Developer Guide

Intel® oneAPI DPC++/C++ Compiler Handbook for FPGAs

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Date 6/24/2024
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Document Table of Contents
Document Table of Contents x
Intel oneAPI DPC++/C++ Compiler Handbook for FPGAs Overview Introduction To FPGA Design Concepts Intel oneAPI FPGA Development Getting Started with the Intel oneAPI DPC++/C++ Compiler for Intel FPGA Development Defining a Kernel for FPGAs Debugging and Verifying Your Design Analyzing Your Design Optimizing Your Kernel Optimizing Your Host Application Integrating Your Kernel into DSP Builder for Intel FPGAs Integrating Your RTL IP Core Into a System RTL IP Core Kernel Interfaces Loops Pipes Data Types and Arithmetic Operations Parallelism Memories and Memory Operations Libraries Additional FPGA Acceleration Flow Considerations FPGA Optimization Flags, Attributes, Pragmas, and Extensions Quick Reference Additional Information Document Revision History for the Intel oneAPI DPC++/C++ Compiler Handbook for Intel FPGAs Notices and Disclaimers
Introduction To FPGA Design Concepts x
FPGA Architecture Overview Concepts of FPGA Hardware Design How Source Code Becomes a Custom Hardware Datapath
How Source Code Becomes a Custom Hardware Datapath x
Mapping Source Code Instructions to Hardware Scheduling Mapping Parallelism Models to FPGA Hardware Memory Types
Intel oneAPI FPGA Development x
FPGA Flow Terminology Intel oneAPI FPGA Development Flow Types of SYCL* FPGA Compilation FPGA Compilation Flags FPGA Workflows in IDEs
Types of SYCL* FPGA Compilation x
Separating Device and Host Code Compilation
Getting Started with the Intel oneAPI DPC++/C++ Compiler for Intel FPGA Development x
Installing the Intel oneAPI FPGA Development Environment FPGA Development for Intel oneAPI Toolkits with Visual Studio* Code
Installing the Intel oneAPI FPGA Development Environment x
Simulation Prerequisites Installing the Questa*-Intel FPGA Edition Software Set Up the Simulation Environment
FPGA Development for Intel oneAPI Toolkits with Visual Studio* Code x
Set the Environment Variables and Launch Visual Studio* Code Create an FPGA Visual Studio* Code Project Enable Code Completion in a Visual Studio* Code Project Configure Running and Debugging in a Visual Studio* Code Project Debugging Your Kernel in Visual Studio* Code with a Native Debugger Generate and View the FPGA Optimization Report Build and Run the FPGA Hardware Image
Defining a Kernel for FPGAs x
Suggested Kernel Coding Styles Single Work-Item Kernels
Single Work-Item Kernels x
Single Work-item Kernel Design Guidelines Single-Cycle Floating-Point Accumulator for Single Work-Item Kernels
Single-Cycle Floating-Point Accumulator for Single Work-Item Kernels x
Strategies for Inferring the Accumulator
Debugging and Verifying Your Design x
Device Selectors for FPGA printf Command Restrictions Emulate and Debug Your Design Evaluate Your Kernel Through Simulation
Emulate and Debug Your Design x
Emulator Environment Variables Compile and Emulate Your Design Limitations of the Emulator Troubleshooting Discrepancies in Hardware and Emulator Results Emulator Known Issues
Evaluate Your Kernel Through Simulation x
Debug During Verification Compile a Kernel for Simulation Simulate Your Kernel Viewing Simulation Waveforms Troubleshooting Simulator Issues
Analyzing Your Design x
Review the FPGA Optimization Report Quartus (Static) Summary Intel® FPGA Dynamic Profiler for DPC++
Review the FPGA Optimization Report x
Loop Analysis Bottlenecks Viewer Area Estimates System Viewer Kernel Memory Viewer Kernel Memory List Kernel Memory Viewer Code View Details Schedule Viewer Access FPGA Optimization Reports in JSON Format
Quartus (Static) Summary x
Timing Failures
Intel® FPGA Dynamic Profiler for DPC++ x
Measure Kernel Performance Instrument the Kernel Pipeline with Performance Counters (-Xsprofile) Obtain Profiling Data During Run Time Reduce Area Resource Use While Profiling Profiler Analyses of Example SYCL* Design Scenarios Limitations
Obtain Profiling Data During Run Time x
Invoke the Profiler Runtime Wrapper to Obtain Profiling Data Use Intel® VTune™ Profiler
Use Intel® VTune™ Profiler x
Interpret Performance Counter Data
Optimizing Your Host Application x
Throughput Resource Use System-level Profiling Using the Intercept Layer for OpenCL™ Applications Multithreaded Host Application Utilizing Hardware Kernel Invocation Queue Double Buffering Host Utilizing Kernel Invocation Queue N-Way Buffering to Overlap Kernel Execution Prepinning Memory Simple Host-Device Streaming Buffered Host-Device Streaming
System-level Profiling Using the Intercept Layer for OpenCL™ Applications x
Set Up the Intercept Layer for OpenCL™ Applications
Double Buffering Host Utilizing Kernel Invocation Queue x
Analyzing Buffering Using the Intercept Layer for OpenCL™ Applications
Integrating Your RTL IP Core Into a System x
Synthesize Your RTL IP Core with Quartus Prime Software Encrypting RTL IP Cores Add an RTL IP Core into a Platform Designer System Add an RTL IP Core into a Quartus Prime Project
Encrypting RTL IP Cores x
Encrypting RTL IP Cores Without Licensing Encrypting RTL IP Core With Licensing
RTL IP Core Kernel Interfaces x
Kernel Argument Interfaces Memory-Mapped (MM) Agent Kernel Invocation Interface Ready/Valid Handshaking Kernel Invocation Interface Memory-Mapped Host Interfaces Structs in RTL IP Core Interfaces IP core Reset Behavior
Memory-Mapped Host Interfaces x
Memory-Mapped Host Interfaces Using Unified Shared Memory Pointers and the annotated_arg Class Memory-Mapped Host Interfaces Using Accessors
Memory-Mapped Host Interfaces Using Unified Shared Memory Pointers and the annotated_arg Class x
Buffer Locations in Memory-Mapped Host Interfaces The annotated_arg Template Class
Loops x
Refactor the Loop-Carried Data Dependency Relax Loop-Carried Dependency Transfer Loop-Carried Dependency to Local Memory Minimize the Memory Dependencies for Loop Pipelining Unroll Loops Fuse Loops to Reduce Overhead and Improve Performance Optimize Loops With Loop Speculation Remove Loop Bottlenecks Improve fMAX/II with Shannonization Optimize Inner Loop Throughput Improve Loop Performance by Caching Data in On-Chip Memory
Pipes x
Host Pipes Pipes Extension
Host Pipes x
Host Pipe Declaration Host Pipe API Host Pipes RTL Interfaces
Pipes Extension x
Key Properties of a Pipe Accessing Pipes The pipe Class and its Use I/O Pipes Characteristics of Pipes Restrictions of Pipes Guidelines for Designing Pipes The atomic_fence Function and Pipes
I/O Pipes x
Emulate Applications with a Pipe That Reads or Writes to an I/O Pipe
Data Types and Arithmetic Operations x
Optimize Floating-point Operation Minimize the Use of Expensive Functions Variable-Precision Data Type Support
Variable-Precision Data Type Support x
Advantages and Limitations of Variable Precision Data Types Declare and Use the AC Data Types
Declare and Use the AC Data Types x
Declare the ac_int Data Type Declare the ac_fixed Data Type Declare the ac_complex Data Type Declare the ap_float Data Type
Declare the ap_float Data Type x
Conversion Rules for the ap_float Data Type Operations with Explicit Precision Controls Comparison Operators Additional ap_float Functions Additional Data Types Provided by the ap_float.hpp Header File Quality of Results and the ap_float Data Type
Parallelism x
Pipelined Kernels NDRange Kernels Asynchronous Parallelism Within Kernels (task_sequence)
Pipelined Kernels x
Stable Arguments
Asynchronous Parallelism Within Kernels (task_sequence) x
Task Functions task_sequence Use Cases
Memories and Memory Operations x
The device_global Extension (Beta) The annotated_ptr Template Class (Beta) Memory Accesses Kernel Variable Accesses
Memory Accesses x
Load-Store Units Global Memory Accesses Optimization Perform Kernel Computations Using Local or Private Memory Local and Private Memory Accesses Optimization Annotating Unified Shared Memory Pointers Zero-Copy Memory Access Additional Recommendations
Load-Store Units x
Load-Store Unit Styles Load-Store Unit Modifiers Load-Store Unit Controls
Global Memory Accesses Optimization x
Global Memory Bandwidth Use Calculation Manual Partition of Global Memory Partitioning Buffers Across Different Memory Types (Heterogeneous Memory) Partitioning Buffers Across Memory Channels of the Same Memory Type Ignoring Dependencies Between Accessor Arguments Contiguous Memory Accesses Static Memory Coalescing
Libraries x
Use SYCL Shared Library With Third-Party Applications Use of RTL Libraries for FPGA Object Manifest File Syntax of an RTL Library Restrictions and Limitations in RTL Support Agilex 7 and Stratix 10 Design-Specific Reset Requirements for Stall-Free and Stallable RTL Libraries Stall-Free RTL
Additional FPGA Acceleration Flow Considerations x
FPGA-CPU Interaction FPGA Boards and Board Support Packages (BSPs) Targeting Multiple Identical FPGA Devices Targeting Multiple Platforms Split Kernel into Multiple FPGA Images (Linux only)
FPGA Boards and Board Support Packages (BSPs) x
The FPGA Board Utility Commands Managing an FPGA Board Advanced Board Management The OpenCL™ Installable Client Driver (ICD)
Advanced Board Management x
Extracting the FPGA Device Image (.aocx) File from a Multiarchitecture Binary File
FPGA Optimization Flags, Attributes, Pragmas, and Extensions x
Optimization Flags Optimization Targets Kernel Variables Kernel Attributes Memory Attributes Loop Directives Floating-Point Pragmas Latency Controls (Beta)
Optimization Flags x
Specify Schedule fMAX Target for Kernels (-Xsclock=<clock target>) Create a 2xclock Interface (-Xsuse-2xclock) Disable Burst-Interleaving of Global Memory (-Xsno-interleaving) Force Ring Interconnect for Global Memory (-Xsglobal-ring) Force a Single Store Ring to Reduce Area (-Xsforce-single-store-ring) Force Fewer Read Data Reorder Units to Reduce Area (-Xsnum-reorder) Disable Hardware Kernel Invocation Queue (-Xsno-hardware-kernel-invocation-queue) Modify the Handshaking Protocol Between Clusters (-Xshyper-optimized-handshaking) Disable Automatic Fusion of Loops (-Xsdisable-auto-loop-fusion) Fuse Adjacent Loops With Unequal Trip Counts (-Xsenable-unequal-tc-fusion) Pipeline Loops in Non-task Kernels (-Xsauto-pipeline) Control Semantics of Floating-Point Operations (-fp-model=<value>) Modify the Rounding Mode of Floating-point Operations (-Xsrounding=<rounding_type>) Global Control of Exit FIFO Latency of Stall-free Clusters (-Xssfc-exit-fifo-type=<value>) Enable the Read-Only Cache for Read-Only Accessors (-Xsread-only-cache-size=<N>) Control Hardware Implementation of the Supported Data Types and Math Operations (-Xsdsp-mode=<option>) Generate Register Map Wrapper (-Xsregister-map-wrapper-type) Allow Wide Memory Initialization (-Xsallow-wide-device-globals)
Optimization Targets x
Minimum Latency Flow Minimum Area Flow Balanced Throughput-Area Trade-Offs Flow
Kernel Attributes x
Specify Schedule fMAX Target for Kernels (scheduler_target_fmax_mhz) Specify a Workgroup Size (max_work_group_size/reqd_work_group_size) Specify Number of SIMD Work Items (num_simd_work_items) Omit Hardware that Generates and Dispatches Kernel IDs (max_global_work_dim) Omit Hardware that Supports Global Work Offsets (no_global_work_offset) Reduce Kernel Area and Latency (use_stall_enable_clusters)
Loop Directives x
disable_loop_pipelining Attribute initiation_interval Attribute ivdep Attribute loop_coalesce Attribute max_concurrency Attribute max_interleaving Attribute speculated_iterations Attribute unroll Pragma Loop Fuse Functions and nofusion Attribute max_reinvocation_delay Attribute (Beta)
Quick Reference x
Algorithmic C Data Types Floating Point Pragmas FPGA Accessor Properties FPGA Extensions FPGA Kernel Attributes FPGA Local Memory Function Latency Control Properties (Beta) FPGA LSU Controls FPGA Loop Directives FPGA Memory Attributes FPGA Optimization Flags Pipe API
Intel oneAPI DPC++/C++ Compiler Handbook for FPGAs Overview
Introduction To FPGA Design Concepts
Intel oneAPI FPGA Development
Getting Started with the Intel oneAPI DPC++/C++ Compiler for Intel FPGA Development
Defining a Kernel for FPGAs
Debugging and Verifying Your Design
Analyzing Your Design
Optimizing Your Kernel
Optimizing Your Host Application
Integrating Your Kernel into DSP Builder for Intel FPGAs
Integrating Your RTL IP Core Into a System
RTL IP Core Kernel Interfaces
Loops
Pipes
Data Types and Arithmetic Operations
Parallelism
Memories and Memory Operations
Libraries
Additional FPGA Acceleration Flow Considerations
FPGA Optimization Flags, Attributes, Pragmas, and Extensions
Quick Reference
Additional Information
Document Revision History for the Intel oneAPI DPC++/C++ Compiler Handbook for Intel FPGAs
Notices and Disclaimers

Kernel Memory Viewer

Data movement is a bottleneck in many algorithms. The Kernel Memory Viewer shows you how the Intel® oneAPI DPC++/C++ Compiler interprets the data connections and synthesizes memory for your kernel. Use the Kernel Memory Viewer to help identify data movement bottlenecks in your kernel design.

Some patterns in memory accesses can cause undesired arbitration in the load-store units (LSUs), affecting the throughput performance of your kernel. Use the Kernel Memory Viewer to identify unwanted arbitration in the LSUs.

To analyze your SYCL* system, click Views > Kernel Memory Viewer.

The following image illustrates the layout of the Kernel Memory Viewer:

Kernel Memory Viewer Layout

The Kernel Memory Viewer has the following panes:

Kernel Memory Viewer Panes

Pane

Description

Kernel Memory List

Lists all memories present in your design. When you select a memory name, you can view its graphical representation in the Kernel Memory Viewer pane.

Kernel Memory Viewer

Shows a graphical representation of the memory system or memory bank selected in the Kernel Memory List pane.

Code View

Shows the source code file for which the reports are generated.

Details

Shows the details of the memory system or memory bank selected in the Kernel Memory List pane.

Kernel Memory List

The Kernel Memory List pane displays a kernel hierarchy with memories synthesized (RAMs, ROMs, and registers) and optimized away in that kernel.

Features and Details of the Kernel Memory List Pane

The following table describes each numbered feature highlighted in the above image:

Kernel Memory List Pane Icons and Labels

No.

Icon or Label

Name

Description

1



Kernel name

You can expand or collapse the list of memories in your kernel. Memories that do not belong to any kernel are displayed under (Other).

2



RAM

A RAM is a memory that has at least one write to it. The name of the RAM memory is the same as its name in your design.

When you select a memory name, you can view a logical representation of the RAM in the Kernel Memory Viewer pane. By default, only the first bank of the memory system is displayed.

To select banks that you want the Kernel Memory Viewer pane to display:

  • Expand the memory name.
  • Clear the memory name check box to collapse all memory banks in the view.
  • Select the memory name check box to show all memory banks in the view.

3



ROM

A ROM is a read-only memory. The name of the ROM memory is same as its name in your design.

When you select a memory name, you can view a logical representation of the ROM in the Kernel Memory Viewer pane. By default, only the first bank of the memory system is displayed.

To select banks that you want the Kernel Memory Viewer pane to display:

  • Expand the memory name.
  • Clear the memory name check box to collapse all memory banks in the view.
  • Select the memory name check box to show all memory banks in the view.

4

Bank #num

Bank

A memory bank is always associated with a RAM or a ROM. Each bank is named Bank #num, where #num is the memory bank's ID starting from 0.

  • Click on the bank name to display the bank view in the Kernel Memory Viewer pane, which displays a graphical representation of the bank with all its replicates and private copies. This view can help you focus on specific memory banks of a complex memory design.
  • Clear the memory bank name check-box to collapse the bank in the logical representation of the memory.
  • Select the memory bank name check-box to display the bank in the logical representation of the memory.

5



Register

A register is a kernel variable carried through the pipeline in registers (rather than being stored in a RAM or ROM). The name of the register is the same as its name in your design.

A register variable is implemented either exclusively in FFs or in a combination of FFs and RAM-based FIFOs.

6

Text label

Optimized Away

A kernel variable can be optimized away because it is unused in your design, or compiler optimizations have transformed all uses of the variable such that it is unnecessary. The name of the optimized away variable is the same as its name in your design.

7



Filter

Use the Kernel Memory List filter to selectively view the list of RAMs, ROMs, registers, and optimized away variables in your design.

When you clear the checkbox associated with an item in the filter, you hide all occurrences of that kind of item in the Kernel Memory List. Filter your Memory List to help you focus on a specific type of memory in your design.

Kernel Memory Viewer

In the Kernel Memory Viewer pane, you can view connections between loads and stores to specific logical ports on the banks in a memory system. You can also view the number of replicates and private copies created per bank for your memory system. You can see the following types of nodes in the Kernel Memory Viewer pane, depending on the kernel memory system and your selection in the Kernel Memory List pane:

Node Types Observed in the Kernel Memory Viewer Pane

Node Type

Description

Memory node

The memory system for a given variable in your design.

Bank node

A bank in the memory system. A memory system contains at least one bank. A memory bank can connect to one or more port nodes.

Replication node

A replication node shows memory bank replicates created to support multiple accesses to a local memory efficiently. A bank contains at least one replicate. You can view replicate nodes when you view a memory bank by clicking its name in the Kernel Memory List pane.

Private-copy node

A private-copy node shows private copies within a replicate created to allow simultaneous execution of multiple loop iterations. A replicate contains at least one private copy. You can view private-copy nodes when you view a memory bank by clicking its name in the Kernel Memory List pane.

Port node

Each read or write access to local memory is mapped to a port. The logical port for a bank. There are three types of ports:

  • R: A read-only port
  • W: A write-only port
  • RW: A read and write port

LSU node

A store (ST) or load (LD) node connected to the memory through port nodes.

Arbitration node

An arbitration (ARB) node shows that LSUs compete for access to a shared port node, which can lead to stalls.

Port-sharing node

A port-sharing node (SHARE) shows that LSUs have mutually exclusive access to a shared port node, so the load-store units are free from stalls.

Within the graphical representation of a memory in the Kernel Memory Viewer pane, you can perform the following:

  • Hover over any node to view the attributes of that node.
  • Hover over an LSU node to highlight the path from the LSU node to all ports to which the LSU connects.
  • Hover over a port node to highlight the path from the port node to all LSUs that read or write to the port node.
  • Click a node to select it and display the node attributes in the Details pane.

The following images illustrate examples of what you see in the Kernel Memory Viewer:

Logical Representation of a Memory in the Kernel Memory Viewer Pane

Bank View of a Memory Bank in the Kernel Memory Viewer Pane

Code View

The Code View pane displays your source code. When you click on a memory or a bank in the Kernel Memory Viewer pane, the code view pane highlights the line of your code where you declared the memory.

Details

The Details pane shows the attributes of the node selected in the Kernel Memory Viewer pane. For example, when you select a memory in a kernel, the Details pane displays the following information:

  • Width and depths of memory banks
  • Memory layout
  • Address-bit mapping
  • Memory attributes that you specified in your source code

The content of the Details pane persists until you select a different node in the Kernel Memory Viewer pane.

Parent topic: Review the FPGA Optimization Report
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