System Architecture Directions for Networked Sensors Jason Hill, Robert Szewczyk, Alec Woo, Seth Hollar, David Culler, Kris Pister Presented by Yang Zhao

Networked Sensors What is a Networked Sensor? Small (I.e. 2”x2” and smaller) Onboard processor and communication device (e.g IR, Radio) Self-contained power source (e.g. Battery, Solar) How do we combine sensing, communication and computation into a complete architecture? What are the requirements of the software?

Outline Networked Sensor Characteristics =>Architecture Directions Mote – the Hardware TinyOS System Architecture System evaluation

Networked Sensor Characteristics => Key Architecture Directions Small physical size and low power consumption => Limited Physical Parallelism and Controller Hierarchy => primitive direct-to-device interface Concurrency-intensive operation => must handle multiple inputs and outputs simultaneously

Networked sensor characteristics => Key Architecture directions Diverse in Design and Usage  application specific, not general purpose  huge device variation => efficient modularity => migration across HW/SW boundary Largely Unattended & Numerous => robust operation => narrow interfaces

Outline Networked sensor characteristics =>Architecture Directions Mote – the hardware TinyOS system architecture System evaluation

Mote – the hardware Assembled from off-the-shelf components 4MHz, 8bit MCU (ATMEL) 512 bytes RAM, 8K ROM 900MHz Radio (RF Monolithics) Temperature Sensor & Light Sensor LED outputs Serial Port Coprocessor 1.5” x 1.5”

Second Generation ‘Mote’ Two Board Sandwich Main CPU board with Radio Communication Secondary Sensor Board Allows for expansion and customization berkeley.edu

Mote – Power Characteristics Lithium Battery runs for 35 hours at peak load and years at minimum load! Make unused component inactive whenever possible The system must get the work done quickly and go to sleep ActiveIdleSleep MCU core5 mA2 mA1 μA MCU pins1.5 mA00 Radio12 mA (TX)4.5 mA (RX)5 μA EE-Prom3 mA01 μA LED’s4.6 mA each00 Photocell0.3 mA00 Temperature1 mA0.6 mA1.5 μA

Outline Networked sensor characteristics =>Architecture Directions Mote – the hardware TinyOS system architecture System evaluation

TinyOS system architecture What can software do to conserve energy, support concurrency-intensive operation and achieve efficient modularity and robustness?

Event-based Programming Model Event-based programming model, not Thread based Command and event handlers transition a component from one state to another Quick, low overhead, non-blocking state transitions Many independent component allowed to efficiently share a single execution context “Tasks” are used to perform computational work Run to completion, Atomic with respect to each other, but can be preempted by events

TinyOS – the Software Scheduler and a graph of components. Component: Frame (storage) Tasks (concurrency) Commands, and Handlers (events) Two level scheduling system allows events to preempt tasks. Capable of maintaining necessary levels of concurrency. Provides a component based model abstracting hardware specifics from application programmer

Composition into a Complete Application RFM Radio byte Radio Packet UART Serial Packet i2c Temp photo Active Messages clocks bit byte packet Ad hoc Routing App. application HW SW

Outline Networked sensor characteristics =>Architecture Directions Mote – the hardware TinyOS system architecture System evaluation

Evaluation Small physical size Complete applications in 3.45 Kbytes Useful applications developed for 4MHz, 8-bit CPU Concurrency-intensive operations 50 cycle thread overhead, 10 cycle event overhead Limited physical parallelism and controller hierarchy Demonstrated by the ability to use a single controller to manage multiple I/O sources Event-based programming model allows efficient use of CPU and memory Efficient modularity Component model allows efficient composition of task specific applications Diversity in usage and Robust operation

Related Work QNX context switch = 2400 cycles on x86 pOSEK context switch > 40 µs

Conclusion System Architecture Directions Small physical size Capable of supporting concurrency-intensive operation Efficient Resource Utilization High Modularity TinyOS TinyOS is a highly modular software environment tailored to the requirements of Network Sensors, stressing efficiency, modularity and concurrency

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