Linux recommended / compatible RTOS [LWN.net]

Linux recommended / compatible RTOS

Posted Sep 2, 2014 23:32 UTC (Tue) by tdwebste (guest, #18154)
Parent article: Kernel tinification

I am going to assume the simple statement is true.
"Linux can not run in the confined flash and ram of cortex-M0 and cortex-M4 ARM processors."

These processors are used in many IOT devices. Examples include nordic, stmicro cortex-M0 MCU with programmable ble radio, Toshiba cortex-M4 MCU with accelerometer, programmable ble radios, lcd controller.

What is the recommended opensource Linux compatible RTOS?
With compatible: Event queue, Asynchronous message queue, mailbox intercommunication.

to post comments

Linux recommended / compatible RTOS

Posted Sep 3, 2014 0:47 UTC (Wed) by pizza (subscriber, #46) [Link] (2 responses)

> I am going to assume the simple statement is true.
> "Linux can not run in the confined flash and ram of cortex-M0 and cortex-M4 ARM processors."

It depends entirely on how much RAM and flash those parts have.

Many of these Cortex-M processors support the use of external RAM and flash. Those that do are generally capable of running uClinux; in particular there's mainline support for at least some of the EFM32 parts.

Linux recommended / compatible RTOS

Posted Sep 3, 2014 2:57 UTC (Wed) by tdwebste (guest, #18154) [Link] (1 responses)

I was hoping the discussion was NOT going to revolve around whether Linux can be shoe horned into cortex m0, m4 ARM processors.

cortex m0 processors are in extremely price sensitive markets, which makes external flash very undesirable. These processors usually have under 512k flash and 64k ram.
cortex m4 processors maybe able to run Linux. But there is many reasons not to. The main being the m4 and m0 are often performing similar applications. Applications that often need to be compiled without unused file system and networking support to reduced flash and ram requirements.

Currently running the same OS on cortex m0 and m4 ARM processors makes the most since.

It is increasingly common for a cortex-m0/4 to be connected by pcb/usb/serial bus to a more powerful ARM processor running Linux. The imx6 is a example combining ARM Cortex-A9 and Cortex-M4 cores.

Back to my original question.
Recommended opensource Linux compatible RTOS?
Compatible: Event queue, Asynchronous message queue, mailbox intercommunication.

Linux recommended / compatible RTOS

Posted Sep 3, 2014 11:31 UTC (Wed) by pizza (subscriber, #46) [Link]

> These processors usually have under 512k flash and 64k ram.

Indeed, 512/64 is actually a pretty high-end part.

> Recommended opensource Linux compatible RTOS?
> Compatible: Event queue, Asynchronous message queue, mailbox intercommunication.

In short, such a thing does not exist, at least not if you're looking to be API-compatible with Linux. Or even behaivorally-compatible.

Come to think of it, eCOS may be the closest, but by the time you enable all the nice APIs and features the RAM/Flash requirements are such that you may as well be running uClinux.

nuttx is pretty full-featured too at this point, and RTX has been freed by ARM and is actually bundled with CMSIS these days. Personally, I'm particularly fond of FreeRTOS, but it's fairly bare bones in comparison to the others.

Linux recommended / compatible RTOS

Posted Sep 15, 2014 17:22 UTC (Mon) by tinti (guest, #98866) [Link]

You may try Nuttx. I don't know how much compatible it is.

http://www.nuttx.org/