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Wireless Sensor Network. A Second-Generation Sensor Network Processor with Application-Driven Memory Optimizations and Out-of-Order Execution* by Banit Agrawal. *Paper published in CASES 2005 by U Michigan Group. Outline. Introduction Applications of wireless sensor networks
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Wireless Sensor Network A Second-Generation Sensor Network Processor with Application-Driven Memory Optimizations and Out-of-Order Execution* by Banit Agrawal *Paper published in CASES 2005 by U Michigan Group Banit Agrawal @ UCSB
Outline Introduction Applications of wireless sensor networks Wireless Sensor Network (WSN) Architecture WSN’s Microprocessor UMich first generation processor UMich second generation processor Conclusion Banit Agrawal @ UCSB
What is wireless sensor network Wireless Sensor Network (WSN) Network of many small distributed computers for processing the sensor data Usually consists of microprocessor, memory, transceiver, sensing device, battery/energy scavenging unit, etc Resource constrained Everything optimized for low-energy operations Banit Agrawal @ UCSB
Current Challenges Energy Conservation Limited Computation/Storage Scalability Fault-tolerance Routing/Communication Bandwidth Autonomous and Distributed Systems Security Banit Agrawal @ UCSB
Applications (1) Environmental Monitoring Habitat Monitoring Integrated Biology Structural Monitoring Building/Border/Battlefield detection Road/traffic monitoring Health monitoring Banit Agrawal @ UCSB
Applications (2) Business Applications Supply Chain Management Expired/Damaged Goods Tracking Automatic Checkout Systems Security, surveillance Context-aware computing Automation Banit Agrawal @ UCSB
WSN Node Architecture Ref: Energy-Aware Wireless Microsensor Networks Banit Agrawal @ UCSB
Berkeley Motes Banit Agrawal @ UCSB
Flash RAM Processor 10/100 Ethernet Address/Data Bus Preprocessor Interface Modular Wireless and Digital Interfaces Imager Module Imager Interface RF Modem 1 RF Modem 2 Digital I/O GPS Analog Front End Multi- Channel Sensor Interface DSP Preprocessor Sensoria SGATE hardware Banit Agrawal @ UCSB
UCLA Sensor Nodes Banit Agrawal @ UCSB
MIT AMPS Banit Agrawal @ UCSB
Intel StarGate Banit Agrawal @ UCSB
Micro Controller Sensors Addr/Data Radio Addr/Data Event Processor Message Processor System Bus Interrupt Power Ctrl Data Filter SRAM Timer Harvard’s University (ISCA’05) Banit Agrawal @ UCSB
Telos 4/04 Robust Low Power 250kbps Easy to use WeC 99 “Smart Rock” Rene 11/00 Dot 9/01 Mica 1/02 Small microcontroller 8 kB code 512 B data Simple, low-power radio 10 kbps ASK EEPROM (32 KB) Simple sensors Mica2 12/02 38.4kbps radioFSK Demonstrate scale • Designed for experimentation • sensor boards • power boards NEST open exp. Platform128 kB code, 4 kB data40kbps OOK/ASK radio512 kB Flash Spec 6/03 “Mote on a chip” Berkeley’s Experimental Platform Services Networking TinyOS Ref: HotChips 2004 – “Mote Evolution…” Banit Agrawal @ UCSB
Mote Evolution Ref: HotChips 2004 – “Mote Evolution…” Banit Agrawal @ UCSB
WSN’s Microcontroller AT/ATmega/ATMEL (AVR) Family TI Family Intel XScale StrongARM Harvard’s microcontroller UMich’s first generation processor UMich’s second generation processor Banit Agrawal @ UCSB
Processor Requirements Banit Agrawal @ UCSB
Voltage Reduction Not Performance, Energy is important. Banit Agrawal @ UCSB
Sensor Network Applications Representative set to evaluate architecture Banit Agrawal @ UCSB
Optimizing Energy Efficiency Reduce the area to minimize the static power Transistor utility must be maximized CPI must be minimized Banit Agrawal @ UCSB
Processor’s Characteristics 12-bit RISC ISA 8-bit datapaths Flexible Operand Handling Application specific instructions Prefetch mechanism Memory Architecture Branch speculation and out-of-order execution Banit Agrawal @ UCSB
ISA: RISC Encoding 12-bit RISC encoding simple decoding logic Reducing code-density and hence area to reduce the leakage energy 96.2% encoding efficiency Banit Agrawal @ UCSB
ISA Organization Banit Agrawal @ UCSB
ISA Design Load-store architecture 8 registers Simple to design and pipeline 2-operand based design Preserve bit to save the source Various addressing modes available Banit Agrawal @ UCSB
ISA Design (2) Micro-operations Application specific instructions Efficient pointer and carry manipulation Event scheduler control Timer control Reduction in code-size Banit Agrawal @ UCSB
Memory Optimizations Data memory predecode architecture [May not be useful for pointers] Banit Agrawal @ UCSB
Memory Optimizations (2) Instruction memory predecode architecture 2 words and automatically increment the page when PC reaches the end of page Banit Agrawal @ UCSB
Processor pipeline design 3-stage pipeline [optimum, not 4 not 2] Banit Agrawal @ UCSB
Microarchitectural Optimizations Out-of-order execution Taken branch speculation Banit Agrawal @ UCSB
Results Banit Agrawal @ UCSB
Results: Contributions Storage unit and other components Banit Agrawal @ UCSB
Related Works 8-bit ATmega - 1.5 nJ/instruction Clever Dust 2 – 12 pJ/instruction StrongARM/XScale - 1nJ/instruction SNAP/LE – 24 pJ/instruction Umich first generation – 1.6 pJ/instruction Umich second generation – 600fJ/instruction Banit Agrawal @ UCSB
Conclusion Energy-efficient processor (600 fJ/instruction, will run 312 years on single AAA) Microarchitectural and ISA optimizations to reduce the leakage energy IBM 130nm fabrication Intra-ocular pressure sensor Banit Agrawal @ UCSB
Thanks for your attention. Questions ? Banit Agrawal @ UCSB