Date: Wed, 15 May 1996 06:21:36 -0400 (EDT) From: Peter Dufault <dufault@hda.com> To: h.nalen@mbox300.swipnet.se (H Nalen) Cc: hackers@freebsd.org Subject: Re: Hello, Message-ID: <199605151021.GAA06937@hda.com> In-Reply-To: <01BB41D8.FF393060@dialup105-3-3.swipnet.se> from "H Nalen" at May 14, 96 09:04:21 pm
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> I've needed help about DMA and searched the Web and found a good article = > at your site.=20 > > I'm working with electronics and I have a app. that is rather = > time-critical (if you know what I mean). I have a fast AD that need to = > be served at a high rate, i.e store the data in realtime. I belive the = > only way is to do it with DMA. I've using Intels 386-EX as CPU = > (embedded) that has 2 DMA-channels. The AD need to store a 16 bits = > parallell data at a rate of 5 us (up to 8 Mb). > =20 > What operating mode do YOU suggest? Single, chained? Do you think the = > CPU and the other software "feels" this DMA-transfer?=20 > > One more question, the DRAM-refresh. Do it need much bustime? The DRAM = > need refresh every 16ms and I wounder how much bus-time the refresh = > takes? (Would the DMA-transfer been destroyed or delayed so the data = > could not be saved correct?) > > I would be grateful if anyone could answer this few questions. If you = > can't, can you tell me someone that can help me with this? Here are a few points. You've left out some pieces of the puzzle. 2 bytes every five microseconds is 400K/s, not a high data rate. What speed 386EX and memory are you using? What are you doing with that up to 8MB sample - do you reduce it and act on it or store it somewhere? You need to sketch out the full continuous I/O and processing load for each frame to size things and choose hardware and software. If you have a FIFO between the part and your system you can go that route and have better control over bandwidth scheduling. Are you building this or is this an off the shelf A-D board that limits what you can do? Which CPU board is it? As for FreeBSD: I don't think anyone has booted FreeBSD on a 386EX board, though I'd like to see it. You'd need at least 4MB of memory and it would probably take some hacking to get it working - I'm not too familiar with that chip but I know it has some differences in terms of number of DMA channels supported versus a real ISA board, etc. If you had a system with a floppy you could boot a standard release of DOS off of it would be interesting to try to boot one of the FreeBSD boot floppies. I'm not sure how far you'd get. For commercial support you can look at QNX in Canada (info@qnx.com I guess, and I think comp.os.qnx), and also Intel was giving away IRMX with 386EX purchases so you may have a licence for that. -- 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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