1. June 2008 WEI L3 - TinyOS 1 Wireless Embedded Inter-Networking Foundations of Ubiquitous Sensor Networks Operating Systems for WEI Devices TinyOS – Design and Philosophy David E. Culler University of California, Berkeley

2. June 2008WEI L3 - TinyOS2 Technology Perspective tier1 tier2 Client Server embedded net Physical World IT Enterprise internet Sensor tier4Mote tier3 Routers, APs, Gateways Embedded Tier: (mote) Router/Gateway Tier: Linux, Linux, Linux Server Tier: Unix (Linux, Solaris, AIX, HPux), Windows App Servers (Axis, J2EE, Weblogic, SAP, Oracle, …) Client Tier: (desk,lap,PDA,MP3, phone) Windows, Wince, Symbian, Linux/Java

3. June 2008WEI L3 - TinyOS3 Mote MCU Computer Systems Traditional systems: separate chips Microcontroller: integrate on single chip Timer MemoryStorage CPU Peripherals Network

4. June 2008WEI L3 - TinyOS4 Microcontrollers 48K ROM 10K RAM 250 kbps

5. June 2008WEI L3 - TinyOS5 Mote Characteristics Limited resources –RAM, ROM, Computation, Energy  Wakeup, do work as quickly as possible, sleep Hardware modules operate concurrently –No parallel execution of code (not Core 2 Duos!)  Asynchronous operation is first class Diverse application requirements  Efficient modularity Robust operation –Numerous, unattended, critical  Predictable operation

6. June 2008WEI L3 - TinyOS6 TinyOS Basics What is an OS? –Manages sharing of resources (hardware and software) –Interface to access those resources TinyOS Basics –System  Graph of components –Components »Provides interfaces »Uses interfaces –Interfaces »Commands »Events Network Link Web Server

7. June 2008WEI L3 - TinyOS7 Traditional Systems Well established layers of abstractions Strict boundaries Ample resources Independent Applications at endpoints communicate pt-pt through routers Well attended User System Physical Layer Data Link Network Transport Network Stack Threads Address Space Drivers Files Application Routers

8. June 2008WEI L3 - TinyOS8 by comparison, WSNs... Highly Constrained resources –processing, storage, bandwidth, power Applications spread over many small nodes –self-organizing Collectives –highly integrated with changing environment and network –communication is fundamental Concurrency intensive in bursts –streams of sensor data and network traffic Robust –inaccessible, critical operation Unclear where the boundaries belong –even HW/SW will move => Provide a framework for: Resource-constrained concurrency Defining boundaries Appl’n-specific processing and power management allow abstractions to emerge

9. June 2008WEI L3 - TinyOS9 Storage ProcessingWireless Sensors WSN mote platform Abstractions Emerge from Experience Radio Serial FlashADC, Sensor I/F MCU, Timers, Bus,… Link Network Protocols Blocks, Logs, Files Scheduling, Management Streaming drivers Over-the-air Programming Applications and Services Communication Centric Resource-Constrained Event-driven Execution TinyOS 2.0

10. June 2008WEI L3 - TinyOS10 TinyOS New operating system built specifically for wireless sensor networks –Small, robust, communication centric design –Resource-constrained concurrency –Structured Event-driven SW architecture –Tool for protocols and dist. Algorithms Designed for synthesis and verification –Eg. Ptolemy, Metropolis, … –Whole-system compile-time analysis Rich set of services and development environment World-wide adoption –Open source, lead by UCB / Intel –Corporate and academic (1000s) –Dozen of platforms –de facto sensor net standard CC2420 Radio byte Radio Packet UART Serial Packet ADC Tempphoto Active Messages clocks bit byte packet Route map routersensor appln application HW SW

11. June 2008WEI L3 - TinyOS11 A worldwide community Storage Wireless Processing Sensors SmartDust NEST Wireless Sensor Networks

12. June 2008WEI L3 - TinyOS12 Stack Library Alternative MicroController 802.15.4 Radio Hardware Software cmds interrupts Proprietary Network Stack (zigbee spec or other) cmds interrupts send start stop OEM / Developer Custom Code, RTOS, or other TICK OEM/Dev Hardware Link & networks protocols buried in block-box library –Ember, Figure8,... No execution model or storage model Arbitrary system/user code must TICKle it “sufficiently often” Undefined call duration No system services Difficult to validate Same hardware, but a very different approach

13. June 2008WEI L3 - TinyOS13 Sensors Modern Mote Tier TinyOS Architecture tier1 tier2 client server tier3 SensorNet GW/Proxy physical info net MCURadioSensors Hardware Abstraction Layer TinyOS Runtime Services Common Link Abstraction Networking Protocols Management Embedded applications built on a rich set of node services. –Timing, sensor streams, storage –Local processing –Reliable, low-power communication –Platform independent + extensions Embedded Application tier4 “mote” Physical World

14. June 2008WEI L3 - TinyOS14 TinyOS from First Principles

15. June 2008WEI L3 - TinyOS15 Characteristics of Network Sensors Small physical size and low power consumption Concurrency-intensive operation –multiple flows, not wait-command-respond Limited Physical Parallelism and Controller Hierarchy –primitive direct-to-device interface –Asynchronous and synchronous devices Diversity in Design and Usage –application specific, not general purpose –huge device variation => efficient modularity => migration across HW/SW boundary Robust Operation –numerous, unattended, critical => narrow interfaces sensors actuators network storage

16. June 2008WEI L3 - TinyOS16 Classical RTOS approaches Responsiveness => Provide some form of user-specified interrupt handler »User threads in kernel, user-level interrupts –Guarantees? Deadlines / Controlled Scheduling –Static set of tasks with prespecified constraints »Generate overall schedule => Doesn’t deal with unpredictable events, especially communication –Threads + synchronization operations => Complex scheduler to coerce into meeting constraints Priorities, earliest deadline first, rate monotonic Priority inversion, load shedding, live lock, deadlock »Sophisticated mutex and signal operations Communication among parallel entities –Shared (global) variables: ultimate unstructured programming –Mail boxes (msg passing) => external communication considered harmful –Fold in as RPC Requires multiple (sparse) stacks –Preemption or yield

17. June 2008WEI L3 - TinyOS17 Alternative Starting Points Event-driven models –Easy to schedule handfuls of small, roughly uniform things »State transitions (but what storage and comm model?) –Usually results in brittle monolithic dispatch structures Structured event-driven models –Logical chunks of computation and state that service events via execution of internal threads Threaded Abstract machine –Developed as compilation target of inherently parallel languages »vast dynamic parallelism »Hide long-latency operations –Simple two-level scheduling hierarchy –Dynamic tree of code- block activations with internal inlets and threads Active Messages –Both parties in communication know format of the message –Fine-grain dispatch and consume without parsing Concurrent Data-structures –Non-blocking, lock-free (Herlihy)

18. June 2008WEI L3 - TinyOS18 TinyOS design goals Simple framework for resource constrained concurrency –Single stack Flexible hardware/software and system boundary Expressive enough to build sophisticated, application specific system structures –Avoid arbitrary constraints on optimization Communication is integral to execution –Asynchrony is first class Promote robustness –Modular –Static allocation –Explicit success/fail at all interfaces –Reuse Ease of interpositioning

19. June 2008WEI L3 - TinyOS19 Embedded System Design: Hardware Abstraction Abstract a hardware unit for convenient software access. Datasheet describes set of interfaces (pins, wires, busses) and operations –Commands that can be asserted or issued to it –Events that it will signal or raise –Interfaces to other hardware units that it is attached to Internally the unit has state and computational processes that operate in parallel with other units. state

20. June 2008WEI L3 - TinyOS20 Embedded System Design: Data Acquisition Configure and command ADC to sample external I/O attached to sensor. –Either directly or over a bus protocol Obtain readings upon notification by polling or handling interrupts –One short or periodic Perform processing on the readings (smoothing, thresholding, transformation) and possibly signal higher level notification Similar for DAC to actuator ADC Analog sensor Digital sensor Digital Signal Processing Software storage threads Bus

21. June 2008WEI L3 - TinyOS21 Embedded System Design: Protocol Implementation For –Bus Protocols within a node, –Link Protocols between two nodes in direct communication, –Network Protocols between possibly widely separate node. Each has –Set of operations that it issues –Set responses that it receives »synchronous or asynchronous, –state it maintains, –state-transition diagram that it implements And various commands and events that define its interface above and below –Exceptions, etc. Communication Protocol State processing Lower Level of stack Higher Level of stack Logical Peer Comm.

22. June 2008WEI L3 - TinyOS22 Tiny OS Concepts System = Scheduler + graph of Components –Hierarchical Component: –Set of bidirectional Command/Event Interfaces –Commands Handlers –Event Handlers –Frame (storage) –Tasks (concurrency) Constrained two-level scheduling model –tasks + events Constrained Storage Model –frame per component, –Single shared stack, –no heap Structured event-driven processing Very lean multithreading Efficient Layering –Events can signal events Extremely modular construction –Separates creation and composition of functional elements Component Internal State CommandsEvents interface Task

23. June 2008WEI L3 - TinyOS23 Application = Graph of Components RFM Radio byte Radio Packet UART Serial Packet ADC Tempphoto Active Messages clocks bit byte packet Route map routersensor appln application HW SW Graph of cooperating state machines on shared stack Execution driven by interrupts * Early TinyOS 0.x component graph going all the way down to modulating the RF channel in software. Modular construction of Protocols.

24. June 2008WEI L3 - TinyOS24 TOS Execution Model commands request action –ack/nack at every boundary –call cmd or post task events notify occurrence –HW intrpt at lowest level –may signal events –call cmds –post tasks Tasks provide logical concurrency –preempted by events Migration of HW/SW boundary RFM Radio byte Radio Packet bit byte packet event-driven bit-pump event-driven byte-pump event-driven packet-pump message-event driven active message application comp encode/decode crc data processing

25. June 2008WEI L3 - TinyOS25 TinyOS Execution Contexts Events generated by interrupts preempt tasks Tasks do not preempt tasks Both essential process state transitions Hardware Interrupts events commands Tasks

26. June 2008WEI L3 - TinyOS26 Dynamics of Events and Threads bit event filtered at byte layer bit event => end of byte => end of packet => end of msg send thread posted to start send next message radio takes clock events to detect recv

27. June 2008WEI L3 - TinyOS27 Programming TinyOS - nesC TinyOS 1.x and TinyOS 2.x are written in an extension of C, called nesC Applications are too! –just additional components composed with the OS components Provides syntax for TinyOS concurrency and storage model –commands, events, tasks –local frame variables Rich Compositional Support –separation of definition and linkage –robustness through narrow interfaces and reuse –interpositioning Whole system analysis and optimization Platform independent data types and structure –because packets are sent between different kinds of processors!

28. June 2008WEI L3 - TinyOS28 Composition A component specifies a set of interfaces by which it is connected to other components –provides a set of interfaces to other components –uses a set of interfaces provided by other components Interfaces are bi-directional –include commands and events Interface methods form the external namespace of the component –Composition by “wiring” Timer Component StdControl Timer Clock provides uses provides interface StdControl; interface Timer: uses interface Clock

29. June 2008WEI L3 - TinyOS29 Split-phase abstraction of HW Command synchronously initiates action Device operates concurrently Signals event(s) in response –ADC –Clock –Send (UART, Radio, …) –Recv – depending on model –Coprocessor Higher level (SW) processes don’t wait or poll –Allows automated power management Higher level components behave the same way –Tasks provide internal concurrency where there is no explicit hardware concurrency Components (even subtrees) replaced by HW and vice versa

30. June 2008WEI L3 - TinyOS30 TASKS provide concurrency internal to a component –longer running operations –are preempted by events –able to perform operations beyond event context –may call commands –may signal events –not preempted by tasks Simple (pluggable) Scheduler –Composition exercises substantial control over scheduling {... post TskName();... } task void TskName {... }

31. June 2008WEI L3 - TinyOS31 Typical application use of tasks event driven data acquisition schedule task to do computational portion event result_t sensor.dataReady(uint16_t data) { putdata(data); post processData(); return SUCCESS; } task void processData() { int16_t i, sum=0; for (i=0; i ‹ maxdata; i++) sum += (rdata[i] ›› 7); display(sum ›› shiftdata); } 128 Hz sampling rate simple FIR filter dynamic software tuning for centering the magnetometer signal (1208 bytes) digital control of analog, not DSP ADC (196 bytes)

32. June 2008WEI L3 - TinyOS32 Tasks in low-level operation transmit packet –send command schedules task to calculate CRC –task initiated byte-level data pump –events keep the pump flowing receive packet –receive event schedules task to check CRC –task signals packet ready if OK i2c component –i2c bus has long suspensive operations –tasks used to create split-phase interface –events can procede during bus transactions Timer –Post task in-critical section, signal event when current task complete Make SW look like HW

33. June 2008WEI L3 - TinyOS33 Structured Events vs Multi-tasking Storage Control Paradigm –Always block/yield – rely on thread switching –Never block – rely on event signaling Communication & Coordination among potentially parallel activities –Threads: global variables/mailboxes, mutex, signaling –Preemptive – handle many potential races –Non-premptive »All interactions protected by costs system synch ops –Events: signaling Scheduling: –Complex threads require sophisticating scheduling –Collections of simple events ??

34. June 2008WEI L3 - TinyOS34 Modern TinyOS Service Architecture Net Prog Hardware Init/Boot Persistent Attributes & Event Streams Device Attributes & Event Streams Service Interface Commands Attributes Events Discovery Messages Management & Power Domain-Specific Application Components OS & Net Interface Motor Light Blocks Vibration Logs Files Network Collection, Dissemination, & Routing Links Device Abstraction Interface FlashRadio / SerialSensor / Actuator Microcontroller Core, Timers, Buses, Onboard ADCs Microcontroller Abstraction Interface TelosB MicaZ Intel Mote2 Domain-Specific Device Drivers

35. June 2008WEI L3 - TinyOS35 TinyOS 2.0 – abstraction architecture Flexible Hardware Abstraction for Wireless Sensor NetworksFlexible Hardware Abstraction for Wireless Sensor Networks, Vlado Handziski, Joseph Polastre, Jan- Hinrich Hauer, Cory Sharp, Adam Wolisz, David Culler,In Proceedings of the Second European Workshop on Wireless Sensor Networks (EWSN '05), January 31-February 2, 2005.

36. June 2008WEI L3 - TinyOS36 Sample of TinyOS Platforms

37. June 2008WEI L3 - TinyOS37 Silicon World Storage ProcessingWireless Sensors WSN mote platform Wireless Embedded Networks Physical World Digital World Radio Serial FlashADC, Sensor I/F MCU, Timers, Bus,… Link Blocks, Logs, Files Scheduling, Management Streaming drivers Over-the-air Programming Applications and Services Network Protocols

38. June 2008WEI L3 - TinyOS38 Embedded Networking Requirements Reliable Dissemination Data Collection and Aggregation Point-to-point Transfers Reliably over lossy links At low power –Idle listening, management, monitoring Adapting to changing conditions Scalar and Bulk Versions

39. June 2008WEI L3 - TinyOS39 TEP - TinyOS Enhancement Proposals TEP 1: TEP Structure and Key Words [HTML]HTML TEP 2: Hardware Abstraction Architecture [HTML]HTML TEP 3: Coding Standards [HTML]HTML TEP 101: ADC [HTML]HTML TEP 102: Timers [HTML]HTML TEP 103: Storage [HTML]HTML TEP 106: Schedulers and Tasks [HTML]HTML TEP 107: Boot Sequence [HTML]HTML TEP 108: Resource Arbitration [HTML]HTML TEP 109: Sensorboards [HTML]HTML TEP 111: message_t [HTML]HTML TEP 112: Microcontroller Power Management [HTML]HTML TEP 113: Serial Communication [HTML]HTML TEP 114: SIDs: Source and Sink Independent Drivers [HTML]HTML TEP 115: Power Management of Non- Virtualized Devices [HTML]HTML TEP 116: Packet Protocols [HTML]HTML TEP 117: Low-Level I/O [HTML]HTML TEP 118: Dissemination [HTML]HTML TEP 119: Collection [HTML]HTML TEP 123: Collection Tree Protocol (CTP) [HTML]HTML TEP 124: Link Estimation Exchange Protocol (LEEP) [HTML]HTML TEP 125: TinyOS 802.15.4 Frames [HTML]HTML TEP 126: CC2420 Radio Stack [HTML]HTML

40. June 2008WEI L3 - TinyOS40 TinyOS IPv6 Network Kernel Actuator Sensors TimerFlashRadioSensorActuator Network Kernel –Manages communication and storage –Scheduler (decides when to signal events) IPv6 Network Kernel Driver Application

41. June 2008WEI L3 - TinyOS41 Event-Based Execution All execution occurs in event handlers –Events do not preempt each other Commands –Get information from underlying components »Get current time –Configure underlying components »Start timer (will cause a future event) »Bind socket to a port –Helper functions »Format an IPv6 address

42. June 2008WEI L3 - TinyOS42 Example Flow Event: Boot –Command: Start timer Event: Timer fired –Command: Send message Event: Message received –Command: Toggle an LED event void Boot.booted() { call Timer.startPeriodic(100); } event void Timer.fired() { call Udp.sendto(buf, len, &to); } event void Udp.recvfrom(void *buf, uint16_t len, sockaddr_in6_t *from) { call Leds.led0Toggle(); } Start Timer System Init … Sleep … Send Msg Radio Transmit … Sleep … Radio Receive Toggle LED

43. June 2008WEI L3 - TinyOS43 What’s Happening Underneath? MCU hardware modules operate concurrently  Must handle events in a timely manner Hardware events preempt application events –Allows system to operate asynchronously from app –Tasks are used to signal application events –Kernel scheduler executes tasks one-by-one Start Timer System Init … Sleep … Send Msg Radio Transmit … Sleep … Radio Receive Toggle LED = HW Timer Overflow

44. June 2008WEI L3 - TinyOS44 Transit Network (IP or not) Access point - Base station - Proxy Sensor Patch Patch Network Data Service Intranet/Internet (IP) Client Data Browsing and Processing Sensor Node Gateway Verification links Other information sources Sensor Node Canonical SensorNet Network Architecture

45. June 2008WEI L3 - TinyOS45 TinyOS 2x Embedded IP Architecture GPIO Pins Ext. INT ADCSPI, i2c, UART Low-Power 802.15.4 Virtual ms Timer  s Timer RTC Scheduler Flash Storage arbiters Pwr Mgr UDP/TCP L4 Basic Health & Mgmt Services Basic Configuration Services Sensor Drivers OTA IP 6LowPAN L2 IP route L3 Higher Level Embedded Web Services

46. June 2008WEI L3 - TinyOS46 TinyOS Execution Philosophy Sleep almost all the time. Wake-up (quickly) when there is something to do. Process it and all other concurrent or serial activities as rapidly as possible. –Structured, event driven concurrency Never wait!!! Automatically go back to sleep

47. June 2008WEI L3 - TinyOS47 TinyOS Structured Design Philosophy Think hard about components –Well-define behavior, well-define interfaces Compose components into larger components Flexible structured design of entire system –And application Dealing with distributed system of many resource-constrained devices embedded in hard to reach places and coping with noise, uncertainty and variation. Make the node, the network, and the system as robust as possible. KEEP IT SIMPLE!