Intel® High Level Synthesis Compiler Pro Edition: Reference Manual

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Date 12/13/2021
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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
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
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™ 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

13.9. Intel® HLS Compiler Pro Edition Component Attributes

Table 45.   Intel® HLS Compiler Component Attributes Summary
Attribute Description
hls_component_ii Force the component to which you apply this attribute to have a specified component initiation interval (II).
hls_disable_component_pipelining Prevents the creation of the pipelined component datapath. Multiple invocations of this component now occur sequentially and not simultaneously.
hls_max_concurrency Request more copies of the component memory so that the component can run multiple invocations in parallel.
hls_scheduler_target_fmax_mhz Specify the target clock frequency of your component.
hls_use_stall_enable_clusters Group related operations into stall-enabled clusters to try to improve latency and area usage while possibly sacrificing throughput, when compared to the default stall-free clustering implementation.

hls_component_ii Component Attribute

Syntax
hls_component_ii(<N>)
Description
Forces the component to which you apply this attribute to have a component initiation interval (II) of <N>, where <N> is a positive integer value.

This can have an adverse effect on the fMAX of your component because using this attribute to get a lower II combines pipeline stages together and creates logic with a long propagation delay.

Using this attribute with a larger II inserts more pipeline stages and can give you a better component fMAX value.

hls_disable_component_pipelining Component Attribute

Syntax
hls_disable_component_pipelining
Description
Tells the compiler to not create a pipelined datapath for the component. An unpipelined component datapath can save FPGA area utilization in some cases.

Use this attribute when a pipelined datapath does not improve your component throughput or when the component is not invoked repeatedly.

Example 
#include "HLS/hls.h"

hls_disable_component_pipelining
component void baz ( /* arguments */ ){
  // component code
}

hls_max_concurrency Component Attribute

Syntax
hls_max_concurrency(<N>)
Description
In some cases, the concurrency of a component is limited to 1. This limit occurs when the generated hardware cannot be shared across component invocations. For example, when using component memories for a non-static variable.

You can use this attribute to request more copies of the component memory so that the component can run multiple invocations in parallel.

This attribute can accept any non-negative whole number, including 0.
Value greater than 0
A value greater than 0 indicates how many copies of the component memory to instantiate as well as how many component invocations can be in flight at once.
Value equal to 0
Setting hls_max_concurrency to a value of 0 is useful in cases when there is no component memory but the component still has a poor dynamic loop initiation interval (II) even if you believe your component II should be 1. You can review the II for loops in your component in the high level design report.

To learn more, review the design example: <quartus_installdir>/hls/examples/inter_decim_filter.

Example 
hls_max_concurrency(2)
component void foo(ihc::stream_in<int> &data_in,
      ihc::stream_out<int> &data_out) {
 int arr[N];
 for (int i = 0; i < N; i++) {
   arr[i] = data_in.read();
 }
 // Operate on the data and modify in place
 for (int i = 0; i < N; i++) {
   data_out.write(arr[i]);
 }
}

hls_scheduler_target_fmax_mhz Component Attribute

Syntax
hls_scheduler_target_fmax_mhz(<N>)
Description
Apply the hls_scheduler_target_fmax_mhz component attribute to have the compiler target a specific fMAX value. Specify the target fMAX value in MHz.

The component is not guaranteed to close timing at the specified frequency, and any tasks in a system of tasks use the same clock regardless of having different scheduling targets.

hls_use_stall_enable_clusters Component Attribute

Syntax
hls_use_stall_enable_clusters
Description
Apply the hls_use_stall_enable component attribute to reduce the area of your component while possibly decreasing your component fMAX and throughput.

The Intel® HLS Compiler typically groups related operations into clusters. In many cases, the clusters are stall-free clusters. A stall-free cluster executes the operations without any stalls and contains a FIFO at the end of the cluster that holds the results if the cluster is stalled. This FIFO adds area and latency to the component, but might allow a higher fMAX and increased throughput.

If you prefer lower FPGA area usage and lower latency over higher throughput, use the hls_use_stall_enable component attribute to bias the compiler to produce stall-enabled clusters. Stall-enabled clusters lack the FIFO, which reduces area and latency, but pass stall signals to the contained operations.

Passing stall signals might reduce fMAX.

Not all operations support stall, and these operations cannot be contained in a stall-enabled cluster. The compiler generates a warning if some operations cannot be placed into a stall-enabled cluster.

The compiler automatically uses stall-enabled clusters for HLS components if it can determine that stall-enable is always beneficial. This attribute requests the compiler to form stall-enabled clusters if possible.

Intel Agilex and Stratix 10 Restriction: This attribute does not apply to designs that target Intel® Agilex™ or Intel® Stratix® 10 devices unless you specify the --hyper-optimized-handshaking=off option of the Intel® HLS Compiler i++ command.

To learn more, review the following tutorial: <quartus_installdir>/hls/examples/tutorials/best_practices/stall_enable

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