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Normally-Off MCU Architecturefor Low-power Sensor Node

Masanori Hayashikoshi (Speaker),Yohei Sato,

Hiroshi Ueki,Hiroyuki Kawai,Toru Shimizu,

Renesas Electronics Corporation

ASP-DAC 2014, Session 1S-3Jan. 21, 2014

Outline

Introduction Lower power requirements of sensor nodes in

smart society Challenges for low-power sensor node Proposal for normally-off architecture for low-power

sensor node Summary and Conclusions

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Outline

Introduction Lower power requirements of sensor nodes in

smart society Challenges for low-power sensor node Proposal for normally-off architecture for low-power

sensor node Summary and Conclusions

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Paradigm shift for power savings Intermittent system operation by NVRAM will be a promising

solution to low-power requirements.

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pow

er

time

active standby

Large SRAM standby leak

SRAM based operation

pow

er

time

active standby

eFlash start-up

eFlash based operation

Data evacuation to eFlash

pow

er

time

active standby

NVRAM based operation

<Advantages>- Very low power consumption- Reliability improvement of Trs in peripheral circuits

<Features>- Fast power-on/off- No DC current during standby

Challenge for further power saving in NVRAM system application

“Normally-off computing technology” is enable to cut off the power, except for the component in work truly even in operation as a system, with synergy of NVRAM and power gating technology.

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applicationalgorithm

scheduling

op1

op2

op3 op5

op4 op6

op7 op8

Dependence of activity

Maximize the power-off period with activity localization

(BET: Break Even Time)

If t<BET,No chance for Power-Off

op1 op5 op6 op8

op2 op3 op4 op7

activity

activity time

time

If t>BET,Chance for Power-Off

op1 op5op6op8

op2 op3 op4 op7

activity

activity time

time

PowerOff

PowerOn

Unit A

Unit B

ActivityLocalization

tBET BET

t

Technologies to realize “Normally-Off Computing”

Power-Off as long as possible, as large area as possible, if QOS is satisfied.

Power-Off during IDLE-Time of circuits, function blocks, chips, units and systems.

Application-independent Computing Platform based on Power-gating, Software-control and OS API.

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“Normally-Off Computing” is a System-level platform technology with combining HW and SW technologies.

Power gating Non-volatile RAMDVFS, AVS, etc.Clock gating

Software TechnologyPower on-off control, OS, API

Device TechnologyCircuit Technology

Outline

Introduction Lower power requirements of sensor nodes in

smart society Challenges for low-power sensor node Proposal for normally-off architecture for low-power

sensor node Summary and Conclusions

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Cyber-Physical System is a fundamental technology in Smart City

The advanced service can be realized with collecting real-time information in the social and natural environments.

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Connected

Mobile

Service Vender

Internet

Sensor

Power ControlServer

Smart Grid

Network

Environmentmonitor

Power Network

BEMS, HEMSAir-conditioningmanagement,Seculity Gurd,Maintenance

Power CompanyRemote Meter Reading,Power Supply Control

Content Vender

Data CenterFinance, Government,

School,…

TelecommunicationModem

Home Security

Consumer Electronics Control

Automated Mater Reading

Motion,Thermal,Smoke Sensors

Camera

IntercomDoor Key

Living InformationService

Data Delivery with PC

Light

Power Monitoring

Gas leakDetection

Power Meter Gas MeterWater Meter

Cloud

Air Conditioning Thermal,HumiditySensor

ModemServer

Music, Visual, Game,Network service,…

Gloval Processing <Inter-net> Regional and local information

collection <Sensor-net>Therefore, sensor nodes become used extensively to gather the real-time information.

Production volume of Sensor Node Production Volume: ~10B pcs/year This volume will be much increased with the development of

cyber-physical systems.

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PC & Server Mobile Phone & Terminal

Embedded Sensor-node

0.3Bpcs/year

1.5Bpcs/year

10Bpcs/year

(Production Volume: 2011 Data)

It becomes very important how to reduce the power consumption of huge sensor nodes.

Outline

Introduction Lower power requirements of sensor nodes in

smart society Challenges for low-power sensor node Proposal for normally-off architecture for low-power

sensor node Summary and Conclusions

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Conventional Sensor node Sensor-modules are in “Normally-On”. Microcontroller is in “Normally-On” or “Intermittent”.

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Network

Vcc

Microcontroller

Input

Sensor 0

Sensor n

Sensor 1

Input

Sensor modules

CPU(CPU-2)

Sensor-netInterface

DataIF

PowerControl

VddPOR

OSC

Memory

Normally-On Normally-On or Intermittent

Input

LDO

Peripheral

Sensornetwork

Challenge for Low-power Sensor nodes

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Istby~10uA

PowerOnOverhead

TimeStandby Wakeup

50us~100ms

50ms~10s

Power

(Data communication)

Sensing

CPU processing

Power consumption change of sensor nodes

Breakdown of power consumption of sensor system

Telecom Sensor(AlwaysPower-on)

MCU(Active)MCU

(Stand-by)

11%13%

10%66%

Challenge for low-power consumption

Maximize power-off period. (MCU and Sensor is power on, when necessary)

Reduce the active current.

Power On/Off Overhead Power On and Off has Power and Time overhead. “Normally-off Computing” should manage the overhead to

reduce total-power .

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Maximize Power-Off period- Longer Off-time, and More frequently

Minimize Power-on energy- Lower active current, and Shorter On-time

I(t)

V(t)

t

tSW-ON SW-OFFProgram

start

Power-ON

Power-ON

SW-ON SW-OFFProgramstart

Power-ON

Power-ON

Power-OFF

Power-OFF

Low-leak(OFF-time)

Low-power(ON-time)

Normally-off(Longer and

More frequently)

Outline

Introduction Lower power requirements of sensor nodes in

smart society Challenges for low-power sensor node Proposal for normally-off architecture for low-power

sensor node Summary and Conclusions

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Normally-Off Architecture for Low-power Sensor node

Sensor-modules are in “Normally-Off”. Microcontroller is in “Normally-Off”.

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Vcc

Microcontroller

Input

Sensor 0

Sensor n

Sensor 1

Input

Sensor modules

SensorControl(CPU-1)

(b)

CPU(CPU-2)

Sensor-netInterface

DataIF

PowerControl

VddPOR

OSC

Memory

Control Sig.

n

RTC

Vcc-1 Vcc-4

Normally-Off Power Manager(a)

Power Statement RegisterVcc-3

Sensor data buffers

(C)

Vcc-2

Normally-On

Normally-Off Normally-Off

Input

LDO

Peripheral

Network

Sensornetwork

DataIF

DataIF

Control Sig.n

HighLoad

LowLoad

(d)

Normally-Off Architecture for Low-power Sensor node (Continue)

Challenge is how to control the following key components.

Normally-Off Power Manager (a) “Power Manager” controls power on/off in all units with

data of “Power Statement Register”, and Manages task-level scheduling for activity localization.

Sensor Controller (b) Simple processing (e.g. data sampling) which was carried

out in the microcontroller, are performed in “Sensor Controller”.

Sensor Data Buffer (c) Sensor data are stored in “Sensor Data Buffer”. After that,

microcontroller performs the processing at once to reduce the number of power-on of microcontroller.

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Normally-Off Architecture for Low-power Sensor node (Continue)

CPU in Microcontroller (d) Proposed architecture is consists of heterogeneous CPUs

with Sensor Controller(b) and CPU(d). Sensor required high load task, such as a Image sensor,

is directly processed at CPU(d). Task processed at Sensor Controller(b) and CPU(d)

respectively should be optimized with task-level scheduling method.

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Thus, it is possible to reduce the operating frequency of the microcontroller, and to maximize the power-off time of microcontroller.

Normally-Off Power Management (1)Autonomous standby mode transition

Current microcontroller has some standby modes. “Normally-Off Power Manager” also supports the “Autonomous

standby mode transition technology” to select optimal standby mode for programmer’s usability improvement.

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Power-OffEOHStby mode-3EOHStby mode-2EOHStby mode-1EOHIDLE EOH

ConsumptionEnergy

Task cycleBET1 BET2 BET3 BET4

ActiveEnergy

StandbyEnergy

EOH: Energy Over-HeadBET: Break Even Time

Normally-Off Power Management (2)Activity Localization technology

Sensing data is buffered in sensor data buffer, and after then, microcontroller is activated and performed the process at once.

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It is possible to optimize the number of power on/off cycles and decrease power consumption energy.

Conventional PG control Hierarchical PG control

Td: deadline

Ti: interval

time

Stand-by

Power-on

Datasampling

Sensor MCU

Td’ := Td – Tbufeffective deadline

Ti: interval

Tbuf:buffer OH

time

Processing forN inst. bundle

Sensor MCUSensordata buff.

Power-on

Stand-by

Data sampling

Evaluation Board Evaluation board is consist of,

Sensor (Temperature, Brightness, Pyroelectric(Motion)) Microcontroller Other Peripheral circuits

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MCU

LCD

PowerSupply

Communicationconnector

Memoryconnector

Reset SW

E1 debuggerUSB

Analogconnector

Temperature sensor

Pyroelectric(Motion)sensor

LED

RS-232C

Brightness sensor

Evaluation Results Power consumption energy is reduced by 67%.

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0.00

1.00

2.00

3.00

4.00

5.00

6.00

- MCU: conventional PG control - Sensor: always power-on

Energy[mJ]

Reduction by 67%

- MCU: Hierarchical PG control- Sensor: Intermittent PG control

Sensor Microcontroller(MCU)

[Condition]- 3 sensors (Temp., Brightness, Pyroelectric)- Sampling cycle = 1s- Processing period = 4ms- Room temp.

Demonstration of Normally-Off Microcontroller system

Demonstrate effectiveness and adaptability of normally-off microcontroller system.

Demand transportation system with Normally-Off sensors (Pyroelectric, Camera) are under development as a demonstration with Future University Hakodate.

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Demand transportation system based on Intelligent bus stop

Intelligent Bus Stop System with

Normally-Off.

Control Center

DirectionLocation

Dispatch depending onRequirements

Outline

Introduction Lower power requirements of sensor nodes in

smart society Challenges for low-power sensor node Proposal for normally-off architecture for low-power

sensor node Summary and Conclusions

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Summary and Conclusion Production volume of sensor nodes is much increased with

the development of cyber-physical systems.

Normally-off architecture of microcontroller for future low-power sensor node has been proposed to reduce the power consumption of huge sensor nodes.

To realize true low-power effects with normally-off computing technology, a co-design of hardware and software technology is very important.

In this work, the power consumption energy is reduced by 67%.

Normally-Off Computing is a candidate for future low power sensor networks.

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Thank you for your attention.