FreeRTOS-Kernel VS xv6-riscv

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).

okay, fair. i only got misled by the title of the post, which claims all-rust xv6 port.

now that we cleared the userland part, here’s what I’m contemplating on the kernel side. i can’t think of anything simpler and more staple than this, so:

https://github.com/dancrossnyc/rxv64/blob/main/kernel/src/ua...

https://github.com/mit-pdos/xv6-riscv/blob/riscv/kernel/uart...

honestly - i don’t feel at ease to tell which driver code is more instructional, which is easier to read, which is better documented, which is better covered with tests, which has more unsafety built into it (explicit or otherwise), what size are the object files, and what is easier to cross-compile and run on the designated target from, say, one of now-ubiquitous apple silicon devices.

lest we forget that the whole point of it is “pedagogical”, i.e. to learn something about how a modern OS can be organized, and how computer generally works.

and i’m just not sure.

The x86 version of xv6 is no longer updated, the last updates took place about 7 years ago. Current xv6 supports RISC V in qemu, there are also ports to real RISC V devices (Kendryte/Canaan K210, Allwinner D1, StarFive JH7110, some hacked by me) and FPGA implementations ().

  https://github.com/mit-pdos/xv6-riscv/ (qemu)

I am no help with recruitment, but simple search revealed "https://github.com/mit-pdos/xv6-riscv", were you aware of this?

Different repo under same org https://github.com/mit-pdos/xv6-riscv

I'm reading through the MIT xv6 OS handbook and code (here: https://github.com/mit-pdos/xv6-riscv/) and they mention the fact that they created it as a monolithic kernel since most unix systems are monolithic. They then introduce the microkernel concept. Are there microkernel concepts out there (especially code) I can check out? I'm curious to see how userspace processes communicate to kernel processes to execute privileged actions.

Yeah its from here: https://github.com/mit-pdos/xv6-riscv x86 version here: https://github.com/mit-pdos/xv6-public

I would start with working through an OS textbook. Tanenbaum is highly regarded although I worked through OStep and I felt it was very approachable. Also check out wiki.osdev.org. Also, here's a re-inplementation of Unix version 6. I've been meaning to play around with it for a while.

NOTE: we have stopped maintaining the x86 version of xv6, and switched our efforts to the RISC-V version (https://github.com/mit-pdos/xv6-riscv.git)