Self restarting property of RTOS-How it works?

[snip]

Nonsense. You can't tar an entire class of people based on the worst examples. And I say that as an engineer who knows enough to let the computer science fellows do what they do best.

Reply to
Guy Macon
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You suffer from a misunderstanding. Those things in the block of an engine are there to get the sand out when casting. They are not there to protect the block from cracking if the coolant freezes.

So the plugs are artifacts of the manufacturing process and not idiot savers. You didn't check the coolant in the fall? In the days you refer to "25 years ago" it was customary to change coolant every fall. Probably even listed in the manual. You do read manuals, right?

And even a honda or a mercedes will crack the block if the coolant is wrong. GM had nothing to do with it.

Now about the 200 series transmission in my 77 Impala.....

del

Reply to
Del Cecchi

A) I was not referring to the worst examples - I have seen much, MUCH worse examples than that.

B) I did NOT tar the "entire class". If you had not been so keen on being snippy, you would have included (or at least read) the paragraph where I said that there were exceptions, as well as computer scientists who regret the situation. And, incidentally, the paragraph you quoted contained the little words "generally" and "usually" - they mean something, you know.

C) I have considerable experience with dealing with such people, in academia, commerce and elsewhere. Some of my colleagues and ex colleagues have been among the best - but are YOU prepared to justify the design of the X Windowing System, to take one prime example of what I was referring to?

On the last point, the kindest thing that can be said about its software engineering is that it was never intended to be used in a commercial production context.

Regards, Nick Maclaren.

Reply to
Nick Maclaren

There is no substitute for hiring competent people, no matter what their background.

By implying that design work is not "real work" you have just proved my point.

Ed

Reply to
Ed Beroset

[...]

It's interesting to learn that no engineers were ever involved in building such flaws.

My background happens to be more in the engineering than the computer science end of things, but I don't share your evident contempt for the field. Here's an example: An embedded communication system receives packet-based messages of varying lengths at an average rate of 100 packets per minute, but asynchronously. Because the system also checks its timing against the recovered clock from the messages, which it can easily keep synchronized within limits as long as it doesn't go too long without receiving a packet. What is the probability that no packets will arrive in an interval of five seconds?

I can answer that question easily because I've studied a little computer science. Can you? If not, how can you properly engineer the system?

Ed

Reply to
Ed Beroset

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Reply to
valiana

architecture

paradigm

store

multiple

talking

checks

long

computer

Well, first I would want to know the average utilization of the link. Then I would want to know the distribution of the lengths of the packets, and the distribution of the rate at which they are sent. If the distribution is that the utilization is 0.1 percent and the packets are all sent once a minute by a batching system then the probability is

100 percent. On the other hand if the utilization is 99.9 percent and the distribution is uniform, then the probability is very low.

Yes, I too have studied some computer science. The first time I saw some of the algorithms, and the scheme language, I almost plotzed.

del cecchi

>
Reply to
del cecchi

Hm, I could make some assumptions about the statistical properties of those "100 packets per minute", but simple assumptions can be quite wrong. If I have a web server, and I get 100 requests per minute, I expect the traffic to be shaped over the day, and that the likelyhood to receive a single packet between 3 and 5am of my target audience is quite low, while there'll be several high-activity spots during the day. That means a simply random distribution of the packets is not sufficient to give you the worst case.

At least on my most popular German page, the access frequency drops down to one tenth of the typical day use between 2 and 6am. The traffic during the day is pretty flat, though, about one hit per minute. During late night, there are only about five per hour.

--
Bernd Paysan
"If you want it done right, you have to do it yourself"
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Reply to
Bernd Paysan

Of course they were! All professions make mistakes, only in some fields the consequences are more severe, and the cost of fixing it much higher.

Not enough info!

a) What is the packet arrival time distribution? Should we make the assumptions as for a many independent producers, or does the chance of generating a new packet increase as a function of the time since the last?

a) What is the average packet length (in milliseconds)? This is of course needed to be able to calculate the average and expected gap lengths.

With my old telecomms classes 25+ years behind me, I still remember enough to say that this looks like a classic queueing theory question. Erlang to the resque. (But only if the same simplifications hold true!)

The packet gaps will most probably follow a Poisson distribution, with just ~1.6 packets/second on average, the chance of a 5 second gap never happening seems pretty bad, i.e. this would be bad engineering.

Anyway, this is most definitely an engineering problem (at least at my alma mater), not CS.

Terje

--
- 
"almost all programming can be viewed as an exercise in caching"
Reply to
Terje Mathisen

So you've got the answer narrowed down to somewhere between "very low" and 100%? Impressive work. ;-)

Ed

Reply to
Ed Beroset

here is example of a configuration and workload analysis

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System/1 ?
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Series/1 as NCP (was System/1?)

with the help of performance predictor and configurators on hone:

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hone was the online system(s) that provided support for world-wide sales, marketing, and field people.

performance predictor was outgrowth of work at the science center on performance management, workload profiling, the early technology transition from performance management to capacity polanning:

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that allowed sales people to input customer configuration and operational information (often softcopy extracted from the system itself) and be able to do what-if questions about changes to configuration and workload.

as hardware got more and more complex ... configurators were the applications that allowed a sales person to specify rough product specification ... and the application would make sure that enuf correct information was supplied for ordering the equipment.

now, this particular analysis ... i presented at the SNA architecture review board meeting in raleigh and took lots of arrows on.

the reference about keeping timing sync ... is somewhat related when the telcos stopped letting customers have clear-channel T1 links and required them to conform to the ones-density (and 193rd bit) specification.

--
Anne & Lynn Wheeler | http://www.garlic.com/~lynn/
Reply to
Anne & Lynn Wheeler

That's the way I'd approach it.

The problem was deliberately phrased as an engineering problem. But of course in order to solve it, it's useful to know a little about queueing theory which is certainly in the domain of computer science.

That was my point. It's just the same as using calculus in the service of solving engineering problems. Calculus was invented by scientists, not engineers, but it happens to be extremely useful in engineering. Computer science is also useful in engineering, and in my experience, those who have studied computer science have been useful and productive members of programming teams I've worked with.

Ed

Reply to
Ed Beroset

Huh?

AS I wrote above, this class (Erlang/Queuing theory) was taught only in the EE department, not CS. :-(

Most theoretical breakthroughs were made by scientists, that doesn't mean engineers won't use the results.

I never stated that they weren't useful/productive, only that in my personal experience the very best all happened to be engineers, not CS graduates.

Terje PS. This _might_ be a sore spot for me, since I declined an offer to change from EE to CS for my major. :-)

--
- 
"almost all programming can be viewed as an exercise in caching"
Reply to
Terje Mathisen

If you had been following this group for even a short while, you would realise how foolish that makes you look. I don't believe that anyone could believe that I would post such an implication, though trolls would claim it - though I am NOT claiming you are a troll, merely mistaken.

As every experienced designer, engineer and so on will know, there is a world of difference between a "broad brush" outline and a precise template. One difference between a good designer and a bad one is that the former's outlines can be developed into something practical, and the latter's often can't.

Regards, Nick Maclaren.

Reply to
Nick Maclaren

That is the problem unless you can make it work you can not use it. There may not be a safe way to restart a specific task. It is your system so you get to figure it out. You may only be able to put the system in a "safe" state if there is a problem.

Reply to
Neil Kurzman

get lost.

I agree the code must be good enough that it does not runaway, crash, or become confuse due to bad input. It should stop or recover.

Unlike my car. An engine temperature sensor opened. the computer decided it was very cold. It leaned the mixture till the head gasket blew. It should have notice the engine never got any warmer. Unexpected states should always lead to safe behavior and/or blinking lights and buzzers.

Reply to
Neil Kurzman

Poisson is unlikely to be a good model unless there are a large number of independant flows passing through the link.

Given the problem's parameters I'd expect only a few flows to be present.

The distribution of inter-packet gaps will depend on the behavior of the source, the sink, and on other factors such as the and-to-end round trip delay between the systems.

citeseer found a lot of possible papers on the topic. this one seems to be directly relevant:

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and this looks like one of the first to say "hey, poisson doesn't fit":

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- Bill

Reply to
Bill Sommerfeld

If it's internal clock can't stay synchronized over 5 seconds, or even much longer, I think there is something wrong with the hardware design. Of course you haven't defined synchronized. I certainly couldn't answer it, but I would know enough to hunt up queueing theory, which is quite mature and predates computers. Whatever the synchronizing requires, I would attempt to put something in the transmitter system to ensure satisfaction. Statistics can always burn you.

But you are asking the wrong question. However, if you asked what is the probability that 10 packets will arrive in 5 seconds, you would have a good point. Again, the place to look is queueing theory. I do know that the design is going to require some sort of buffering, and if there is nothing else critical and resources are pre-established I will assign as much buffer space as possible (assuming no other similar requirements) and not bother with the details.

--
"If you want to post a followup via groups.google.com, don't use
 the broken "Reply" link at the bottom of the article.  Click on 
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Reply to
CBFalconer

A local university here teaches the same course under two different numbers in the catalog. The only difference is that one is nominally in the CS department and the other in the EE department. At least one of the books I've got on the subject was written by a university professor who works in the EE department. It's still computer science. The

*application* of it is engineering.

Of course. We agree on that, and naturally engineers invent things all the time that are of use to scientists.

I wasn't disputing your observation. I was just adding to it by noting, from my experience, what CS graduates tend to do better. Others seemed to be implying that CS graduates are incapable of working usefully on embedded systems, hence my comment here.

Evidently it's a sore spot for a lot of people! I expect that will fade over time, in the same way that few people working in electrical engineering had EE degrees in the 1950's (because few universities had EE degree programs then). I've hired people with no degree and people with PhDs in unrelated fields; what matters ultimately was whether they could do the job.

Adm. Grace Hopper had a PhD in mathematics.

Could she program? ;-)

Ed

Reply to
Ed Beroset

well, i can tell you that it has no floating point and that its memory bandwidth sucks. and that your nose falls off if you use it.

--
	mac the naïf
Reply to
Alex Colvin

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