Intel FPGA® OpenCL™ Design Example
Sobel Filter

This readme file for the Sobel Filter OpenCL Design Example contains information about the design example package. For more examples, please visit the Intel FPGA OpenCL Design Examples page.

Description

This example is a simple Sobel filter. The single work-item OpenCL kernel detects edges in an input RGB (8 bits per components) image and outputs a monochrome image as the result. The kernel demonstrates how to use a sliding-window line buffer to efficiently compute the convolution of a pixel's luma value. The result of the convolution is compared against an input threshold value that can be controlled by the user. The resolution of the filter is fixed through defines so that the line buffer can be implemented efficiently in hardware.

Software & Hardware Requirements

Requirement Version OpenCL KernelHost Program
Hardware
Compile
Emulation
Compile
HardwareEmulation
CompileRunCompileRun
Quartus Prime Design Software (Quartus II)16.1 or later
Intel(R) FPGA SDK for OpenCL(TM)16.1 or later
(either)
(either)
(either)
(either)
Intel(R) FPGA Runtime Environment for OpenCL(TM)16.1 or later
Board Support Package16.1-compatible
Board Hardware-
gcc4.4.7 or later
GNU Make3.8.1 or later
SDL (Simple DirectMedia Layer) library(1)2.0.3

Notes

  1. The SDL (Simple DirectMedia Layer) library is included as part of this example design package.

Package Contents

Path Description
sobel_filter/
Makefile Makefile for host program
bin/ Host data files, Host program, AOCX files
device/ OpenCL kernel files
sobel.cl Top-level OpenCL kernel file
host/
inc/ Host include files
src/ Host source files

Compiling the OpenCL Kernel

The top-level OpenCL kernel file is device/sobel.cl.

To compile the OpenCL kernel, run:

aoc device/sobel.cl -o bin/sobel.aocx --board <board>

where <board> matches the board you want to target. The -o bin/sobel.aocx argument is used to place the compiled binary in the location that the host program expects.

If you are unsure of the boards available, use the following command to list available boards:

aoc --list-boards

Compiling for Emulator

To use the emulation flow, the compilation command just needs to be modified slightly:

aoc -march=emulator device/sobel.cl -o bin/sobel.aocx --board <board>

Compiling the Host Program

To compile the host program, run:

make

The compiled host program will be located at bin/host.

Host Preprocessor Definitions

The host program has the following preprocessor definitions:

Define Type Default Description
-DUSE_SVM_API=<#> Optional 0 This option when set to 1 will use the OpenCL 2.0 shared virtual memory (SVM) API.

On Linux, custom values for preprocessor defines can be specified by setting the value of CPPFLAGS when invoking the Makefile.

Running the Host Program

Before running the host program, you should have compiled the OpenCL kernel and the host program. Refer to the above sections if you have not completed those steps.

To run the host program on hardware, execute:

LD_LIBRARY_PATH=../extlibs/lib:$LD_LIBRARY_PATH bin/host

Please note that the command includes directives to modify the environment to point to external libraries needed by the host program.

When the program starts, it will display the unfiltered input image. The controls for the program are listed below:

InputAction
SpacebarToggle the filter on or off
Q/q/Esc/EnterQuit the program
=Restore the filter threshold to the default value
+Increase the filter threshold value
-Decrease the filter threshold value

Running with the Emulator

Prior to running the emulation flow, ensure that you have compiled the kernel for emulation. Refer to the above sections if you have not done so. Also, please set up your environment for emulation. Please see the Intel(R) FPGA SDK for OpenCL(TM) Programming Guide for more information.

For this example design, the suggested emulation command is:

CL_CONTEXT_EMULATOR_DEVICE_ALTERA=1 bin/host

Host Parameters

The general command-line for the host program is:

bin/host [-display=<0|1>]

where the one parameter is:

Parameter Type Default Description
-display=<0|1> Optional 1 Controls whether or not the filter output is displayed on the screen (via SDL).

OpenCL Binary Selection

The host program requires a OpenCL binary (AOCX) file to run. For this example design, OpenCL binary files should be placed in the bin directory.

By default, the host program will look for a binary file in the following order (earlier pattern matches take priority):

  1. A file named sobel.aocx.
  2. A file named sobel_<board>_161.aocx, where <board> is the name of the board (as passed as the --board argument to aoc).

Release History

Example Version SDK Version Date Changes
1.5 16.0 November 2016
  • Add SVM API option.
1.4 16.0 June 2016
  • Fixed makefile.
1.3 14.1 December 2014
  • New readme documentation.
  • Change kernel code to initialize the pixel buffer during initial iterations.
1.2 14.0 July 2014
  • Update documentation for 14.0 release.
1.1 13.1 January 2014
  • On Linux, fix possible compilation issues (missing include files).
1.0 13.1 December 2013
  • First release of example.

Legal

Copyright (C) 2013-2016 Altera Corporation, San Jose, California, USA. All rights reserved.
Permission is hereby granted, free of charge, to any person obtaining a copy of this
software and associated documentation files (the "Software"), to deal in the Software
without restriction, including without limitation the rights to use, copy, modify, merge,
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The above copyright notice and this permission notice shall be included in all copies or
substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

This agreement shall be governed in all respects by the laws of the State of California and
by the laws of the United States of America.

Simple DirectMedia Layer library

Simple DirectMedia Layer
Copyright (C) 1997-2014 Sam Lantinga 
  
This software is provided 'as-is', without any express or implied
warranty.  In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:
  
1. The origin of this software must not be misrepresented; you must not
   claim that you wrote the original software. If you use this software
   in a product, an acknowledgment in the product documentation would be
   appreciated but is not required. 
2. Altered source versions must be plainly marked as such, and must not be
   misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.

Trademarks

OpenCL and the OpenCL logo are trademarks of Apple Inc. used by permission by Khronos.

Product is based on a published Khronos Specification, and has passed the Khronos Conformance Testing Process. Current conformance status can be found at www.khronos.org/conformance.

Contacting Intel

Although we have made every effort to ensure that this design example works correctly, there might be problems that we have not encountered. If you have a question or problem that is not answered by the information provided in this readme file or the example's documentation, please contact Intel support (myAltera).