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

Mihai GALOS - ICECS Outline  Introduction to WSN (Wireless Sensor Networks)  Dynamic Reconfiguration  Existing solutions  Motivation  Our solution  Supported Architectures  Results  Conclusion and Perspecitves

Mihai GALOS - ICECS 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 –ZigBee

Mihai GALOS - ICECS WSN - Node  Small size  Low cost  Low energy consumption  Low processing power commercial " l ab assembled"  Some existing platforms:

Mihai GALOS - ICECS 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

Mihai GALOS - ICECS Existing Solutions for Dynamic Reconfiguration  Operating Systems  Virtual Machines

Mihai GALOS - ICECS 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) NameTypeUpdate Cost Running Costs Heterogeneity support Update Type TinyOSMonolithicHigh LowLimitedMachine Code MantisOS ModularMedium NanoRK SOS

Mihai GALOS - ICECS Existing solutions: Virtual Machines Again, two categories –ASVM (Application-specific virtual machines) –General-purpose virtual machines NameTypeUpdate Cost Running Costs Heterogeneity Support Update Type MatéASVM LowMedium to HighYes Virtual Machine specific Bytecode DarjeelingGPVM VMSTARGPVM

Mihai GALOS - ICECS Desired solution

Mihai GALOS - ICECS 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 High-level language, small bytecount + compilation Execution in Native format

Mihai GALOS - ICECS 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 NameSupported? Identifiers Yes, 2 bytes wide Data types Yes signed/unsigned 8bit or 16bit Arithmetic operations Yes, (+, -, /, * and %) For and While loopsYes If and Switch-Case clausesYes NestingYes StructuresYes PointersExperimental Digital I/O operationsYes ADCYes Preprocessor directivesNo TypedefinitionsNo

Mihai GALOS - ICECS MinTax: an example 1.aUk{ 2.^i=A2; 3.^j=8; 4.^u=i; 5. Wi<99 6. Wj>0 7. Pi,j; j- 10. # 11. i+ 12. # 13. }u; 1.Uint8_t a (uint16_t k){ 2.Uint8_t i = read_analog_pin(pin2); 3.Uint8_t j = 8; 4.Uint8_t u = i; 5.While(i<99){ 6. While(j>0){ 7. Pwm_output(i,j); 8. u=delay(k); 9. j - -; 10. } 11. i++; 12.} 13.return u;}

Mihai GALOS - ICECS 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

Mihai GALOS - ICECS The MinTax Compiler: Supported WSN Nodes  The WSN world usually comprises solutions around microcontrollers from Atmel and Texas Instruments  Mica2  Z1  AVRRaven

Mihai GALOS - ICECS Results  Sending of a “Blink” application, Mica2 platform:  Compile, and reprogram:

Mihai GALOS - ICECS 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

Mihai GALOS - ICECS Thank you !

Mihai GALOS - ICECS