Dynamic reconfiguration in Wireless Sensor Networks Mihai GALOS, Fabien Mieyeville, David Navarro

1. Dynamic reconfiguration in Wireless Sensor Networks Mihai GALOS, Fabien Mieyeville, David Navarro Lyon Institute of Nanotechnology (INL) Lyon, France

2. Outline • Introduction to WSN (Wireless Sensor Networks) • Dynamic Reconfiguration • Existing solutions • Motivation • Our solution • Supported Architectures • Results • Conclusion and Perspecitves

3. WSN - Introduction Wireless sensor networks (WSNs) are composed of resource-constrained sensor nodes that can cooperatively monitor physical or environmental conditions, such as temperature, pressure, acceleration, … • Applications: • environmental data collection • security or health monitoring • Vehicles • … • Network standards: • IEEE 802.15.4 • ZigBee

4. Some existing platforms: commercial " lab assembled" WSN - Node • Small size • Low cost • Low energy consumption • Low processing power

5. WSN Dynamic Reconfiguration • Node, typical application: • Sensing of an analog value • Processing of the read value • Sending it via RF • Dynamic Reconfiguration (firmware update): add, modify or remove functionalities after deployment • Reasons for Dynamic Reconfiguration: • Fine-tuning of algorithms (i.e. : compensating for meteorological conditions) • Adding / remove algorithms • Replacing a failing node

6. Existing Solutions for Dynamic Reconfiguration • Operating Systems Virtual Machines

7. Existing solutions : Operating systems • Fall into two categories • Monolithic (whole firmware image has to be sent over RF to reconfigure a node) • Modular (only the functionality in question is transmitted)

8. Existing solutions: Virtual Machines • Again, two categories • ASVM (Application-specific virtual machines) • General-purpose virtual machines

9. Desired solution

10. Our approach: In situ Compilation • Goal: implement solution to dynamically reconfigure a WSN, with the following requirements: • Running Cost: Low • Updade Cost: Low • Support for Heterogenity: Yes • Modularity: Yes • Specifications • Hardware • 8 or 16 bit CPU architecture running on the node • Less than 128kB of Flash • Less than 20Mhz of CPU speed • Less than 16kB or RAM • Lack of a Memory Management Unit • Software • Size of RAM poses limitations on input file for compilation Execution in Native format High-level language, small bytecount + compilation

11. A new High-level language: MinTax • Name: Minimal Syntax, inspired from C • Small syntax means less radio time to transmit functionality • Strongly typed high-level language • Each clause is delimited from others with the ’;’ delimiter • Functions do not have explicit return types

12. MinTax: an example • aUk{ • ^i=A2; • ^j=8; • ^u=i; • Wi<99 • Wj>0 • Pi,j; • u=d@k; • j- • # • i+ • # • }u; • Uint8_t a (uint16_t k){ • Uint8_t i = read_analog_pin(pin2); • Uint8_t j = 8; • Uint8_t u = i; • While(i<99){ • While(j>0){ • Pwm_output(i,j); • u=delay(k); • j - -; • } • i++; • } • return u;}

13. The MinTax Compiler • Analysis Stage • Lexical Analysis: splitting the input file into atoms or tokens – Implemented, generated with re2c • Syntactical Analysis: validation that the input file corresponds to the language’s formal grammar – Not Needed • Semantical Analysis: context evaluation of symbols (Symbol Table) – Implemented, merged with Lexical Analysis to make single-pass compilation • Synthesis Stage - Implemented • Variables are allocated to internal registers • Small functionalities • Faster execution, less energy used when executing generated code • Position independent Code

14. The MinTax Compiler: Supported WSN Nodes • The WSN world usually comprises solutions around microcontrollers from Atmel and Texas Instruments Mica2 Z1 AVRRaven

15. Results • Sending of a “Blink” application, Mica2 platform: • Compile, and reprogram:

16. Conclusion and perspectives • Conclusion • High-level language (MinTax) coupled with in-situ compilation • Energy-efficient solution for dynamic reconfiguration • Perspectives • Heterogeneous network validation • Multi-OS Integration ?

17. Thank you !