Messages in this thread | | | Subject | Re: Definition of "realtime" | Date | Fri, 2 Oct 1998 14:42:27 -0500 (CDT) | From | kwrohrer@ce ... |
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And lo, Albert D. Cahalan saith unto me: > Olaf Titz writes: > > > A problem is "hard realtime" if time constraints are involved in the > > specification of the problem such that, when the time constraint is > > not met, the behaviour of the program is seen as _not correct_. > ... > > Note the last two words. The definition doesn't deal with possible > > consequences from wrong behaviour, it just states that the behaviour > > This distinction is not useful then, since the success of a hard > real-time process may be far less important than the on-time behavior > of a soft real-time process. Not useful to you, perhaps. However, it is at least a design decision, and in fact has implementation consequences: hard realtime avoids all possibility of missing deadlines, whereas soft realtime avoids missing deadlines where possible and attempts to handle failures when deadlines are missed.
> It is only the consequences that matter, and the OS can not determine > how expensive the consequences are. Humans let the OS know, and the > OS must avoid missing deadlines. Humans must *make* the OS avoid missing deadlines, if they are designing the OS or the system.
> (so it was bad to bother Richard Gooch with such a pointless question) The original error I pointed out (whose, I don't remeber, but it was consistent) was a completely different confusion: shortness of deadline and/or very low slack time/permissible latency was being confused with the hardness of the real time system. You may have pooh-poohed a clarification of a different error, but nonetheless you seem to be scoffing without understanding what you're scoffing at. If I knew of a good RTOS book, I'd be recommending it to you right now.
Keith
-- "The avalanche has already started; |Linux: http://www.linuxhq.com |"Zooty, it is too late for the pebbles to |KDE: http://www.kde.org | zoot vote." Kosh, "Believers", Babylon 5 |Keith: kwrohrer@enteract.com | zoot!" www.midwinter.com/lurk/lurker.html |http://www.enteract.com/~kwrohrer | --Rebo
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