Intel® High Level Synthesis Compiler Pro Edition: Best Practices Guide

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ID 683152
Date 3/28/2022
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Document Table of Contents
Document Table of Contents x
1. Intel® HLS Compiler Pro Edition Best Practices Guide 2. Best Practices for Coding and Compiling Your Component 3. FPGA Concepts 4. Interface Best Practices 5. Loop Best Practices 6. fMAX Bottleneck Best Practices 7. Memory Architecture Best Practices 8. System of Tasks Best Practices 9. Datatype Best Practices 10. Advanced Troubleshooting A. Intel® HLS Compiler Pro Edition Best Practices Guide Archives B. Document Revision History for Intel® HLS Compiler Pro Edition Best Practices Guide
3. FPGA Concepts x
3.1. FPGA Architecture Overview 3.2. Concepts of FPGA Hardware Design 3.3. Methods of Hardware Design
3.1. FPGA Architecture Overview x
3.1.1. Adaptive Logic Module (ALM) 3.1.2. Digital Signal Processing (DSP) Block 3.1.3. Random-Access Memory (RAM) Blocks
3.1.1. Adaptive Logic Module (ALM) x
3.1.1.1. Lookup Table (LUT) 3.1.1.2. Register
3.2. Concepts of FPGA Hardware Design x
3.2.1. Maximum Frequency (fMAX) 3.2.2. Latency 3.2.3. Pipelining 3.2.4. Throughput 3.2.5. Datapath 3.2.6. Control Path 3.2.7. Occupancy
3.3. Methods of Hardware Design x
3.3.1. How Source Code Becomes a Custom Hardware Datapath 3.3.2. Scheduling 3.3.3. Mapping Parallelism Models to FPGA Hardware 3.3.4. Memory Types
3.3.1. How Source Code Becomes a Custom Hardware Datapath x
3.3.1.1. Mapping Source Code Instructions to Hardware 3.3.1.2. Mapping Arrays and Their Accesses to Hardware
3.3.2. Scheduling x
3.3.2.1. Dynamic Scheduling 3.3.2.2. Clustering the Datapath 3.3.2.3. Handshaking Between Clusters
3.3.3. Mapping Parallelism Models to FPGA Hardware x
3.3.3.1. Data Parallelism 3.3.3.2. Task Parallelism
3.3.3.1. Data Parallelism x
3.3.3.1.1. Executing Independent Operations Simultaneously 3.3.3.1.2. Pipelining
3.3.3.1.2. Pipelining x
3.3.3.1.2.1. Pipelining Loops Within A Component 3.3.3.1.2.2. Pipelining Across Component Invocations
3.3.4. Memory Types x
3.3.4.1. Component Memory 3.3.4.2. External Memory
4. Interface Best Practices x
Demonstrating Interface Best Practices 4.1. Choose the Right Interface for Your Component 4.2. Control LSUs For Your Variable-Latency MM Host Interfaces 4.3. Avoid Pointer Aliasing
4.1. Choose the Right Interface for Your Component x
4.1.1. Pointer Interfaces 4.1.2. Avalon® Memory Mapped Host Interfaces 4.1.3. Avalon® Memory Mapped Agent Memories 4.1.4. Avalon® Memory Mapped Agent Registers 4.1.5. Avalon® Streaming Interfaces 4.1.6. Pass-by-Value Interface
5. Loop Best Practices x
5.1. Reuse Hardware By Calling It In a Loop 5.2. Parallelize Loops 5.3. Construct Well-Formed Loops 5.4. Minimize Loop-Carried Dependencies 5.5. Avoid Complex Loop-Exit Conditions 5.6. Convert Nested Loops into a Single Loop 5.7. Place if-Statements in the Lowest Possible Scope in a Loop Nest 5.8. Declare Variables in the Deepest Scope Possible 5.9. Raise Loop II to Increase fMAX 5.10. Control Loop Interleaving
5.2. Parallelize Loops x
5.2.1. Pipeline Loops 5.2.2. Unroll Loops 5.2.3. Example: Loop Pipelining and Unrolling
6. fMAX Bottleneck Best Practices x
6.1. Balancing Target fMAX and Target II
7. Memory Architecture Best Practices x
7.1. Example: Overriding a Coalesced Memory Architecture 7.2. Example: Overriding a Banked Memory Architecture 7.3. Merge Memories to Reduce Area 7.4. Example: Specifying Bank-Selection Bits for Local Memory Addresses
7.3. Merge Memories to Reduce Area x
7.3.1. Example: Merging Memories Depth-Wise 7.3.2. Example: Merging Memories Width-Wise
8. System of Tasks Best Practices x
8.1. Executing Multiple Loops in Parallel 8.2. Sharing an Expensive Compute Block 8.3. Implementing a Hierarchical Design 8.4. Balancing Capacity in a System of Tasks
8.4. Balancing Capacity in a System of Tasks x
8.4.1. Enable the Intel® HLS Compiler to Infer Data Path Buffer Capacity Requirements 8.4.2. Explicitly Add Buffer Capacity to Your Design When Needed
9. Datatype Best Practices x
9.1. Avoid Implicit Data Type Conversions 9.2. Avoid Negative Bit Shifts When Using the ac_int Datatype
10. Advanced Troubleshooting x
10.1. Component Fails Only In Simulation 10.2. Component Gets Poor Quality of Results
1. Intel® HLS Compiler Pro Edition Best Practices Guide
2. Best Practices for Coding and Compiling Your Component
3. FPGA Concepts
4. Interface Best Practices
5. Loop Best Practices
6. fMAX Bottleneck Best Practices
7. Memory Architecture Best Practices
8. System of Tasks Best Practices
9. Datatype Best Practices
10. Advanced Troubleshooting
A. Intel® HLS Compiler Pro Edition Best Practices Guide Archives
B. Document Revision History for Intel® HLS Compiler Pro Edition Best Practices Guide

4. Interface Best Practices

With the Intel® High Level Synthesis Compiler, your component can have a variety of interfaces: from basic wires to the Avalon Streaming and Avalon Memory-Mapped Host interfaces. Review the interface best practices to help you choose and configure the right interface for your component.

Each interface type supported by the Intel® HLS Compiler Pro Edition has different benefits. However, the system that surrounds your component might limit your choices. Keep your requirements in mind when determining the optimal interface for your component.

Demonstrating Interface Best Practices

The Intel® HLS Compiler Pro Edition comes with a number of tutorials that illustrate important Intel® HLS Compiler concepts and demonstrate good coding practices.

Review the following tutorials to learn about different interfaces as well as best practices that might apply to your design:
Tutorial Description
You can find these tutorials in the following location on your Intel® Quartus® Prime system:
<quartus_installdir>/hls/examples/tutorials
interfaces/ overview Demonstrates the effects on quality-of-results (QoR) of choosing different component interfaces even when the component algorithm remains the same.
best_practices/ const_global

Demonstrates the performance and resource utilization improvements of using const qualified global variables. Also demonstrates the type of interface created when you access global variables.

best_practices/ parameter_aliasing

Demonstrates the use of the __restrict keyword on component arguments

best_practices/ lsu_control Demonstrates the effects of controlling the type of LSUs instantiated for variable-latency Avalon® Memory Mapped Host interfaces
interfaces/ explicit_streams_buffer

Demonstrates how to use explicit stream_in and stream_out interfaces in the component and testbench.

interfaces/ explicit_streams_packets_empty Demonstrates how to use the usesPackets, usesEmpty, and firstSymbolInHighOrderBits stream template parameters.
interfaces/explicit_streams_packets_ready_valid Demonstrates how to use the usesPackets, usesValid, and usesReady stream template parameters.
interfaces/ mm_host_testbench_operators Demonstrates how to invoke a component at different indicies of an Avalon Memory Mapped (MM) Host (mm_host class) interface.
interfaces/ mm_agents Demonstrates how to create Avalon-MM Agent interfaces (agent registers and agent memories).
interfaces/ mm_agents_csr_volatile Demonstrates the effect of using volatile keyword to allow concurrent agent memory accesses while your component is running.
interfaces/ mm_agents_double_buffering Demonstrates the effect of using the hls_readwrite_mode macro to control how memory hosts access the agent memories
interfaces/ multiple_stream_call_sites Demonstrates the tradeoffs of using multiple stream call sites.
interfaces/ pointer_mm_host Demonstrates how to create Avalon-MM Host interfaces and control their parameters.
interfaces/ stable_arguments Demonstrates how to use the stable attribute for unchanging arguments to improve resource utilization.

Section Content
Choose the Right Interface for Your Component
Control LSUs For Your Variable-Latency MM Host Interfaces
Avoid Pointer Aliasing

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