From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-0.4 required=5.0 tests=AC_FROM_MANY_DOTS,BAYES_00 autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,8c3f76cf9b2829c4 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2001-01-27 06:36:46 PST Path: supernews.google.com!sn-xit-02!sn-xit-01!supernews.com!feeder.qis.net!dca1-hub1.news.digex.net!intermedia!cpk-news-hub1.bbnplanet.com!news.gtei.net!newshub2.home.com!news.home.com!news.mindspring.net!not-for-mail From: Marin David Condic Newsgroups: comp.lang.ada Subject: Re: Duration vs. Ada.Real_Time Date: Sat, 27 Jan 2001 09:34:07 -0500 Organization: MindSpring Enterprises Message-ID: <3A72DC5E.4C1CE092@acm.org> References: <980495512.529981@edh3> <3A71814B.7E8CCF60@acm.org> <94s5bl$r1r$1@nnrp1.deja.com> <3A71E4F6.6D7015AD@acm.org> <94sqch$fls$1@nnrp1.deja.com> NNTP-Posting-Host: d1.56.bb.f8 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Server-Date: 27 Jan 2001 14:36:01 GMT X-Mailer: Mozilla 4.07 [en] (WinNT; I) Xref: supernews.google.com comp.lang.ada:4599 Date: 2001-01-27T14:36:01+00:00 List-Id: Ted Dennison wrote: > In article <3A71E4F6.6D7015AD@acm.org>, > Marin David Condic wrote: > > > I would think that a reasonable implementation of Ada for realtime > > systems would want to insure that the precision had some relationship > > to the accuracy of the clock available. Obviously, for > Do you mean "accuracy" or "frequency"? O.K. Pick nits. :-) I meant "frequency" but this is in a way related to "accuracy". If my micrometer is marked off in thousanths of an inch, it does me no good to try to measure ten-thousanths of an inch, so in manufacturing parts, I can't be any more accurate than to a thousanth of an inch. My micrometer may have been bounced off the milling machine a few times too many and may actually not be "accurate" in measuring a 1" dimension. > > ... > > be changed for the language. But stating, for example, that the > > precision of a time representation can go down to atto-seconds can > > easily mislead one to believe that the measurement of time is going to > > be something close to that precision. > > This gets back around to the issue we were discussing a couple of weeks > ago. If the language requires units of seconds, but the system's clock > used some incompatable system like Hz (eg: 60 Hz, which can't be > represented exactly in terms of fixed-point seconds), then you (or at > least *I*) would actually prefer a much higher precision, so that your > error in representation isn't so great when you start to do math with it. Well, you do want some precision beyond the smallest unit of the actual clock time if you have this sort of situation. But most of the clocks I've seen are some version of a scaled integer, thus allowing Duration'Small to be whatever it wants to be as long as the LSB is under 20mSec. Am I incorrect in this? MDC -- ====================================================================== Marin David Condic - Quadrus Corporation - http://www.quadruscorp.com/ Send Replies To: m c o n d i c @ q u a d r u s c o r p . c o m Visit my web site at: http://www.mcondic.com/ "I'd trade it all for just a little more" -- Charles Montgomery Burns, [4F10] ======================================================================