Intel® Hyperflex™ Architecture High-Performance Design Handbook

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Date 10/04/2021
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Document Table of Contents
Document Table of Contents x
1. Intel® Hyperflex™ FPGA Architecture Introduction 2. Intel® Hyperflex™ Architecture RTL Design Guidelines 3. Compiling Intel® Hyperflex™ Architecture Designs 4. Design Example Walk-Through 5. Retiming Restrictions and Workarounds 6. Optimization Example 7. Intel® Hyperflex™ Architecture Porting Guidelines 8. Appendices 9. Intel® Hyperflex™ Architecture High-Performance Design Handbook Archive 10. Intel® Hyperflex™ Architecture High-Performance Design Handbook Revision History
1. Intel® Hyperflex™ FPGA Architecture Introduction x
1.1. Intel® Hyperflex™ Architecture Design Concepts
2. Intel® Hyperflex™ Architecture RTL Design Guidelines x
2.1. High-Speed Design Methodology 2.2. Hyper-Retiming (Facilitate Register Movement) 2.3. Hyper-Pipelining (Add Pipeline Registers) 2.4. Hyper-Optimization (Optimize RTL)
2.1. High-Speed Design Methodology x
2.1.1. Set a High-Speed Target 2.1.2. Experiment and Iterate 2.1.3. Compile Components Independently 2.1.4. Optimize Sub-Modules 2.1.5. Avoid Broadcast Signals
2.1.1. Set a High-Speed Target x
2.1.1.1. Speed and Timing Closure 2.1.1.2. Speed and Latency
2.2. Hyper-Retiming (Facilitate Register Movement) x
2.2.1. Reset Strategies 2.2.2. Clock Enable Strategies 2.2.3. Preserving Registers During Synthesis 2.2.4. Timing Constraint Considerations 2.2.5. Clock Synchronization Strategies 2.2.6. Metastability Synchronizers 2.2.7. Initial Power-Up Conditions 2.2.8. Retiming through RAMs and DSPs
2.2.1. Reset Strategies x
2.2.1.1. Removing Asynchronous Resets 2.2.1.2. Synchronous Resets on Global Clock Trees 2.2.1.3. Synchronous Resets on I/O Ports 2.2.1.4. Duplicate and Pipeline Synchronous Resets
2.2.2. Clock Enable Strategies x
2.2.2.1. Localized Clock Enable 2.2.2.2. High Fan-Out Clock Enable 2.2.2.3. Clock Enable with Timing Exceptions
2.2.4. Timing Constraint Considerations x
2.2.4.1. Optimize Multicycle Paths 2.2.4.2. Overconstraints
2.2.5. Clock Synchronization Strategies x
2.2.5.1. Clock Domain Crossing Constraint Guidelines
2.2.7. Initial Power-Up Conditions x
2.2.7.1. Specifying Initial Memory Conditions 2.2.7.2. Initial Conditions and Retiming 2.2.7.3. Initial Conditions and Hyper-Registers 2.2.7.4. Retiming Reset Sequences
2.2.7.3. Initial Conditions and Hyper-Registers x
2.2.7.3.1. Implementing Clock Gating 2.2.7.3.2. Intel® Quartus® Prime Settings for Initial Conditions
2.3. Hyper-Pipelining (Add Pipeline Registers) x
2.3.1. Conventional Versus Hyper-Pipelining 2.3.2. Pipelining and Latency 2.3.3. Use Registers Instead of Multicycle Exceptions
2.3.2. Pipelining and Latency x
2.3.2.1. Pipelining at Variable Latency Locations 2.3.2.2. Automatic Pipeline Insertion
2.3.2.1. Pipelining at Variable Latency Locations x
2.3.2.1.1. Specifying a Latency-Insensitive False Path
2.3.2.2. Automatic Pipeline Insertion x
2.3.2.2.1. Step 1: Create the Variable Latency Module 2.3.2.2.2. Step 2: Instantiate the Variable Latency Module 2.3.2.2.3. Step 3: Verify Automatic Pipeline Insertion Option 2.3.2.2.4. (Optional) Auto-Pipeline Insertion without a Variable Latency Module
2.4. Hyper-Optimization (Optimize RTL) x
2.4.1. General Optimization Techniques 2.4.2. Optimizing Specific Design Structures
2.4.1. General Optimization Techniques x
2.4.1.1. Shannon’s Decomposition 2.4.1.2. Time Domain Multiplexing 2.4.1.3. Loop Unrolling 2.4.1.4. Loop Pipelining 2.4.1.5. Precomputation
2.4.1.1. Shannon’s Decomposition x
2.4.1.1.1. Shannon’s Decomposition Example 2.4.1.1.2. Identifying Circuits for Shannon’s Decomposition
2.4.1.4. Loop Pipelining x
2.4.1.4.1. Loop Pipelining Theory 2.4.1.4.2. Loop Pipelining Demonstration 2.4.1.4.3. Loop Pipelining and Synthesis Optimization
2.4.2. Optimizing Specific Design Structures x
2.4.2.1. High-Speed Clock Domains 2.4.2.2. Restructuring Loops 2.4.2.3. Control Signal Backpressure 2.4.2.4. Flow Control with FIFO Status Signals 2.4.2.5. Flow Control with Skid Buffers 2.4.2.6. Read-Modify-Write Memory 2.4.2.7. Counters and Accumulators 2.4.2.8. State Machines 2.4.2.9. Memory 2.4.2.10. DSP Blocks 2.4.2.11. General Logic 2.4.2.12. Modulus and Division 2.4.2.13. Resets 2.4.2.14. Hardware Re-use 2.4.2.15. Algorithmic Requirements 2.4.2.16. FIFOs 2.4.2.17. Ternary Adders
2.4.2.1. High-Speed Clock Domains x
2.4.2.1.1. Visualizing Clock Networks 2.4.2.1.2. Viewing Clock Networks in the Fitter Report 2.4.2.1.3. Viewing Clocks in the Timing Analyzer
2.4.2.9. Memory x
2.4.2.9.1. Intel® Hyperflex™ Architecture True Dual-Port Memory 2.4.2.9.2. Use Simple Dual-Port Memories 2.4.2.9.3. Intel® Hyperflex™ Architecture Simple Dual-Port Memory Example 2.4.2.9.4. Memory Mixed Port Width Ratio Limits 2.4.2.9.5. Unregistered RAM Outputs
3. Compiling Intel® Hyperflex™ Architecture Designs x
3.1. Compiling Submodules Independently 3.2. Design Assistant Design Rule Checking
3.2. Design Assistant Design Rule Checking x
3.2.1. Running Design Assistant During Compilation 3.2.2. Running Design Assistant in Analysis Mode
3.2.2. Running Design Assistant in Analysis Mode x
3.2.2.1. Cross-Probing from Design Assistant to Visualization Tools 3.2.2.2. Launching Design Assistant from Chip Planner 3.2.2.3. Launching Design Assistant from Timing Analyzer
4. Design Example Walk-Through x
4.1. Median Filter Design Example
4.1. Median Filter Design Example x
4.1.1. Step 1: Compile the Base Design 4.1.2. Step 2: Add Pipeline Stages and Remove Asynchronous Resets 4.1.3. Step 3: Add More Pipeline Stages and Remove All Asynchronous Resets 4.1.4. Step 4: Optimize Short Path and Long Path Conditions
5. Retiming Restrictions and Workarounds x
5.1. Setting the dont_merge Synthesis Attribute 5.2. Interpreting Critical Chain Reports
5.2. Interpreting Critical Chain Reports x
5.2.1. Insufficient Registers 5.2.2. Short Path/Long Path 5.2.3. Fast Forward Limit 5.2.4. Loops 5.2.5. One Critical Chain per Clock Domain 5.2.6. Critical Chains in Related Clock Groups 5.2.7. Complex Critical Chains 5.2.8. Extend to locatable node 5.2.9. Domain Boundary Entry and Domain Boundary Exit 5.2.10. Critical Chains with Dual Clock Memories 5.2.11. Critical Chain Bits and Buses 5.2.12. Delay Lines
5.2.1. Insufficient Registers x
5.2.1.1. Insufficient Registers Example 5.2.1.2. Optimizing Insufficient Registers 5.2.1.3. Critical Chains with Dual Clock Memories
5.2.2. Short Path/Long Path x
5.2.2.1. Hyper-Register Locations Not Available 5.2.2.2. Example for Hold Optimization 5.2.2.3. Optimizing Short Path/Long Path 5.2.2.4. Add Registers 5.2.2.5. Duplicate Common Nodes 5.2.2.6. Data and Control Plane
5.2.3. Fast Forward Limit x
5.2.3.1. Optimizing Path Limit
5.2.4. Loops x
5.2.4.1. Example of Loops Limiting the Critical Chain
6. Optimization Example x
6.1. Round Robin Scheduler
7. Intel® Hyperflex™ Architecture Porting Guidelines x
7.1. Design Migration and Performance Exploration 7.2. Top-Level Design Considerations
7.1. Design Migration and Performance Exploration x
7.1.1. Black-boxing Verilog HDL Modules 7.1.2. Black-boxing VHDL Modules 7.1.3. Clock Management 7.1.4. Pin Assignments 7.1.5. Transceiver Control Logic 7.1.6. Upgrade Outdated IP Cores
8. Appendices x
8.1. Appendix A: Parameterizable Pipeline Modules 8.2. Appendix B: Clock Enables and Resets
8.2. Appendix B: Clock Enables and Resets x
8.2.1. Synchronous Resets and Limitations 8.2.2. Retiming with Clock Enables 8.2.3. Resolving Short Paths
8.2.1. Synchronous Resets and Limitations x
8.2.1.1. Synchronous Resets Summary
8.2.2. Retiming with Clock Enables x
8.2.2.1. Example for Broadcast Control Signals
1. Intel® Hyperflex™ FPGA Architecture Introduction
2. Intel® Hyperflex™ Architecture RTL Design Guidelines
3. Compiling Intel® Hyperflex™ Architecture Designs
4. Design Example Walk-Through
5. Retiming Restrictions and Workarounds
6. Optimization Example
7. Intel® Hyperflex™ Architecture Porting Guidelines
8. Appendices
9. Intel® Hyperflex™ Architecture High-Performance Design Handbook Archive
10. Intel® Hyperflex™ Architecture High-Performance Design Handbook Revision History

2.3.2.1.1. Specifying a Latency-Insensitive False Path

You can specify a latency-insensitive false path to allow the Hyper-Retimer to automatically add pipeline stages to a path. Specify latency-insensitive false paths only on cross-clock domain paths, such as between a low-speed configuration clock domain, and a high-speed data path clock domain, as in a signal processing design.

Specify the latency_insensitive option for the set_false_path exception to designate a false path as latency-insensitive. Specify the clock names for the from and to options, as the following example shows: 

set_false_path -latency_insensitive -from  [get_clocks {clock_a}]  \
     -to  [get_clocks {clock_b}]

Although not a syntax error to specify register, cell, net, pin, or keeper name for the from or to options, the Compiler interprets the false path as a retiming restriction, and prevents the Hyper-Retimer from retiming those endpoints. There is no benefit to using the latency_insensitive option on a register-to-register false path.

Note: The set_false_path constraint has higher precedence than all other path-based SDC constraints. If your latency-insensitive false path is on a clock domain transfer that includes FIFOs, bus synchronizers, or other cross-domain circuits that have path-based constraints (such as set_max_skew, set_max_delay, or set_min_delay), a clock-to-clock set_false_path constraint overrides these constraints. If you constrain a clock domain crossing with any path-based constraint, the latency_insensitive option overrides these constraints. Only use a latency-insensitive false path on clock domain crossing paths that you have actually cut from timing analysis.

In the following figure, the top diagram represents the design RTL, indicating the false path tagged as latency-insensitive false path. The bottom diagram shows how the Hyper-Retimer adds pipeline stages on the other side of the registers at endpoints of the latency-insensitive false path.

The Hyper-Retimer can add registers to the input of the source of the latency-insensitive false path, and to the output of the destination of the latency-insensitive false path. The Hyper-Retimer then retimes the registers backward and forward through the two clock domains.

Figure 32. Effect of Latency-Insensitive False Path on Circuit

The Hyper-Retimer analyzes the performance of each cross-clock-domain path separately to determine the number of stages to automatically add. The Hyper-Retimer may insert different numbers of stages on each cross-clock-domain path.

For example, a bus crossing a clock domain that is cut with the latency_insensitive option can have different latencies for each bit in the bus after the Hyper-Retimer runs. Therefore, ensure that the data crossing the clock domain remains constant for many clock cycles to ensure it becomes constant at the destination. For example, this can occur with a bus with different latencies on each bit.

The compilation report does not show the number of stages that the Hyper-Retimer inserts at a latency-insensitive false path. However, you can examine the connectivity in the timing netlist after the Hyper-Retimer finishes to determine the number of stages.

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