Sensing Platforms and Power Consumption Issues Lecture 2 September 12, 2006 EENG 460a / CPSC 436 / ENAS 960 Networked Embedded Systems & Sensor Networks Andreas Savvides Office: AKW 212 Tel Course Website

Some platforms & applications  Seismic monitoring, personal exploration rover, mobile micro-servers, networked info-mechanical systems, hierarchical wireless sensor networks [NIMS, UCLA][Robotics, CMU] [Intel + UCLA] [CENS, UCLA] [Intel + UCLA] [Slide from V. Ragunanthan]

Need for Sensing Platforms Fundamental Problems Close coupling between fundamental research questions and the physical world Experimental Systems In situ data collection Architectural requirements Numerous unknown factors and conditions with no prior knowledge Sensing channels not well characterized - very complex environment dynamics Power consumption hard to characterize – need to understand battery behaviors and how SW & HW components affect power consumption

Factors driving platform development  Researchers develop sensor nodes for Cost, power, sensors, computation  Things that change New radio technologies, new sensors, processor features and technologies Changing application demands Need to sustain operation in difficult places

Telos: New OEP Mote*  Single board philosophy Robustness, Ease of use, Lower Cost Integrated Humidity & Temperature sensor  First platform to use CC2420 radio, 2.4 GHz, 250 kbps (12x mica2) 3x RX power consumption of CC1000, 1/3 turn on time Same TX power as CC1000  Motorola HCS08 processor Lower power consumption, 1.8V operation, faster wakeup time 40 MHz CPU clock, 4K RAM  Package Integrated onboard antenna +3dBi gain Removed 51-pin connector Everything USB & Ethernet based 2/3 A or 2 AA batteries Weatherproof packaging  Support in upcoming TinyOS Release  Codesigned by UC Berkeley and Intel Research  Available February from Moteiv (moteiv.com) *D. Culler, UC Berkeley

What is Stargate?

Example Platform 2: UCLA Heliomote Slide from Jonathan Friedman, UCLA, NESL

Wireless DPM: Hierarchical radios  Three vastly different wireless radios supported  Combined to form power-efficient, heterogeneous communication subsystem Hierarchical device discovery and connection setup scheme leads to up to 40X savings in discovery power Technolog y Data Rate Tx Current Energy per bit Idle Current Startup time Mote 76.8 Kbps 10 mA430 nJ/bit7 mALow Bluetooth1 Mbps45 mA149 nJ/bit22 mAMedium Mbps300 mA90 nJ/bit160 mAHigh IEEE Bluetooth Mote Energy per bit Startup time Idle current

In this class: XYZ Node Research and education node to do tasks not doable with existing nodes Need for 32 bit computation for distributed signal processing protocols oE.g Localization protocol stacks and optimizations Need to be closer to the Sensors oDo fast sampling and processing close to the sensors –E.g real-time acceleration or gyro measurements –Acoustic sampling and correlation – need memory, peripherals and processing to be close to the computation resource – simplifies programming Accommodate custom form factors and interfaces for experimenting with mobile computing applications oMobility support interfaces (stronger connectors, output for motor contollers) oWearable applications – small package Very low power, long term sleep modes

XYZ’s Architecture

Features ARM7TDMI ROM-less (ML675001) 256KB MCP Flash (ML67Q5002) 512KB MCP Flash (ML67Q5003) 8KB Unified Cache 32KB RAM Interrupts FIQ I2C (1-ch x master) DMA (2-ch) Timers (7 x 16-bit) WDT (16-bit) PWM (2 x 16-bit) UART (2-ch)/ SIO (1-ch) GPIO (5 x 8-bit) ADC (4-ch x 10-bit) up to 66MHz -40 ~ +85  C Package 144 LFBGA 144 QFP XYZ Computation: The OKI ARM ML675001/67Q5002/67Q5003 [Slide from OKI Semiconductor]

OKI ARM ML675001/67Q5002/67Q5003 ARM7TDMI

XYZ’s Multiple Operational Modes  Frequency scaling  6 different operating frequencies.  1.8MHz – 57.6MHz  Radio management  8 discrete transmission power levels.  Sleep mode.  Turn on/off.  Individual peripherals  I/O clock is different than the CPU clock  enable/disable  internal clock divider.  Sleep modes  STANDBY Clock oscillation is stopped. Only an external interrupt can cause CPU to exit this mode. Wait for clock to stabilize after waking up.  HALT Clock oscillation is not stopped. Clock signal is blocked to specific blocks. Any interrupt (internal or external) can cause the CPU to exit this mode No need to wait for the clock to stabilize after waking up  Deep Sleep mode  XYZ is turned off! Only the Real Time Clock is operational.  Only the Real Time Clock can wake up the node.  Current drawn: ≈30μΑ

XYZ’s Deep Sleep mode: Supervisor Circuitry Step 1: Turn on the node. Step 2: The μC takes control of the Enable pin of the voltage regulator. Step 3: Turn the power switch to the STBY position. Step 4: The μC selects the total time that wants to be turned off and programs the DS1337 accordingly, through the 2-wire serial interface. Step 5: The DS1337 disables the voltage regulator and uses its own crystal to keep the notion of time. The entire sensor node is turned off! Step 6: The DS1337 enables the voltage regulator after the programmed amount of time has elapsed. Step 7: The μC takes control of the Enable pin of the voltage regulator OKI μC RTC DS1337 Voltage Regulator 3 x AA batteries 2.5V 3.3V I2CI2C WAKEUP Enable Interrupt (SQW) GPIO INT_1 INT_2 ON STBY

XYZ: Power Characterization Frequency Scaling  Current consumption varies from 15.5mA(1.8MHz) to 72mA(57.6MHz)  Disabling all the peripherals (except the timers) results to a reduction of 0.5mA (1.8MHz) to 12mA(57.6MHz)  Peripherals cause most of the overhead  SOS and Zigbee MAC layer overhead:  2 schedulers  4 hardware timers  1 software timer  20 maximum frequency

XYZ: Power Characterization Frequency Scaling  Current consumption varies from 15.5mA(1.8MHz) to 72mA(57.6MHz)  Disabling all the peripherals (except the timers) results to a reduction of 0.5mA (1.8MHz) to 12mA(57.6MHz)  Peripherals cause most of the overhead  SOS and Zigbee MAC layer overhead:  2 schedulers  4 hardware timers  1 software timer  20 maximum frequency

Power Mode Transitioning Overheads Frequency (MHz) STANDBYHALT SleepWake upSleepWake up Time(μ s) Energy( μJ) Time(ms ) Energy( mJ) Time(μs)Energy( μJ) Time(μs)Energy( μJ) / /  Power Consumption in the HALT mode depends on the previous operating mode!  The reason is that most of the peripherals are active in the HALT mode!  Waking up the node takes orders of magnitude more time than putting it into sleep mode. This time is not software-controlled and can vary from 10 to 24ms for the maximum operating frequency.  The time that is required to wake up the processor depends on the next operating mode! Transistion from (MHz) STANDBYHALT Current (mA) CoreTotalCoreTotal 57.6(radio IDLE)≈ /32(radio IDLE) ≈ (radio listening) ≈ /32(radio listening) ≈

XYZ: Power Characterization Radio’s Power Consumption  The current drawn by the radio while listening the channel is higher than the current drawn when the radio is transmitting packets at the highest power level LevelTX Power(dBm) Power Consumed (mW) 0(max) (min)

XYZ: Software Infrastructure SOS Operating System IEEE MACLow Power APIApplication Layer Dynamic Loadable Binary Modules CPU and Radio APIs Zigbee MAC protocol Operating System Hardware Drivers

Heliomote Charging Circuit Slide from Jonathan Friedman, UCLA, NESL

Manufacturers of Sensor Nodes  Millenial Net ( iBean sensor nodes  Ember ( Integrated IEEE stack and radio on a single chip  Crossbow ( Mica2 mote, Micaz, Dot mote and Stargate, XSM  Intel Research Stargate, iMote  Dust Inc Smart Dust  Cogent Computer ( XYZ Node (CSB502) in collaboration with  Mote iv – tmote sky  Sensoria Corporation ( WINS NG Nodes  More….

What does one need to understand about nodes?  Where does power go? Useful power vs. overhead  Difference between low-power, power-efficient, power-aware  How do you keep the cost low?  What is the best node choice for each application?  Can you predict lifetime?  How do you may the node resilient to faults?  If your node is out there (e.g floating in the Long Island sound), how do you do maintenance on it?

Challenge Question  Assuming you are given 10 different radios 10 different processors 5 different sensors  How would you pick and choose to make a node that will give you the longest lifetime? (Remind me to tell you about Broadcatch)

Assignment 1: 1 week research topics Each person picks a topic to investigate. Your goal is to collect links and parameters about the state of the art. We will use these to solve different problems during the course. You need to turn-in a list of links together with your comments in 1 week.  Low-power radios IEEE , IEEE , UWB, make alist of as many vendors and specs as you can: power, bandwidth range  Inertial sensors – focus on wearable ones MEMS 3-D accelerometers & gyroscopes price, power, accuracy  Make a list of as many sensor node applications as you can find  Wearable sensing in medical applications  Suggest a topic or talk to me for more ideas

Power Perspective Comparison of Energy Sources With aggressive energy management, ENS might live off the environment. Source: UC Berkeley & CENS

Typical Operating Characteristics for 4 classes of Sensor Nodes Source: J. Hill, M. Horton, R. King and L. Krishnamurthy,”The Platforms Enabling Wireless Sensor Networks”, Communications of the ACM June 2004

Many ways to Optimize Power Consumption  Power aware computing Ultra-low power design in microcontrollers Dynamic power management HW oDynamic voltage scaling (e.g Intel’s PXA, Transmeta’s Crusoe) oComponents that switch off after some idle time  Energy aware software Power aware OS: dim displays, sleep on idle times, power aware scheduling  Power management of radios Sometimes listen overhead larger than transmit overhead Modulation scaling Apply network-wide topology management schemes  Energy aware packet forwarding Radio automatically forwards packets at a lower level, while the rest of the node is asleep  Energy aware wireless communication Exploit performance energy tradeoffs of the communication subsystem, better neighbor coordination, choice of modulation schemes

Computing Power Review Power: P=I * V Energy: E=P * T Duty Cycle = Time ON / Time OFF Processor Metrics for Computation:  MIPS/MHz  Number of instructions in a program  Execution time

Microprocessor Power Consumption CMOS Circuits (Used in most microprocessors) Dynamic Component Digital circuit switching inside the processor Static Component Bias and leakage currents O(1mW) Static Dynamic

Power Consumption in Digital CMOS Circuits - current constantly drawn from the power supply - determined by fabrication technology - short circuit current due to the DC path between the supply rails during output transitions - load capacitance at the output node - clock frequency- power supply voltage

Dynamic Voltage Scaling  Dynamic power consumption is the dominant component  Design processors that can scale their frequency and time: Crusoe Processor, Intel’s PXA and others use this technique  Example: Transmeta’s Crusoe processor

DVS on Low Power Processor Maximum gain when voltage is lowered BUT lower voltage increases circuit delay CMOS transistor threshold voltage Transistor gain factor Dynamic Power Component Number of gates Load capacitance of gate k Propagation delay

Example: Voltage Scaling on LART  Dynamically lower the processor voltage and frequency to reduce power consumption  LART wearable board StrongARM 1100 Processor 190MHz Various I/O capabilities 32 MB volatile memory 4 MB non-volatile memory Programmable voltage regulator

Processor Envelope At 1.5V Max clock frequency 251MHz Min frequency the processor functions correctly is 59MHz

LART Power Measurement Note the measurement setup at Different levels on the board Always provide hooks for measurement, testing and debugging during your design. Both for software and hardware!!! Total Power Consumption on the LART Platform Based on dhrystone benchmark

System Support Requirements  To manage DVS effectively, the computation requirements must be known in advance  Predictive scheme Try to learn that behavior based on the computation profile  Better scheme: Applications should be power aware  Processor frequency and scaling should be changed without much delay This is specific to each processor 150us for the LART processor

Example: Power Aware Video Playback  Annotate a H.263 video decoder with information on the clock speed required to decode a known video sequence  Using a 12.6s video, 15fps  Power consumption measurements for LART No-DVS: 198mW for CPU, 207mW for memory subsystem DVS: 100mW for CPU and 204mW for the memory subsystem 2X improvement, but 25% improvement when memory accesses are considered

LART Memory Performance  Memory access is optimal when high resolution memory access timing is available  For LART the optimal memory pattern: 148MHz 92 MB/s memory bandwidth Power consumption 514.2mW Energy cost 5.6mJ/MB

Basic Examples: Duty Cycling Node max voltage consumption: 120mW Power Supply Voltage: 2.5V Battery power source: 2000mAhr Standby current: 20uA If we need the node to last for 1 year, what duty cycle do we need to operate the node at?

Basic Examples: DVS #1 A device has the ability to scale its clock frequency from 64MHz to 4MHz, a 16 time frequency reduction CPU = 60mW Radio power = 120mW Other components = 20mW  What would be the lifetime gain if one operated it at 4MHz instead of 64MHz?

Basic Examples: DVS #2 A certain embedded processor can vary its clock speed from 59MHz to 250MHz and can compute at 1 MIPS/MHz. Assuming that the processor can vary its voltage from 0.8V to 1.5V for the lowest and highest frequency respectively. The processor can execute at 1MIPS/MHz a) What is the maximum energy saving of the processor? b) A certain task needs 200MIPS to compute. You have the option of running the task at the low speed or at maximum speed. Which would consume the least amount of energy?

Next Time: Study Cases We will examine some platforms using more advanced models iMote2 Hitachi node LEAP node What to look out for:  Measurements, not datasheet values  Where are the hidden costs?  Be very careful where to plug-in numbers….  Use tools that may be out there

Some Platform Links Check out the IPSN 2005 program The poster and demo sessions contain links to several projects using a very wide variety of platforms