On Tue, 2008-07-15 at 08:52 +0200, Roberto A. Foglietta wrote: > 2008/7/14 Bernd Petrovitsch <bernd@xxxxxxxxx>: > > On Mon, 2008-07-14 at 20:47 +0200, Roberto A. Foglietta wrote: > >> 2008/7/14 Robert P. J. Day <rpjday@xxxxxxxxxxxxxx>: > >> > > >> > is there a good online explanation of the difference WRT linux? > >> > thanks. > >> > >> Sorry for the attachment but an image is better than many words (sometime)! > >> :-) > >> > >> <word on> > >> hwrt: missing the deadline means crashing the system > > "system" meaning the controlled thing (like an airplane or a train) and > > not only the computer. > > Usually the value of the computer are much lesser than the value of > controlled thing otherwise using a computer does not worth the > effort/investment. > ;-) Yes, but if one fails the deadline in a soft RT environment, nothing serious is destroyed. You just might loose QoS (as in your example below) or just have no real benefit from the system. > However I was thinking at the system as the sum of computer + > software + controlled thing. The difference between sw/hw rt is the > smoothness of the curve after the missed deadline: hard or soft system > dead. The word "crash" as been used to transmit the concept of > irreversible damage (crashing a plane, car, etc. etc.) while loosing > some frame in a audio/video transmission usually reduce the > quality/value/pleasure of the transmission but it is not such a crash > becase we can live with it and keep on. ACK, that's precisely what I wanted to say. Yes, there may be other interpretations (ignoring the ones from sales and marketing departments) of "soft RT" and "hard RT" but the above makes IMHO the most sense. > >> swrt: missing the deadline means loosing quality of service > > or just loosing the benefit > >> <word off> > > Loosing the benefit could happen sharply at the missing of the > deadline or smoothly, in the second case I think "loosing the quality Yes, but even "sharp" vs "smooth" above is IMHO vague enough to not use it to distinguish between 2 quite different types of system. And I don't think an airplane is a "soft RT system" because it falls from the air after a smooth violation of a time constraint somewhere;-) > of service" (whatever the service is) is meaningful enough about > loosing smoothly. Bernd -- Firmix Software GmbH http://www.firmix.at/ mobil: +43 664 4416156 fax: +43 1 7890849-55 Embedded Linux Development and Services -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
