Impressive! Very complete on first glance. You might want to soften or qualify the RTOS statement so people focus on its compactness and low latency. As you are already seeing in the comments the RTOS aspect has a lot of opinions depending on what one is trying to accomplish.
I would appreciate an honest comparison with FreeRTOS. Building something like this is an excellent learning exercise for the coder, but someone who has to balance the risks, learning curve and feature set has to justify the adventure in a different way.
One thing that would be interesting to hear more about would be your own recounting of the places where you made opinionated decisions about how things should work.
Question: Do you mean real time, meaning there is some kind of expectation of task switching time, nothing can stop other threads from executing, etc; or do you really mean embedded?
I have no practical insight on RTOS in general, if anyone bothers to give me a hint, please.
From all what I've looked into, RTOS does mean to create software systems that are almost perfectly predictable and safe to execute. Predictable latency, runtime and memory usage, plus maybe side channels to do the unpredictable stuff in between. It's actual rocket science, as no systemic mistakes are allowed.
The confusion is that this project doesn't mention any of it. Is it just hijacking of a fancy acronym, are there two worlds side by side or am I completely misled?
RTOS can be used a lot looser than you describe. Like a build system, scheduling, and interrupt framework that allows you to program an MCU like you describe. Zephyr RTOS and Free RTOS provide easy enough ways to write code that uses blocking APIs but probably runs your code according to the timing constraints if you hold it right. As an alternative, you could write for “bare metal” and handle the control flow, scheduling, interrupting, etc. yourself. If you are writing to “random” addresses according to some datasheet to effect some real world change, you are probably reaching for an RTOS or bare metal unless you are writing OS driversn. If you look at the linux drivers, you will see a lot of similarities to the Zephyr RTOS drivers, but one of them is probably clocking in the MHz while the other in the GHz
I would suggest that a slightly more approachable way to view an RTOS for MCUs is a library that sits on your bare metal that takes primary responsibility for efficiently dividing up available resources across multiple task functions.
An RTOS will usually provide a well documented SDK with support for memory safe queues, semaphores and message brokering.
Think of it as a software enforced contract + best practices to ensure that you get stable, predictable timing loops without ugly polling and blocking.
You're probably thinking of a hard real-time RTOS with time slices and WCET constraints.
For soft real-time, you basically only need low latency.
Threads with priorities, synchronization primitives and some way of handling interrupts is generally considered good enough.
From the description, this sounds like the kind of RTOS that runs most embedded RT applications currently if perhaps a bit heavier in features than the average with filesystem and networking support.
> It's actual rocket science, as no systemic mistakes are allowed
Lots of everyday stuff is running on bare metal code that exceeds so-called "real time" requirements without an OS at all, and those programmers are definitely not rocket scientists! :)
Hi HN,
I’ve been working on a tiny RTOS as a personal project to better understand how operating systems and schedulers work internally.
This project includes: - Basic task scheduler - Context switching - Simple memory management - Runs on (your target hardware or environment)
Motivation: I wanted to learn OS internals by building everything from scratch rather than relying on existing frameworks.
Challenges: - Implementing context switching correctly - Designing a minimal but usable scheduler - Keeping the codebase simple and readable
I’d really appreciate feedback, especially on: - Architecture design - Scheduler implementation - Code structure
GitHub: https://github.com/cmc-labo/tinyos-rtos
Impressive! Very complete on first glance. You might want to soften or qualify the RTOS statement so people focus on its compactness and low latency. As you are already seeing in the comments the RTOS aspect has a lot of opinions depending on what one is trying to accomplish.
Very cool! Thanks for sharing.
I would appreciate an honest comparison with FreeRTOS. Building something like this is an excellent learning exercise for the coder, but someone who has to balance the risks, learning curve and feature set has to justify the adventure in a different way.
One thing that would be interesting to hear more about would be your own recounting of the places where you made opinionated decisions about how things should work.
Question: Do you mean real time, meaning there is some kind of expectation of task switching time, nothing can stop other threads from executing, etc; or do you really mean embedded?
What ever happened to μC/OS?
Seemed both well documented and well suited to have taken over for the current MCU explosion. I almost never see anyone talk about it.
Looks like it open-sourced in 2020.
https://github.com/weston-embedded
How much of this was by AI?
I have no practical insight on RTOS in general, if anyone bothers to give me a hint, please. From all what I've looked into, RTOS does mean to create software systems that are almost perfectly predictable and safe to execute. Predictable latency, runtime and memory usage, plus maybe side channels to do the unpredictable stuff in between. It's actual rocket science, as no systemic mistakes are allowed. The confusion is that this project doesn't mention any of it. Is it just hijacking of a fancy acronym, are there two worlds side by side or am I completely misled?
RTOS can be used a lot looser than you describe. Like a build system, scheduling, and interrupt framework that allows you to program an MCU like you describe. Zephyr RTOS and Free RTOS provide easy enough ways to write code that uses blocking APIs but probably runs your code according to the timing constraints if you hold it right. As an alternative, you could write for “bare metal” and handle the control flow, scheduling, interrupting, etc. yourself. If you are writing to “random” addresses according to some datasheet to effect some real world change, you are probably reaching for an RTOS or bare metal unless you are writing OS driversn. If you look at the linux drivers, you will see a lot of similarities to the Zephyr RTOS drivers, but one of them is probably clocking in the MHz while the other in the GHz
TIL I learned that I am also a rocket scientist!
I would suggest that a slightly more approachable way to view an RTOS for MCUs is a library that sits on your bare metal that takes primary responsibility for efficiently dividing up available resources across multiple task functions.
An RTOS will usually provide a well documented SDK with support for memory safe queues, semaphores and message brokering.
Think of it as a software enforced contract + best practices to ensure that you get stable, predictable timing loops without ugly polling and blocking.
You're probably thinking of a hard real-time RTOS with time slices and WCET constraints.
For soft real-time, you basically only need low latency.
Threads with priorities, synchronization primitives and some way of handling interrupts is generally considered good enough.
From the description, this sounds like the kind of RTOS that runs most embedded RT applications currently if perhaps a bit heavier in features than the average with filesystem and networking support.
> It's actual rocket science, as no systemic mistakes are allowed
Lots of everyday stuff is running on bare metal code that exceeds so-called "real time" requirements without an OS at all, and those programmers are definitely not rocket scientists! :)
I've learnt something new: RTOS stands for Real-Time Operating System. Thanks for sharing; your README is top-notch!