This readme file for the Fast Fourier Transform (2D) OpenCL Design Example contains information about the design example package. For more examples, please visit the Altera OpenCL Design Examples page.
This benchmark demonstrates an OpenCL implementation of a 2D Fast Fourier Transform (2D FFT) on Altera FPGAs. The benchmark processes a 2D matrix of 1k × 1k complex single-precision floating-point data. The 2D transform is decomposed as a 1D FFT applied to each row followed by a 1D FFT applied to each column.
The device portion of the code applies a 1D transform to each row and transposes the matrix. This computation is enqueued twice from the host code. The second iteration applies a 1D transform to each transposed row, producing the column-wise FFT. The second transposition restores the original matrix layout.
The 1D FFT engine is written as a single work-item kernel. To achieve efficient memory access two additional ND range kernels are used to read / write data from / to global memory. All three kernels run concurrently and exchange data through channels, an Altera specific extension. See device/fft2d.cl for more implementation details.
Requirement | Version | OpenCL Kernel | Host Program | ||||
---|---|---|---|---|---|---|---|
Hardware Compile | Emulation Compile | Hardware | Emulation | ||||
Compile | Run | Compile | Run | ||||
Altera Complete Design Suite (Quartus II) | 16.0 or later | ✓ | ✓ | ||||
Altera SDK for OpenCL | 16.0 or later | ✓ | ✓ | ✓ (either) | ✓ (either) | ✓ (either) | ✓ (either) |
Altera Runtime Environment for OpenCL | 16.0 or later | ||||||
Board Support Package | 16.0-compatible | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
Board Hardware | - | ✓ | |||||
gcc | 4.4.7 or later | ✓ | ✓ | ✓ | ✓ | ||
GNU Make | 3.8.1 or later | ✓ | ✓ |
Path | Description |
---|---|
fft2d/ | |
Makefile | Makefile for host program |
bin/ | Host program, AOCX files |
device/ | OpenCL kernel files |
fft2d.cl | Top-level OpenCL kernel file |
host/ | |
inc/ | Host include files |
src/ | Host source files |
The top-level OpenCL kernel file is device/fft2d.cl.
To compile the OpenCL kernel, run:
where <board> matches the board you want to target. The -o bin/fft2d.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:
To use the emulation flow, the compilation command just needs to be modified slightly:
The kernel has the following preprocessor definitions:
Define | Type | Default | Description |
---|---|---|---|
-DLOGN=<#> | Optional | 10 | log(total number of points) / 2. The same value must be used for host and kernel compilation. |
To compile the host program, run:
The compiled host program will be located at bin/host.
The host program has the following preprocessor definitions:
Define | Type | Default | Description |
---|---|---|---|
-DLOGN=<#> | Optional | 10 | log(total number of points) / 2. The same value must be used for host and kernel compilation. |
On Linux, custom values for preprocessor defines can be specified by setting
the value of
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:
Example output of running this benchmark is shown below:
Launching FFT transform (ordered data layout) Kernel initialization is complete. Processing time = 3.4020ms Throughput = 0.3082 Gpoints / sec (30.8224 Gflops) Signal to noise ratio on output sample: 124.236435 --> PASSED Launching inverse FFT transform (ordered data layout) Kernel initialization is complete. Processing time = 3.3848ms Throughput = 0.3098 Gpoints / sec (30.9787 Gflops) Signal to noise ratio on output sample: 124.227971 --> PASSED Launching FFT transform (alternative data layout) Kernel initialization is complete. Processing time = 2.1122ms Throughput = 0.4964 Gpoints / sec (49.6450 Gflops) Signal to noise ratio on output sample: 124.236876 --> PASSED Launching inverse FFT transform (alternative data layout) Kernel initialization is complete. Processing time = 2.1369ms Throughput = 0.4907 Gpoints / sec (49.0689 Gflops) Signal to noise ratio on output sample: 124.231472 --> PASSEDOutput
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 Altera SDK for OpenCL Programming Guide for more information.
For this example design, the suggested emulation command is:
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):
Example Version | SDK Version | Date | Changes |
---|---|---|---|
1.5 | 16.0 | June 2016 |
|
1.4 | 14.1 | December 2014 |
|
1.3 | 14.0 | July 2014 |
|
1.2 | 14.0 | July 2014 |
|
1.1 | 13.1 | January 2014 |
|
1.0 | 13.1 | December 2013 |
|
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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.
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 Altera support (myAltera).