[SOLVED] ESP32/FreeRTOS stop scheduler at beginning of main - then init tasks and restart scheduler

ESP32/FreeRTOS stop scheduler at beginning of main - then init tasks and restart scheduler

I am working on a project using the ESP32 in combination with VS Code and the ESP IDF. Software is basically working. From some other standard ARM 32 bit controllers I have usually a sequence in the main routine to init all the needed peripherals and modules and then start the normal operation in the while(1) loop.

In my init sequence on the ESP32 I have several tasks that are created during the init. Now I notized that those tasks that I add during the init run inbetween of my init sequence. Actually I don't understand why the scheduler is started before calling the main function. Makes no sense on first view. I would suspect the sequence to be:

execute main function
do all the inits that are needed, create the tasks that are needed
start the scheduling (device is then in normal operation)

How would I do that on the esp32 platform?

Kind regards, Markus

Solution

If you read the ESP IDF documentation on Application Startup then it describes three stages where user code can be injected

Port Initialization: very low level initialization to get the CPU and critical peripherals up and running.
You very probably don't want to touch this one.
System Initialization: regular system initialization before FreeRTOS scheduler is started.
It calls a weak function start_cpu0() which you can override and initialize your hardware. Just don't forget to call start_cpu0_default() as first thing, or you'll skip the built-in initialization code.
Main Task: the FreeRTOS scheduler is started, so now the system is running in full multithreading mode. For your convenience it creates one task solely for running app_main() which you are expected to define.This is the intended place for initializing your application and for launching other tasks. I would suggest you try to use it for your init purposes - usually there's nothing wrong with initializing high-level hardware after the scheduler has started (the HAL is built to work in multi-threading mode).

It's all laid out in the (quite well readable) ESP IDF source code, should you wish to see the details. Have a look at how start_cpu0_default() initializes the system in step 2 or how esp_startup_start_app() creates the main task and starts the scheduler in step 3.