are embedded systems usually real-time systems?

are embedded systems usually real-time systems?

Post by John » Sun, 12 Nov 2006 09:30:56


Embedded systems are computer controlled systems. Real-time systems are
systems that has real-time constraints; it can be soft real-time or
hard real-time. The distinct concepts are clear, but if we put too
concepts together, then I get connfused.

The question is

1) are embedded systems usually real-time systems?

2) are real-time systems usually embedded systems?

please advice. thanks...
 
 
 

are embedded systems usually real-time systems?

Post by Vladimir V » Sun, 12 Nov 2006 11:03:50


"You are asking the wrong questions.
The right questions are:
1. What should be done.
2. How much time and money do we have."

(c) YK

VLV

 
 
 

are embedded systems usually real-time systems?

Post by David T. A » Sun, 12 Nov 2006 11:31:49


Yes to both questions.

It is rare to find an embedded system that doesn't have some hard real-time
deadlines, such as processing an interrupt before the next one occurs. Most
also have soft real-time deadlines.

It is also rare to find a real-time system that isn't embedded. If the
system has hard real-time deadlines and is important, than you put it on its
own circuit board and not on a desktop PC with Windows.

There are exceptions, but since you phrased it as "usually" ... I'd say
"yes" to both questions.
 
 
 

are embedded systems usually real-time systems?

Post by Paul Keina » Sun, 12 Nov 2006 17:19:01

On Fri, 10 Nov 2006 21:31:49 -0500, "David T. Ashley" < XXXX@XXXXX.COM >







And even if you use Windows for some non-critical soft real time
applications, make sure that the computer system does not have any
visible floppy/CD-ROM drives or USB connectors, since bored users seem
to be eager to load all kinds of computer games into the system, when
they realise it is a Windows system :-).

While other systems work properly even when loaded by other low
priority programs, there is always the risk that the unspecified
program might hog all memory resources etc., unless the OS has a
strict quota system (such as VMS) limiting the amount of resources a
single process can grab.

Thus, any critical real-time system would be embedded in the sense
that only predefined programs are allowed.

Paul
 
 
 

are embedded systems usually real-time systems?

Post by Martin Raa » Sun, 12 Nov 2006 17:54:47

Hello John,

John schrieb:

The answer is

1) No and yes, it depends.
e.g. many micro controller have a simple runtime environment
but no RTOS because they only have 4 KB RAM/ROM!

2) No and yes, it depends.
e.g. cash management in bank firms have to be realtime,
since time is money and those systems are huge, not embedded!

Hope it helps to formulate the question better suiting for news groups!!!
--
BaSystem Martin Raabe
E: Martin.Raabe<at>B-a-S-y-s-t-e-m<dot>de
 
 
 

are embedded systems usually real-time systems?

Post by Hans-Bernh » Sun, 12 Nov 2006 23:49:05


Not necessarily. Just because a computer system is embedded doesn't
necessarily mean it controls something. At least not where "to control"
means what control theory talks about.


Usually, but not necessarily.


Not necessarily. Some of them aren't even computes. A good example for
a real-world, completely non-computerized real-time system is a train
station. Arrive 2 seconds after your train departed, and it won't
matter at all how fast or efficient you got there. Same for the post
box if you have to send out some mail to meet a deadline. Late is late,
period.
 
 
 

are embedded systems usually real-time systems?

Post by Vladimir V » Mon, 13 Nov 2006 00:59:18


There is no connection between the "embedded" and the "real time".


Real time systems which are not embedded are everywhere: computer games,
multimedia, communication... There is also many embedded systems which
are *not* real time.


Just the matter of what do you have at hand and what has to be accomplished.


Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.yqcomputer.com/
 
 
 

are embedded systems usually real-time systems?

Post by Adrian Spi » Mon, 13 Nov 2006 03:59:38


[snip]

I agree, in theory, they are separate concepts. I practise, I would say most
embedded systems are also real-time.

[snip]

Perhaps not that "many", but there might be. I couldn't think of any though.
Some examples, please?

Regards,
Adrian
 
 
 

are embedded systems usually real-time systems?

Post by Darin John » Mon, 13 Nov 2006 08:26:27


Make sure you don't confuse "real-time program" with "real-time
system".

A computer running a real-time application that is dedicated to
operating external control systems would be a real-time system,
without necessarily being considered "embedded". Ie, a monitoring and
alarm system, a phone switching network, etc. A custom computer
doesn't need to be designed if an existing one can be reused.

In the past this was especially true, when reinventing a minicomputer
would have been prohibitively expensive compared to just buying one.
It's easier today though, with 32-bit computers fitting onto tiny
boards and simpler customization with PLDs and FPGAs, but I'm sure
standard off the shelf computers are used in some real time systems
still (with custom or standard boards).
 
 
 

are embedded systems usually real-time systems?

Post by Jim Stewar » Mon, 13 Nov 2006 09:43:51


Hmmm, first post with the group and
semester finals coming up. Better
ask your professor.
 
 
 

are embedded systems usually real-time systems?

Post by Paul Keina » Mon, 13 Nov 2006 10:25:55

On Sat, 11 Nov 2006 15:59:18 GMT, Vladimir Vassilevsky




If these are examples of realtime systems, most of these are extremely
soft realtime systems :-).

In computer games, it is very hard to define when the game becomes
useless due to lack of computing power.

For multimedia, dropping a video frame now and then is not so bad,
however failing to deliver audio samples in time is a bad thing.

In communication, most systems rely on flow control (e.g. RTS/CTS for
RS-232 or TCP in network communication), so only a few systems are
truly realtime systems.

Paul
 
 
 

are embedded systems usually real-time systems?

Post by Vladimir V » Mon, 13 Nov 2006 12:03:03


Cards and card readers, data storage and loggers, RKE, displays,
keyboards, clocks, answering machines, appliances...

Actually, there are very few cases where hard deadlines are really
mandated.


VLV
 
 
 

are embedded systems usually real-time systems?

Post by Donal » Mon, 13 Nov 2006 13:51:39


I would say _most_ embedded systems are _not_ real-time systems.


"A RTOS facilitates the creation of a real-time system, but does not
guarantee the finished product will be real-time "


http://www.yqcomputer.com/
 
 
 

are embedded systems usually real-time systems?

Post by Vladimir V » Tue, 14 Nov 2006 04:47:53


]

Cards and card readers, data storage and loggers, RKE, displays,
keyboards, clocks, answering machines, appliances...

Actually, there are not so many cases where the hard deadlines are
really required.


VLV
 
 
 

are embedded systems usually real-time systems?

Post by dmctek.goo » Tue, 14 Nov 2006 05:29:51


It is probably much more "objective" to consider the
"degree of determinism" required by the "actual
application" and what happens if deadlines are missed.



soft realtime<----------------------->hard realtime

multimedia telco switching vehicle tracking ctrl/mgmt
precision machine milling
scada

ruined movie ignored calls machine parts ruined, car wrecks


nb.these are all both embedded and realtime.




David Moore
Systems consultant

http://www.yqcomputer.com/



=====================================