External Memory Interfaces (EMIF) IP User Guide: Agilex™ 5 FPGAs and SoCs

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ID 817467
Date 7/08/2024
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Document Table of Contents
Document Table of Contents x
1. About the External Memory Interfaces Agilex™ 5 FPGA IP 2. Agilex™ 5 FPGA EMIF IP – Introduction 3. Agilex™ 5 FPGA EMIF IP – Product Architecture 4. Agilex™ 5 FPGA EMIF IP – End-User Signals 5. Agilex™ 5 FPGA EMIF IP – Simulating Memory IP 6. Agilex™ 5 FPGA EMIF IP - DDR4 Support 7. Agilex™ 5 FPGA EMIF IP - DDR5 Support 8. Agilex™ 5 FPGA EMIF IP - LPDDR4 Support 9. Agilex™ 5 FPGA EMIF IP - LPDDR5 Support 10. Agilex™ 5 FPGA EMIF IP – Timing Closure 11. Agilex™ 5 FPGA EMIF IP – Controller Optimization 12. Agilex™ 5 FPGA EMIF IP – Debugging 13. Document Revision History for External Memory Interfaces (EMIF) IP User Guide
1. About the External Memory Interfaces Agilex™ 5 FPGA IP x
1.1. Release Information
2. Agilex™ 5 FPGA EMIF IP – Introduction x
2.1. Agilex™ 5 EMIF IP Protocol and Feature Support 2.2. Agilex™ 5 EMIF IP Design Flow
2.2. Agilex™ 5 EMIF IP Design Flow x
2.2.1. Agilex™ 5 EMIF IP Design Checklist
3. Agilex™ 5 FPGA EMIF IP – Product Architecture x
3.1. Agilex™ 5 EMIF Architecture: Protocol and Maximum Interface Width Support 3.2. Agilex™ 5 EMIF Architecture: Introduction 3.3. Agilex™ 5 EMIF Sequencer 3.4. Agilex™ 5 EMIF Controller 3.5. Agilex™ 5 EMIF IP for Hard Processor Subsystem (HPS)
3.2. Agilex™ 5 EMIF Architecture: Introduction x
3.2.1. Agilex™ 5 EMIF Architecture: I/O Subsystem 3.2.2. Agilex™ 5 EMIF Architecture: I/O SSM 3.2.3. Agilex™ 5 EMIF Architecture: HSIO Bank 3.2.4. Agilex™ 5 EMIF Architecture: I/O Lane 3.2.5. Agilex™ 5 EMIF Architecture: Input DQS Clock Tree 3.2.6. Agilex™ 5 EMIF Architecture: PHY Clock Tree 3.2.7. Agilex™ 5 EMIF Architecture: PLL Reference Clock Networks 3.2.8. Agilex™ 5 EMIF Architecture: Clock Phase Alignment 3.2.9. User Clock in Different Core Access Modes
3.2.3. Agilex™ 5 EMIF Architecture: HSIO Bank x
3.2.3.1. Lockstep Configuration 3.2.3.2. Pin Placement 3.2.3.3. HSIO Sub-Bank Usage
3.3. Agilex™ 5 EMIF Sequencer x
3.3.1. Agilex™ 5 Mailbox Structure and Register Definitions
3.3.1. Agilex™ 5 Mailbox Structure and Register Definitions x
3.3.1.1. Mailbox Supported Commands 3.3.1.2. Mailbox Command Definitions
3.4. Agilex™ 5 EMIF Controller x
3.4.1. Hard Memory Controller
3.4.1. Hard Memory Controller x
3.4.1.1. Hard Memory Controller Features
4. Agilex™ 5 FPGA EMIF IP – End-User Signals x
4.1. Agilex 5 EMIF IP Interfaces for DDR4 4.2. Agilex 5 EMIF IP Interfaces for DDR5 4.3. Agilex 5 EMIF IP Interfaces for LPDDR4 4.4. Agilex 5 EMIF IP Interfaces for LPDDR5 4.5. Agilex 5 EMIF IP Interfaces for the EMIF Calibration Component
4.1. Agilex 5 EMIF IP Interfaces for DDR4 x
4.1.1. ref_clk for EMIF IP 4.1.2. core_init_n for EMIF IP 4.1.3. usr_async_clk for EMIF IP 4.1.4. usr_clk for EMIF IP 4.1.5. usr_rst_n for EMIF IP 4.1.6. s0_axi4 for EMIF IP 4.1.7. mem for EMIF IP 4.1.8. oct for EMIF IP
4.2. Agilex 5 EMIF IP Interfaces for DDR5 x
4.2.1. ref_clk for EMIF IP 4.2.2. core_init_n for EMIF IP 4.2.3. usr_async_clk for EMIF IP 4.2.4. usr_clk for EMIF IP 4.2.5. usr_rst_n for EMIF IP 4.2.6. s0_axi4 for EMIF IP 4.2.7. mem for EMIF IP 4.2.8. i3c for EMIF IP 4.2.9. mem_lbd for EMIF IP 4.2.10. mem_lbs for EMIF IP 4.2.11. oct for EMIF IP
4.3. Agilex 5 EMIF IP Interfaces for LPDDR4 x
4.3.1. ref_clk for EMIF IP 4.3.2. core_init_n for EMIF IP 4.3.3. usr_async_clk for EMIF IP 4.3.4. usr_clk for EMIF IP 4.3.5. usr_rst_n for EMIF IP 4.3.6. s0_axi4 for EMIF IP 4.3.7. mem for EMIF IP 4.3.8. oct for EMIF IP
4.4. Agilex 5 EMIF IP Interfaces for LPDDR5 x
4.4.1. ref_clk for EMIF IP 4.4.2. core_init_n for EMIF IP 4.4.3. usr_async_clk for EMIF IP 4.4.4. usr_clk for EMIF IP 4.4.5. usr_rst_n for EMIF IP 4.4.6. s0_axi4 for EMIF IP 4.4.7. mem for EMIF IP 4.4.8. oct for EMIF IP
4.5. Agilex 5 EMIF IP Interfaces for the EMIF Calibration Component x
4.5.1. s0_axi4lite_clk for EMIF IP Calibration Component 4.5.2. s0_axi4lite_rst_n for EMIF IP Calibration Component 4.5.3. s0_axil for EMIF IP Calibration Component
5. Agilex™ 5 FPGA EMIF IP – Simulating Memory IP x
5.1. Simulation Walkthrough
5.1. Simulation Walkthrough x
5.1.1. Calibration 5.1.2. Simulation Scripts 5.1.3. Functional Simulation with Verilog HDL 5.1.4. Simulating the Design Example
6. Agilex™ 5 FPGA EMIF IP - DDR4 Support x
6.1. Agilex 5 FPGA EMIF IP Parameter Descriptions for DDR4 6.2. Agilex™ 5 FPGA EMIF IP Pin and Resource Planning 6.3. Agilex™ 5 EMIF Pin Swapping Guidelines 6.4. DDR4 Layout Design Guidelines
6.1. Agilex 5 FPGA EMIF IP Parameter Descriptions for DDR4 x
6.1.1. Agilex 5 FPGA External Memory Interfaces (EMIF) IP Parameter Descriptions for DDR4 6.1.2. Agilex 5 FPGA EMIF Memory Device Description IP (DDR4) Parameter Descriptions 6.1.3. Agilex 5 FPGA EMIF Calibration IP Parameter Descriptions
6.2. Agilex™ 5 FPGA EMIF IP Pin and Resource Planning x
6.2.1. Agilex™ 5 FPGA EMIF IP Resources 6.2.2. Pin Guidelines for Agilex™ 5 FPGA EMIF IP 6.2.3. Pin Placements for Agilex™ 5 FPGA DDR4 EMIF IP
6.2.1. Agilex™ 5 FPGA EMIF IP Resources x
6.2.1.1. OCT 6.2.1.2. PLL
6.2.2. Pin Guidelines for Agilex™ 5 FPGA EMIF IP x
6.2.2.1. Agilex™ 5 FPGA EMIF IP Pin and Resource Planning
6.2.2.1. Agilex™ 5 FPGA EMIF IP Pin and Resource Planning x
6.2.2.1.1. Agilex™ 5 FPGA EMIF IP Interface Pins 6.2.2.1.2. Estimating Pin Requirements 6.2.2.1.3. Maximum Number of Interfaces
6.2.3. Pin Placements for Agilex™ 5 FPGA DDR4 EMIF IP x
6.2.3.1. Address and Command Pin Placement for DDR4 6.2.3.2. DDR4 Data Width Mapping 6.2.3.3. General Guidelines 6.2.3.4. x4 DIMM Implementation 6.2.3.5. Specific Pin Connection Requirements 6.2.3.6. Command and Address Signals 6.2.3.7. Clock Signals 6.2.3.8. Data, Data Strobes, DM/DBI, and Optional ECC Signals
6.3. Agilex™ 5 EMIF Pin Swapping Guidelines x
6.3.1. DDR4 Byte Lane Swapping 6.3.2. DDR4 Address and Command and CLK Lane 6.3.3. DDR4 Interface x8 Data Lane 6.3.4. DDR4 Interface x4 Data Lane
6.4. DDR4 Layout Design Guidelines x
6.4.1. DDR4 PCB Stackup and Design Considerations 6.4.2. DDR4 General Design Considerations 6.4.3. DDR4 Routing Guidelines - Memory-Down (Discrete) Topologies
6.4.3. DDR4 Routing Guidelines - Memory-Down (Discrete) Topologies x
6.4.3.1. 1 Rank x 8 Discrete (Memory Down) Topology 6.4.3.2. 1 Rank x 16 Discrete (Memory Down) Topology 6.4.3.3. VREF_CA/RESET Signal Routing Guidelines for 1 Rank x 8 and 1 Rank x 16 Discrete (Memory Down) Topology 6.4.3.4. Skew Matching Guidelines for DDR4 (Memory Down) Discrete Configurations 6.4.3.5. Power Delivery Recommendation for DDR4 Discrete Configurations 6.4.3.6. DDR4 Simulation Strategy
7. Agilex™ 5 FPGA EMIF IP - DDR5 Support x
7.1. Agilex 5 FPGA EMIF IP Parameter Descriptions for DDR5 7.2. Agilex™ 5 FPGA EMIF IP Pin and Resource Planning
7.1. Agilex 5 FPGA EMIF IP Parameter Descriptions for DDR5 x
7.1.1. Agilex 5 FPGA External Memory Interfaces (EMIF) IP Parameter Descriptions for DDR5 7.1.2. Agilex 5 FPGA EMIF Memory Device Description IP (DDR5) Parameter Descriptions 7.1.3. Agilex 5 FPGA EMIF Calibration IP Parameter Descriptions
7.2. Agilex™ 5 FPGA EMIF IP Pin and Resource Planning x
7.2.1. Agilex™ 5 FPGA EMIF IP Interface Pins 7.2.2. Agilex™ 5 FPGA EMIF IP Resources 7.2.3. Pin Guidelines for Agilex™ 5 FPGA EMIF IP 7.2.4. Pin Placements for Agilex™ 5 FPGA DDR5 EMIF IP 7.2.5. Agilex™ 5 EMIF Pin Swapping Guidelines
7.2.1. Agilex™ 5 FPGA EMIF IP Interface Pins x
7.2.1.1. Estimating Pin Requirements 7.2.1.2. DIMM Options 7.2.1.3. Maximum Number of Interfaces
7.2.2. Agilex™ 5 FPGA EMIF IP Resources x
7.2.2.1. OCT 7.2.2.2. PLL
7.2.3. Pin Guidelines for Agilex™ 5 FPGA EMIF IP x
7.2.3.1. General Guidelines - DDR5 7.2.3.2. x4 DIMM Implementation 7.2.3.3. Specific Pin Connection Requirements 7.2.3.4. Command and Address Signals 7.2.3.5. Clock Signals 7.2.3.6. Data, Data Strobes, DM, and Optional ECC Signals
7.2.4. Pin Placements for Agilex™ 5 FPGA DDR5 EMIF IP x
7.2.4.1. Address and Command Pin Placement for DDR5 7.2.4.2. DDR5 Data Width Mapping
7.2.5. Agilex™ 5 EMIF Pin Swapping Guidelines x
7.2.5.1. DDR5 Byte Lane Swapping 7.2.5.2. DDR5 Address and Command and CLK Lane 7.2.5.3. DDR5 Interface x8 Data Lane 7.2.5.4. DDR5 Interface x4 Data Lane 7.2.5.5. Pin Swizzling
8. Agilex™ 5 FPGA EMIF IP - LPDDR4 Support x
8.1. Agilex 5 FPGA EMIF IP Parameter Descriptions for LPDDR4 8.2. Agilex™ 5 FPGA EMIF IP Pin and Resource Planning 8.3. LPDDR4 Layout Design Guidelines
8.1. Agilex 5 FPGA EMIF IP Parameter Descriptions for LPDDR4 x
8.1.1. Agilex 5 FPGA External Memory Interfaces (EMIF) IP Parameter Descriptions for LPDDR4 8.1.2. Agilex 5 FPGA EMIF Memory Device Description IP (LPDDR4) Parameter Descriptions 8.1.3. Agilex 5 FPGA EMIF Calibration IP Parameter Descriptions
8.2. Agilex™ 5 FPGA EMIF IP Pin and Resource Planning x
8.2.1. Agilex™ 5 FPGA EMIF IP Interface Pins 8.2.2. Agilex™ 5 FPGA EMIF IP Resources 8.2.3. Pin Guidelines for Agilex™ 5 FPGA EMIF IP
8.2.1. Agilex™ 5 FPGA EMIF IP Interface Pins x
8.2.1.1. Estimating Pin Requirements 8.2.1.2. LPDDR4 Component Options 8.2.1.3. Maximum Number of Interfaces
8.2.2. Agilex™ 5 FPGA EMIF IP Resources x
8.2.2.1. OCT 8.2.2.2. PLL
8.2.3. Pin Guidelines for Agilex™ 5 FPGA EMIF IP x
8.2.3.1. General Guidelines 8.2.3.2. Specific Pin Connection Requirements 8.2.3.3. Command and Address Signals 8.2.3.4. Clock Signals 8.2.3.5. Address and Command Pin Placement for LPDDR4 8.2.3.6. LPDDR4 Data Width Mapping 8.2.3.7. Pin Swapping Guidelines
8.3. LPDDR4 Layout Design Guidelines x
8.3.1. LPDDR4 PCB Stackup and Design Considerations 8.3.2. LPDDR4 General Design Considerations General DDR Signal Routing Guideline on PCB DDR FPGA Break Out Routing DDR Differential Signals Routing Ground Plane and Return Path DRAM Break Out in Layout Guideline 8.3.3. LPDDR4 Interface Design Guidelines
8.3.3. LPDDR4 Interface Design Guidelines x
8.3.3.1. LPDDR4 Discrete Component/Memory Down Topology (up to 32 bits interface) 8.3.3.2. LPDDR4 Simulation Strategy
9. Agilex™ 5 FPGA EMIF IP - LPDDR5 Support x
9.1. Agilex 5 FPGA EMIF IP Parameter Descriptions for LPDDR5 9.2. Agilex™ 5 FPGA EMIF IP Pin and Resource Planning 9.3. LPDDR5 Layout Design Guidelines
9.1. Agilex 5 FPGA EMIF IP Parameter Descriptions for LPDDR5 x
9.1.1. Agilex 5 FPGA External Memory Interfaces (EMIF) IP Parameter Descriptions for LPDDR5 9.1.2. Agilex 5 FPGA EMIF Memory Device Description IP (LPDDR5) Parameter Descriptions 9.1.3. Agilex 5 FPGA EMIF Calibration IP Parameter Descriptions
9.2. Agilex™ 5 FPGA EMIF IP Pin and Resource Planning x
9.2.1. Agilex™ 5 FPGA EMIF IP Interface Pins 9.2.2. Agilex™ 5 FPGA EMIF IP Resources 9.2.3. Pin Guidelines for Agilex™ 5 FPGA EMIF IP 9.2.4. Pin Placements for Agilex™ 5 FPGA LPDDR5 EMIF IP
9.2.1. Agilex™ 5 FPGA EMIF IP Interface Pins x
9.2.1.1. Estimating Pin Requirements 9.2.1.2. LPDDR5 Component Options 9.2.1.3. Maximum Number of Interfaces
9.2.2. Agilex™ 5 FPGA EMIF IP Resources x
9.2.2.1. OCT 9.2.2.2. PLL
9.2.3. Pin Guidelines for Agilex™ 5 FPGA EMIF IP x
9.2.3.1. General Guidelines - LPDDR5 9.2.3.2. Specific Pin Connection Requirements 9.2.3.3. Command and Address Signals 9.2.3.4. Clock Signals
9.2.4. Pin Placements for Agilex™ 5 FPGA LPDDR5 EMIF IP x
9.2.4.1. Address and Command Pin Placement for LPDDR5 9.2.4.2. LPDDR5 Data Width Mapping 9.2.4.3. LPDDR5 Byte Lane Swapping
9.3. LPDDR5 Layout Design Guidelines x
9.3.1. LPDDR5 PCB Stackup and Design Considerations 9.3.2. LPDDR5 General Design Considerations 9.3.3. LPDDR5 Interface Design Guidelines
9.3.3. LPDDR5 Interface Design Guidelines x
9.3.3.1. LPDDR5 Discrete Component/Memory Down Topology (Single Rank or Dual-Rank) 9.3.3.2. Example of an LPDDR5 Layout on an Intel FPGA Platform Board 9.3.3.3. LPDDR5 Simulation Strategy
10. Agilex™ 5 FPGA EMIF IP – Timing Closure x
10.1. Timing Closure 10.2. Optimizing Timing
10.1. Timing Closure x
10.1.1. Timing Analysis
10.1.1. Timing Analysis x
10.1.1.1. PHY or Core
11. Agilex™ 5 FPGA EMIF IP – Controller Optimization x
11.1. Interface Standard 11.2. Bank Management Efficiency 11.3. Data Transfer 11.4. Improving Controller Efficiency
11.4. Improving Controller Efficiency x
11.4.1. Frequency of Operation 11.4.2. Series of Reads or Writes
12. Agilex™ 5 FPGA EMIF IP – Debugging x
12.1. Interface Configuration Performance Issues 12.2. Functional Issue Evaluation 12.3. Timing Issue Characteristics 12.4. Verifying Memory IP Using the Signal Tap Logic Analyzer 12.5. Debugging with the External Memory Interface Debug Toolkit 12.6. Generating Traffic with the Test Engine IP 12.7. Guidelines for Developing HDL for Traffic Generator 12.8. Guidelines for Traffic Generator Status Check 12.9. Hardware Debugging Guidelines 12.10. Create a Simplified Design that Demonstrates the Same Issue 12.11. Measure Power Distribution Network 12.12. Measure Signal Integrity and Setup and Hold Margin 12.13. Vary Voltage 12.14. Operate at a Lower Speed 12.15. Determine Whether the Issue Exists in Previous Versions of Software 12.16. Determine Whether the Issue Exists in the Current Version of Software 12.17. Try A Different PCB 12.18. Try Other Configurations 12.19. Debugging Checklist 12.20. Categorizing Hardware Issues 12.21. Signal Integrity Issues 12.22. Characteristics of Signal Integrity Issues 12.23. Evaluating Signal Integrity Issues 12.24. Skew 12.25. Crosstalk 12.26. Power System 12.27. Clock Signals 12.28. Address and Command Signals 12.29. Read Data Valid Window and Eye Diagram 12.30. Write Data Valid Window and Eye Diagram 12.31. Hardware and Calibration Issues 12.32. Memory Timing Parameter Evaluation 12.33. Verify that the Board Has the Correct Memory Component or DIMM Installed
12.1. Interface Configuration Performance Issues x
12.1.1. Interface Configuration Bottleneck and Efficiency Issues
12.2. Functional Issue Evaluation x
12.2.1. Altera IP Memory Model 12.2.2. Vendor Memory Model 12.2.3. Transcript Window Messages
12.3. Timing Issue Characteristics x
12.3.1. Evaluating FPGA Timing Issues 12.3.2. Evaluating External Memory Interface Timing Issues
12.5. Debugging with the External Memory Interface Debug Toolkit x
12.5.1. Prerequisites for Using the EMIF Debug Toolkit 12.5.2. Configuring a Design to Use the Debug Toolkit 12.5.3. Launching the EMIF Debug Toolkit 12.5.4. Using the EMIF Debug Toolkit
12.5.2. Configuring a Design to Use the Debug Toolkit x
12.5.2.1. Generating a Design Example with the Debug Toolkit
12.5.4. Using the EMIF Debug Toolkit x
12.5.4.1. Running Re-Calibration 12.5.4.2. Running the Test Engine
12.8. Guidelines for Traffic Generator Status Check x
12.8.1. Status Check Using the Signal Tap Logic Analyzer 12.8.2. Exporting the Status Interface to the Top-Level Design
1. About the External Memory Interfaces Agilex™ 5 FPGA IP
2. Agilex™ 5 FPGA EMIF IP – Introduction
3. Agilex™ 5 FPGA EMIF IP – Product Architecture
4. Agilex™ 5 FPGA EMIF IP – End-User Signals
5. Agilex™ 5 FPGA EMIF IP – Simulating Memory IP
6. Agilex™ 5 FPGA EMIF IP - DDR4 Support
7. Agilex™ 5 FPGA EMIF IP - DDR5 Support
8. Agilex™ 5 FPGA EMIF IP - LPDDR4 Support
9. Agilex™ 5 FPGA EMIF IP - LPDDR5 Support
10. Agilex™ 5 FPGA EMIF IP – Timing Closure
11. Agilex™ 5 FPGA EMIF IP – Controller Optimization
12. Agilex™ 5 FPGA EMIF IP – Debugging
13. Document Revision History for External Memory Interfaces (EMIF) IP User Guide

8.3.2. LPDDR4 General Design Considerations

General DDR Signal Routing Guideline on PCB

Altera recommends to route all data signals within a specific group on the same layer.

The figure below illustrates a routing example for a type-III PCB board for an LPDDR4 design. Data Group signals such as DQ, DM and DQS signals should be routed on shallow layers as stripline with the least Z-height via transition to avoid vertical crosstalk to achieve high performance.

For example, the recommended routing layers for data group on a 20-layers board and using PTH via will be on the top half of the PCB such as L3, L5 and L7. Other signals such as CA, CTRL and clock signals can be routed with longer Z-height via transition on the bottom half of the PCB such as L14, L16 and L18.

Minimal stub effect or back drill is recommended, but not required, to avoid high reflection for maximum data rate performance. Long via stubs will affect the ISI of channel but the impact of ISI is less than impact of crosstalk for the max data rate performance.

Figure 38. Case A Routing is Suggested for Data Group Signals Over Case B

To minimize crosstalk horizontally between signals on the same layer, PCB designers must maintain adequate signal trace-to-trace (edge to edge) space, with a minimum spacing of 3xH separation distance, where H is the dielectric thickness to the closest reference plane as illustrated in the figure below.

Figure 39. Minimum Trace-to-Trace Separation Distance

DDR FPGA Break Out Routing

Agilex™ 5 devices come with various pitch sizes for different FPGA pins. The GPIO pin pitch is very small, the device BGA pad stack is also very small, therefore, it is highly recommended to use a dog bone configuration for inner GPIO pins fanout along with stripline routing; however, for the GPIO pins on the edge of device, it is recommended to use microstrip routing. Both microstrip and stripline routing guidelines are presented in this document for all supported EMIF interfaces and topologies.

DDR Differential Signals Routing

DQS and CLK signals in the DDR interface are differential signals and must be routed on PCB as differential signals unless there is a limitation for PCB routing such as having a very small pitch at DRAM area.

Altera recommends a symmetrical fan-out routing at the FPGA pin field. Non-symmetrical routing for differential signals will cause shifting on common-mode voltage and contributes to reduced timing margins at the receiver. The following figures show the recommended differential routing at the FPGA pin field for DQS/CLK signals.

The figure below shows the symmetrical routing of differential signals (DQS/CLK) at FPGA pin field along with length/skew matching between P/N lanes right after FPGA device edge.

Figure 40. Symmetrical Routing of Differential Signals (DQS/CLK) at FPGA Pin Field

The figure below shows the single-ended routing for differential signals (DQS/CLK) at DRAM pin field if the pitch is very small along with skew matching right at edge of DRAM pin field.

Figure 41. Single-ended Routing for Differential Signals (DQS/CLK) at DRAM

Altera recommends to implement length/skew matching for differential signals (if there is) right after FPGA device to avoid additional shifting on differential signals common mode voltage.

In case of having limitation for implementing symmetrical routing at DRAM pin field for differential signals due to very small pitch, Altera recommends to route the differential signals as single-ended signals within the DRAM pin field, ensuring to keep the same impedance while changing from differential to single-ended configuration. Designers must also keep the same length of routing for each P and N single-ended lane within the DRAM pin field. The skew matching between P/N lanes must be applied before reaching the DRAM pin field.

Ground Plane and Return Path

A continuous and solid ground reference plane is crucial for data lines to ensure good signal integrity performance. Low impedance ground return path from the FPGA to DRAM devices should be provisioned. In addition, it is desirable to keep ground stitching vias within 80 mils from signal transition for better return path on signal via and better signal integrity performance.

DRAM Break Out in Layout Guideline

For discrete DRAM components on PCB, you can either use the dog-bone or via in pad at DRAM for the signal transition from inner layer to DRAM. If dog-bone via transition is used, it is recommended to separate them with larger pitch to avoid crosstalk between signal vias.

Figure 42. Data Signal Group Routing on PCB for Memory Down Configuration
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