Timer TimerComponent Clock setrate fire 87

9 Building components out of simpler ones Wire together components to form more complex components out of simpler ones New interfaces for the complex component StdCtrl Timer StdCtrl Timer TimerComponent Clock Clock HWClock CompleteTimer 88

10 Defining modules and components in nesc 89

11 Wiring components to form a configuration StdCtrl; 90

12 A TinyOS Demonstration (1/2) Some supported methods (Windows & Linux) Manually (Windows: cygwin & RPM, Linux: RPM) Virtual machine image (VMWare, VirtualBox) Example: starting the Xubuntos 2.1 VMWare image Plug in Sensor node first! Start XubunTOS image Login: user = xubuntos, password = tinyos y $ z! setxkbmap de VMPlayer VM Removable Devices USB Devices: Future Technology Devices USB device (Port 1) 91

13 A TinyOS Demonstration (2/2) Hello World Call motelist Call cd /opt/tinyos-2.1-0/apps/blink Call make telosb install Look at BlinkAppC.nc and BlinkC.nc The resource: Demo: Plug in USB device Start Xubuntos 92

14 Zusammenfassung und Literatur Beispielanwendungen Sensor-Hardware und Netzarchitektur Herausforderungen und Methoden MAC-Layer-Fallstudie IEEE Energieeffiziente MAC-Layer WSN-Programmierung 93

15 Zusammenfassung Herausforderungen Energieeffizienz Geringe Rechen- und Speicherkapazität Geringe Kommunikationsbandbreite Erfordert neue Ansätze auf den einzelnen Protokollschichten: z.b. energieeffiziente MAC-Layer Aufweichen von striktem Protokoll-Layering: Cross-Layer- Optimierungen Geräte sind in der Regel keiner Person direkt zugeordnet Neue Sichtweise auf Kommunikation ID-Zentrisch versus Datenzentrisch Maschine-zu-Maschine-Kommunikation 94

16 Literatur Holger Karl and Andreas Willig, Protocols and Architectures for Wireless Sensor Networks, John Wiley & Sons, Jason Hill, Robert Szewczyk, Alec Woo, Seth Hollar, David E. Culler and Kristofer S. J. Pister, System Architecture Directions for Networked Sensors, Proceedings of the 9th International ACM Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS), Philip Buonadonna, Jason Hill and David Culler, Active Message Communication for Tiny Networked Sensors, Proceedings of the 20th Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM), David Gay, Philip Levis, Robert von Behren, Matt Welsh, Eric Brewer and David Culler, The nesc language: A holistic approach to networked embedded systems, Proceedings of the ACM Conference on Programming Language Design and Implementation (PLDI),