5 ms·

How I ended up writing a new real-time kernel (2015)

194 points by travisgriggs 8y ago

anitil 8y ago
I had a great time following this a couple years ago. It inspired me to write a tiny micro-kernel with pre-emtive multitasking. It was probably a bug-ridden mess, but it was incredibly satisfying having a handful of threads printing 'Hello from thread #1', 'Hello from thread #2' etc.
- wickerman 8y ago
  I had to code a small OS in C in third year of college and the main piece of it was the scheduler. I remember my semaphore routines quite fondly actually.
  - anitil 8y ago
    What I wrote was nothing as advanced as that. Simple round-robin got it off the ground and I don't think I ever looked at it again
3xblah 8y ago
Pardon the digression but I like the text-only "captcha". Don't see that too often.
- minitech 8y ago
  Doesn’t seem very accessible or effective when targeted, though.
  - 3xblah 8y ago
    True. More commonly, I see banner/figlet/etc. type fonts put into html apparently for no purpose other than artistic reasons.
fernly 8y ago
Very readable article with the fun of first-person problem solving.
keithnz 8y ago
I have done this before. I'm actually in the process right now of writing a new version of an existing product on a new platform we have developed, and after evaluating various off the shelf OS's, including RIOT and FreeRTOS, and also considering a custom RTK, I have instead gone with a cooperative lightweight actor based system with some special handling around interrupts. It works quite nicely, and can easily be moved into a preemptive kernel if needed at a later stage.
- andyidsinga 8y ago
  I'm currently looking at FreeRTOS and mbed for a project on an STM32F07 mcu. Anything you can share about either of those that made you decide against? Also considering a super simple no-os fw loop with some light abstractions because our real time constraints aren't very tight..
  - travisgriggs 8y ago
    I tried to use FreeRTOS on two projects. The first was an Atmel Xmega. The second was an Atmel SamD21. FreeRTOS has its quirks, but it's pretty straightforward and easy to understand. Unlike Zephyr and many of the current slew of "IoT platforms", it doesn't try to be anything but a microkernel. Just drop the C files in your sources, tweak the master defines file, and you're good to go. Use whatever build system fits you best. The one area (and this may be dated; my last attempt was nearly 2 years ago) where FreeRTOS let us down was in tickless mode. I think FreeRTOS's place of primary use was originally FreeScale and automotive, where running tickfull and powered all of the time makes sense. But we needed to be tickless and sleep lots. There was a hook for doing that, but it was definitely "on your own" and figure it what else you needed to tweak outside of the hook (like I say, this may have improved of late). I got distracted by RIOT because they spoke at ELC and I got it in my head that it was more FOSS/open-sourcy than FreeRTOS. When I grew with frustrated with RIOT, I stumbled on https://www.osrtos.com https://www.osrtos.com and gave TNEO a spin and was really happy with it. I've only played briefly with mbed, but had the same frustration as many of the others. It want's to be a full-stack end-to-end development solution. That demos well, until you find you want to tweak the build process for some reason. Or integrate it in your source control system some other way.
josemanuel 8y ago
Why not use RTEMS ?
- naasking 8y ago
  See the comments section of the article where author addresses this.

194 points by travisgriggs 8y ago

I had a great time following this a couple years ago. It inspired me to write a tiny micro-kernel with pre-emtive multitasking. It was probably a bug-ridden mess, but it was incredibly satisfying having a handful of threads printing 'Hello from thread #1', 'Hello from thread #2' etc.

wickerman 8y ago
I had to code a small OS in C in third year of college and the main piece of it was the scheduler. I remember my semaphore routines quite fondly actually.
- anitil 8y ago
  What I wrote was nothing as advanced as that. Simple round-robin got it off the ground and I don't think I ever looked at it again

3xblah 8y ago

Pardon the digression but I like the text-only "captcha". Don't see that too often.

minitech 8y ago
Doesn’t seem very accessible or effective when targeted, though.
- 3xblah 8y ago
  True. More commonly, I see banner/figlet/etc. type fonts put into html apparently for no purpose other than artistic reasons.

fernly 8y ago

Very readable article with the fun of first-person problem solving.

keithnz 8y ago

I have done this before. I'm actually in the process right now of writing a new version of an existing product on a new platform we have developed, and after evaluating various off the shelf OS's, including RIOT and FreeRTOS, and also considering a custom RTK, I have instead gone with a cooperative lightweight actor based system with some special handling around interrupts. It works quite nicely, and can easily be moved into a preemptive kernel if needed at a later stage.

andyidsinga 8y ago
I'm currently looking at FreeRTOS and mbed for a project on an STM32F07 mcu. Anything you can share about either of those that made you decide against? Also considering a super simple no-os fw loop with some light abstractions because our real time constraints aren't very tight..
- travisgriggs 8y ago
  I tried to use FreeRTOS on two projects. The first was an Atmel Xmega. The second was an Atmel SamD21. FreeRTOS has its quirks, but it's pretty straightforward and easy to understand. Unlike Zephyr and many of the current slew of "IoT platforms", it doesn't try to be anything but a microkernel. Just drop the C files in your sources, tweak the master defines file, and you're good to go. Use whatever build system fits you best. The one area (and this may be dated; my last attempt was nearly 2 years ago) where FreeRTOS let us down was in tickless mode. I think FreeRTOS's place of primary use was originally FreeScale and automotive, where running tickfull and powered all of the time makes sense. But we needed to be tickless and sleep lots. There was a hook for doing that, but it was definitely "on your own" and figure it what else you needed to tweak outside of the hook (like I say, this may have improved of late). I got distracted by RIOT because they spoke at ELC and I got it in my head that it was more FOSS/open-sourcy than FreeRTOS. When I grew with frustrated with RIOT, I stumbled on https://www.osrtos.com https://www.osrtos.com and gave TNEO a spin and was really happy with it. I've only played briefly with mbed, but had the same frustration as many of the others. It want's to be a full-stack end-to-end development solution. That demos well, until you find you want to tweak the build process for some reason. Or integrate it in your source control system some other way.

josemanuel 8y ago

Why not use RTEMS ?

naasking 8y ago
See the comments section of the article where author addresses this.