examples: add Gyro FFT using CMSIS 5 on Cortex-m (#15104)

- this is a work in progress experiment to compute real time FFTs from raw gyro FIFO data on Cortex-m hardware (stm32f4/f7/h7, etc)

src/examples/fake_gyro/FakeGyro.cpp

@@ -0,0 +1,132 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2020 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+#include "FakeGyro.hpp"
+
+using namespace time_literals;
+
+FakeGyro::FakeGyro() :
+	ModuleParams(nullptr),
+	ScheduledWorkItem(MODULE_NAME, px4::wq_configurations::hp_default)
+{
+}
+
+bool FakeGyro::init()
+{
+	ScheduleOnInterval(SENSOR_RATE, SENSOR_RATE);
+	return true;
+}
+
+void FakeGyro::Run()
+{
+	if (should_exit()) {
+		ScheduleClear();
+		exit_and_cleanup();
+		return;
+	}
+
+	sensor_gyro_fifo_s sensor_gyro_fifo{};
+	sensor_gyro_fifo.timestamp_sample = hrt_absolute_time();
+	sensor_gyro_fifo.device_id = 1;
+	sensor_gyro_fifo.samples = GYRO_RATE / (1e6f / SENSOR_RATE);
+	sensor_gyro_fifo.dt = 1e6f / GYRO_RATE; // 8 kHz fake gyro
+	sensor_gyro_fifo.scale = math::radians(2000.f) / static_cast<float>(INT16_MAX - 1); // 2000 degrees/second max
+
+	const float dt_s = sensor_gyro_fifo.dt / 1e6f;
+	const float x_freq = 15.f;  // 15 Hz x frequency
+	const float y_freq = 63.5f; // 63.5 Hz y frequency
+	const float z_freq = 99.f;  // 99 Hz z frequency
+
+	for (int n = 0; n < sensor_gyro_fifo.samples; n++) {
+		_time += dt_s;
+		const float k = 2.f * M_PI_F * _time;
+
+		sensor_gyro_fifo.x[n] = (INT16_MAX - 1) * sinf(k * x_freq);
+		sensor_gyro_fifo.y[n] = (INT16_MAX - 1) / 2 * sinf(k * y_freq);
+		sensor_gyro_fifo.z[n] = (INT16_MAX - 1) * cosf(k * z_freq);
+	}
+
+	sensor_gyro_fifo.timestamp = hrt_absolute_time();
+	_sensor_gyro_fifo_pub.publish(sensor_gyro_fifo);
+}
+
+int FakeGyro::task_spawn(int argc, char *argv[])
+{
+	FakeGyro *instance = new FakeGyro();
+
+	if (instance) {
+		_object.store(instance);
+		_task_id = task_id_is_work_queue;
+
+		if (instance->init()) {
+			return PX4_OK;
+		}
+
+	} else {
+		PX4_ERR("alloc failed");
+	}
+
+	delete instance;
+	_object.store(nullptr);
+	_task_id = -1;
+
+	return PX4_ERROR;
+}
+
+int FakeGyro::custom_command(int argc, char *argv[])
+{
+	return print_usage("unknown command");
+}
+
+int FakeGyro::print_usage(const char *reason)
+{
+	if (reason) {
+		PX4_WARN("%s\n", reason);
+	}
+
+	PRINT_MODULE_DESCRIPTION(
+		R"DESCR_STR(
+### Description
+
+)DESCR_STR");
+
+	PRINT_MODULE_USAGE_NAME("fake_gyro", "driver");
+	PRINT_MODULE_USAGE_COMMAND("start");
+	PRINT_MODULE_USAGE_DEFAULT_COMMANDS();
+	return 0;
+}
+
+extern "C" __EXPORT int fake_gyro_main(int argc, char *argv[])
+{
+	return FakeGyro::main(argc, argv);
+}