14.2. RFFT Example

14.2.1. Overview

This example demonstrates how to use the Real Fast Fourier Transform (RFFT) functionality in HPM SDK. The example generates a composite signal containing three sine waves with different frequencies and amplitudes, performs RFFT transformation, and verifies the results.

14.2.2. Features

  • Generate composite signal with three sine waves

  • Perform real fast Fourier transform

  • Calculate magnitude spectrum of transformed results

  • Verify frequency and amplitude accuracy

  • Test RFFT performance with different points (64-1024 points)

14.2.3. Hardware Requirements

  • HPM6750EVKMINI development board

  • HPM6200EVK development board

  • HPM5300-FPGA development board

  • HPM6800-VALIDATION development board

14.2.4. Software Requirements

  • HPM SDK

  • CMake 3.20.0 or higher

  • Cross-compilation toolchain with DSP extension support

Note

This example requires a DSP-enabled toolchain to utilize hardware DSP instructions for optimal performance:

  • IDE: Segger Embedded Studio (or other IDEs with DSP toolchain support)

  • GCC Toolchain: Andes RISC-V toolchain with DSP extension support or ZCC toolchain with DSP extension support

Standard GCC toolchains without DSP extensions will not be able to compile and run this demo correctly.

14.2.5. Build Instructions

  1. Enter the example directory

  2. Create and enter build directory

  3. Run CMake configuration

  4. Build the project

14.2.6. Run Instructions

  1. Flash the compiled binary to the development board

  2. View output through serial port

  3. Observe RFFT transformation results and performance data

14.2.7. Output Description

The program will output the following information: - CPU frequency - Execution time for different point RFFT - Amplitude of frequency components - Test results (PASS/FAIL)

14.2.8. Programming

The software generates several sine waves with different amplitudes and phases and superimposes them to generate a waveform. The RFFT transform is then used to find the amplitude and frequency characteristics. The sine waves are shown below:

  • Amplitude 11, frequency 8

  • Amplitude 19, frequency 17

  • Amplitude 13, frequency 24

14.2.9. Performance Optimization

  • segger turns on O3 optimization by default

14.2.10. Running the example

When the project runs correctly, the serial terminal outputs the number of samples, the amplitude and frequency characteristics data, and the running time of each unit, and outputs PASS or ERROR NUM at the end.

The serial port output is shown below:

Rfft demo: 64.
total times:5133 tick.
------------------------------------
DC component amplitude:5.000004.
Frequency:8.000000, Amplitude:11.000010.
Frequency:17.000000, Amplitude:18.999992.
Frequency:24.000000, Amplitude:13.000002.
------------------------------------
Rfft demo: 128.
total times:7956 tick.
------------------------------------
DC component amplitude:4.999997.
Frequency:8.000000, Amplitude:11.000002.
Frequency:17.000000, Amplitude:18.999996.
Frequency:24.000000, Amplitude:13.000004.
------------------------------------
Rfft demo: 256.
total times:25266 tick.
------------------------------------
DC component amplitude:4.999996.
Frequency:8.000000, Amplitude:11.000001.
Frequency:17.000000, Amplitude:19.000000.
Frequency:24.000000, Amplitude:13.000004.
------------------------------------
Rfft demo: 512.
total times:37868 tick.
------------------------------------
DC component amplitude:4.999998.
Frequency:8.000000, Amplitude:11.000000.
Frequency:17.000000, Amplitude:19.000000.
Frequency:24.000000, Amplitude:13.000000.
------------------------------------
Rfft demo: 1024.
total times:122305 tick.
------------------------------------
DC component amplitude:4.999998.
Frequency:8.000000, Amplitude:11.000000.
Frequency:17.000000, Amplitude:19.000000.
Frequency:24.000000, Amplitude:13.000000.
------------------------------------
PASS.
----------------END--------------------

14.2.11. Performance Data

The RFFT performance for different sample points is shown in the following table:

Samples

64

128

256

512

1024

DSP rfft

5133

7956

25266

37868

122305