Welcome to Micron Engineering Clinic Analysis and Optimization of Multi Gb/s Chip to-Chip Communication Micron Engineering Clinic Fall ‘08 – Spring ‘09

Micron Engineering Clinic Team Members Documentation Lead Raheem Alhamdani - CE Technical Leads Bryson Kent - EE Jordan Kemp - EE Lucas Loero - EE Team Lead Ben Meakin – CE Fall ‘08 – Spring ‘09

Introduction and Motivation for Modeling and Verification of Interconnects Raheem Alhamdani

Documentation Lead Computer Engineer [email protected]

Micron Engineering Clinic Fall ‘08 – Spring ‘09

Introduction The Sponsor: • Manufacturer of DRAM, Flash Memory, and Image Sensor Integrated Circuits What Have They Asked Us To Do?

• Design a software application for modeling and verification of chip-to-chip interconnects Micron Engineering Clinic Fall ‘08 – Spring ‘09

Introduction What is Verification?

• Proving through tests and formal methods that a design does what it is intended to do What are Chip-to-Chip Interconnects?

• Electrical systems for communication between two integrated circuits Micron Engineering Clinic hardwaresecrets.com

Fall ‘08 – Spring ‘09

Motivation Background Memory and I/O Devices Operate Much Slower than CPU Access to Off-Chip Resources is Expensive ~ 300 cycles - Usually Cycles are Wasted Demand for Low-Power yet High-Performance Can’t Have Wasted Cycles!

Goal: Speed Up Devices and Speed Up Interconnect Micron Engineering Clinic Fall ‘08 – Spring ‘09

Problem As Devices Move Towards Being Smaller, Faster, Lower Power Interconnects Become Slower, Noisier, and Unreliable     Issues: Inter-Symbol Interference (ISI) Co-Channel Interference Timing Jitter Voltage Noise Conventional Testing Methodologies are not Feasible or Sufficient Micron Engineering Clinic Fall ‘08 – Spring ‘09

Eye Diagram •What is an eye diagram?

A useful tool for the qualitative analysis of signal used in digital transmission . Voltage Time Micron Engineering Clinic Fall ‘08 – Spring ‘09

Eye Diagram How is it created?

Voltage Time Voltage Micron Engineering Clinic Bits Superimposed 1 Unit Interval (UI) Time Fall ‘08 – Spring ‘09

Eye Diagram (Noise) What Causes Noise?

• Interference from neighboring wires (Co Channel Interference) • Electromagnetic Interference •Link resistance, capacitance, and inductance Voltage Voltage Bit-stream Micron Engineering Clinic Voltage Noise Time Bits Superimposed 1 Unit Interval (UI) Time Fall ‘08 – Spring ‘09

Eye Diagram (Jitter) What Causes Jitter?

• Clock Variation (Skew) • Reflection • General Timing Uncertainty Voltage Bit-stream Voltage Jitter Time Micron Engineering Clinic Time Bits Superimposed 1 Unit Interval (UI) Fall ‘08 – Spring ‘09

How to interpret it?

Data Jitter Real Eye Diagram Clock Jitter Vref Micron Engineering Clinic Signal Noise Vref Noise + Receiver Sensitivity Data Signal Clock Signal Fall ‘08 – Spring ‘09

Solution Our Objective is Not to Solve These Problems Through Better Design, but to Provide Designers with a Tool That Correctly Models and Verifies Interconnects With These Problems Deliverables:  Cross Platform App with Graphical User Interface  Provide Worst-Case and Statistical Based Link Analysis  Spice Compatible  Correctly Model Co-Channel Interference and Tx/Rx Jitter Micron Engineering Clinic Fall ‘08 – Spring ‘09

My Roles

 Project Documentation Meeting minutes, Time-line, Progress Report , Presentations, Proposal and links are all on the team ’s website: www.eng.utah.edu/~alhamdan/Micron/Micron.html

 Graphical User Interface and Software Development GUI Software skeleton Plotting code Code documentation Micron Engineering Clinic Fall ‘08 – Spring ‘09

Team ’s website Micron Engineering Clinic Fall ‘08 – Spring ‘09

Meeting Minutes Micron Engineering Clinic Fall ‘08 – Spring ‘09

Bibliography B. K. Casper, M. Haycock, and R. Mooney, “An accurate and efficient analysis method for multi-Gb/s chip-to chip signaling scheme ”, in Digest of Technical Papers from the IEEE Symposium on VLSI Circuits, June 2002, pp. 54 –57.

B. K. Casper , G. Balamurugan, J. E. Jaussi, J. Kennedy, M. Mansuri, “Future microprocessor interfaces: Analysis, design and optimization ”, in Proceedings of the IEEE Custom Integrated Circuits Conference, Sept. 2007, pp. 479-486.

P. K. Hanumolu, B. K. Casper, R. Mooney, G. Y. Wei, and U. K. Moon, “Jitter in high-speed serial and parallel links ”, in Proceedings of the IEEE International Symposium on Circuits and Systems, May 2004, pp. 425 –428.

Pavan Kumar Hanumolu

, Bryan Casper, Randy Mooney,

Gu-Yeon Wei

, and Un-Ku Moon,

“Analysis of PLL Clock Jitter in High-Speed Serial Links ”, in IEEE Transactions on Circuits and Systems, November 2003, pp.879-886 Micron Engineering Clinic Fall ‘08 – Spring ‘09

Micron Engineering Clinic

Questions?

Fall ‘08 – Spring ‘09

Worst Case Verification of High Speed Interconnects Bryson Kent

Technical Lead Electrical Engineer [email protected]

Fall ‘08 – Spring ‘09 Micron Engineering Clinic

Introduction • What is Worst Case analysis • Why is the Worst Case important • How to calculate the Worst Case • What are the results • Conclusion and implementation

Micron Engineering Clinic Fall ‘08 – Spring ‘09

Worst Case Analysis

• Summation of all negative effects • Good representation of what can happen if certain conditions arise • Verification of error free transmission • Classic analysis of 1 trillion bits

•(1*10^12 bits) * (10^-6sec) = over 10 days

Micron Engineering Clinic Fall ‘08 – Spring ‘09

Worst Case Eye Diagram

WC 1 WC 2 WC 3 Pass/Fail

• Voltage Vs one period of time • Distortion sources add to close the eye • From the eye diagram we can calculate a system pass fail

Tim Hollis, Micron Senior Project Proposal Micron Engineering Clinic Fall ‘08 – Spring ‘09

Tim Hollis, Micron Senior Project Proposal Micron Engineering Clinic

Inter-Symbol Interference

• Inter-Symbol interference is the main source of interference • Data dependent jitter and Co-channel interference add to signal degradation

Fall ‘08 – Spring ‘09

Worst-Case Computation

• C(t) = transmitter symbol response • P(t) = impulse response of the channel •Worst case eye diagram due to Inter-symbol interference •Worst case eye diagram due to Inter-symbol interference and cochannel interference J. G. Proakis, “Digital Communication”, McGraw-Hill, 3rd Ed., 1995.

B. K. Casper, M. Haycock, and R. Mooney, “ An accurate and efficient analysis method for multi-Gb/s chip-to-chip signaling schemes ”, in Digest of Technical Papers from the IEEE Symposium on VLSI Circuits, June 2002, pp. 54 –57.

Micron Engineering Clinic Fall ‘08 – Spring ‘09

Calculating the eye diagram

1 0.5

Pulse Response Pre-Cursor Cursor Post-Cursor 0 891 1091 1291 1491 1691 1891 2091 2291 2491 2691 2891 3091 ISI pp = 815.9948 mV DDJ pp = 34.3117 ps 1 0.5

0 -100 Tim Hollis, Micron Senior Project Proposal Micron Engineering Clinic -50 0 50 100 Fall ‘08 – Spring ‘09

Results

• Calculated performance Vs given performance

Micron Engineering Clinic 0.4

0.2

0 1 0.8

0.6

-1 -0.5

0 0.5

1 x 10 -10 Fall ‘08 – Spring ‘09

Conclusion

• Worst case analysis is beneficial • Computation is pulse based analysis • User can define and add any distortion as desired • Results of worst case analysis match results of given test case

Micron Engineering Clinic Fall ‘08 – Spring ‘09

Micron Engineering Clinic

Questions?

Fall ‘08 – Spring ‘09

Statistical Analysis of Electrical Signaling

Jordan Kemp

Technical Lead Electrical Engineering [email protected]

Fall ‘08 – Spring ‘09 Micron Engineering Clinic

• Introduction • Why • What • How • Summary

Micron Engineering Clinic Fall ‘08 – Spring ‘09

Introduction

• Worst Case Eye good for Pass/Fail Mask, but doesn’t give details • Need for probability of error, rather than rigid “Pass/Fail” Pass/Fail Mask Micron Engineering Clinic Fall ‘08 – Spring ‘09

• Use channel impulse response, p(t), and transmitter symbol response, c(t)

Introduction

() () • Find PDF (Probability Density Function) & CDF (Cumulative Distribution Function) of the channel output Micron Engineering Clinic Fall ‘08 – Spring ‘09

• Plot BER eye-diagram as a function of sample time, sample voltage, and probability of error • Shows BER of transmitted data given timing uncertainty (data jitter, clock jitter) and voltage uncertainty (V REF , Rx sensitivity, ISI) Micron Engineering Clinic

Introduction

Fall ‘08 – Spring ‘09

Why

•

Trends

Increase: Speed, Capacity Decrease: Form-Factor, Power, Cost All above decrease Signal Integrity • Theoretically impossible to send error free data

t

  0 0 0 1 0 1 0 • Certain number of errors per number of bits sent specified by user/system • Usually specified below 1 1 trillion Bit Error Rate (BER) = tra s itte its • Would require a 1 TRILLION bit simulation!

Micron Engineering Clinic Fall ‘08 – Spring ‘09

• Probabilistic data eye using channel impulse response, p(t), and transmitter symbol response, c(t) to find the PDF & CDF of the channel output • What is a PDF?

- Probability Density Function - Shows the probability that a specific value is likely to happen - Integrates to 1 • What is a CDF?

- Cumulative Distribution Function - Shows the probability is less than or equal to a specific value - Integral of the PDF Micron Engineering Clinic

What

Fall ‘08 – Spring ‘09

How (1) 1

st

Way (from *Casper paper):

Recursively convolve 1UI sample terms assuming equal probability of a transmitted ‘0’ or ‘1’ 1UI [0 -0.01]  [0 0.59]

y

(

t

)  [0 -0.07]  [0 0.015]  [0 0.055]  [0 0.2]  [0 0.5]  [0 0]  0.59

0.0

[0 0.7] (Each step scaled by ½ to account for P(0) = P(1) ) Micron Engineering Clinic Fall ‘08 – Spring ‘09

How (1) Problems:

• VERY hardware intensive (must compute multiple convolutions) [0 -0.01]  [0 0.055]  [0 0.59]  [0 0.2]  [0 -0.07] [0 0.5]   [0 0.015]  [0 0]  . . . .

• Must maintain certain amount of resolution, slowing computations down even more 1.452  1.452  1.452  … … 1 (no decimal resolution) 1.4 (one decimal resolution) 1.45 (two decimal resolution) • Very quickly run out of memory performing calculations delta function @ 1: [0 1 0 …] 0 1 2 . . .

delta function @ 1.4: [0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 …] 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1 1.1 1.2 1.3 1.4 1.5 . . .

Micron Engineering Clinic Fall ‘08 – Spring ‘09

How (2) Implemented Method (modified from previous):

• Same points taken as before, but add instead of convolve • Keeps track of locations of delta functions • Keeps track of heights of each delta • Plot locations versus heights [0 -0.01] + [0 0.59] + [0 -0.07] + [0 0.015] + [0 0.055] + [0 0.2] + [0 0.5] + [0 0] + [0 0.7] Micron Engineering Clinic Fall ‘08 – Spring ‘09

How (2)

Height = 0.5

-.01 0 Height = 0.5

0 .59

-.01 0 .58 .59

Height = 0.25

•

[0 -0.01]



[0 0.59] = [0 -.01 (0+.59) (-.01+.59)] = [-.01 0 .58 .59]

•

Instead of convolving, proposed method adds & concatenates

Micron Engineering Clinic Fall ‘08 – Spring ‘09

Advantages:

• VERY quick • Easy to implement • Infinite precision (in theory)

Micron Engineering Clinic

How (2)

Fall ‘08 – Spring ‘09

• Use channel impulse response, p(t), and transmitter symbol response, c(t) • Find PDF (Probability Density Function) & CDF (Cumulative Distribution Function) of the channel • Plot BER eye-diagram as a function of sample time, sample voltage, and probability of error

Summary

() () Micron Engineering Clinic • Shows BER of transmitted data given timing uncertainty (data jitter, clock jitter) and voltage uncertainty (V REF , Rx sensitivity, ISI) Fall ‘08 – Spring ‘09

Micron Engineering Clinic

Questions?

Fall ‘08 – Spring ‘09

MODELING JITTER IN CHIP-to-CHIP COMMUNICATION

M. Lucas Loero

Technical Lead Electrical Engineer [email protected]

Micron Engineering Clinic Fall ‘08 – Spring ‘09

PRESENTATION OBJECTIVES

•

Defining Jitter

•

Problems caused by Jitter

•

Modeling Jitter

•

Receiver Jitter

•

Transmitter Jitter

•

Total Jitter Micron Engineering Clinic Fall ‘08 – Spring ‘09

Voltage DEFINING JITTER Edge location shifted Jitter Micron Engineering Clinic Ideal edge location Ideal edge location Time Fall ‘08 – Spring ‘09

PROBLEMS CAUSED BY JITTER • Power supply and environment noise causes Jitter.

• Jitter can lead to: • Time uncertainty • Suboptimal sampling time • Reduce noise margin Micron Engineering Clinic Fall ‘08 – Spring ‘09

PROBLEMS CAUSED BY JITTER Micron Engineering Clinic Fall ‘08 – Spring ‘09

MODELING JITTER • Model the effects of Jitter in high-speed serial links • Serial links are used for high-speed chip-to-chip communications Micron Engineering Clinic Fall ‘08 – Spring ‘09

MODELING JITTER Serial Links Transmitter generates a train of pulses Decision circuit Transmitter clock Micron Engineering Clinic Sampler Fall ‘08 – Spring ‘09

MODELING JITTER • Traditional approach to modeling jitter • There is two main problems with this approached • First, simulation time • Second, difficulty simulating serial links Micron Engineering Clinic Fall ‘08 – Spring ‘09

MODELING JITTER Receiver Jitter Step response Transmitted bits Channel impulse response Jitter sequence Micron Engineering Clinic Independent and Identically Distributed Fall ‘08 – Spring ‘09

MODELING JITTER Calculated eye diagram Micron Engineering Clinic Simulated eye diagram Fall ‘08 – Spring ‘09

MODELING JITTER Worst-case receiver jitter Micron Engineering Clinic Fall ‘08 – Spring ‘09

MODELING JITTER Worst-case receiver eye Voltage Time Worst-case ISI Micron Engineering Clinic Voltage Time Worst-case receiver jitter Fall ‘08 – Spring ‘09

MODELING JITTER Worst-case receiver eye Micron Engineering Clinic Fall ‘08 – Spring ‘09

Transmitted bits MODELING JITTER Transmitter Jitter Jitter sequence Step response Micron Engineering Clinic Channel impulse response Fall ‘08 – Spring ‘09

MODELING JITTER Worst-case transmitter Jitter Micron Engineering Clinic Fall ‘08 – Spring ‘09

MODELING JITTER Worst-case transmitter eye Voltage Time Worst-case ISI Micron Engineering Clinic Voltage Time Worst-case transmitter jitter Fall ‘08 – Spring ‘09

MODELING JITTER Worst-case transmitter eye Micron Engineering Clinic Fall ‘08 – Spring ‘09

MODELING JITTER Total Jitter Receiver Jitter Transmitter Jitter Micron Engineering Clinic Fall ‘08 – Spring ‘09

MODELING JITTER Worst-case total Jitter Micron Engineering Clinic Fall ‘08 – Spring ‘09

MODELING JITTER Worst-case total eye Voltage Time Worst-case ISI Micron Engineering Clinic Voltage Time Worst-case total jitter Fall ‘08 – Spring ‘09

MODELING JITTER Worst-case total eye Micron Engineering Clinic Fall ‘08 – Spring ‘09

CONCLUSION Voltage Micron Engineering Clinic Time Fall ‘08 – Spring ‘09

Micron Engineering Clinic

Questions?

Fall ‘08 – Spring ‘09

Project Software Engineering, Development, and Results Ben Meakin

Team Lead Computer Engineer [email protected]

Micron Engineering Clinic Spring '09 Micron Engineering Clinic Fall ‘08 – Spring ‘09

Introduction Open Eye : A Formal Verification Tool for High Speed Electrical Signaling What is Open Eye?

• Provides Software Infrastructure Required to Deliver a Useful Verification Platform Based on Existing State-of-the-Art Methods Presentation Outline • Requirements and Objectives • Software Architecture • Graphical User Interface (GUI) • Software Infrastructure • Use Case • Summary and Conclusions Micron Engineering Clinic Fall ‘08 – Spring ‘09

Product Requirements  Cross Platform (Windows, Linux, etc)  Graphical User Interface  No Proprietary Software License (i.e. Matlab License)  Correctly Implement Worst-Case and Statistical Link Analysis  Pass Fail Mask and Data Eye Visualization  Selectable Transmitter and Receiver Jitter  Multiple Sources of Co Channel Interference  Spice Data File Input Micron Engineering Clinic Fall ‘08 – Spring ‘09

Feature

Worst-Case Analysis Statistical Analysis Static Analysis Basic Plotting Advanced Plotting Jitter Modeling Co-Channel Interference File Input File Output Graphical User Interface Multi-threading Documentation Micron Engineering Clinic Product Release Status

Phase

Release Testing Release Release Development Debug Testing Release Development Testing Testing Development

Status

25% 50% 75% 75% 75% 50% 75% 50% Fall ‘08 – Spring ‘09

 Portability  Extensibility  Usability Design Goals Micron Engineering Clinic Fall ‘08 – Spring ‘09

View Open Eye App.

Control Status Q Open Eye View Other GUI Classes Object Oriented Design Model Model Data Structures Static Data Parameters Signal Analysis Data IO Statistical Data Worst-Case Data Range Math Utility Signal Modify Micron Engineering Clinic Fall ‘08 – Spring ‘09

Graphical User Interface Features Micron Engineering Clinic Fall ‘08 – Spring ‘09

Graphical User Interface Features Continued Micron Engineering Clinic Fall ‘08 – Spring ‘09

Data I/O Features  Input Data from SPICE or Any Other Column Formatted Text File  Simulation Data Objects Save State to Text Files  No Need to Rerun To View Data  Simulation Data Output to Matlab Format Text File Micron Engineering Clinic Fall ‘08 – Spring ‘09

Mathematical Utility Features  Discrete-Time Convolution Function   Random Number Generation over Gaussian Distribution Assortment of Vector Operations

MathUtil

+ convolution(List, List):List + getRandom(double):double + max(List):double + maxAt(List):int + min(List):double + minAt(List):int + indexOfClosest(List,double):int + extendTimeScale(List):List + getTimeUnit(List):double

Micron Engineering Clinic Fall ‘08 – Spring ‘09

Signal Analysis Features  Static Signal Analysis (Naive Method)  Data Sequence Bits Superimposed To Form Eye Diagram Micron Engineering Clinic Fall ‘08 – Spring ‘09

Signal Analysis Features  Worst-Case Signal Analysis (Formal Method)  Mathematically Generated Worst-Case Eye Diagram  Pass/Fail Based on User Defined Sampling Window  Statistical Signal Analysis (Formal Method)  Generates a Scatter Plot of BER Diagram  Formal Methods Consider Multiple Sources of CCI and Tx/Rx Jitter SignalAnalysis + WCData : WorstCaseData + StatData : StatisticalData + EyeData : StaticData + doWorstCase(double,double):void + doStatistical(double,double):void + generateEye(double):void + computeCCI(List,List,List,int,int):void + passOrFail(double,double,double,double):boolean Micron Engineering Clinic Fall ‘08 – Spring ‘09

Performance Enhancement Through Multi-Threading  Convolution: Yn(t) = convolution( Pn(t), Cn(t) ), n = channel  Requires Significant Execution Time for Large Data Sets  Can Be Done Concurrently For Each Channel on Multi-Process Machines Convolution for Channel N Convolution for Channel 1 Convolution for Channel 0 Sequential Part Concurrent Part Micron Engineering Clinic

Execution Time

Fall ‘08 – Spring ‘09

Worst-Case Eye with User Defined Sampling Window Micron Engineering Clinic Use Case (Worst-Case Analysis) C(t) – Transmitter Symbol Response P(t) – Channel Impulse Response Data Rate: 4 Gbps No CCI, No Jitter Fall ‘08 – Spring ‘09

V(t) Periods Superimposed to Get Data Eye Diagram Micron Engineering Clinic Use Case (Static Analysis) V(t) – Data Stream {0, 1, 0, 0, 1, 1, 0, 1, 0, 1} Data Rate: 1Gbps Random Voltage Noise No Jitter Added Fall ‘08 – Spring ‘09

Summary and Conclusions What Has Been Accomplished?

 First Application to Correctly Perform Worst-Case and Statistical Link Analysis in the Public Domain  Development of a Flexible and Efficient Platform for Formal Verification of Electrical Signaling Systems Why Does This Matter?

• Easy Verification of Aggressively Optimized Designs • Off-Chip Memory Access Bottleneck is a Growing Problem • Open Source Application Stimulates Academic Solutions Micron Engineering Clinic Fall ‘08 – Spring ‘09

Micron Engineering Clinic

Questions?

Fall ‘08 – Spring ‘09