System Architecture Directions for Networked Sensors J Hill

System Architecture Directions for Networked Sensors (J. Hill, et al) Presented By: Sarah Bergbreiter EE 249 Discussion Section October 15, 2002 1 EE 249 Discussion

What are Networked Sensors? Mica Mote 1 mm Smart Dust • Cheap, plentiful, low-power, small, communication-enabled (radio, optical, etc) 2 EE 249 Discussion

Networked Sensor Characteristics • Small physical size and low power consumption • Concurrency Intensive Operation – sensing data, forwarding packets, etc. • Limited Physical Parallelism and Controller Hierarchy – can’t have one processor per sensor • Diversity in Design and Usage – modular components allow for application specific design • Robust Operation – numerous and unattended 3 EE 249 Discussion

Sample Hardware Design Coprocessor - reprogramming Sensors Radio - 1 m. J/bit - real time constraints Atmel AVR - power save modes - memory constrained 4 EE 249 Discussion

Tiny. OS Overview • Small size and power limitations decided by the hardware platform • Two-Level Scheduling – long running tasks (processing data) – hardware events (radio, sensors, etc. ) • Event-Driven Design – better concurrency – power savings • Modular Component-Based Design 5 EE 249 Discussion

MSG_SEND _DONE MSG_REC SEND_MSG POWER • Commands • Events • Frame INIT Tiny. OS Design – Components – static, fixed 6 TX_PACKET _DONE INTERNAL STATE (FRAME) RX_PACKET _DONE TX_PACKET • Type depends on hardware connection POWER – simulate concurrency MESSAGING COMPONENT INIT • Tasks SEND_MSG THREAD EE 249 Discussion

Ad hoc Routing Application 3 6 4 5 4 7 5 3 8 6 2 9 7 1 2 1 7 EE 249 Discussion

How Does Tiny. OS Perform? • Small Physical Size – scheduler uses 178 bytes program memory, 16 bytes data memory – application ~3 k program memory, 226 bytes data memory • Concurrency-intensive Operations – context switching relatively cheap (equivalent to writing 6 bytes in memory) – interrupt handling more expensive in software 8 EE 249 Discussion

How Does Tiny. OS Perform? • Efficient Modularity – using function calls to propagate events and commands keeps costs low 40 ms 9 EE 249 Discussion

How Does Tiny. OS Perform? • Limited Physical Parallelism and Controller Hierarchy – make design choices about parallelism based on data • Diversity in Usage and Robust Operation – reconfigurable for node failure 10 EE 249 Discussion

Related Work • Other Operating Systems – These operating systems address embedded PCs – Control v. dataflow (context switching difficult) • FSM Description Language • New Hardware Platforms and Applications 11 EE 249 Discussion

Architectural Implications • Physical parallelism is optional • Deciding where to draw the hardware/software boundary line may improve performance and/or power usage • Quantified effect of additional hardware support (early benchmarks) 12 EE 249 Discussion

Conclusions/Questions • Sample hardware/software architecture presented for networked sensors • Bigger is no longer better • Platform-based design? • Complexity limits? 13 EE 249 Discussion