View from the trenches: it doesn't [LWN.net]

View from the trenches: it doesn't

Posted Mar 28, 2004 23:42 UTC (Sun) by jonth (subscriber, #4008)
Parent article: Linux Kernel 2.6: the Future of Embedded Computing, Part I (Linux Journal)

Sorry guys, I love Linux, I use it exclusively at home, and develop it at work, but it just doesn't cut it in the embedded devices I develop for: mobile phones. For this we need a true RTOS: absolutely guaranteed (and short - 10s of cycles, typically) times for context switching, interrupt latency, message passing, memory allocation etc. And the whole thing must be very small. We're talking here about sub 20-MIP devices, with .5-2MB RAM, and maybe 1-4MB ROM. Of this, typically the OS takes <32KB.

Nucleus is the most commonly used RTOS in this space, but there are others. Linux competes most successfully with VxWorks, as it tends to offer a similarly rich feature set. But in this domain we aren't interested in a large feature set: we're after the feature set of a microkernel, and are only interested in speed and size. Every byte/MIP spent in the OS is one we could have spent in user space.

cheers,

Jonth

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View from the trenches: it doesn't

Posted Mar 29, 2004 11:49 UTC (Mon) by jonth (subscriber, #4008) [Link]

Well.... sort of. The typical architecure of a smartphone is multi-core, where you have something like an XScale/StrongARM running the user OS (Windows, Symbian, PalmOS), and another, completely separate processor like an ARM9 running Nucleus as a "Modem processor". (The DSPs to do equalisation & channel decoding typically run without an OS at all.)

Your comment is true for the first processor, but not for the second one.

View from the trenches: it doesn't

Posted Mar 29, 2004 11:45 UTC (Mon) by jonth (subscriber, #4008) [Link]

I realise that - that's why I qualified my comment with "in the field I work in." Linux is great for set top boxes, hard disk mp3 players, etc., but in the world of mobile phones, cost and power is king, so we need something that doesn't soak up the MIPs, and has a small footprint.

The reason Linux doesn't fit in this space is the same reason Windows doesn't. It's just too big and clunky. (However, with RTLinux and RTAI, Linux comes much closer!)

View from the trenches: it doesn't

Posted Mar 29, 2004 12:53 UTC (Mon) by alonso (subscriber, #2828) [Link]

But if i remember well, last incarnation of symbian (v. 7), is very important because has real-time capability and allow one chip samrt-phone. If this is right, do you think linux has the ability to follow symbian?

The evolution of RTOSes

Posted Mar 29, 2004 13:13 UTC (Mon) by alex (subscriber, #1355) [Link]

It depends on what your looking for out of your OS. It seems to me a lot of the "smaller" RTOS's are gearing up to offer more and more features you find with more complete OS's like Linux. At some point you have to make a decision about when you abandon the lock-in of the proprietry OS and move to a more widely used OS.

Symbian is/was aimed squarely at he PDA/Phone market as is PocketPC/WinCE. They both offer features for resource starved GUI's and have had there share of success in that field. They are still way behind vxWorks in terms of devices shipped. vxWorks itself is being squeezed from the high end by embedded Linux where it struggles to compete to offer features without adding overly burdonsome cost.

I think the existing real-time features of stock Linux (2.6) will do for most non-critical applications. However I don't think it will be able to follow down to the very cheap devices with limited hardware resources where the microkernels still hold and advantage. However as hardware becomes more and more powerful I think the hardware will scale up to Linux's sweet point.