Xref: utzoo comp.sys.amiga.tech:8149 comp.realtime:305 Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!texbell!sugar!peter From: peter@sugar.hackercorp.com (Peter da Silva) Newsgroups: comp.sys.amiga.tech,comp.realtime Subject: Realtime and UNIX (Re: An opportunity for Commodore (Re: Windows without Front/Back gadgets)) Message-ID: <4537@sugar.hackercorp.com> Date: 13 Nov 89 13:35:06 GMT References: <22175@gryphon.COM> Reply-To: peter@sugar.hackercorp.com (Peter da Silva) Followup-To: comp.realtime Organization: Sugar Land Unix - Houston Lines: 60 This message is only tangentially relevent to the Amiga, and the chain is likely to veer off into a UNIX vs realtime discussion. I'm directing followups to comp.realtime, where there is likely to be more light and less heat. In article <22175@gryphon.COM> bagpiper@pnet02.gryphon.com (Michael Hunter) writes: > peter@sugar.hackercorp.com (Peter da Silva) writes: > >UNIX is not real time. Many of the things we now take for granted would just > Now Now Now...not quite so hasty. There are extensions to Unix' that make > doing real time work easier. I know. I'm in the SCADA business. None of the extensions that make UNIX real time are generally available. Apparently V.4 will have a preemptable kernel, and that's a start. But it's not enough: a task can still be indefinitely deferred by swapping, UNIX floating priorities, etc. It's possible to build a realtime system that looks like UNIX, but Commodore does not have the resources to do this. > I think your following comments are more along > the lines of Unix has more overhead then Intuit. [I presume you mean AmigaOS] No. There is more to realtime than performance. You can do realtime work on a Cosmac 1802 (almost a 4-bit machine) at 500 KHz. A realtime problem is one in which if an answer is late, it's wrong. Music, for example, is realtime. If a note is late, you've blown it. I suspect you're thinking of the NeXT here, which has been used for music demos. Given enough MIPS, a simple enough problem, and a controlled environment, you can get close enough to realtime for a canned demo. But you've heard what happens to some poorly written music programs on the Amiga when you start excersising the blitter? In UNIX, that sort of thing can go on at arbitrary intervals, and the sorts of things you have to do to make a program real-time aren't possible. > which is very true. But it > also is more portable (even BSD to ATT) then any set of micro OS. This is true but irrelevant. A helicopter is more mobile than a car, but it is also prohibitively expensive for individuals. A real-time UNIX would be wonderful, but there's nobody who can afford to do one for a low-end machine. > A curious though that just came to mind is that Ada is suppose to be part of > the POSIX standard....Ada is (suppose to) react to certain real time stimili > so I think that implies that POSIX will be able to be used for real time > tasks...??? ADA is NOT a real-time system. ADA is a language with certain real-time concepts built in. I've done most of my real-time work in Forth, Fortran, PL/M, and C. All of these languages can be used for real-time work. But running under a non-real-time O/S it's just another language. > Personal gripe: The acronym MIPS has no real hard meaning. It is a relative > measurement that is not relative to anything easily tied down.... I'm using commonly accepted VAX MIPS ratings, based on the latest Dhrystone benchmark. That solid enough for you? -- Peter "Have you hugged your wolf today" da Silva `-_-' "IT'S THE TWO GODDAMNED CULTURES AGAIN !*! Bit-brained nerdery on one 'U` side, effete fin-de-siecle malaise on the other. And kingdoms of hybrid delight abandoned in the middle." -- burns@latcs1.oz (Jonathan Burns)