1. 1 Operating System Support for Mobile Devices 4/5/2004 Richard Yang

2. 2 Outline r Admin. and recap r CPU scheduling r Operating systems for mobile devices

3. 3 Admin. r Homework 1 r Homework 2 r Midterm r Homework 3 m on localization m due: 11:59PM April 12 r Project m please make an appointment with me and the TA so that we can have some detailed discussions

4. 4 Project Proposals r Increasing Connectivity through Controlled Mobility James Terry and Mike Bell r Using Mobility for Localization and Coverage Ana Cerejo, John Corwin, and Diego Montenegro r Controlled Mobility: Mobile Beacons For Clock Synchronization Ashish Vatsal and Gregory Edwards r Optimizing Clock Synchronization in Mobile Networks Hang Cheng, Tomislav Nad, and Mirtcho Spassov r Controlled Mobility for Multicast Ashley Green and Brad Rosen r Dynamic Boundary Estimation Using Mobile Sensor Networks Dimitrios Lymberopoulos, Jia Fang, and Akin Babayigit

5. 5 Project Proposals (cont’) r Wireless Communication and Localization in Rapidly Changing Real-time Environments with Air-Plane Trainers Johnny Yeh and Praneeth Wanigasekera r Prevent Source-cheating in Incentive Compatible Routing in Wireless Ad-Hoc Networks Hao Wang and Yinghua Wu r Security against DOS attacks in Wireless Ad-Hoc Networks Andrew Park and Bobby Vellanki r Improving SEER Through Generalized Learning Algorithms Reuben Grinberg and Joshua Barnard r DarkTooth: Anonymous H2H (Human to Human) File Transfer Over Non-cooperative, Untrusted Wireless Networks Anthony Young, Wesley Maness, and David Hughes

6. 6 Recap: Mobile File Systems r Problems: give user file access while disconnected or weakly connected m read miss m delayed write r Solution m CODA hoarding: persistently store files in local caches m SEER automatic hoarding prediction m Bayou basic idea: application specific conflict detection and update

7. 7 Outline r Admin. and recap  CPU scheduling r Operating systems for mobile devices

8. 8 Discussion r What does CPU scheduling do in a traditional operating system? r What (new) problems does CPU scheduling face in mobile computing?

9. 9 CPU Power Consumption r CPU consumes 30%-50% of notebook power r the power P of a CMOS processor satisfies where k is a constant, C the capacitance of the circuit, f the CPU frequency, V the voltage, and V t a threshold voltage r Thus power consumption ~ O(V 3 ) m a convex function of V (and/or f)

10. 10 Dynamic Voltage Scaling r Dynamic Voltage Scaling (DVS) allows voltage to be dynamically adjusted to save power r DVS-enabled processors, e.g., m AMD (PowerNow!) http://www.amd.com/us-en/assets/content_type/DownloadableAssets/Power_Now2.pdf m Intel (SpeedStep, XScale) m Texas Instrument m Transmata r Discussion: what voltage to operate on? throughput

11. 11 Dynamic Voltage Scaling r Basic idea: determining voltage according to program response time requirement r For normal applications, give reasonable response time r For multimedia applications, use the deadline to determine voltage

12. 12 Architecture CPU monitoring scheduling speed scaling demand distribution Scheduler Speed Adaptor Profiler Multimedia Applications requirements time constraint

13. 13 Demand Prediction  Online profiling and estimation: count number of cycles used by each job b 1 b 2 C min =b 0 b r =C max 1 b r-1 cumulative probability CDF F(x) = P [X  x]

14. 14 Observations Demand distribution is stable or changes slowly

15. 15 CPU Resource Allocation How many cycles to allocate to a multimedia job? Application requires  percent of deadlines  each job meets deadline with probability   allocate C cycles, such that F (C ) =P [X  C ]   b 1 b 2 b 0 brbr 1 b r-1 cumulative probability F(x)F(x)  C

16. 16 Scheduling of Multimedia Applications  Earliest deadline first (EDF) scheduling  - allocate cycle budget per job  - execute job with earliest deadline and positive budget  - charge budget by number of cycles consumed  - preempt if budget is exhausted

17. 17 How Fast to Run the CPU?  Assume job i need C i cycles during P i period  Fact: since power is a convex function of frequency, if a job needs C cycles in a period P, then the optimal frequency is C/P, namely the lowest constant frequency:

18. 18 Why Not Uniform Speed? Intuitively, uniform speed - minimum energy if use the allocated exactly However, jobs use cycles statistically - often complete before using up the allocated - potential to save more energy  stochastic DVS

19. 19 Stochastic DVS For each job 1.Find speed S x for each allocated cycle x  Time is 1/S x and energy is (1 - F(x))S 2 x such that

20. 20 Stochastic DVS r Approximate solution to the preceding optimization problem r Speed schedule m list of points (cycle bi, speed S bi ) m change speed to S bi at bi cycles

21. 21 Example Speed Schedule 100 MHz200 MHz400 MHz cycle: speed: Job 1 2.5 x10 6 cycles speed (MHz) 100 400 200 Job 2 1.2 x10 6 cycles Observation: speed up the processor with increasing clock cycles

22. 22 SRT + DVS speed A1 B1 A1 execution speed up within job context switch 1.Store speed for switched-out 2.New speed for switched-in switch back A2

23. 23 Implementation Hardware: HP N5470 laptop –Athlon CPU (300, 500, 600, 700, 800, 1000MHz)  round speed schedule to upper bound process control block standard Linux scheduler SRT-DVS modules PowerNow speed scaling Soft real-time scheduling system call Extension to Linux kernel 2.4.18 716 lines of C code

24. 24 Reduces power consumption However, limited due to few speed options Evaluation: Normalized Energy

25. 25 Outline r Admin. and recap r CPU scheduling r Operating systems  Windows CE for PDAs m TinyOS for devices with extremely limited resources

26. 26 Windows CE/Pocket PC r Microsoft’s attempt for writing an operating system for mobile devices r Several versions m Pocket PC m Pocket PC Phone version m Smart phone version r A scaled down version of Windows m still provides most functionalities such as multithreading …

27. 27.NET Compact Framework r Programming languages compile to MSIL m MSIL is JIT compiled on the device m MSIL code is smaller than native executables m MSIL allows your code to be processor independent. Important for Pocket PC developers because Pocket PC devices use many types of processors r The.NET CF is a subset of the full.NET framework with some additions m designed for resource constrained devices m 1,400 classes for.NET CF vs. 8,000 for full m 27 UI controls for.NET CF vs. 52 for full m 1.5 MB for.NET CF vs. 30 MB for full

28. 28 Outline r Admin. and recap r CPU scheduling r Operating systems m Windows CE for PDAs  TinyOS for devices with extremely limited reosurces

29. 29 Motivation r Devices such as sensors with extremely limited by resource m today, sensors exist on the scale of a square inch in size, and a fraction of a watt in power. m in the future, it may be possible to reduce sensors to the size of a cubic millimeter, or smaller r Objective m build an operating system for devices with extremely limited resources

30. 30 Today’s Hardware r Assembled from off-the-shelf components r 4Mhz, 8bit MCU (ATMEL) m 512 bytes RAM, 8KB ROM r 900Mhz Radio (RF Monolithics) m 10-100 ft. range r Temperature sensor & light sensor r LED outputs r Serial Port 1.5” x 1.5”

31. 31 Operating System Requirements r Small foot print m devices have limited memory and power resources r Diversity in design and usage m provide a high degree of software modularity for application specific sensors r Concurrency intensive operation m need a simple concurrency model r Many other requirements, e.g., m Robust operation OS should be reliable, and assist applications in surviving individual device failures

32. 32 TinyOS r A microthreaded OS that draws on previous work done for lightweight thread support, and efficient network interfaces r Developed at Berkeley

33. 33 Important Concepts: First Step r TinyOS concepts are expressed in nesC, a C-like language r Concurrency model: a two level scheduling structure m Long running tasks that can be interrupted by hardware event handlers r Component model: specification m A tinyOS consists of one or more components linked together m Each component provides and uses interfaces m An interface declares a set of functions called commands that provider must implement and another set of functions called events that the interface user must implement r Component: implementation m two types of components: modules and configurations m modules: provide application code, implementing one or more interface m configurations: assemble other components together, connecting interfaces used by components to interfaces provided by others

34. 34 Example: Blink r A simple TinyOS application which causes the red LED on a mote to turn on and off at 1Hz

35. 35 Example: Blink Blink.nc configuration Blink { } implementation { components Main, BlinkM, SingleTimer, LedsC; Main.StdControl -> BlinkM.StdControl; Main.StdControl -> SingleTimer.StdControl; BlinkM.Timer -> SingleTimer.Timer; BlinkM.Leds -> LedsC; }

36. 36 The StdControl Interface StdControl.nc interface StdControl { command result_t init(); command result_t start(); command result_t stop(); }

37. 37 The BlinkM Module BlinkM.nc module BlinkM { provides { interface StdControl; } uses { interface Timer; interface Leds; } implementation { command result_t StdControl.init() { call Leds.init(); return SUCCESS; } command result_t StdControl.start() { return call Timer.start(TIMER_REPEAT, 1000) } command result_t StdControl.stop() { return call Timer.stop(); } event result_t Timer.fired() { call Leds.redToggle(); return SUCCESS; } Timer.nc interface Timer { command result_t start( char type, uint32_t interval); command result_t stop(); event result_t fired(); }

38. 38 Running the Program r make mica r ncc -o main.exe -target=mica Blink.nc r avr-objcopy --output-target=srec main.exe main.srec r Use uisp to install