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-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,5bcf30769d6d9599 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2001-08-30 07:51:27 PST Path: archiver1.google.com!newsfeed.google.com!newsfeed.stanford.edu!news.ems.psu.edu!news3.cac.psu.edu!usenet From: Robert Spooner Newsgroups: comp.lang.ada Subject: Re: ADA os talk Date: Thu, 30 Aug 2001 10:44:32 -0400 Organization: Penn State University, Center for Academic Computing Message-ID: <3B8E5150.625B9F3E@psu.edu> References: <9mdmck$rs1$1@nh.pace.co.uk> <9me6q4$aai1@news.cis.okstate.edu> <9mg7fr$rm1$1@nh.pace.co.uk> <3CeB8M0VaOC6@eisner.encompasserve.org> <9mgg0p$26j$1@nh.pace.co.uk> NNTP-Posting-Host: sor.arl.psu.edu Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 4.77 [en] (Windows NT 5.0; U) X-Accept-Language: en,de,fr-FR To: Larry Kilgallen Xref: archiver1.google.com comp.lang.ada:12592 Date: 2001-08-30T10:44:32-04:00 List-Id: Larry Kilgallen wrote: > > In article <9mgg0p$26j$1@nh.pace.co.uk>, "Marin David Condic" writes: > > > Like I said, my memory of the situation whas that techniques were possible > > under VMS to run realtime, but that VMS wasn't designed to specifically > > provide some kind of realtime mode. Sort of a case where if you had enough > > privileges and enough priority and could keep anything else from taking > > precidence, you could convince yourself that you had fixed latency and > > weren't going to get swapped out. This is different than having a process > > that the OS manages in realtime mode and guarantees you that none of this is > > going to fail. > > Absolutely VMS is designed so that you need privilege to alter its > behavior. By default there is fair treatment for all, and that is > certainly inadequate for realtime needs. The controls to tweak, > however, are all documented as being "for realtime", and those of > us who pass them every day (and ignore them) tend to presume the > priority mechanisms are adequate. The scheduling algorithm has > a different behavior in the upper half of the priority range, > for instance, specifically for realtime. VMS is useful for a wide variety of things, including some near real-time applications, but the predictability of how long it will take for the O/S to perform certain operations was not good enough for us, and it also takes too long to boot. We ended up using VAXELN for our real time O/S on the KAV30, a real-time VME single-board VAX, and VAXELN Ada for our applications. VAXELN has more deterministic algorithms and is an execution only environment with address space protection and a lot of other nice things that some other real-time O/Ss are just now coming out with. Unfortunately, after years of DEC preaching "we have the migration path you need" they did not port VAXELN to the Alpha, did not move to Ada 95, "retired" VAXELN Ada and DEC^H^H^HCompaq is in the process of retiring the rest of the environment we were using. It's really sad, because the quality of the hardware, software, and support was in a class by itself. We were able to use the same compiled code and file system (except for O/S dependent interfaces in a few package bodies) on both VMS and VAXELN. Try that with a Sun/Solaris host and 68060/VxWorks target. At least we have GNAT for both those environments. Even the default record layout was the same since we used the VAX processor for host (data reduction) and target (experiment) so we didn't have to use a lot of record representation clauses. It was as seamless as could be. We had the advantages of both a real-time operating system and a good host O/S with that setup. Bob -- Robert L. Spooner Registered Professional Engineer Associate Research Engineer Intelligent Control Systems Department Applied Research Laboratory Phone: (814) 863-4120 The Pennsylvania State University FAX: (814) 863-7841 P. O. Box 30 State College, PA 16804-0030 rls19@psu.edu