Try using installable Preferences library

Two variants are redundant

.github/workflows/build.yml

@@ -29,6 +29,13 @@ jobs:
       run: sed -i 's/^#define WIFI_ENABLED 1$/#define WIFI_ENABLED 0/' flix/flix.ino && make
     - name: Check c_cpp_properties.json
       run: tools/check_c_cpp_properties.py
+    - name: Build for Black Pill F411CE (STM32)
+      run: |
+        arduino-cli config set board_manager.additional_urls https://github.com/stm32duino/BoardManagerFiles/raw/main/package_stmicroelectronics_index.json
+        arduino-cli core install STMicroelectronics:stm32
+        arduino-cli board listall STMicroelectronics:stm32
+        arduino-cli lib install "Preferences"
+        make BOARD=STMicroelectronics:stm32:GenF4:pnum=BLACKPILL_F411CE
 
   build_macos:
     runs-on: macos-latest

docs/troubleshooting.md

@@ -32,6 +32,6 @@ Do the following:
   * `mfl` — should rotate front left motor (clockwise).
   * `mrl` — should rotate rear left motor (counter-clockwise).
   * `mrr` — should rotate rear right motor (clockwise).
-* **Calibrate the RC** if you use it. Type `cr` command in Serial Monitor and follow the instructions.
-* **Check the RC data** if you use it. Use `rc` command, `Control` should show correct values between -1 and 1, and between 0 and 1 for the throttle.
+* **Check the remote control**. Using `rc` command, check the control values reflect your sticks movement. All the controls should change between -1 and 1, and throttle between 0 and 1.
+* If using SBUS receiver, **calibrate the RC**. Type `cr` command in Serial Monitor and follow the instructions.
 * **Check the IMU output using QGroundControl**. Connect to the drone using QGroundControl on your computer. Go to the *Analyze* tab, *MAVLINK Inspector*. Plot the data from the `SCALED_IMU` message. The gyroscope and accelerometer data should change according to the drone movement.

flix/cli.ino

@@ -74,9 +74,10 @@ void doCommand(String str, bool echo = false) {
 	// parse command
 	String command, arg0, arg1;
 	splitString(str, command, arg0, arg1);
+	if (command.isEmpty()) return;
 
 	// echo command
-	if (echo && !command.isEmpty()) {
+	if (echo) {
 		print("> %s\n", str.c_str());
 	}
 
@@ -170,8 +171,6 @@ void doCommand(String str, bool echo = false) {
 		attitude = Quaternion();
 	} else if (command == "reboot") {
 		ESP.restart();
-	} else if (command == "") {
-		// do nothing
 	} else {
 		print("Invalid command: %s\n", command.c_str());
 	}

flix/imu.ino

@@ -5,6 +5,7 @@
 
 #include <SPI.h>
 #include <FlixPeriph.h>
+#include "vector.h"
 #include "lpf.h"
 #include "util.h"
 

flix/mavlink.ino

@@ -12,6 +12,7 @@
 #define PERIOD_FAST 0.1
 #define MAVLINK_CONTROL_YAW_DEAD_ZONE 0.1f
 
+bool mavlinkConnected = false;
 String mavlinkPrintBuffer;
 
 extern float controlTime;
@@ -41,12 +42,14 @@ void sendMavlink() {
 			mode, MAV_STATE_STANDBY);
 		sendMessage(&msg);
 
+		if (!mavlinkConnected) return; // send only heartbeat until connected
+
 		mavlink_msg_extended_sys_state_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg,
 			MAV_VTOL_STATE_UNDEFINED, landed ? MAV_LANDED_STATE_ON_GROUND : MAV_LANDED_STATE_IN_AIR);
 		sendMessage(&msg);
 	}
 
-	if (t - lastFast >= PERIOD_FAST) {
+	if (t - lastFast >= PERIOD_FAST && mavlinkConnected) {
 		lastFast = t;
 
 		const float zeroQuat[] = {0, 0, 0, 0};
@@ -80,6 +83,7 @@ void sendMessage(const void *msg) {
 void receiveMavlink() {
 	uint8_t buf[MAVLINK_MAX_PACKET_LEN];
 	int len = receiveWiFi(buf, MAVLINK_MAX_PACKET_LEN);
+	if (len) mavlinkConnected = true;
 
 	// New packet, parse it
 	mavlink_message_t msg;

flix/motors.ino

@@ -25,30 +25,32 @@ const int MOTOR_FRONT_LEFT = 3;
 
 void setupMotors() {
 	print("Setup Motors\n");
-
-	// configure pins
+#ifdef ESP32
 	ledcAttach(MOTOR_0_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
 	ledcAttach(MOTOR_1_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
 	ledcAttach(MOTOR_2_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
 	ledcAttach(MOTOR_3_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
-
+#else
+	analogWriteResolution(PWM_RESOLUTION);
+	analogWriteFrequency(PWM_FREQUENCY);
+#endif
 	sendMotors();
 	print("Motors initialized\n");
 }
 
 int getDutyCycle(float value) {
 	value = constrain(value, 0, 1);
-	float pwm = mapff(value, 0, 1, PWM_MIN, PWM_MAX);
+	float pwm = mapf(value, 0, 1, PWM_MIN, PWM_MAX);
 	if (value == 0) pwm = PWM_STOP;
-	float duty = mapff(pwm, 0, 1000000 / PWM_FREQUENCY, 0, (1 << PWM_RESOLUTION) - 1);
+	float duty = mapf(pwm, 0, 1000000 / PWM_FREQUENCY, 0, (1 << PWM_RESOLUTION) - 1);
 	return round(duty);
 }
 
 void sendMotors() {
-	ledcWrite(MOTOR_0_PIN, getDutyCycle(motors[0]));
-	ledcWrite(MOTOR_1_PIN, getDutyCycle(motors[1]));
-	ledcWrite(MOTOR_2_PIN, getDutyCycle(motors[2]));
-	ledcWrite(MOTOR_3_PIN, getDutyCycle(motors[3]));
+	analogWrite(MOTOR_0_PIN, getDutyCycle(motors[0]));
+	analogWrite(MOTOR_1_PIN, getDutyCycle(motors[1]));
+	analogWrite(MOTOR_2_PIN, getDutyCycle(motors[2]));
+	analogWrite(MOTOR_3_PIN, getDutyCycle(motors[3]));
 }
 
 bool motorsActive() {

flix/parameters.ino

@@ -8,7 +8,6 @@
 extern float channelZero[16];
 extern float channelMax[16];
 extern float rollChannel, pitchChannel, throttleChannel, yawChannel, armedChannel, modeChannel;
-extern float mavlinkControlScale;
 
 Preferences storage;
 

flix/util.h

@@ -6,17 +6,15 @@
 #pragma once
 
 #include <math.h>
+#ifdef ESP32
 #include <soc/soc.h>
 #include <soc/rtc_cntl_reg.h>
+#endif
 
 const float ONE_G = 9.80665;
 extern float t;
 
-float mapf(long x, long in_min, long in_max, float out_min, float out_max) {
-	return (float)(x - in_min) * (out_max - out_min) / (float)(in_max - in_min) + out_min;
-}
-
-float mapff(float x, float in_min, float in_max, float out_min, float out_max) {
+float mapf(float x, float in_min, float in_max, float out_min, float out_max) {
 	return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
 }
 
@@ -41,7 +39,9 @@ float wrapAngle(float angle) {
 
 // Disable reset on low voltage
 void disableBrownOut() {
+#ifdef ESP32
 	REG_CLR_BIT(RTC_CNTL_BROWN_OUT_REG, RTC_CNTL_BROWN_OUT_ENA);
+#endif
 }
 
 // Trim and split string by spaces