Altera^® OpenCL™ Design Example

Fast Fourier Transform (1D)

This benchmark demonstrates an OpenCL implementation of a Fast Fourier Transform (FFT) on Altera FPGAs. The benchmark processes multiple sets of 4k complex single-precision floating-point data. The input data is ordered and the output data is in a bit-reversed order.

For demonstration purposes, this application instantiates a single radix-4 FFT engine capable of processing 8 data points per clock cycle. Subject to available device resources, the user may instantiate additional engines to achieve higher performance. The user may also customize the size of transform.

The FFT engine is implemented as a single work-item kernel which uses a sliding window to represent delay elements. The application reads input data from global memory, feeds the data into the FFT engine and stores the results back to global memory. The performance is capped by the memory bandwidth of the board. See device/fft1d.cl for implementation details.

The top-level OpenCL kernel file is device/fft1d.cl.

To compile the OpenCL kernel, run:

where <board> matches the board you want to target. The -o bin/fft1d.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 compile the host program, run:

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

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 for 2000 iterations
        FFT kernel initialization is complete.
        Processing time = 6.0449ms
        Throughput = 1.3552 Gpoints / sec (81.3113 Gflops)
        Signal to noise ratio on output sample: 128.121214 --> PASSED

Launching inverse FFT transform for 2000 iterations
        Inverse FFT kernel initialization is complete.
        Processing time = 6.0485ms
        Throughput = 1.3544 Gpoints / sec (81.2627 Gflops)
        Signal to noise ratio on output sample: 128.113471 --> PASSED
Output

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