Software Architecture of Sensors

Hardware - Sensor Nodes Sensing: sensor --a transducer that converts a physical, chemical, or biological parameter into an electrical signal Processing: microprocessor(CPU) data storage(Mem) AD converter Communicating: data transceiver(Radio), Energy source: battery

Hardware – Sensor Nodes cont. Characteristics of Sensor Nodes Limited capacity of – Battery (Lifetime: day - 10 years) – Processing capabilities (10MHz) – Transmission range ( meters) Data rates: Bit/s - KB/s Transmission methods: – (WiFi) – Bluetooth – short distance, other applications – ZigBee – for sensor network Price: some cents

Software - Operating System Sensor Manager – provides access to the sensors – manage the delivery of sensor data – provides and manages the resources provided to a sensor Integrity Service/ Access Control Query Manager Storage Sensor Manager

Software - Operation System Storage – persistent storage for data streams Integrity Service/ Access Control Query Manager Storage Sensor Manager

Software - Operating System cont. Query Manager – manages active queries – query processing – delivery of events and query results to registered, local or remote consumers Integrity Service/ Access Control Query Manager Storage Sensor Manager

Software - Operation System cont. Integrity Service/ Access Control Query Manager Storage Sensor Manager Top layer: access control and integrity service OS examples: – TinyOS: when an event occurs, it calls the appropriate event handler to handle the event. – Others: Contiki, MANTIS, and SOS.

8 TinyOS De facto OS for sensor nodes – Early research effort – Open source development – Wide presence in commercial products – Component-based architecture Adaptive to hardware changes Lightweight for various applications – Event-driven processing Responsive to sensor signals and radio messages

9 TinyOS Application Sensor devices Mote main board Hardware manipulation components Abstraction: Hardware: Core system components Lib componentsTinyOS interface components CommandsEvents Kernel: Application TinyOS startup (“Main”) Runable image of a TinyOS application A TinyOS application is compiled with TinyOS components.

10 Some Limitations of TinyOS Static code and memory – No virtual memory – No dynamic memory allocation – No dynamic code update – Task execution without priorities Single thread Global Free Stack TinyOS memory allocation

11 MANTIS Multi-threading Remote testing Scheduler for duty-cycle sleeping Small code size – Uses less than 500B RAM and 14KB flash memory Device driver Communication Layer Kernel / Scheduler Sensor Node Hardware MANTIS System API #1 User threads #n … Network Stack Command Server

The design of an operating system for Wireless Sensor Network (WSN) deviates from traditional operating system design due to significant and specific characteristics like constrained resources, high dynamics and inaccessible deployment. A wireless sensor node is a good example for a System on Chip (SoC) that has communication, computation, sensing and storage capabilities.

Middleware and application layers are distributed across the nodes. Core kernel of the operating system sits at each individual node. On top of it, middleware and applications run as interacting modules across nodes.

The current generation of micro-controllers family such as Mica, its successors and some microcontrollers specific to various research projects have nearly 128kbytes of program memory.

Reprogramming is a mandatory feature for OS and it simplifies the management of software in sensor nodes. It is the process of dynamically updating the software running on the sensor nodes. Without reprogramming, it is difficult to add, modify or delete the software from the running system in WSN.