Here is the first cross-MCU code which was used as a test.

A simple blink, which runs on a FreeRTOS task.

#include "mps.h"

void TaskBlink(void *pvParams)
{
  for (;;)
  {
    digitalWrite(LED_BUILTIN, HIGH);
    Serial.println("LED on");
    delay(1000);
    digitalWrite(LED_BUILTIN, LOW);
    Serial.println("LED off");
    delay(1000);
  }
}

void setup() {
  initializeMPS();
  pinMode(LED_BUILTIN, OUTPUT);
  task(TaskBlink);
}

void loop() {}

• Includes the MCU pin setup tool's generated main header. (Which includes all necessary headers as well)
• Defines the task which blinks the led in an infinite loop, and prints out text on Serial.
• Calls the MCU pin setup initialization function which does the initial setup. If our case for example "Serial.begin()" is called inside, if the UART was enabled in the tool.
• Sets the builtin LED pin to output.
• Starts the task, and does nothing in the idle loop.

For Arduino, the Arduino-FreeRTOS library is needed, can be installed in Arduino IDE's Library Manager.

For ESP32, the ESP-IDF needs to be set up, leave the "main.c" totally empty, and put this code into e.g.: "app.cpp". I know it is a bad workaround, will think about it more.

In "make menuconfig", the idle loop for FreeRTOS must be enabled! It uses that for the main loop. It is ugly too, I know.

But with this, the code is nice and readable, and is the same for Arduino Pro Mini and ESP32.

Next step, do a video tutorial about this.