1. Justin

2. Outline  Introduction  The Challenge of Preemption  TOSThreads Architecture  Implementation  Evaluation

3. Introduction  Operating System for WSNs Support multiple concurrent execution ○ Network protocol, storage and data filter…etc Event-driven execution ○ TinyOS  Disadvantage Develop higher-level services and application ○ Compression

4. The Challenge of Preemption  Challenge: Ability to call kernel code (code interact with hardware)  Common techniques Cooperative threading – using yield Kernel locking – using mutex Message passing

5. TOSThreads Architecture  TinyOS – two classes of execution Synchronous (tasks) Asynchronous (interrupts)  TOSThreads – third class User-level application threads  Goals Minimun TinyOS kernel modification

6. TOSThreads Architecture Original TinyOS

7. Implementation  Platform independent Thread scheduler Thread and system call structure Dynamic linking and loading  Platform dependent Context switch (assembly language) Post-amble for interrupt handler

8. Flexible User/Kernel Boundary  Blocking system call API  Dynamic Linker and Loader System Call Task Application-level thread 1,2,3… SendRecv SenseFile Kernel-level thread TinyOS Original code

9. Kernel-level thread TinyOS Original code App-level thread 1 App-level thread 2 App-level thread 3 Thread Scheduler TinyOS Modification  Boot sequence Hardware Initialize Task Scheduler

10. Evaluation - Microbenchmark Overhead can be tolerated

11. Evaluation - Energy analysis  SSF application (Sense, Store and Forward) Sense and write to flash per 5 mins Send via radio per 12hours

12. Evaluation - Tenet  A linear dataflow programs consisting of a sequence of tasklets. Repeat(1000ms) > Sample(ADC1,T) > LEQ(A,T,50) > DeleteDataIf(A) > Send()

13. Evaluation - Tenet  Tenet – C Implement in TOSThread and TinyLD

14. Evaluation - Tenet  Tenet – C Implement in TOSThread and TinyLD Repeat(100ms) > ReadBlock(A,1024) > Avg(B,A) > MeanDev(C,A) > Send() Repeat(50ms) > TimeStamp(A) > Sample(ADC5,V) > Send() TaskLong TaskSample

15. Evaluation - Tenet

16. Conclusion  TOSThread Thread-safe Non-invasive  Overhead is less Dynamic linking and loading is less – 0.92%