Towards System Architecture for Tiny Networked Devices

1. Towards System Architecture for Tiny Networked Devices Jason Hill http://www.cs.berkeley.edu/~jhill http://www.cs.berkeley.edu/~jhill/tos U.C. Berkeley 6/20/2000

2. Scalable Infrastructure • highly available • persistent state (safe) • databases, agents • service programming environment Service Path • Ubiquitous Devices • billions • sensors / actuators • PDAs / smartphones / PCs • heterogeneous An End-to-end Perspective • Desktops • max out at few 100M • in your face • connected to the infrastructure Endeavor Retreat

3. Key Characteristics of TNDs • Small physical size and low power consumption • Concurrency-intensive operation • flow-thru, not wait-command-respond • Limited Physical Parallelism and Controller Hierarchy • primitive direct-to-device interface • Diversity in Design and Usage • application specific, not general purpose • huge device variation => efficient modularity => migration across HW/SW boundary • Robust Operation • numerous, unattended, critical => narrow interfaces Endeavor Retreat

4. ‘Mote’ Initial Platform • 4Mhz, 8bit MCU 512 bytes RAM, 8K ROM • 900Mhz Radio 10-30 ft. range • Temperature Sensor • Light Sensor • LED outputs • Serial Port Endeavor Retreat

5. Tiny OS • Scheduler and Graph of Components • constrained two-level scheduling model: threads + events • Component: • Frame (storage) • Threads (concurrency) • Commands, and Handlers (events) • Constrained Storage Model • frame per component, shared stack, no heap • Very lean multithreading • Layering • components issue commands to lower-level components • event signal high-level events, or call lower-level commands • Guarantees no cycles in call chain Endeavor Retreat

6. Messaging Component Internal State send_msg_thread TX_packet(buf) Power(mode) init send_msg(addr, type, data) power(mode) msg_rec(type, data) msg_send_done (success) init RX_packet_done (buffer) TX_packet_done (success) TOS Component /* Messaging Component Declaration */ //ACCEPTS: char TOS_COMMAND(AM_SEND_MSG)(char addr,char type, char* data); void TOS_COMMAND(AM_POWER)(char mode); char TOS_COMMAND(AM_INIT)(); //SIGNALS: char AM_MSG_REC(char type, char* data); char AM_MSG_SEND_DONE(char success); //HANDLES: char AM_TX_PACKET_DONE(char success); char AM_RX_PACKET_DONE(char* packet); //USES: char TOS_COMMAND(AM_SUB_TX_PACKET)(char* data); void TOS_COMMAND(AM_SUB_POWER)(char mode); char TOS_COMMAND(AM_SUB_INIT)(); Endeavor Retreat

7. Composition Route map router sensor appln application Active Messages packet Serial Packet Temp Radio Packet SW byte HW UART Radio byte i2c photo bit clocks RFM Endeavor Retreat

8. Programming with CAD • Can assemble overall system using structural VHDL • Scripts pre-process VHDL at compile time • Allows for compile time resolution of event handlers • Eliminates need for registration mechanisms and dynamic dispatch • Automatically allows events to be handled by multiple components. (TX_Done) • Significantly more flexibility than library based component models Endeavor Retreat

9. Migration of the Hardware Software Boundary • TinyOS component model propagates hardware abstractions into software • Allows for a migrations of software components into hardware: • Example: • Bit level radio procession component could be implemented as specialized FIFO with complex pattern matching. Endeavor Retreat

10. Timing diagram of event propagation Dynamics of Events and Threads • Message Send Transition Endeavor Retreat

11. Components Packet reception work breakdown Percent CPU Utilization Energy (nj/Bit) AM 0.05% 0.20% 0.33 Packet 1.12% 0.51% 7.58 Ratio handler 26.87% 12.16% 182.38 Radio decode thread 5.48% 2.48% 37.2 RFM 66.48% 30.08% 451.17 Radio Reception - - 1350 Idle - 54.75% - Total 100.00% 100.00% 2028.66 Empirical Breakdown of Effort • can take apart time, power, space, … • 50 cycle thread overhead, 10 cycle event overhead Endeavor Retreat

12. Storage Breakdown (C Code) 3450 B code 226 B data Endeavor Retreat

13. Projects this Term • Device Proxy Architecture • mobile-IP RDP variant • Integration with infrastructure • JINI and Ninja • Multithreaded vs. federated architecture • Pluggable adaptive MAC layer • often periodic, moment of crisis • sleep cycling • Ad Hoc routing component • Connectivity-based location detection • smart badge + sensor in smart space Endeavor Retreat

14. Multi-Hop Routing Demo • Sensors automatically detect routing topology • Base station broadcasts out routing information • Individuals listen for an propagate route update • N messages sent • Generational scheme to prevent cycles in routing table Base Endeavor Retreat

15. Multi-Hop Routing Demo (cont.) • Sensor information propagated up routing tree • Statistics kept as to number of readings received and number of packets forwarded for each node • Sensors transmit data when “significant” events occur or when time limit is exceeded • Must be continuously listening for packets to be forwarded Endeavor Retreat

16. Second generation hardware design is under way • Mote “designed for experimentation” • Additional Sensors • 2 Axis Accelerometer and 2 Axis Magnetometers • Allows dead reckoning in 2-D plane • Humidity, Temperature, and Pressure sensor • Transmission strength sensor and control • Expansion capabilities through external BUS • The hardware sandwich • Ability to directly plug into logic analyzer for debugging purposes Endeavor Retreat

17. Current and Future Work • Quantify error characteristics of RFM Radio • Allows selection of coding techniques that optimize throughput and reliability • Aggressive inlining to minimize overhead of modules • Document and release code for others to use • Determine limitations of TinyOS • Incorporate more exciting HW architectures • Integrate with Ninja active proxies and Base services Endeavor Retreat