Re: Self restarting property of RTOS-How it works?

From: CBFalconer (cbfalconer_at_yahoo.com)
Date: 02/12/05 

Date: Sat, 12 Feb 2005 20:50:36 GMT

CBFalconer wrote:
> Ed Beroset wrote:
>> Del Cecchi wrote:
>>> Ed Beroset wrote:
>>>
>>>> I have also noticed that the programmers from a computer science
>>>> background tend to be much better at working out a system
>>>> architecture and planning first.
>> [...]
>>>>
>>> Those comp-sci geniuses are the ones that gave us a software
>>> paradigm that is susceptible to attacks as simple as buffer
>>> overruns, and store data in randomly scattered chunks linked by
>>> pointers. And put multiple unrelated locks in the same cache
>>> line? That the ones you are talking about?
>>
>> 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?
>
> 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.

I think I misconstrued your 'synchronized clock'. You are not
talking about time, but about a data clock, i.e. a strobe. In this
case I consider the whole design flawed, because once more I don't
want to trust to statistics. The transmitter should be emitting a
preamble to synchronize the clocks. 

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