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=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Thread: 115aec,47cd14062de43094 X-Google-Thread: 103376,47cd14062de43094 X-Google-Attributes: gid115aec,gid103376,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news2.google.com!newsread.com!newsprint.newsread.com!63.218.45.11.MISMATCH!newshosting.com!nx02.iad01.newshosting.com!140.99.99.194.MISMATCH!newsfeed1.easynews.com!easynews.com!easynews!cyclone.swbell.net!bos-service1.raytheon.com!dfw-service2.ext.ray.com.POSTED!53ab2750!not-for-mail From: Mark H Johnson User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.realtime,comp.lang.ada Subject: Re: next_period = start + n*period; versus next_period = next_period+period; References: <87sm81o0vt.fsf@deneb.enyo.de> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Message-ID: Date: Thu, 28 Oct 2004 08:37:17 -0500 NNTP-Posting-Host: 192.27.48.106 X-Complaints-To: news@ext.ray.com X-Trace: dfw-service2.ext.ray.com 1098970638 192.27.48.106 (Thu, 28 Oct 2004 08:37:18 CDT) NNTP-Posting-Date: Thu, 28 Oct 2004 08:37:18 CDT Organization: Raytheon Company Xref: g2news1.google.com comp.realtime:527 comp.lang.ada:5797 Date: 2004-10-28T08:37:17-05:00 List-Id: Dmitry A. Kazakov wrote: > On Wed, 27 Oct 2004 08:46:29 -0500, Mark H Johnson wrote: >>It all depends on the application being designed and the safety (or >>accuracy) considerations of that design. > > > Yes, if you change the requirements. (:-)) However, surely, it is > questionable whether jitter and even more so, a small absolute time lag is > a real issue in say 80-100% cases. In my ignorance I always had an > impression that guys developing controllers are just too lazy. They are > pushing the problems with their bad models to us, pure programmers! (:-)) > Nah. I just don't try to build brittle systems. Jitter is a fact of life. A 1 msec jitter on start time may be OK in one case but completely unacceptable in another. I know one system with a 50 usec window (every 12.5 msec) to receive a message otherwise it will go into "safe mode" and take several minutes to recover. We don't even TRY to feed that data with a software interrupt handler - we set up the transfer in advance and use a hardware trigger to send the data. In the case of missing a deadline, the action still should be application specific. --Mark