Convergence at the Extremes – HPDC meets Tiny Networked Sensors

1. Convergence at the Extremes –HPDC meets Tiny Networked Sensors David Culler Computer Science Division U.C. Berkeley Intel Research @ Berkeley www.cs.berkeley.edu/~culler

2. ...and Small Characteristics of the Large • Concurrency intensive • data streams and real-time events, not command-response • Communications-centric • Limited resources (relative to load) • Huge variation in load • Robustness (despite unpredictable change) • Hands-off (no UI) • Dynamic configuration, discovery • Self-organized and reactive control • Similar execution model (component-based events) • Complimentary roles (eyes/ears of the grid) • Huge space of open problems HPDC

3. Low-power Wireless Communication I SD Q SD baseband PLL filters mixer LNA Emerging Microscopic Devices • CMOS trend is not just Moore’s law • Micro Electical Mechanical Systems (MEMS) • rich array of sensors are becoming cheap and tiny • Imagine, all sorts of chips that are connected to the physical world and to cyberspace! HPDC

4. Circulatory Net What can you do with them? Disaster Management • Embed many distributed devices to monitor and interact with physical world • Network these devices so that they can coordinate to perform higher-level tasks. => Requires robust distributed systems of hundreds or thousands of devices. Habitat Monitoring HPDC

5. Getting started in the small • 1” x 1.5” motherboard • ATMEL 4Mhz, 8bit MCU, 512 bytes RAM, 8K pgm flash • 900Mhz Radio (RF Monolithics) 10-100 ft. range • ATMEL network pgming assist • Radio Signal strength control and sensing • I2C EPROM (logging) • Base-station ready (UART) • stackable expansion connector • all ports, i2c, pwr, clock… • Several sensor boards • basic protoboard • tiny weather station (temp,light,hum,prs) • vibrations (2d acc, temp, light) • accelerometers, magnetometers, • current, acoustics HPDC

6. read header read header read header read header read header read header exec cache check write resp cache miss Emerging execution model (at large) • Application is graph of event-driven components • robust to huge surges in demand HPDC

7. ...and in the small Route map router sensor appln application Active Messages Serial Packet Radio Packet packet Temp photo SW HW UART Radio byte ADC byte Example: ad hoc, multi-hop routing of photo sensor readings clocks RFM bit HPDC

8. A Operating System for Tiny Devices? • Traditional approaches • command processing loop (wait request, act, respond) • monolithic event processing • bring full thread/socket posix regime to platform • Alternative • provide framework for concurrency and modularity • never poll, never block • interleaving flows, events, energy management • allow appropriate abstractions to emerge HPDC

9. msg_rec(type, data) msg_send_done) Tiny OS Concepts • Scheduler + Graph of Components • constrained two-level scheduling model: threads + events • Component: • Commands, • Event Handlers • Frame (storage) • Tasks (concurrency) • Constrained Storage Model • frame per component, shared stack, no heap • Very lean multithreading • Efficient Layering Events Commands send_msg(addr, type, data) power(mode) init Messaging Component internal thread Internal State TX_packet(buf) Power(mode) TX_packet_done (success) init RX_packet_done (buffer) HPDC

10. TinyOS Execution Contexts Tasks events commands Interrupts Hardware HPDC

11. Radio Packet packet Radio byte byte RFM bit 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 data processing application comp message-event driven active message event-driven packet-pump crc event-driven byte-pump encode/decode event-driven bit-pump HPDC

12. Dynamics of Events and Threads bit event => end of byte => end of packet => end of msg send thread posted to start send next message bit event filtered at byte layer radio takes clock events to detect recv HPDC

13. Event-Driven Sensor Access Pattern char TOS_EVENT(SENS_OUTPUT_CLOCK_EVENT)(){ return TOS_CALL_COMMAND(SENS_GET_DATA)(); } char TOS_EVENT(SENS_DATA_READY)(int data){ return TOS_CALL_COMMAND(SENS_OUTPUT_OUTPUT)((data >> 2) &0x7); } • clock event handler initiates data collection • sensor signals data ready event • data event handler calls output command • common pattern HPDC

14. Tiny Active Messages TOS_FRAME_BEGIN(INT_TO_RFM_frame) { char pending; TOS_Msg msg; } TOS_FRAME_END(INT_TO_RFM_frame); . . . ok = TOS_COMMAND(SUB_SEND_MSG)(TOS_MSG_BCAST, AM_MSG(INT_READING), &VAR(msg))) ... char TOS_EVENT(SUB_MSG_SEND_DONE)( TOS_MsgPtr sentBuffer){ ...} TOS_MsgPtr TOS_MSG_EVENT(INT_READING)(TOS_MsgPtr val){ ... return val; } • Sending • Declare buffer storage in a frame • Request Transmission • Naming a handler • Handle Completion signal • Receiving • Declare a handler • Firing a handler • automatic • behaves like any other event • Buffer management • strict ownership exchange • tx: done event => reuse • rx: must rtn a buffer HPDC

15. Example: multihop network discovery • message handler: • if this is a ‘new’ discover message, • record its source as parent • retransmit with self as source HPDC

16. Network Discovery: Radio Cells HPDC

17. Network Discovery HPDC

18. Multihop Network Topology HPDC

19. Storage Breakdown (C Code) 3450 B code 226 B data HPDC

20. DARPA-esq demo • UAV drops nodes along road, • hot-water pipe insulation for package • Nodes self configure into linear network • Calibrate magnetometers • Each detects passing vehicle • Share filtered sensor data with 5 neighbors • Each calculates estimated direction & velocity • Share results • As plane passes by, • joins network • upload as much of missing dataset as possible from each node when in range • 7.5 KB of code! HPDC

21. Cory Energy Monitoring/Mgmt System • 50 nodes on 4th floor • 5 level ad hoc net • 30 sec sampling • 250K samples to database over 6 weeks HPDC

22. 20-ton chiller GW GW GW MYSQL Energy Monitoring Network Arch sensor net control net 802-11 telegraph PC PC modbus scada term UCB power monitor net Browser HPDC

23. Huge Space of Open Problems • Working across levels of abstractions • ex: DC-balanced packet encoding • low-power listening • CSMA MAC for highly correlated traffic • adaptive transmission control when every node is originating and forwarding traffic • Packets can carry time and place information • implicit network discovery • Scale • ex: discovery for 1,000 nodes with ~30 per ‘cell’ • probabalistic flooding • Long term management • sleep/wakeup when need to be awake to hear • in situ network programming • operating within ambient energy envelop HPDC

24. Larger Challenges • Security / Authentication / Privacy • Programming support for systems of generalized state machines • language, debugging, verification • Simulation and Testing Environments • Programming the unstructured aggregates • Resilient Aggregators • Understanding how an extreme system is behaving and what is its envelope • adversarial simulation • Constructive foundations of self-organization HPDC

25. and of course • Mobility • Efficiency • Application execution resource estimation • Automatically interface networks of tiny devices with grid frameworks HPDC

26. To learn more • http://www.cs.berkeley.edu/~culler • http://tinyos.millennium.berkeley.edu/ • http://webs.cs.berkeley.edu/ • http://ninja.cs.berkeley.edu/ HPDC

27. HPDC

28. Typical application use of tasks • event driven data acquisition • schedule task to do computational portion char TOS_EVENT(MAGS_DATA_EVENT)(int data){ struct adc_packet* pack = (struct adc_packet*)(VAR(msg).data); printf("data_event\n"); VAR(reading) = data; TOS_POST_TASK(FILTER_DATA); ... • 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) HPDC

29. Tasks in low-level operation • transmit packet • send command schedules task to calculate CRC • task initiated byte-level datapump • events keep the pump flowing • receive packet • receive event schedules task to check CRC • task signals packet ready if OK • byte-level tx/rx • task scheduled to encode/decode each complete byte • must take less time that byte data transfer • i2c component • i2c bus has long suspensive operations • tasks used to create split-phase interface • events can procede during bus transactions HPDC

30. Deadline avoidance • Pipelines transmission – transmits single byte while encoding next byte • Trades 1 byte of buffering for easy deadline • Separates high level latencies from low level real-time requirements • Encoding Task must complete before byte transmission completes • Decode must complete before next byte arrives … Encode Task Byte 1 Byte 2 Byte 3 Byte 4 Bit transmission start Byte 1 Byte 2 Byte 3 RFM Bits HPDC