Intel® High Level Synthesis Compiler Pro Edition: Reference Manual

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Date 10/02/2023
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Document Table of Contents
Document Table of Contents x
1. Intel® HLS Compiler Pro Edition Reference Manual 2. Compiler 3. C Language and Library Support 4. Component Interfaces 5. Component Memories (Memory Attributes) 6. Loops in Components 7. Component Concurrency 8. Arbitrary Precision Math Support 9. Component Target Frequency 10. Systems of Tasks 11. Libraries 12. Advanced Hardware Synthesis Controls 13. Intel® High Level Synthesis Compiler Pro Edition Reference Summary A. Advanced Math Source Code Libraries B. Supported Math Functions C. Cyclone® V Restrictions D. Intel® HLS Compiler Pro Edition Reference Manual Archives E. Document Revision History of the Intel® HLS Compiler Pro Edition Reference Manual
1. Intel® HLS Compiler Pro Edition Reference Manual x
1.1. Pending Deprecation of the Intel® HLS Compiler
2. Compiler x
2.1. Intel® HLS Compiler Pro Edition Command Options 2.2. Using Libraries in Your Component 2.3. Compiler Interoperability 2.4. Intel® HLS Compiler Hardware Model
2.3. Compiler Interoperability x
2.3.1. Compiling Your Testbench and Component Separately
3. C Language and Library Support x
3.1. Supported C and C++ Subset for Component Synthesis 3.2. C and C++ Libraries 3.3. Templated and Overloaded Functions 3.4. Intel® HLS Compiler Pro Edition Compiler-Defined Preprocessor Macros
3.3. Templated and Overloaded Functions x
3.3.1. Templated Functions 3.3.2. Overloaded Functions 3.3.3. Function Name Mapping
4. Component Interfaces x
4.1. Component Invocation Interface 4.2. Avalon® Streaming Interfaces 4.3. Pipes 4.4. Avalon® Memory-Mapped Host Interfaces 4.5. Agent Interfaces 4.6. Stable Component Parameters 4.7. Global Variables 4.8. Structs in Component Interfaces 4.9. Reset Behavior
4.1. Component Invocation Interface x
4.1.1. Scalar Parameters 4.1.2. Pointer and Reference Parameters 4.1.3. Interface Definition Example: Component Invocation Interface Control Attributes 4.1.4. Interface Definition Example: Component with Both Scalar and Pointer Arguments
4.3. Pipes x
4.3.1. The pipe Class and Its Use
4.4. Avalon® Memory-Mapped Host Interfaces x
4.4.1. Memory-Mapped Host Testbench Constructor 4.4.2. Implicit and Explicit Examples of Describing a Memory Interface 4.4.3. Avalon® Memory-Mapped Host Interfaces and Load-Store Units
4.4.3. Avalon® Memory-Mapped Host Interfaces and Load-Store Units x
4.4.3.1. Load-Store Unit Types 4.4.3.2. Memory-Access Coalescing and Load-Store Units
4.5. Agent Interfaces x
4.5.1. Control and Status Register (CSR) Agent 4.5.2. Agent Memories
5. Component Memories (Memory Attributes) x
5.1. Static Variables
6. Loops in Components x
6.1. Loop Initiation Interval (ii Pragma) 6.2. Loop-Carried Dependencies (ivdep Pragma) 6.3. Loop Coalescing (loop_coalesce Pragma) 6.4. Loop Unrolling (unroll Pragma) 6.5. Loop Concurrency (max_concurrency Pragma) 6.6. Loop Iteration Speculation (speculated_iterations Pragma) 6.7. Loop Pipelining Control (disable_loop_pipelining Pragma) 6.8. Loop Interleaving Control (max_interleaving Pragma) 6.9. Loop Fusion
6.9. Loop Fusion x
6.9.1. Loop Fusion Control (loop_fuse Pragma) 6.9.2. Loop Fusion Exemption (nofusion pragma)
7. Component Concurrency x
7.1. Serial Equivalence within a Memory Space or I/O 7.2. Concurrency Control (hls_max_concurrency Attribute) 7.3. Component Pipelining Control (hls_disable_component_pipelining Attribute)
8. Arbitrary Precision Math Support x
Advantages of Arbitrary Precision Data Types Limitations of AC Data Types Limitations of the Intel® HLS Compiler Arbitrary Precision Floating Point Data Type 8.1. Declaring ac_int Data Types 8.2. Declaring ac_fixed Data Types 8.3. Declaring ac_complex Data Types 8.4. AC Data Types and Native Compilers 8.5. Declaring hls_float Data Types
8.1. Declaring ac_int Data Types x
8.1.1. Important Usage Information on the ac_int Data Type 8.1.2. Integer Promotion and ac_int Data Types 8.1.3. Debugging Your Use of the ac_int Data Type
8.2. Declaring ac_fixed Data Types x
8.2.1. Arbitrary Precision Fixed-Point Literals in Operations
8.5. Declaring hls_float Data Types x
8.5.1. Operators and Return Types Supported by the hls_float Data Type 8.5.2. Additional Data Types Provided By hls_float.h
9. Component Target Frequency x
9.1. Effects of Specifying Target II and Target fMAX
10. Systems of Tasks x
10.1. Task Functions 10.2. Internal Streams 10.3. System of Tasks Simulation
11. Libraries x
11.1. Static-Object Libraries 11.2. Creating a Static-Object Library 11.3. Creating Objects From HLS Code 11.4. Creating Objects From RTL Code 11.5. Packaging Object Files Into a Library
11.3. Creating Objects From HLS Code x
11.3.1. Creating an Object File From HLS Code 11.3.2. Supported OpenCL* Language Constructs
11.4. Creating Objects From RTL Code x
11.4.1. RTL Modules and the HLS Pipeline 11.4.2. Creating a Static-Object File from an RTL Module
11.4.1. RTL Modules and the HLS Pipeline x
11.4.1.1. Integration of an RTL Module into the HLS Pipeline 11.4.1.2. RTL Module Interfaces 11.4.1.3. RTL Reset and Clock Signals 11.4.1.4. Object Manifest File Syntax 11.4.1.5. Mapping HLS Data Types to RTL Signals 11.4.1.6. HLS Emulation Models for RTL-Based Functions 11.4.1.7. Potential Incompatibility between RTL Modules and Partial Reconfiguration 11.4.1.8. Stall-Free RTL 11.4.1.9. RTL Module Restrictions and Limitations for HLS Libraries
11.4.1.2. RTL Module Interfaces x
11.4.1.2.1. RTL Module Interface Signals
11.4.1.3. RTL Reset and Clock Signals x
11.4.1.3.1. Intel Agilex® 7 and Intel® Stratix® 10 Design-Specific Reset Requirements for Stall-Free and Stallable RTL Modules
11.4.1.4. Object Manifest File Syntax x
11.4.1.4.1. XML Elements for ATTRIBUTES 11.4.1.4.2. XML Elements for INTERFACE 11.4.1.4.3. XML Elements for RESOURCES
11.4.1.4.1. XML Elements for ATTRIBUTES x
11.4.1.4.1.1. Interaction Between ALLOW_MERGINGand HAS_SIDE_EFFECTS Elements
12. Advanced Hardware Synthesis Controls x
12.1. Hardware Implementation Control for Math Functions 12.2. The hls_fpga_reg() Function
12.1. Hardware Implementation Control for Math Functions x
12.1.1. Math Function Hardware Implementation Summary 12.1.2. The --dsp-mode Command Option 12.1.3. The ihc::math_dsp_control Function
13. Intel® High Level Synthesis Compiler Pro Edition Reference Summary x
13.1. Intel® HLS Compiler Pro Edition i++ Command-Line Arguments 13.2. Intel® HLS Compiler Pro Edition Header Files 13.3. Intel® HLS Compiler Pro Edition Compiler-Defined Preprocessor Macros 13.4. Intel® HLS Compiler Pro Edition Keywords 13.5. Intel® HLS Compiler Pro Edition Simulation API (Testbench Only) 13.6. Intel® HLS Compiler Pro Edition Component Memory Attributes 13.7. Intel® HLS Compiler Pro Edition Loop Pragmas 13.8. Intel® HLS Compiler Pro Edition Scope Pragmas 13.9. Intel® HLS Compiler Pro Edition Component Attributes 13.10. Intel® HLS Compiler Pro Edition Component Default Interfaces 13.11. Intel® HLS Compiler Pro Edition Component Invocation Interface Control Attributes 13.12. Intel® HLS Compiler Pro Edition Component Macros 13.13. Intel® HLS Compiler Pro Edition Systems of Tasks API 13.14. Intel® HLS Compiler Pro Edition Pipes API 13.15. Intel® HLS Compiler Pro Edition Streaming Input Interfaces 13.16. Intel® HLS Compiler Pro Edition Streaming Output Interfaces 13.17. Intel® HLS Compiler Pro Edition Memory-Mapped Interfaces 13.18. Intel® HLS Compiler Pro Edition Load-Store Unit Control 13.19. Intel® HLS Compiler Pro Edition Arbitrary Precision Data Types
13.13. Intel® HLS Compiler Pro Edition Systems of Tasks API x
13.13.1. ihc::stream Class
A. Advanced Math Source Code Libraries x
A.1. Random Number Generator Library A.2. Matrix Multiplication Library A.3. Cholesky Decomposition Library
B. Supported Math Functions x
B.1. Math Functions Provided by the math.h Header File B.2. Math Functions Provided by the extendedmath.h Header File B.3. Math Functions Provided by the ac_fixed_math.h Header File B.4. Math Functions Provided by the hls_float.h Header File B.5. Math Functions Provided by the hls_float_math.h Header File B.6. Default Rounding Schemes and Subnormal Number Support
1. Intel® HLS Compiler Pro Edition Reference Manual
2. Compiler
3. C Language and Library Support
4. Component Interfaces
5. Component Memories (Memory Attributes)
6. Loops in Components
7. Component Concurrency
8. Arbitrary Precision Math Support
9. Component Target Frequency
10. Systems of Tasks
11. Libraries
12. Advanced Hardware Synthesis Controls
13. Intel® High Level Synthesis Compiler Pro Edition Reference Summary
A. Advanced Math Source Code Libraries
B. Supported Math Functions
C. Cyclone® V Restrictions
D. Intel® HLS Compiler Pro Edition Reference Manual Archives
E. Document Revision History of the Intel® HLS Compiler Pro Edition Reference Manual

8. Arbitrary Precision Math Support

The Intel® HLS Compiler Pro Edition supports a range of FPGA-optimized arbitrary-precision data types that are defined in header files that you can include in your designs.

Some of these header files are based on the Algorithmic C (AC) data types that Mentor Graphics* provides under the Apache license. For more information about the Algorithmic C data types, refer to Mentor Graphics Algorithmic C (AC) Datatypes, which is available as a part of your Intel® HLS Compiler installation: <quartus_installdir>/hls/include/ref/ac_datatypes_ref.pdf.

The Intel® HLS Compiler also supports arbitrary-precision IEEE 754 compliant floating point data types that is not based on the AC data types.

The Intel® HLS Compiler supports the following arbitrary precision data types:
Table 18.  Arbitrary Precision Data Types Supported by the Intel® HLS Compiler Pro Edition
Data Type Intel Header File Description
ac_int HLS/ac_int.h Arbitrary-width integer support
To learn more, review the following tutorials:
  • <quartus_installdir>/hls/examples/tutorials/ac_datatypes/ac_int_basic_ops
  • <quartus_installdir>/hls/examples/tutorials/ac_datatypes/ac_int_overflow
  • <quartus_installdir>/hls/examples/tutorials/best_practices/struct_interfaces
ac_fixed HLS/ac_fixed.h Arbitrary-precision fixed-point number support

To learn more, review the tutorial: <quartus_installdir>/hls/examples/tutorials/ac_datatypes/ac_fixed_constructor

HLS/ac_fixed_math.h Support for some nonstandard math functions for arbitrary-precision fixed-point data types

To learn more, review the tutorial: <quartus_installdir>/hls/examples/tutorials/ac_datatypes/ac_fixed_math_library

ac_complex HLS/ac_complex.h Complex number support
hls_float HLS/hls_float.h Arbitrary-precision floating-point number support
HLS/hls_float_math.h Support for commonly used exponential, logarithmic, power, and trigonometric functions.
To learn more, review the following tutorials:
  • <quartus_installdir>/hls/examples/tutorials/hls_float/1_reduced_doubl
  • <quartus_installdir>/hls/examples/tutorials/hls_float/2_explicit_arithmetic
  • <quartus_installdir>/hls/examples/tutorials/hls_float/3_conversions
The Intel® HLS Compiler also supports some nonstandard math functions for the following data types when you include an additional header file:
  • ac_fixed data type

    Include the HLS/ac_fixed_math.h header file

  • hls_float data type

    Include the HLS/hls_float_math.h header file

Advantages of Arbitrary Precision Data Types

The arbitrary precision data types have the following advantages over using standard C/C++ data types in your components:

  • You can achieve narrower data paths and processing elements for various operations in the circuit.
  • The data types ensure that all operations are carried out in a size guaranteed not to lose any data. However, you can still lose data if you store data into a location where the data type is too narrow.

Limitations of AC Data Types

The AC data types have the following limitations:

  • Multipliers are limited to generating 512-bit results.
  • Dividers for ac_int data types are limited to a maximum of 128 bit unsigned or 127 bit signed.
  • Dividers for ac_fixed data types are limited to a maximum of 64 bits (unsigned or signed).
  • The FPGA-optimized header files provided by the Intel® HLS Compiler are not compatible with GCC or MSVC. When you use the Intel® HLS Compiler header files, you cannot use GCC or MSVC to compile your testbench. Both your component and testbench must be compiled with the Intel® HLS Compiler.

    To compile AC data types with GCC or MSVC, use the reference AC data types headers also provided with he Intel® HLS Compiler. For details, see AC Data Types and Native Compilers.

  • The bit_fill_hex utility function for ac_int data types is not supported on Cyclone® V devices.

Limitations of the Intel® HLS Compiler Arbitrary Precision Floating Point Data Type

The hls_float data type has the following limitations:
  • When you use the ihc_pown function, the exponent must be a signed type. If the exponent is an unsigned type, redefine the exponent to have a signed type and increase the bit width if needed.

    If you use an unsigned type as the exponent, the results from the ihc_pown function are incorrect.

    For example, the following code snippet generates incorrect results: 
    // Sample Code: 
hls_float<8, 7> a = 2; 
ac_int<4, false> b = 12;
… = ihc_pown(a , b); // !!! Produces incorrect result
    The following code snippet generates correct results: 
    // Workaround: 
hls_float<8, 7> a = 2;
ac_int<5, true> b = 12; // Use a signed type for the exponent.
                        // The bit width is increased from 
                        //4 bits to 5 bits
… = ihc_pown(a , b); // Produces correct result
  • Casting an hls_float datatype to an unsigned integer generates signed integer cast. Ensure that the hls_float value is cast into a signed integer that is large enough to contain the hls_float value being casted (for example, by using an ac_int datatype).
  • Floating point optimization into constants performed for float and double data types is not done for the hls_float data type.
  • The hls_float header files provided by the Intel® HLS Compiler are not compatible with GCC or Microsoft Visual Studio. When you use the Intel® HLS Compiler header files, you cannot use GCC or Microsoft Visual Studio to compile your testbench. Both your component and testbench must be compiled with the Intel® HLS Compiler. For details, refer to Compiler Interoperability.
  • The high-level design reports do not show bit widths for the hls_float data type.
  • Constant initialization works only with the round-towards-zero (RZERO) rounding mode.

Section Content
Declaring ac_int Data Types
Declaring ac_fixed Data Types
Declaring ac_complex Data Types
AC Data Types and Native Compilers
Declaring hls_float Data Types

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