Power efficient Ethernet PHY features for camera and displayAmir Bar-NivGeorge ZimmermanPaul Langner

IEEE Automotive Tech DaySeptember 2019

Contributors

• Saied Benyamin• Ramin Farjadrad

The Path Towards Full Autonomy

Level 1-2Simple Aid

2010 - 2015 2015 - 2020 2020 - 2025

CPU/GPU

Local Computing ”Behind” Every Sensor

Centralized Computing Integrates Input From All Sensors

(Sensor Fusion) Similar to a Human Driver’s Brain

High-Performance Brain

High-Speed, Reliable & Secure Nervous System

Compute Power

(TFLOPS)

0.1

10

1

100

NetworkingSpeed (Gbit/s)

0.1

10

1

25

Level 2-3Decision Assistant

Level 4-5Self Driving

CamerasIncreasing resolution from 720p to 4K and improving dynamic range

Multi-Gigabit/s of raw bandwidth=

100BASE-T1 1000BASE-T1

Multi-Gig Ethernet 2,5

Gbps

Multi-Gig Ethernet 5

Gbps

Multi-Gig Ethernet 10

Gbps

No Use Case Available Speed grades which are currently discussed

Sensor Fusion & Rich Data Drive Bandwidth To Multi-Gig

Hres Vres Fps 8bit 12bit 16bit 20bit 24bit1280 720 30 0,22 0,33 0,44 0,55 0,661280 1080 30 0,33 0,50 0,66 0,83 11280 720 60 0,44 0,66 0,88 1,11 1,331920 1080 30 0,50 0,75 1,00 1,24 1,491280 1080 60 0,66 1,00 1,33 1,66 1,991920 1080 60 1,00 1,49 1,99 2,49 2,993840 2160 30 1,99 2,99 3,98 4,98 5,973840 2160 60 3,98 5,97 7,96 9,95 11,94

Sensor FusionMoving processing of data from sensors to a centralized GPU

Multi-Gigabit/s data over the network=

Processing Unit

Radar, Lidar, Sonar

GPU

100M – 1 Gbps

2G – 8Gbps

In-Vehicle-Network (IVN) for ADAS

Camera

Radar, Lidar, Sonar

CPU/GPU

CPU/GPU

ISPPHYSoCGPU PHY

Control

Video 1Gbps to >10Gbps

Control 1Mbps to 100Mbps

Ethernet link –2.5/5/10G

Switch

PHYs/Bridges

Ethernet link –> 10Gbps

Ethernet Advantages for Automotive

• Standard based. Multiple vendors.

• Switching, VLAN: IEEE 802.1

• MAC Speeds: 2.5G, 5G, 10G, 25G, 50Gbps (soon 100G)

• Security: IEEE-802.1AE MACsec plus Encryption (AES-256)

• Synchronization: IEEE-1588v2 PTP (802.1AS and Rev)

• Power over Data Line: IEEE PoDL 802.3bu (0.5W to 50W)

• Audio/Video Bridging: AVB/TSN

• Support all topologies: point-to-point, mesh, star, ring, daisy-chain,

Automotive Ports Transition to Multi-Gig Ethernet

2010 - 2018 2019 - 2023 2024 - 2028

100Mbps / 1Gbps

LVDS

Multi-Gig

ECU ECU ECU

System backbone

100M / 1G Eth.

1G Eth.

LVDS

ECU

100M / 1G / Multi-Gig

Eth.

Multi-Gig Eth.

LVDS

ECU ECU ECU ECU

GPUGPU GPU

System backbone

100M / 1G Multi-Gig

Eth.

Multi-Gig Eth.

Multi-GigEth.

ECU ECU ECU ECU

GPU GPU

ECU ECU ECU ECU ECU

ECU

GPU GPU

System backbone

Multi-GigEth.

Sensor backbone

Ethernet vs. LVDSLVDS Ethernet

Speed 3G, 6G, 12Gbps 2.5G, 5G, 10G, 25Gbps

Bit Error Rate (BER) 10^-10 10^-12

Switching (standard based) None IEEE – Dynamic, packet based

Synchronization (standard based) None IEEE – 1588 PTP

Prioritization (standard based) None IEEE – AVB, TSN

MAC/PHY Security (standard based) None IEEE – 802.1AE

Bridges to Ethernet Required IEEE – Part of the stack

For camera/sensor interface, the main advantage of LVDS today is that it is asymmetrical, which is lower power then symmetrical mode.

Ethernet can leverage the Energy Efficient Ethernet (EEE) mode to ran the PHY in asymmetrical mode, for power saving.

IEEE Energy Efficient Ethernet - Overview

• Energy Efficient Ethernet (EEE) was introduced in BASE-T PHYs to help computers meet Energy Star power consumptions targets

• Basic idea is to turn the link off as much as possible when there is no traffic, and turn it on as quickly as possible when there is traffic (50 us)

• State is referred to as Low-power Idle (LPI)

• EEE allows:• Up to 90% power savings on a link in LPI state• Full flexibility in BW versus power consumption• The ability to use a standard MAC/PHY interface, as EEE is also standardized on

these interfaces

How EEE Works• EEE is controlled by the Low Power Idle

(LPI) client• Allows the MAC & higher layers to go to

sleep• Physical layer only knows it is in LPI state

and is quiet most of the time

• LPI client signals and controls the transition in/out of Low Power Idle state

• Asymmetric Operation: each direction only wakes and sends data as needed

Source: IEEE Std. 802.3-2018, IEEE Standard for Ethernet, Clause 78, Energy Efficient Ethernet

Source: “Energy Efficiency and Regulation” Bruce Nordman, et al. (IEEE 802 tutorial, July 2008)http://www.ieee802.org/802_tutorials/2009-07/802 july energy 8.pdf

IEEE 802.3az Designed for bursty data – with rapid wake up

• Designed for bursty data and requiring minimal buffering• Fast, application-transparent recovery

• “The link status shall not change as a result of the transition”

Source: “IEEE 802 Tutorial – Energy Efficient Ethernet”, Hugh Barrass, et al. (IEEE 802 tutorial, July 2007)http://www.ieee802.org/802_tutorials/07-July/IEEE-tutorial-energy-efficient-ethernet.pdf

Adjusting EEE parameters for Asymmetric Links

• PHY gets to specify system wake up timing parameters• While Tw_phy is a minimum, Tw_sys_tx can be set longer, to

accommodate longer PHY wake up.

Source: IEEE Std. 802.3-2018, IEEE Standard for Ethernet, Clause 78, Energy Efficient Ethernet

Additional Extensions for EEE in Automotive

• A natural extension to the 802.3ch EEE scheme is to introduce a mode to totally shut off transmission when not in use

• Referred to as “Link Suspension Mode”• This is specifically designed for I2C control of cameras, where the

downstream is continuously transmitting, and the upstream only occasionally (on the order of seconds) transmits a low-speed command

• This extension uses the same “Alert signal”, transmitted at specific known times, and a new Idle character to signal total shut-off of the link

• It means the camera has to provide the link timing (master) and the far end is phase-locked to it (slave)

• The result is that when the GPU wants to send an I2C command, it sends an alert, and then the camera’s PHY just has to reconverge the filters and potentially timing phase, allowing a relatively quick wake-up

• Allows close to 100% total power savings in this mode

Compare to Asymmetric PHY approach

Low speed Equalizer

RX Clock recovery/ generation

Slicer / FEC Decoder

FEC Encoder PCS Transmit

PCS Receive

Interference Isolation1

ADC

DAC High speed transmitter

–Cable (s)1

Data IN

Data OUT

Always on at transmit rate

Always on receive rateOn only when both are active,

operates at highest rate

Block Diagram of “Tx” PHY (High speed video transmission PHY)

TX Clock generation

1Interference isolation increases receiver power and complexity and lowers performance OR use of separate cables has weight and cost impact on vehicle

–

Asymmetric EEE Operation

Equalizer

Clock generation

Slicer / FEC Decoder

FEC Encoder PCS Transmit

PCS Receive

Echo Canceller

ADC

DAC PAM-4 transmitter

–Cable

–

Data IN

Data OUT

On when transmit is activeOn when receive is active

On when either is activeOn only when both are active

Implementation and allowable transition time drives power savings

Longer duty cycles and slow wake for automotive asymmetric links allow greater power savings than in LAN EEE

Summary Ethernet allows automotive networking to build on existing standards experience

Energy Efficient Ethernet provides a flexible toolbox, allowing trades of power savings with recovery time

Ethernet is Inherently Asymmetric!

Slow wake mode further improves PHY savings for asymmetric traffic

Savings in packet processing circuitry beyond PHY, minimizes time processor is active

ISPPHYSoCGPU PHY

Control

Video 1Gbps to >10Gbps

Control 1Mbps to 100Mbps

Comparison of Asymmetrical and Symmetrical PHYs

For asymmetrical PHY, the circuits and blocks that are not required:

“Tx” PHY (transmits at high speed):Echo Canceller, ADC (simplified), Equalizer/Decoder (simplified)

“Rx” PHY (receives at high speed):Echo Canceller, DAC/Encoder (simplified)

Save in size :“Tx” PHY – about 35%“Rx” PHY – about 20%

Asymmetrical PHYs:

Typical size of 10Gbps symmetrical PHY is ~2 mm^2

Save in size :“Tx” PHY – about 0.7 mm^2“Rx” PHY – about 0.4 mm^2

ISP“Tx”PHY

SoCGPU

“Rx”PHY

Control

Video 1Gbps to >10Gbps

Control 1Mbps to 100Mbps

© 2019 Marvell Confidential, All Rights Reserved. 18

BACKUP

Sources for EEE Overviews

• “An Overview of Energy Efficient Ethernet” Mike Bennett, youtube talk (TeamNANOG, June 2014)• Includes discussion of fast wake/deep sleep, optics, recent projects

• “IEEE 802.3az: The road to energy efficient Ethernet”, Ken Christensen, et. Al, IEEE Communications Magazine, December 2010

• “Energy Efficiency and Regulation” Bruce Nordman, et al. (IEEE 802 tutorial, July 2008)• (see slides 27-50) EEE and WiFi energy management

• “Baseline Summary”, IEEE 802.3az Task Force Home Page, March 2009• A nice summary of the 802.3az PHY modes

• “IEEE 802.3az Energy Efficient Ethernet Task Force Update”, 802.1/802.3 joint meeting Mike Bennett, July 2008

• Update on 802.3az approaches, scope related to systems issues• “IEEE 802 Tutorial – Energy Efficient Ethernet”, Hugh Barrass, et al. (IEEE 802 tutorial, July 2007)

• Objectives, explanation of 802.3az motivations and approaches• A Brief Tutorial on Power Management in Computer Systems, Dave Chalupsky & Emily Qi (IEEE

802.3 EEE Study Group, March 2007)• Covers both link and Systems level power management

IEEE Energy Efficient Ethernet – 802.3ch Modifications

• 802.3ch copied the EEE mechanism from 2.5G – 10GBASE-T PHYs• Allows either direction to go in LPI independent of the other direction

• Since 802.3ch implements a hybrid system (which means Tx and Rx are on the same physical copper pairs), it is a strict requirement to keep both ends of the link phase-locked to make the signal processing work

• This means a link in the LPI state must periodically transmit a burst of data to keep the far-end receiver phase-locked, and the filters converged

• With EEE, a single 802.3ch PHY can be deployed in various system scenarios, effectively supporting all traffic scenarios and scaling the power usage accordingly

• Versus fixed, non-standard transmission schemes for each scenario