real-time operating system?

[dpopiz]

I've been reading about VXworks (a "real-time operating system"), but I'm still confused.

any experts out there who can explain the concept to me? what makes an RTOS different from an OS?

 

[GhettoFob]

As opposed to a turn based OS? I've never heard of a real-time operating system.

 

[MrMilney]

Linky for both your edumacations.

 

[Nothinman]

Basically the difference is a RT OS guarantees latency, meaning you know for a fact your process will run every 5ms so you can rely on that for things like controlling mechanical devices, without a RT OS your process might not run for 20ms and in the wrong situation someone could get hurt or even die from the added latency.

 

[drag]

Yep. RTOS are usually used for embedded situations, and often are pretty much custom made (or heavily modified) for each application. There are a few commercial ones out there, people try to modify linux for this, but it's more of a Realy close to rtos, thing.


QNX is (or at least has versios that are) a RTOS. And is fairly well known. here is a linky

 

[Netopia]

VXworks is what is on Spirit (the Mars rover) and what helped enable them to get the thing rebooted when they were having all of the problems.

Joe

 

[Baronz]

Vxworks is in some routers too apparently.

 

[Nothinman]

And there's RTLinux, not sure where it's used though.

 

[Yomicron]

Originally posted by: Baronz
Vxworks is in some routers too apparently.

My Netgear 802.11a access point runs VxWorks.

 

[Ynog]

Originally posted by: Yomicron

Originally posted by: Baronz
Vxworks is in some routers too apparently.

My Netgear 802.11a access point runs VxWorks.

Is that a high end access point, because from my experience,
VxWorks is extremely expensive, I am just surpised they put it
on an access point.

 

[Ynog]

Originally posted by: Nothinman
And there's RTLinux, not sure where it's used though.

I've used RTLinux, but its not on enough platforms yet,
and there is disbute between some of the guys I work
with if you can guarentee RTLinux real time performance.

I personally haven't had a problem with it, but then again,
I was working on a very simple PC 104 stack, that probably
could have run fine with just a preemptive and low lantency
kernel patch.

 

[Nothinman]

Is that a high end access point, because from my experience,
VxWorks is extremely expensive, I am just surpised they put it
on an access point.

I'm surprised by that too, there's no need for a RTOS for just an accesspoint. Linksys uses Linux in a lot of it's access points, or atleast they used to. I believe they were bought by Cisco not too far back so they may migrate to IOS.

 

[Barnaby W. Füi]

My cable modem uses vxworks.

Here's an interesting project I stumbled upon recently: http://os.inf.tu-dresden.de/drops/

 

[Yomicron]

Originally posted by: Ynog

Originally posted by: Yomicron

Originally posted by: Baronz
Vxworks is in some routers too apparently.

My Netgear 802.11a access point runs VxWorks.

Is that a high end access point, because from my experience,
VxWorks is extremely expensive, I am just surpised they put it
on an access point.

I've got a Netgear HE102 that has Tornado for Home Gateways, which includes VxWorks.

from the datasheet:

TORNADO® FOR HOME GATEWAYS, an integrated software platform and development environment for broadband access gateway equipment, provides the core set of functions needed for virtually any gateway device for the home and small office. This platform comprises Wind River?s leading VxWORKS® REALTIME OPERATING SYSTEM (RTOS), networking protocols, network management components and drivers, packaged with the Tornado Tools and development environment.

But, I'm sure it's a pretty stripped down version of VxWorks.

 

[spyordie007]

Originally posted by: Nothinman

Is that a high end access point, because from my experience,
VxWorks is extremely expensive, I am just surpised they put it
on an access point.

I'm surprised by that too, there's no need for a RTOS for just an accesspoint. Linksys uses Linux in a lot of it's access points, or atleast they used to. I believe they were bought by Cisco not too far back so they may migrate to IOS.

Right, just like Netspeed products

"Let's just take the NSOS and rename it to CBOS and change the interface so it acts sort of like IOS..."

 

[Nothinman]

You sound bitter.

 

[spyordie007]

not bitter really. I just recall being confused several times when in those 67x DSL routers and wondering why it wouldnt take my command only to realize that the syntax was slightly differant...

 

[Nothinman]

Yeh, at work we have a combination thing that has a little of IOS and a little of CatOS. Luckily I don't work on the networking equipment much.

 

[jhu]

how does an rtos handle a situation where many processes need to be run at a specific time and the time needed to execute one process runs past the time that another process requires?

 

[drag]

Originally posted by: jhu
how does an rtos handle a situation where many processes need to be run at a specific time and the time needed to execute one process runs past the time that another process requires?

My guess is....

That they just don't. RTOS are designed for embedded situations were everything is highly tuned and running on minimal resources. Some of that stuff runs on things that make a pentium2 look like a super computer.

It's not designed for multitasking OS like Linux or Windows. It's more like DOS.

One example of something you use it for would be the controller for the hydrolic stablizers for heavy duty construction equipment.

Or could be used in a complex GPS unit. Or in a big office-style printer.

 

[Ynog]

Originally posted by: jhu
how does an rtos handle a situation where many processes need to be run at a specific time and the time needed to execute one process runs past the time that another process requires?

In my experience your dealing with badly written code and your now not running in real time.
Just because your running a real time OS doesn't mean your code runs in real time.

I ran into this case once porting real time code.

We used to run a very very old system with 30 process nodes for 30 worker processes and
one process that spawned the rest. However when we were porting the code, we no longer
needed the 30 process nodes, the new nodes were considerably faster, could handle more
than one process. Someone spec the system out and found out we only required 6 nodes.

However the problem we ran into was that when we had 30 nodes, the process that spawned
the other processes off would die, so you had no problem making sure each node had a process.
However in the new system there was a slight bug in the ported code that let the system decide
how to split up the processes. What we wanted and expected to happen is that one of the nodes
would get the first process and then 5 others would be assigned to that node as well. So you
would end up wanting 5 processes per node. And you really didn't care about the first process because
it would die off anyway and wouldn't require CPU time. However what ended up happening was that
the system would put that process on a node with only 4 others. Leaving one node with 6 worker
processes, which wouldn't cause it to run outside of real time. Which for us was very bad.
That one was boggled the mind for alittle bit, especially when the someones first conclusion was
the original assessments of processes per node was incorrect and we needed an extra node, which
solved the problem, but wasn't the correct solution.