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

2.4.2.4. Flow Control with FIFO Status Signals

High clock speeds require consideration when dealing with flow control signals. This consideration is particularly important with signals that gate a data path in multiple locations at the same time. For example, with clock enable or FIFO full or empty signals. Instead of working with immediate control signals, use a delayed signal. You can build a buffer within the FIFO block. The control signals indicate to the upstream data path that the path is almost full, leaving a few clock cycles for the upstream data to receive their gating signal. This approach alleviates timing closure difficulties on the control signals.

When you use FIFO full and empty signals, you must process these signals in one clock cycle to prevent overflow or underflow.

Figure 65. FIFO Flow Control LoopThe loop forms while reading control signals from the FIFO.

If you use an almost full or almost empty signal instead, you can add pipeline registers in the flow control loop. The lower the almost full threshold, and the higher the almost empty threshold, the more registers you can add to the signal.

Figure 66. Improved FIFO Flow Control Loop with Almost Full instead of Full FIFOThe following example shows two extra registers in the full control flow signal. After the FIFO generates the almost full flag, it takes two cycles for the signal to reach the data producer block. Two additional cycles are then required before the data sent stops arriving at the FIFO. This condition results in four cycles of latency. Anytime the almost full flag is asserted, the data producer can send 4 more words before the FIFO is actually full. Size the FIFO block to allow for proper storage of those extra valid data. The extra two pipeline registers in the control path help with routing, and enable higher speed than with traditional single-cycle FIFO control scheme.
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