Intel® High Level Synthesis Compiler Standard Edition: Reference Manual

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ID 683310
Date 12/18/2019
Public
Document Table of Contents
Document Table of Contents x
1. Intel® HLS Compiler Standard 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. Intel® High Level Synthesis Compiler Standard Edition Compiler Reference Summary A. Supported Math Functions B. Intel® HLS Compiler Standard Edition Reference Manual Archives C. Document Revision History of the Intel® HLS Compiler Standard Edition Reference Manual
2. Compiler x
2.1. Intel® HLS Compiler Standard Edition Command Options 2.2. Using Libraries in Your Component 2.3. Compiler Interoperability 2.4. Intel® HLS Compiler Pipeline Approach
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. Intel® HLS Compiler Standard Edition Compiler-Defined Preprocessor Macros
4. Component Interfaces x
4.1. Component Invocation Interface 4.2. Avalon® Streaming Interfaces 4.3. Avalon® Memory-Mapped Master Interfaces 4.4. Slave Interfaces 4.5. Component Invocation Interface Arguments 4.6. Unstable and Stable Component Arguments 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 with Both Scalar and Pointer Arguments
4.3. Avalon® Memory-Mapped Master Interfaces x
4.3.1. Memory-Mapped Master Testbench Constructor 4.3.2. Implicit and Explicit Examples of Describing a Memory Interface
4.4. Slave Interfaces x
4.4.1. Control and Status Register (CSR) Slave 4.4.2. Slave 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 Concurrency (max_concurrency Pragma) 6.5. Loop Unrolling (unroll Pragma)
7. Component Concurrency x
7.1. Serial Equivalence within a Memory Space or I/O 7.2. Concurrency Control (hls_max_concurrency Attribute)
8. Arbitrary Precision Math Support x
8.1. Declaring ac_int Data Types 8.2. Integer Promotion and ac_int Data Types 8.3. Debugging Your Use of the ac_int Data Type 8.4. Declaring ac_fixed Data Types 8.5. AC Data Types and Native Compilers
8.1. Declaring ac_int Data Types x
8.1.1. Important Usage Information on the ac_int Data Type
10. Intel® High Level Synthesis Compiler Standard Edition Compiler Reference Summary x
10.1. Intel® HLS Compiler Standard Edition i++ Command-Line Arguments 10.2. Intel® HLS Compiler Standard Edition Header Files 10.3. Intel® HLS Compiler Standard Edition Compiler-Defined Preprocessor Macros 10.4. Intel® HLS Compiler Standard Edition Keywords 10.5. Intel® HLS Compiler Standard Edition Simulation API (Testbench Only) 10.6. Intel® HLS Compiler Standard Edition Component Memory Attributes 10.7. Intel® HLS Compiler Standard Edition Loop Pragmas 10.8. Intel® HLS Compiler Standard Edition Component Attributes 10.9. Intel® HLS Compiler Standard Edition Component Default Interfaces 10.10. Intel® HLS Compiler Standard Edition Component Invocation Interface Arguments 10.11. Intel® HLS Compiler Standard Edition Component Macros 10.12. Intel® HLS Compiler Standard Edition Streaming Input Interfaces 10.13. Intel® HLS Compiler Standard Edition Streaming Output Interfaces 10.14. Intel® HLS Compiler Standard Edition Memory-Mapped Interfaces 10.15. Intel® HLS Compiler Standard Edition Arbitrary Precision Data Types
A. Supported Math Functions x
A.1. Math Functions Provided by the math.h Header File A.2. Math Functions Provided by the extendedmath.h Header File A.3. Math Functions Provided by the ac_fixed_math.h Header File
1. Intel® HLS Compiler Standard 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. Intel® High Level Synthesis Compiler Standard Edition Compiler Reference Summary
A. Supported Math Functions
B. Intel® HLS Compiler Standard Edition Reference Manual Archives
C. Document Revision History of the Intel® HLS Compiler Standard Edition Reference Manual

3.2. C and C++ Libraries

The Intel® High Level Synthesis (HLS) Compiler provides a number of header files to provide FPGA implementations of certain C and C++ functions.
Intel® HLS Compiler Standard Edition Header Files Summary
HLS Header File Description
HLS/hls.h Required for component identification and component parameter interfaces.
HLS/math.h Includes FPGA-specific definitions for the math functions from the math.h for your operating system.
HLS/extendedmath.h Includes additional FPGA-specific definitions of math functions not in math.h.
HLS/ac_int.h Provides FPGA-optimized arbitrary width integer support.
HLS/ac_fixed.h

Provides FPGA-optimized arbitrary precision fixed point support.

HLS/ac_fixed_math.h

Provides FPGA-optimized arbitrary precision fixed point math functions.

HLS/stdio.h Provides printf support for components so that printf statements work in x86 emulations, but are disabled in component when compiling to an FPGA architecture.
"HLS/iostream" (Linux only) Provides cout and cerr support for components so that cout and cerr statements work in x86 emulations, but are disabled in component when compiling to an FPGA architecture.

math.h

To access functions in math.h from a component to be synthesized, include the "HLS/math.h" file in your source code. The header ensures that the components call the hardware versions of the math functions.

For more information about supported math.h functions, see Supported Math Functions.

stdio.h

Synthesized component functions generally do not support C and C++ standard library functions such as FILE pointers.

A component can call printf by including the header file HLS/stdio.h. This header changes the behavior of printf depending on the compilation target:

  • For compilation that targets the x86-64 architecture (that is, -march=x86-64 ), the printf call behaves as normal.
  • For compilation that targets the FPGA architecture (that is, ‑march="<FPGA_family_or_part_number>"), the compiler removes the printf call.

If you use printf in a component function without first including the #include "HLS/stdio.h" line in your code, you get an error message similar to the following error when you compile hardware to the FPGA architecture: 

$ i++ -march="<FPGA_family_or_part_number>" --component dut test.cpp
Error: HLS gen_qsys FAILED.
See ./a.prj/dut.log for details.

You can use C and C++ standard library functions such as fopen and printf as normal in all testbench functions.

iostream

Synthesized component functions do not support C++ standard library functions such as C++ stream objects (for example, cout).

A component can call cout or cerr by including the header file "HLS/iostream". This header changes the behavior of cout and cerr depending on the compilation target:

  • For compilation that targets the x86-64 architecture (that is, -march=x86-64), the cout or cerr call behaves as normal.
  • For compilation that targets the FPGA architecture (that is, -march="<FPGA_family_or_part_number>"), the compiler removes the cout or cerr call.

If you attempt to use cout or cerr in a component function without first including the #include "HLS/iostream" line in your code, you will see an error message similar to the following error when you compile hardware to the FPGA architecture: 

$ i++ -march="<FPGA_family_or_part_number>" run.cpp 
run.cpp:5: Compiler Error: Cannot synthesize std::cout used inside of a component.
HLS Main Optimizer FAILED.
Important: When you include the header file "HLS/iostream", only writes to cout and cerr are affected. If you use any of the other standard input/output stream objects, you get a compile-time error. Avoid using the "HLS/iostream" header file if you have large sections of testbench code that use standard input/output stream objects.
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