Ultra-Low-Power Wireless Sensor Node Programmable in Java
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The document discusses the development of ultra-low-power wireless sensor nodes and a Java-compatible virtual runtime environment, aimed at maximizing energy efficiency. It outlines various power modes and improvements to the software stack to optimize energy consumption and maintain timing accuracy. The experimental results indicate significant reductions in power usage, demonstrating the feasibility of the design for real-world applications.
![ICC 2012 – E2NETS workshop
OTTAWA – CANADA – JUNE 10-15 2012
Power modes
CPU Clock Memory
Active mode 1-10mW
Self wake up [1-10us]
Standby mode 1-100uW
External interrupt [<1ms]
Sleep mode 1uW
Reboot at external interrupt [1-100ms]
Hibernation mode 100nW
10/25
alessandro.bogliolo@uniurb.it](https://image.slidesharecdn.com/virtualsense-e2nets-slideshare-120612162236-phpapp01/85/Ultra-Low-Power-Wireless-Sensor-Node-Programmable-in-Java-10-320.jpg)
Ultra-Low-Power Wireless Sensor Node Programmable in Java
- 1. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 E2NETS Workshop Energy Efficiency in Wireless Networks & Wireless Networks for Energy Efficiency Ultra-Low-Power Sensor Nodes Featuring a Virtual Runtime Environment EMANUELE LATTANZI ALESSANDRO BOGLIOLO DiSBeF University of Urbino & NeuNet 1/25 alessandro.bogliolo@uniurb.it
- 2. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Agenda • Introduction • HW-SW platform • Power states • DPM issues and solutions • Experimental results 2/25 alessandro.bogliolo@uniurb.it
- 3. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Introduction • Need for energy efficient wireless sensor nodes – Lifetime maximization – Compatibility with energy harvesters • Attractiveness of runtime virtual environment – Development – Deployment – Re-use/Re-programming • Availability of ultra-low-power micro controller units (MCUs) featuring – 16-bit RISC architectures clocked at tens of MHz – 16kbytes of main memory – 64kbytes of flash memory – Voltage-frequency scaling – Low-power modes with sub-ms wake-up time 3/25 alessandro.bogliolo@uniurb.it
- 4. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Objective • Ultra-low power sensor node • Java-compatible virtual run-time environment • Full exploitation of low-power modes • Off-the-shelf low-cost components • Open-hardware PCB • Open-source software stack 4/25 alessandro.bogliolo@uniurb.it
- 5. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Agenda • Introduction • HW-SW platform • Power states • DPM issues and solutions • Experimental results 5/25 alessandro.bogliolo@uniurb.it
- 6. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 HW platform • TI MSP430F54xxa MCU – 16-bit RISC – 8.9mA @ 25MHz – 6 LP modes – 0.1-73 uA – 5us wake-up 6/25 alessandro.bogliolo@uniurb.it
- 7. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 SW stack Contiki OS • Open-source real-time OS for sensor networks and networked embedded systems – Portability – Multi-tasking – Memory efficiency – Event-driven organization – Elementary DPM which exploits the stand-by state of the MCU and wakes it up every 10ms to keep timing coherence 7/25 alessandro.bogliolo@uniurb.it
- 8. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 SW stack Darjeeling VM • Open-source VM for extremely limited devices – Java compatibility – Limited requirements (10kbytes of RAM) – Bytecode efficiency (infuser) – Runs as a single process – Supports multi-threading – Preemptive round-robin scheduling 8/25 alessandro.bogliolo@uniurb.it
- 9. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Agenda • Introduction • HW-SW platform • Power states • DPM issues and solutions • Experimental results 9/25 alessandro.bogliolo@uniurb.it
- 10. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Power modes CPU Clock Memory Active mode 1-10mW Self wake up [1-10us] Standby mode 1-100uW External interrupt [<1ms] Sleep mode 1uW Reboot at external interrupt [1-100ms] Hibernation mode 100nW 10/25 alessandro.bogliolo@uniurb.it
- 11. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 SW-stack dimension OS VM Int OS VM Active boot boot hand sch sch Vtask Standby Sleep Hibernation 11/25 alessandro.bogliolo@uniurb.it
- 12. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Wake-up transitions OS VM Int OS VM Active boot boot hand sch sch Vtask Standby Sleep Hibernation 12/25 alessandro.bogliolo@uniurb.it
- 13. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Agenda • Introduction • HW-SW platform • Power states • DPM issues and solutions • Experimental results 13/25 alessandro.bogliolo@uniurb.it
- 14. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Standby mode Int OS VM ContikiOS schedules hand sch sch Vtask a self-wakeup every 10ms There are 3 cases: a) The VM has no tasks to resume a 14/25 alessandro.bogliolo@uniurb.it
- 15. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Standby mode Int OS VM ContikiOS schedules hand sch sch Vtask a self-wakeup every 10ms There are 3 cases: a) The VM has no tasks to resume a a) The OS has no proc. to resume b 15/25 alessandro.bogliolo@uniurb.it
- 16. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Standby mode Int OS VM ContikiOS schedules hand sch sch Vtask a self-wakeup every 10ms There are 3 cases: a) The VM has no tasks to resume a a) The OS has no processes to resume b a) The VM has a task to resume Actual wake up 16/25 alessandro.bogliolo@uniurb.it
- 17. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Standby mode abstract state diagram Active 1-10mW Vtask c Exploitation issues: a The self-loop longer than 10ms 1-10mW No power saving Standby b Not supported by the SW 1-100uW stack (VM always active) 1-10uW Not supported by Contiki OS Lack of timing info Stanby mode is not compatible with the SW stack! 17/25 alessandro.bogliolo@uniurb.it
- 18. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Standby mode improvements • Modified Contiki OS to make it able to dynamically adjust the INTERVAL of timer interrupts • Modified Darjeeling VM scheduler to make it able to set the OS timer and suspends the VM PROCESS_WAIT_EVENT_UNTIL() • Implemented a timed standby mode with just-in-time predictive wake-up • Mounted an external low-power (0.3uW) real-time clock (RTC) to preserve timing accuracy 18/25 alessandro.bogliolo@uniurb.it
- 19. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Standby mode modified state diagram 6.6mW Vtask 4.5uW + 153.72uJ/T Standby.a(T) Families of low-power states Standby.b(T) depending on T 4.5uW + 0.33uJ/T 4.5uW + 0.3uW Standby.t 4.5uW Standby 19/25 alessandro.bogliolo@uniurb.it
- 20. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Sleep mode issues • Unable to issue self-events – Wakup can only be triggered by external interrupts – Cannot be exploited if there are processes/tasks that need to resume at a given time (e.g., periodic monitoring tasks typical of many WSN applications) • Lack of timing information – No information about the time elapsed since last shut down – No time stamps associated with external interrupts Sleep mode can ony be exploited in case of time- independent reactive applications 20/25 alessandro.bogliolo@uniurb.it
- 21. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Sleep mode improvements • Implemented a timed sleep mode with just in time predictive wakeup based on the external RTC • Used the external RTC to provide relative and absolute timing information at wake up 1.5uW + 0.3uW Sleep.t 1.5uW Sleep 21/25 alessandro.bogliolo@uniurb.it
- 22. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Hibernation mode issues • Unable to issue self-events – As for Sleep mode • Lack of timing information – As for Sleep mode • Lack of data retention – Requires a complete reboot – Impossible to resume a process/task Hibernation mode can ony be exploited in case of memory-less reactive applications 22/25 alessandro.bogliolo@uniurb.it
- 23. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Hibernation mode improvements • Used the external RTC as for the Sleep mode • Implemented a native method in the main of the VM to save and restore the heap of the VM in flash memory 1.5uW + 0.3uW Hibernation.t 1.5uW Hibernation 23/25 alessandro.bogliolo@uniurb.it
- 24. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Agenda • Introduction • HW-SW platform • Power states • DPM issues and solutions • Experimental results 24/25 alessandro.bogliolo@uniurb.it
- 25. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Characterization results Data refer to a MSP430F2618 MCU powered at 3V and clocked at 16MHz 25/25 alessandro.bogliolo@uniurb.it
- 26. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Experimental results 6.6mW Average power consumption of the MCU used to execute a periodic monitoring 110uW task which keeps the CPU busy for 1s 6.9uW Once Once per hour per day 26/25 alessandro.bogliolo@uniurb.it
- 27. ICC 2012 – E2NETS workshop OTTAWA – CANADA – JUNE 10-15 2012 Conclusions • Ultra-low-power sensor node • Java-compatible virtual runtime environment • Power consumption ranging from 6.6mW to 0.1uW (in Hibernation) • Capable of reacting to external events and resume execution from any low-power state • All low-power modes directly exploitable from the Java runtime environment • Open-HW / Open-SW approach 27/25 alessandro.bogliolo@uniurb.it