add some code

managed_components/espressif__esp-dsp/examples/fft4real/CMakeLists.txt

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+# The following lines of boilerplate have to be in your project's
+# CMakeLists in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.5)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(fft4real)

managed_components/espressif__esp-dsp/examples/fft4real/README.md

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+# FFT 4 Real Input Example 
+
+(See the README.md file in the upper level 'examples' directory for more information about examples.)
+
+This example demonstrates how to use FFT functionality from esp-dsp library. Example does the following steps:
+
+1. Initialize the library
+2. Initialize input signals with 1024 samples: one 0 dB, second with -20 dB
+3. Calculate FFT Radix-2 for 1024 complex samples
+4. Calculate FFT Radix-4 for 1024 complex samples
+5. Apply bit reverse operation for output complex vectors
+6. Show results on the plots
+7. Show execution time of FFTs
+
+## How to use example
+
+### Hardware required
+
+This example does not require any special hardware, and can be run on any common development board.
+
+### Configure the project
+
+Under Component Config ---> DSP Library ---> DSP Optimization, it's possible to choose either the optimized or ANSI implementation, to compare them.
+
+### Build and flash
+
+Build the project and flash it to the board, then run monitor tool to view serial output (replace PORT with serial port name):
+
+```
+idf.py -p PORT flash monitor
+```
+
+(To exit the serial monitor, type ``Ctrl-]``.)
+
+See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
+
+## Example output
+
+Here is an typical example console output. 
+
+```
+I (344) main: Start Example.
+W (424) main: Signal x1
+I (424) view: Data min[673] = -103.113297, Data max[328] = 20.490950
+ ________________________________________________________________
+0                                                                |
+1                    |                                           |
+2                    |                                           |
+3                    |                                           |
+4                    |                                           |
+5                    |                                           |
+6                    |                                           |
+7                   | |                                          |
+8                   | |                                          |
+9|||||||||||||||||||   |||||||||||||||||||||||||||||||||||||||||||
+ 0123456789012345678901234567890123456789012345678901234567890123
+I (494) view: Plot: Length=1024, min=-60.000000, max=40.000000
+W (504) main: Signal x2
+I (504) view: Data min[582] = -103.113297, Data max[328] = 20.490950
+ ________________________________________________________________
+0                                                                |
+1                    |                                           |
+2                    |                                           |
+3                    |                                           |
+4                    |                                           |
+5                    |                                           |
+6                    |                                           |
+7                   | |                                          |
+8                   | |                                          |
+9|||||||||||||||||||   |||||||||||||||||||||||||||||||||||||||||||
+ 0123456789012345678901234567890123456789012345678901234567890123
+I (584) view: Plot: Length=1024, min=-60.000000, max=40.000000
+W (593) main: Difference between signals x1 and x2 on one plot
+I (594) view: Data min[0] = 0.000000, Data max[392] = 0.313019
+ ________________________________________________________________
+0                                                                |
+1                                                                |
+2                                                                |
+3                                                                |
+4                                                                |
+5                                                                |
+6                                                                |
+7                                                                |
+8----------------------------------------------------------------|
+9                                                                |
+ 0123456789012345678901234567890123456789012345678901234567890123
+I (674) view: Plot: Length=1024, min=0.000000, max=40.000000
+I (674) main: FFT Radix 2 for 1024 complex points take 168652 cycles
+I (684) main: FFT Radix 4 for 1024 complex points take 104665 cycles
+I (694) main: End Example.
+```

managed_components/espressif__esp-dsp/examples/fft4real/main/CMakeLists.txt

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+idf_component_register(SRCS "dsps_fft4real_main.c")

managed_components/espressif__esp-dsp/examples/fft4real/main/dsps_fft4real_main.c

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+// Copyright 2018-2019 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+#include "esp_system.h"
+#include "driver/spi_master.h"
+#include "soc/gpio_struct.h"
+#include "driver/gpio.h"
+#include "driver/uart.h"
+#include "soc/uart_struct.h"
+#include <math.h>
+
+#include "esp_dsp.h"
+
+static const char *TAG = "main";
+
+// This example shows how to use FFT from esp-dsp library
+
+#define N_SAMPLES 2048 // Amount of real input samples
+int N = N_SAMPLES;
+// Input test array
+__attribute__((aligned(16)))
+float x1[N_SAMPLES];
+__attribute__((aligned(16)))
+float x2[N_SAMPLES];
+// Window coefficients
+__attribute__((aligned(16)))
+float wind[N_SAMPLES];
+// Pointers to result arrays
+float *y1_cf = &x1[0];
+float *y2_cf = &x2[0];
+
+// diff of y1 and y2
+__attribute__((aligned(16)))
+float diff_y[N_SAMPLES / 2];
+
+void app_main()
+{
+    esp_err_t ret;
+    ESP_LOGI(TAG, "Start Example.");
+    ret = dsps_fft2r_init_fc32(NULL, N >> 1);
+    if (ret  != ESP_OK) {
+        ESP_LOGE(TAG, "Not possible to initialize FFT2R. Error = %i", ret);
+        return;
+    }
+
+    ret = dsps_fft4r_init_fc32(NULL, N >> 1);
+    if (ret  != ESP_OK) {
+        ESP_LOGE(TAG, "Not possible to initialize FFT4R. Error = %i", ret);
+        return;
+    }
+
+    // Generate hann window
+    dsps_wind_hann_f32(wind, N);
+    // Generate input signal for x1 A=1 , F=0.1
+    dsps_tone_gen_f32(x1, N, 1.0, 0.16,  0);
+
+    // Convert two input vectors to one complex vector
+    for (int i = 0 ; i < N ; i++) {
+        x1[i] = x1[i] * wind[i];
+        x2[i] = x1[i];
+    }
+    // FFT Radix-2
+    unsigned int start_r2 = dsp_get_cpu_cycle_count();
+    dsps_fft2r_fc32(x1, N >> 1);
+    // Bit reverse
+    dsps_bit_rev2r_fc32(x1, N >> 1);
+    // Convert one complex vector with length N/2 to one real spectrum vector with length N/2
+    dsps_cplx2real_fc32(x1, N >> 1);
+    unsigned int end_r2 = dsp_get_cpu_cycle_count();
+
+    // FFT Radix-4
+    unsigned int start_r4 = dsp_get_cpu_cycle_count();
+    dsps_fft4r_fc32(x2, N >> 1);
+    // Bit reverse
+    dsps_bit_rev4r_fc32(x2, N >> 1);
+    // Convert one complex vector with length N/2 to one real spectrum vector with length N/2
+    dsps_cplx2real_fc32(x2, N >> 1);
+    unsigned int end_r4 = dsp_get_cpu_cycle_count();
+
+    for (int i = 0 ; i < N / 2 ; i++) {
+        x1[i] = 10 * log10f((x1[i * 2 + 0] * x1[i * 2 + 0] + x1[i * 2 + 1] * x1[i * 2 + 1] + 0.0000001) / N);
+        x2[i] = 10 * log10f((x2[i * 2 + 0] * x2[i * 2 + 0] + x2[i * 2 + 1] * x2[i * 2 + 1] + 0.0000001) / N);
+        // Simple way to show two power spectrums as one plot
+        diff_y[i] = fabs(x1[i] - x2[i]);
+    }
+
+    // Show power spectrum in 64x10 window from -100 to 0 dB from 0..N/4 samples
+    ESP_LOGW(TAG, "Signal x1");
+    dsps_view(x1, N / 2, 64, 10,  -60, 40, '|');
+    ESP_LOGW(TAG, "Signal x2");
+    dsps_view(x2, N / 2, 64, 10,  -60, 40, '|');
+    ESP_LOGW(TAG, "Difference between signals x1 and x2 on one plot");
+    dsps_view(diff_y, N / 2, 64, 10,  0, 40, '-');
+    ESP_LOGI(TAG, "FFT Radix 2 for %i complex points take %i cycles", N / 2, end_r2 - start_r2);
+    ESP_LOGI(TAG, "FFT Radix 4 for %i complex points take %i cycles", N / 2, end_r4 - start_r4);
+
+    ESP_LOGI(TAG, "End Example.");
+}

managed_components/espressif__esp-dsp/examples/fft4real/main/idf_component.yml

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+dependencies:
+  espressif/esp-dsp:
+    override_path: "../../../"
+    version: "*"

managed_components/espressif__esp-dsp/examples/fft4real/main/linker.ld

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+[mapping:dsp]
+archive: libdsp.a
+entries:
+    *  (noflash)
+
+[mapping:esp-dsp]
+archive: libesp-dsp.a
+entries:
+    *  (noflash)

managed_components/espressif__esp-dsp/examples/fft4real/sdkconfig.defaults

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+CONFIG_PARTITION_TABLE_OFFSET=0x9000