What’s New with Tiny Devices

1. What’s New with Tiny Devices David Culler U.C. Berkeley Endeavour MiniRetreat 1/9/2001

2. Ready for “Prime Time” • Hardware Platform suited for Experimentation • TinyOS well exercised and ready for release • Several Exciting Studies digging in deeper • Time for applications and serious tools Endeavour Retreat

3. “Rene” wireless networked sensor platform • 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 • stackable expansion connector (all ports, i2c, pwr, clock…) Endeavour Retreat

4. “Rene”simple sensor card proto • 1” x 1.5”sensorboard • Stackable connector • Thermistor (temp, analog) • Proto • Breadboard area Endeavour Retreat

5. “Rene” motion sensor card • 1” x 1.5” sensorboard • Accelerometers • Magnetrometers • Humidity, light, temp, sound, … Endeavour Retreat

6. Laptop “lab kit” Parallel Port for programming serial Port for base station “Sensor stacks” on central connector Endeavour Retreat

7. Lab analysis board • Logical analyzer connectors • Serial port • Device bay Endeavour Retreat

8. Panasonic CR2354 560 mAh Power Breakdown… • But what does this mean? • Lithium Battery runs for 35 hours at peak load and years at minimum load! • That’s three orders of magnitude difference! • A one byte transmission uses the same energy as approx 11000 cycles of computation. • Idleness is not enough, sleep! Endeavour Retreat

9. TinyOS • Extremely small code & data • Address two appln behavior modes • Bursts of high concurrency (multiple streams) • Long periods of no important activity • Efficient fine-grain multithreading • Bit-by-bit processing in software • hard real-time requirements • Percolate events through multiple levels • Power control on every interface • Shut it all down when idle • Simple two-level scheduler • Modularity for robustness & specialization Endeavour Retreat

10. UART Packet Radio Packet TinyOS Program Structure • Application = graph of components + schedule sensing application application Routing Layer routing Messaging Layer messaging packet Radio byte UART byte Temp byte photo SW HW RFM ADC i2c bit clocks Endeavour Retreat

11. Application Demo Code size for ad hoc networking application Scheduler: 144 Bytes code Totals: 3430 Bytes code 226 Bytes data Endeavour Retreat

12. AM_SEND_MSG AM_POWER AM_INIT AM_MSG_SEND_DONE AM_MSG_REC Messaging Component Internal State Internal Tasks AM_SUB_POWER AM_TX_PACKET_DONE AM_SUB_TX_PACKET AM_RX_PACKET_DONE AM_SUB_INIT Commands Events Program Representation: component • Component = foo.comp + foo.c • .comp defines interface • Commands it accepts • Events it signals • Commands it uses • Events it handler • .c file is the implementation • TOS_COMMAND - interface • TOS_SIGNAL_EVENT • TOS_CALL_COMMAND • TOS_EVENT • TOS_FRAME - internal state • TOS_TASK - internal concurrency • TOS_POST_TASK • Only refer to internal and interface names • All commands/events may return “No” Endeavour Retreat

13. Example Component //AM.comp// TOS_MODULE AM; ACCEPTS{ char AM_SEND_MSG(char addr, char type, char* data); void AM_POWER(char mode); char AM_INIT(); }; SIGNALS{ char AM_MSG_REC(char type, char* data); char AM_MSG_SEND_DONE(char success); }; HANDLES{ char AM_TX_PACKET_DONE(char success); char AM_RX_PACKET_DONE(char* packet); }; USES{ char AM_SUB_TX_PACKET(char* data); void AM_SUB_POWER(char mode); char AM_SUB_INIT(); }; AM_SEND_MSG AM_POWER AM_INIT AM_MSG_SEND_DONE AM_MSG_REC Messaging Component Internal State Internal Tasks AM_SUB_POWER AM_TX_PACKET_DONE AM_SUB_TX_PACKET AM_RX_PACKET_DONE AM_SUB_INIT Commands Events Endeavour Retreat

14. Component graph • Application described by .desc file • List of components • “wiring” on interface ports • Including “dispatch” ports • Active message demux • ADC (shared resource) demux • May “name” connections or not • Descriptions may be hierarchical • Tools translate names across component interfaces • Structured wiring => optimize across component boundaries • Can interpose or exchange components Endeavour Retreat

15. Example description include modules{ MAIN; CHIRP; GENERIC_COMM; PHOTO; CLOCK; LEDS; }; MAIN:MAIN_SUB_INIT CHIRP:CHIRP_INIT MAIN:MAIN_SUB_SEND_MSG DUMMY:vSTART CHIRP:CHIRP_START DUMMY:vSTART … CHIRP:CHIRP_CLOCK_INIT CLOCK:CLOCK_INIT CHIRP:CHIRP_CLOCK_EVENT CLOCK:CLOCK_FIRE_EVENT … CHIRP:CHIRP_SUB_SEND_MSG GENERIC_COMM:GENERIC_COMM_SEND_MSG CHIRP:CHIRP_SUB_MSG_SEND_DONE GENERIC_COMM:GENERIC_COMM_MSG_SEND_DONE … Endeavour Retreat

16. Example (cont) TOS_MODULE GENERIC_COMM; IMPLEMENTED_BY GENERIC_COMM; ACCEPTS{ char GENERIC_COMM_INIT(); void GENERIC_COMM_POWER(char mode); char GENERIC_COMM_SEND_MSG(char addr, char type, char* data); }; SIGNALS{ char GENERIC_COMM_MSG_REC(char type, char* data); char GENERIC_COMM_MSG_SEND_DONE(char success); }; GENERIC_COMM.desc include modules{ AM; RED_PACKETOBJ; FOUR_B_RADIO_BYTE; RFM; }; …. Endeavour Retreat

17. Real time operating systems • QNX context switch = 2400 cycles on x86 • pOSEK context switch > 40 µs • Creem -> no preemption Endeavour Retreat

18. Thoughts about robust Algorithms • Active Dynamic Route Determination • When route_beacon handler fires with M(hops) < hops • UP = M(source); hops = M(hops)++; M(source) = self; send; • Periodically increase hops • Radio cell structure very unpredictable • Builds and maintains good breadth-first forest • Each node only records own state and parent(s) • Fundamental operation pruning retransmission • Monotonic variables • Message signature caches • Exercise: no beacons, just piggyback on data Endeavour Retreat

19. Low-Power Listening (J. Hill) • Costs about as much to listen as to xmit, even when nothing is received • Only way to save power is to turn radio off when there is nothing to hear. • Can turn radio on/of in about 1 bit • Can detect transmission at cost of ~2 bit times • Small sub-msg recv sampling • Application-level synchronization rendezvous to determine when to sample sleep preamble message Xmit: Recv: b Optimal Preamble = (2/3 Sxb)1/2 Endeavour Retreat

20. Packet Encoding / Layers • Radio requires rough DC balance • No more than three ones between zeros • Manchester encoding • 4b/6b • Bit error rate significant and increases with distance • CRC, 3-redundant • …or SECDED with DC-balanced coding Radio byte components Radio packet components Endeavour Retreat

21. Channel Utilization (A. Woo) • Per-cell channel utilization important near base • MAC studies revealed subtle TinyOS jitter bug • Simple CSMA algorithm proved effective • Listen random delay (16 bit LFB SR) • On busy, wait till idle • Aggregate Util • Detected collisions • Fraction of attempted BW delivered Endeavour Retreat

22. Bandwidth Management • Hidden nodes between each pair of “levels” • CSMA is not enough • RTS/CTS acks too costly (power & BW) • P[msg-to-base] drops rapidly with hops • Investment in packet increases with distance • Local rate control to approx. fairness • Priority to forwarding, adjust own data rate • Additive increase, multiplicative decrease • Listen for retransmission as ack ~ ½ of packets get through 4 levels out Endeavour Retreat

23. Proximity / Location detection • Signal strength sensing • Circuit works, falls off cleanly in good environment • Incredibly sensitive to obstructions! • Error rates a useful proximity metric • Bit errors vs. packet errors • Klemmer,Waterson, Whitehouse study => signal strength + Kalman filter provides good position detection Endeavour Retreat

24. Authentication / Security (Szewczyk, et al) mote <-> basestation authentication and confidentiality • stream cipher RC5 encryption => no extra bits transmitted on encryped data • 8 byte MAC, based on RC5 • authenticated basestation broadcast based on TESLA • protocol based on delayed key disclosure and time synch. • distribute routing beacons using authenticated broadcast => authenticated routing • additional protocols to guarantee freshness • Implementation of above consumes about 1/3 of the mote resources (code space, RAM, processing) • Shared key cryptography based on RC5 • public key cryptography is much too expensive • heavy code reuse - RC5 used for a variety of tasks • a key shared between mote and basestation programmed into the mote at initial programming time • first computationally expensive application on the motes Endeavour Retreat

25. Application-Specific Virtual Machine • Small byte-code interpreter component • Code, static data, stack • Accepts clock-event capsules • Other events too • Hides split-phase operations below interpreter • HW + collection of components defines space of applications • Allows very efficient coding within this space • Capsules define specific query / logic Endeavour Retreat

26. Application Deployment http://nighthawk.cs. berkeley.edu:8080/tracking • Light sensing + location inference based on landmarks • 16 motes deployed on 4th floor Soda Hall • 10 round motes as office landmarks • 2 base stations around corners of the building • 4 Rene motes as active badges for location tracking • AA batteries (3 weeks) • Tracking precision +/- one office Endeavour Retreat

27. Open Projects / Problems • Ambient-power devices • Debugging • Many-mote simulator • Logging component + trace analysis • Message fragmentation • Query processing • Visualization • Static critcal-path, jitter analysis • REAL APPLICATIONS Endeavour Retreat