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Embedded and Realtime Linux basics

By Anonymous Zero in News
Thu May 11, 2000 at 10:05:50 AM EST
Tags: Software (all tags)
Software

This article in LinuxWorld outlines the state of Linux in the realtime and embedded systems markets. The article does a good job of explaining that embedded isn't the same as realtime and the different flavors of realtime systems. From the article:

The most common approach to offering a realtime version of Linux is to write what amounts to a tiny RTOS (an executive), which runs Linux as a background process and handles the realtime tasks. Linux runs as a low-level process on this RTOS, which means it runs as it normally would but is interrupted by the higher priority, time-critical tasks.
In the embedded market Linux has the advantage of already having a larger developer mindshare than other embedded perating systems, however Linux is also a
relatively large OS [which] overtaxes the systems' resources. Processors in such systems have been usually 16 bits or less, memory has been limited to less than 100 KB, and storage hasn't been much bigger [although] Size is becoming less of a problem because of the trends in the embedded market.
The article includes a list of useful links such as realtimelinux.org, the embedded Linux miniHOWTO, and Lynx makers of their own realtime OS which today announced their new name is "LynuxWorks".


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Related Links
o This article
o realtimeli nux.org
o the embedded Linux miniHOWTO
o Lynx
o Also by Anonymous Zero


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Embedded and Realtime Linux basics | 15 comments (15 topical, editorial, 0 hidden)
Embedded Linux... is this like what... (none / 0) (#4)
by evro on Wed May 10, 2000 at 06:41:15 PM EST

evro voted 1 on this story.

Embedded Linux... is this like what TiVo has?
---
"Asking me who to follow -- don't ask me, I don't know!"

Some fairly good info there.. but (... (5.00 / 1) (#9)
by Marcin on Wed May 10, 2000 at 06:44:36 PM EST

Marcin voted 1 on this story.

Some fairly good info there.. but (as someone pointed out to me via email when I commented on the last story about embedded linux) Linux isn't an OS, Linux is just the kernel itself. Sure there are ports of linux to other architectures now but fundamentally it's a x86 architecture kernel, everything else really is an afterthought. The real problem, he says, is that Linux is "a good operating system designed to a different purpose." This was my point last time, so i'm glad someone else has made it too (that quote is from the linuxworld article). I think for embedded applications nothing beats an OS written for the specific architecture it'll run on. Just look at PalmOS compared with WinCE. Of two people I work with one has a Palm V, and one just got a HP Jordana 545 WinCE thingie.

The Palm V can run for about 1 - 2 months of normal usage before it needs a recharge. The model my colleague has contains 2 Mb of RAM and he says that's more than enough.. he says applications are usually a few kb at most.

The WinCE machine on the other hand runs for about 8 hours before it needs to be recharged. Applications are several 100k. It has (and needs) 16MB of memory.

My point is that WinCE is a stripped down version of a fully featured OS designed for the x86 processor. The Jordana has like a 133Mhz processor to run this thing! (which explains the battery life). PalmOS was designed for the processor in the Palm (Dragonball?).. the Palm only has/needs a 25Mhz (or close?) CPU.

So my point is, i'm not convinced Linux will be very efficient as an embedded kernel. Is there even a point in making it into one? I mean, who wants to run emacs on a toaster? :) It's not like you want portability of existing applications. (Or maybe I'm wrong).

Anyway, end of rant. :)
M.

Re: Some fairly good info there.. but (... (none / 0) (#14)
by bgdarnel on Thu May 11, 2000 at 12:13:09 PM EST

he says applications are usually a few kb at most.
"a few kb" is a bit of an understatement. For an app that does something useful, and it's not uncommon for an app to be bigger than 50k. I think the recordholder for code size (excluding data) is DateBk4, which tips the scales at just over 400k. Apps are more than "a few kb", but it's still amazing what they can fit in limited space

the Palm only has/needs a 25Mhz (or close?) CPU.
Actually, it's even slower than that - the Palm Vx and IIIc have 20MHz, all other Palm devices (and AFAIK this includes Handspring and TRG devices) have 16MHz.

[ Parent ]
I fail to see why linux is moving i... (none / 0) (#10)
by deimos on Wed May 10, 2000 at 07:31:48 PM EST

deimos voted 0 on this story.

I fail to see why linux is moving into "linux everywhere". Nothing like trusting your life to some unknown coder who wrote the I/O function that keeps your heart beating on that life support machine. "BSD everywhere" would be a different story. :P
irc.kuro5hin.org: Good Monkeys, Great Typewriters.

informative post. hope others think... (none / 0) (#13)
by kracker on Wed May 10, 2000 at 08:09:36 PM EST

kracker voted 1 on this story.

informative post. hope others think so too . . .

Please sir can I have some more? ... (none / 0) (#3)
by kraant on Wed May 10, 2000 at 09:15:53 PM EST

kraant voted -1 on this story.

Please sir can I have some more?

More? You want more?
--
"kraant, open source guru" -- tumeric
Never In Our Names...

Linux is too porky for the Embedded... (none / 0) (#11)
by Strongtium90 on Wed May 10, 2000 at 09:32:23 PM EST

Strongtium90 voted -1 on this story.

Linux is too porky for the Embedded market. Why does everyone think that this thing is the best tool for all jobs? Give a man a hammer and all problems look like nails. Get real! Or try a Unix *designed* for embedded devices, like QNX! It has posix, has all the GNU tools (which run natively). But, most important it has a microkernel that has only neccesary services, and a very small full featured windowing system (Photon). All of which use very little system resources. Or Epoc, or Palm, but Linux? Give me a break.

I remember when people were using t... (none / 0) (#2)
by FlinkDelDinky on Wed May 10, 2000 at 09:58:00 PM EST

FlinkDelDinky voted 1 on this story.

I remember when people were using the Amiga for real time stuff. The article was good.

The thing is it doesn't talk about the chips that are being used and which ones can/do run Linux. I know that the embedded market is starting to use varaitions of the Intel 386 but Motorola has various 68000 based chips for embedded stuff.

What about the old 8 bit chips? You know, their are multi-tasking realtime os's for the 6502? Pretty amazing.

A post with links to an article whi... (none / 0) (#6)
by pvg on Wed May 10, 2000 at 10:26:46 PM EST

pvg voted -1 on this story.

A post with links to an article which includes further useful links, which are also quoted in the submission? It's a veritable MLP web! :)

RandomLink Propogation... (none / 0) (#8)
by Mrs Edna Graustein on Thu May 11, 2000 at 07:41:43 AM EST

Mrs Edna Graustein voted 0 on this story.

RandomLink Propogation
--
And if any of you put that in a .sig, I'll hunt you down and kill you twice. ;-)
Rusty

I don't think that Linux should be ... (none / 0) (#1)
by hattig on Thu May 11, 2000 at 08:10:21 AM EST

hattig voted 1 on this story.

I don't think that Linux should be aimed at the embedded market at all. It is good at what it does, but it is not designed for these other tasks. A cut down AmigaOS would be better, then there is QNX, Tao and a host of other dedicated embedded and/or real-time operating systems that would do the job much better.



It would be nice, in more write-ups... (none / 0) (#7)
by Rasputin on Thu May 11, 2000 at 09:22:31 AM EST

Rasputin voted 1 on this story.

It would be nice, in more write-ups, if the author actually expressed an opinion about the topic as well. If the author doesn't have an opinion about the subject, s/he is probably the wrong person to submit the story.

On Linux as an RTOS, it isn't really. As the article states. the Linux is really a low-priority task on the same machine as the RTOS. As well, i386 architectures, which are the main focus of Linux, are a poor choice (at best) for a real-time system.

On Linux as an embedded OS, whatever blows your hair back ;) It's another choice among many with good points and bad points.
Even if you win the rat race, you're still a rat.

looks cool, some further or more in... (none / 0) (#5)
by bse on Thu May 11, 2000 at 10:03:20 AM EST

bse voted 1 on this story.

looks cool, some further or more in depth details would have been nice =)

---
"Please sir, tell me why, my life's so pitiful, but the future's so bright? When I look ahead, it burns my retinas." -- Pitchshifter - Please Sir

This is interesting like any other ... (none / 0) (#12)
by maynard on Thu May 11, 2000 at 10:05:50 AM EST

maynard voted 1 on this story.

This is interesting like any other bread and butter tech article. There's little controversy here, but in this context that's a good thing. I rate it as worthy of discussion.

Read The Proxies, a short crime thriller.

Embedded OS Overheads... (none / 0) (#15)
by Anonymous Hero on Thu May 11, 2000 at 10:45:04 PM EST

I spent about ten years writing various embedded systems... all the way from tiny 4 bitters to huge rackmounted doodads with fifteen or twenty 68040 cpus.

Volume is *everything* in the embedded market... Linux is in the sweet spot for lower volume systems (ie: lower volume than toasters, VCRs) where a couple of megs of flash and a fast cpu (x86, 68k, ppc) is nothing if it cuts a month or two of development time.

Higher volumes than that mean reducing part counts, power consumption etc.... that used to be the domain of the 4 - 16 bit machines but times change and I'm pretty sure you can get a Moto embedded PPC machine with almost enough flash for the kernel on chip

another interesting angle is that not every embedded device requires hard RTOS style scheduling... many can do just fine with reasonably fine grained tasking.

For example, most pneumatic and hydraulic systems are pretty slow to react (in the order of 5ms or more for a valve to work) so if you can cycle faster than that, you're doing good enough.

anyway, my 2c (and my first post...)

cheers

dean

Embedded and Realtime Linux basics | 15 comments (15 topical, 0 editorial, 0 hidden)
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