FreeRTOS-Kernel VS nuttx

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).

Hi Rust experts, we are willing to integrate rustix on NuttX RTOS, the initial effort was done by rustix author: https://github.com/bytecodealliance/rustix/tree/nuttx but it hit the wall since we don't know the right way to integrate cargo with the old-school NuttX's Makefiles. Any help or suggestion is welcome. More about NuttX here: https://nuttx.apache.org and here: https://nuttx.apache.org/docs/latest/

Open Source Autopilot for Drone Developers PX4 is an advanced and open source autopilot flight stack for drones. PX4 can flight completely autonomously for pre-programmed missions, or, obviously, it can help a pilot who remote-controls the drone. It runs on NuttX RTOS.

You should definitely have a look at NuttX.

https://gitlab.com/nuttx/NuttX/-/tree/master/drivers/sensors https://github.com/apache/incubator-nuttx/pull/2039

Maybe Nuttx can be an alternative. Have a look: https://nuttx.apache.org/

Zephyr, RIOT, NuttX are all open source RTOSes happy about contributions

Microcontrollers are a good start. Boards are cheap and sensors are plentiful. You could get a yet unsupported board and port RIOT, Zephyr or NuttX.