FreeRTOS-Kernel VS ODrive

Here is the port - https://github.com/FreeRTOS/FreeRTOS-Kernel/tree/main/portable/ThirdParty/GCC/Posix

Freertos has support for generic cortex m3: https://github.com/FreeRTOS/FreeRTOS-Kernel/tree/main/portable/GCC/ARM_CM3 It could very well work almost out of the box with your mcu.

the only OS written in iso c i found was RTOS and they have open bug reports due to strict aliasing in simple things like their linked list implementation, which they don't bother to fix because somehow that causes even more problems (?!): https://github.com/FreeRTOS/FreeRTOS-Kernel/pull/54

You likely put the requirements of POSIX just to have an excuse. Fyi, FreeRTOS kernel, the only thing you need, is here: https://github.com/FreeRTOS/FreeRTOS-Kernel/

- https://github.com/FreeRTOS/FreeRTOS-Kernel (architecture, C)

FreeRTOS comes with 5 quite simple reference implementations of the heap memory allocator. You can study how it works.

The main branch is single-core. You're looking for the SMP branch.

On non-POSIX systems, malloc & free are implemented differently. EG FreeRTOS has some very simple malloc (and optionally free) implementations, eg heap_2.c (has malloc & free, but doesn't consolidate blocks), or heap_4.c (more complex, tries to prevent fragmentation by consolidating blocks, still less optmized & simpler than the glibc malloc/free used by most Linux systems).

ODrive perhaps?

Well I dunno, maybe see how ODrive does it

Then maybe just hook everything to an Odrive and maybe add an Arduino or something to tell it what to do - although this also means you'll probably want an encoder at least on the pedalling motor to get accurate position/speed readings at low speed, since pedalling cadence is typically in the 60-90RPM range

If you want speed, use servomotors

This video may interest you, maybe also check this one and check out simpleFOC and/or ODrive

ODrive time?

Look at using some RC brushless motors driven from an ODrive board

You can probably replicate your own with appropriately sized RC brushless motors driven from ODrive boards. The boards can be linked together via CAN bus to communicate with your Arduino equipped with a CAN bus shield.

Thanks for the link! I know about simplefoc, the problem is the hardware. Simplefoc focuses on low wattage motors, e.g. a gimbal motor for a camera. For high wattage application, there's not much hardware available, and none that is affordable. There's odrive, which will set you back ~300$ just for the controller. Other than that, you'll have to go to traditional robotics companies.