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 http://

tinyos.millennium.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

Active Idle Sleep

MCU core 5 mA 2 mA 1 μA

MCU pins 1.5 mA 0 0

Radio 12 mA (TX) 4.5 mA (RX) 5 μA

EE-Prom 3 mA 0 1 μA

LED’s 4.6 mA each 0 0

Photocell 0.3 mA 0 0

Temperature 1 mA 0.6 mA 1.5 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

clocksbit

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 WorkName Code Size Target CPU

pOSEK 2K MicrocontrollerspSOSystem PII->ARM ThumbVxWorks 286K Pentium -> Strong ARMQNX Nutrino >100K Pentium II -> NECQNX RealTime 100K Pentium II -> SH4OS-9 Pentium -> SH4Chorus OS 10K Pentium -> Strong ARMARIEL 19K SH2, ARM ThumbCreem 560 bytes ATMEL 8051

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

TinyOSTinyOS is a highly modular software environment tailored to the requirements of Network Sensors, stressing efficiency, modularity and concurrency

Follow their progress:

http://tinyos.millennium.berkeley.edu