hi, what is meant by a "real-time OS"? if we have some linux distro, and some organization goes and makes a "real-time" version of that distro, what did they do? im a bit confused cos they didnt say "linux", rather "distro".

thanks.

This beats me, but I would guess that 'real time os' is some commercial soundbite that does not have any real technical meaning. But maybe i'm just a terrible cynic!!

well, no not really. RTOS is well-known, but I just heard this today - "we have made a real-time redhat distro" ... and i didnt bother asking at that time what he meant.

maybe he meant they made a version of redhat for embedded systems?

Real Time : (Took this from WebOpedia)
"Occurring immediately. The term is used to describe a number of different computer features. For example, real-time operating systems are systems that respond to input immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Most general-purpose operating systems are not real-time because they can take a few seconds, or even minutes, to react.

Real time can also refer to events simulated by a computer at the same speed that they would occur in real life. In graphics animation, for example, a real-time program would display objects moving across the screen at the same speed that they would actually move. "

And this link may give you some information about what could be a Real-Time distribution

http://www.linuxdevices.com/news/NS5716364908.html

Hope this answers your question...

thanks.

Actually a RTOS is not only about reacting imediately.. it's about being able to predict how long a task will take..
For example in a car a air bag should not come out to fast so the air will go down before the head hit the air bag and it should not take to long time so the head will hit the steering wheel..

Ya, in a real time OS if you should be able to precisely time things. There is a system called real-time linux which adds patches to the linux kernel to allow you to have kernel modules which run in real time. It is pretty good, but not perfect. There are still better solutions for the truly hard core real time needs.

http://www.fsmlabs.com/products/rtli...tlinuxpro.html

im going to take a look into that. thanks.
also, how different are embedded systems from an ordinary desktop PC? do we consider the controllers (say, GPS) in the car to be an example of them? seems like there is no real input interface like say a mouse/keyboard on a PC - so most all processes running are akin to background processes?
umm, ill just read up on it. thanks again.

All I do these days is pretty much embedded linux systems.

As far as there similarity to Desktop PC's, that really depends.

I have done some things that use embedded Pentium processors or something of that nature and you can pretty much run a slimmed down version of any normal linux distribution you want on them. For me those projects are rare though, as those processor are still fairly expensive when you are talking about building them into custom hardware.

Most of the stuff I do deals with PPC chips. The price point for the embedded PPC processor is quite good. The problem you run into is not all PPC's are created equal. The 860 series which is a great low power device doesn't have an FPU or some other features which the standard gcc PPC compiler assumes. So you end up with a fairly custom version of gcc and glibc and you have to really do a lot of work to get some applications to compile and run. Same goes for the Coldfire embedded m96k processor. But for special tasks (routers, POS terminals, stuff that doesn't really need massive cpu power) they work great and even though the availible linux tools are way stripped down from what most people are used to they provide a wonderful framework to develop software on. It is especially nice when you want to add things like flash drives (JFS,JFS2 are build into kernel), hard drives, network adapters, or any of the other devices the linux kernel supports out of the box.

that's interesting stuff jtshaw.. have you read this book ? would you recommend it, if not, what books on the subject would you recommend?