Date: Wed, 29 Mar 1995 09:20:38 -0500 (EST) From: Peter Dufault <dufault@hda.com> To: fernando@cea.Berkeley.EDU (Fernando Astorga) Cc: freebsd-hackers@FreeBSD.org, freebsd-realtime@hda.com Subject: Re: FreeBSD support for realtime systems Message-ID: <199503291420.JAA01232@hda.com> In-Reply-To: <199503291239.EAA04745@halfmoon.cea.berkeley.edu> from "Fernando Astorga" at Mar 29, 95 04:39:49 am
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Fernando Astorga writes: > > > I was wondering if anyone out there has had previous experience with running > real-time systems on a UNIX environment. But first, here's a description: There is a pretty inactive group of people interested in real time on FreeBSD at freebsd-realtime@hda.com. It was put there instead of freefall in order to see if there was really much interest before petitioning the powers to add it. I do plan to get back to that once I get TCP/IP working over SCSI. The time I can spend on FreeBSD is limited. > > A group in Mech. Eng. department here has developed a real-time scheduler to > control a set of machines in the lab. Well, since they needed control of > interrupts to execute tasks at a set time, their first implementation was in > DOS and used Visual C++. As you can imagine, there's been several problems > with this set-up, especially with DOS crashes as students try writing new > programs to control these machines. > > The first problem is VC++, but that is being fixed by switching to Borland C++ > which is a better compiler. > > The next is a bit more difficult. They want to move this system to run on a > more robust OS, so they've been considering OS/2 and NT. But these systems > have fixed time slices, making the job of the scheduler more difficult, if not > impossible, i.e. if the interval for a task is less than the time slice. > I think OS/2 has a time-slice of 20ms, way too slow for some of these > applications. I can't comment on this other than to say I thought OS/2 had a priority scheduler as well, but if you're sure about that you're sure about that. > I'm pushing for porting this scheduler to UNIX, preferably FreeBSD, since it > will run on the lab's PCs. But there are some issues that I'm not too > familiar with, esp. UNIX's time-slice/process priority system. Can someone > who has had experience with real-time systems on UNIX provide some info > on how it can be done? There is fixed priority scheduling on FreeBSD - see "rtprio". However, there is no way to lock a process in memory to avoid page faults, no kernel preemption (other than interrupts), and no way to way to reserve resources. Ask "freebsd-realtime-requests@hda.com" if you want to be added to that mailing list. I'll cc this to freebsd-realtime. Peter -- Peter Dufault Real Time Machine Control and Simulation HD Associates, Inc. Voice: 508 433 6936 dufault@hda.com Fax: 508 433 5267
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