Free, very portable RTOS?

[jeremy]

hi all,

I'm looking at the moment for a free real time operating system for microcontroller firmware. I'd really like one that was just written in plain C (ANSI or C99) so that it is super portable across vendors and/or architectures. Ideally, it should be so portable that you can compile it for x86 as well as the target (with the appropriate support code of course). Prewritten HAL drivers are not important, but it would be great if there still is a defined HAL interface so that I could implement my own drivers.

Does anyone have any experiences that may aid me in my search? Maybe you have ported one of the more popular RTOSes and have some war stories?

I was interested in chibios as I use STM32 chips a lot, but the licensing situation around it seems a little weird.

[jancumps]

I've used freeRTOS for a  TI Hercules microcontroller.
Here's a list of ports. It includes the (not tried by me) x64:
http://www.freertos.org/RTOS_ports.html

[Jeroen3]

I was interested in chibios as I use STM32 chips a lot, but the licensing situation around it seems a little weird.

Don't get scared by the kernel 3.0 licensing. That version isn't finished yet.
2.6 goes with GPL-exception. Allowing you to use it, as long at you don't modify it. When you do modify it, normal GPL applies. (aka, you must open source it)
A lot of secondary files are on an Apache license that won't pose any issues. You must however be able to supply used code when requested (the gpl code), and your legal sheet must contain a reference.

You're looking for a "free real time operating system", you'll either get GPL, or MIT/Apache license.
Or something without license, but the scope of portability you demand suggests it is probably well known.

[mrflibble]

I was interested in chibios as I use STM32 chips a lot, but the licensing situation around it seems a little weird.

I'd say go for it. I use chibios on stm32, and don't find the licensing particularly troublesome. That and it works quite nicely & is well documented. I've only used chibios 2.x so far, so cannot speak for 3.0.

[Marco]

The GPLv3 with exception "license" is a clusterfuck. Those are clearly additional terms ... if you release a program with GPLv3 (which the exception does not excuse you from) the recipients can ask for the full source code. The additional terms are null and void to them.

[mrflibble]

The GPLv3 with exception "license" is a clusterfuck. Those are clearly additional terms ... if you release a program with GPLv3 (which the exception does not excuse you from) the recipients can ask for the full source code. The additional terms are null and void to them.

How so? Does GPLv3 come with explicit terms that the license is non-modifiable? If that really is the case you can always release the new GPL4suckmabawls license, which just happens to be a verbatim copy of GPLv3 with the exceptions related to linking explicitely pasted in, s/GPLv3/GPL4suckmabawls/g and it's an entirely new license. Problem solved. Besides, for hobby projects, who cares. And for commercial products you use the commercial license and pay the man some money for his efforts.

[Jeroen3]

GPLv3 comes with Tivoization clause. That means that end users should be able to replace ChibiOS in the end product if you're using dynamic linking.