POWER MANAGEMENT TECHNIQUES FOR SOCS

Andrew Byrne

Linh Dinh

ECE260C

May 29, 2014

Overview

Need for Power Management on SoCs Circuit Level Power Management Techniques

Multi-Threshold Power Gating Clock Gating Voltage Scaling

Hardware/Software Power Management Co-Design Drawbacks of Hardware-only Solutions Hardware/Software Power Management Module

Commercial Application

Need for Power Management

Mobile Demand Battery life a key performance specification which can provide a

competitive edge Allows for reduction in battery size, which results in a decrease in

overall system size Operating Costs

Power consumption is still a factor for non-mobile systems Thermal Requirements

Power management helps with system cooling requirements

Source: Cisco VNI Mobile, 2014

Need for Power Management

As CMOS technology improves for faster performance, power consumption increases Speed-power trade-off between technology nodes

Source: A, Anand, Managing Leakage – A Challenge for Designers at Lower Technology Nodes, Elite Quill Technology

Multi-Threshold

Sub-threshold leakage increases exponentially with decreasing threshold voltage

Use higher threshold cells on non-critical paths Decrease overall chip

leakage while maintaining slack on critical path

Requires additional masks during fabrication to adjust the dopant density Source: Shi, Cheng and Kapur, Rohit, How Power-Aware

Test Improves Reliability and Yield, EE Times

Power Gating

Source: Apache RedHawk-ALP Power Integrity Tool Description

Disconnect portions of circuit in standby mode to eliminate leakage current

Header/Footer Switch Configurations

Drawbacks Area overhead Voltage droop Output isolation Routing resources

Clock Gating

Combinational Disables the clock on registers when the output is not

changing

Sequential Targets unused computation and don’t care cycles for

further power optimization

Source: Dale, Mitch, The Power of RTL Clock-Gating, Chip Design Magazine

Source: Texas Instruments, Clock Gating for Power Optimization in ASIC Design Cycle

Voltage Scaling

Dynamic Voltage Frequency Scaling (DVFS) Implements a voltage-frequency lookup table to allow the chip to

run at the minimum voltage required by processing demands Open-loop control based on statistical measurements and often

requires large margins Adaptive Voltage Scaling (AVS)

Actual operating speed dependent upon PVT Implements replica of IC critical path to compare delay and allow

the voltage to be adaptively scaled to achieve optimal operating speed

Source: Khan, Neyaz, Dynamic Power Management – Closed Loop Voltage Scaling, Cadence

Relative Power Reduction

Example Power Savings: Baseband Processing Circuit

Source: Bergman, Eyal and Snir, Ran, Power Optimization for Low Power SoCs Targeting Mobile Devices, New Electronics

HW-SW Co-design PMT: HW mod exploits available

SW resources in microprocessor to achieve joint improvement in power, energy

Hardware-Software Co-design of Embedded PM Module (1)

Drawbacks of Vt and Freq scaling: Requires many power converters Leads to bulky architecture that

introduces serious noise and large power switches

Ultimately increases silicon cost

HW

SWHW

Solution

Hardware-Software Co-design of Embedded PM Module (2)

Technique overview: ( Dr. Rajdeep Bondade and Dr. Dongsheng Ma @ University of Arizona)

Use Single-Inductor Multi-Output Converter Use Multiple Software-defined control schemes to design the Converter These schemes work jointly with power stage to ensure power/energy

optimizationStart-up

Steady Output Loads

Power is delivered simultaneously to o/p

SW Power

Controller

Process Sensed Power Info

Power Sensor

Estimator and Allocator

Hardware-Software Co-design of Embedded PM Module (3)

Technique implementation: Adaptive Global/Local Power Allocation Control

Power Source

Global Power Estimate

Load 1

Load 3

Load 2

Load 4

Power Demand for each Load

Sensor sends power info to

Estimator

Request

Hardware-Software Co-design of Embedded PM Module (4)

Case

Power Demand/ Load

Description

Result

A

• Low

• Inductor charged once with energy of total load demand

• Energy is then distributed equivalent to all Loads

• Less frequent switching actions => less noise and power

B

• Heavy

• Inductor charged/ discharged based on individual load demand

• Higher demand load will have higher priority

• Reduce power/ noise for each switching action

C

• Mixed

• Group of power demands

• Focuses on delivering to high power demand group

• Skip low power demand group

• Reduce switching power loss and noise on LPD group

• Improve response times to HPD group

Hardware-Software Co-design of Embedded PM Module (5)

Reference: Hardware-Software Co-Design of an Embedded Power Management Module with Adaptive On-Chip Power Processing Schemes, Rajdeep Bondade and Dongsheng Ma

Figure shows output voltage and inductance in the steady state

Technique Performance Verification:

Figure shows 3 output Voltage regulated at 3.0, 1.8, 0.9

Each output can independently adjusted from 0.9 to 3.0 based on power need

Result: Peak to peak ripple voltage

are controlled below 10mV Inductor waveform verifies

the proposed software defined controller

Silicon Labs Energy Micro MCUs

Microcontroller family focused on low-power and energy sensitive applications Extreme Low Leakage Process Firmware-controlled Power and

Clock Gating

Source: Silicon Labs, EFM32 Microcontroller Selector Guide

Energy Micro Architecture

Source: Silicon Labs, EFM32 Microcontroller Selector Guide

Conclusion & Future Works

Power Management is a challenging subject PM is not an automatic process, must be designed analyzed

in every step of designed flow 2 separate ideas regarding software defined power

controller: More embedded sensors for real-time power management There are several topics on using statistical learning software

defined module, local/ global power predictor. These techniques don’t use sensors to collect absolute power info, but “predict” the loading power. Pros: save area. Cons: different systems/ technology changes => develop different

statistical model