Date: Mon, 29 Jan 1996 09:03:15 +0100 (MET) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: hasty@rah.star-gate.com (Amancio Hasty Jr.) Cc: terry@lambert.org, jkh@time.cdrom.com, james@miller.cs.uwm.edu, dufault@hda.com, hackers@FreeBSD.org, multimedia@rah.star-gate.com Subject: Re: [FCC Warning!] The Dangerous effect of Direct TV !! Message-ID: <199601290803.JAA04923@labinfo.iet.unipi.it> In-Reply-To: <199601290155.RAA00586@rah.star-gate.com> from "Amancio Hasty Jr." at Jan 28, 96 05:55:13 pm
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> As I am typing this I am watching TV on my FreeBSD box 8) > Whats different is that Matrox Meteor is dumping video directly > to my video graphic card very little CPU intervention. The > reason for the very little intervention is that the program > "tv" is capturing a single frame at a time. There is no point in doing this, I believe. > > How do you deal with bus-to-bus DMA cache effects? It seems likely > > that this type of usage is one that wasn't considered by the > > motherboard manufacturers... considering how many of them have blown > > simple bus-to-memory DMA cache update/invalidate. > > I still can't answer your question however the program seems to > be behaving quite well. Consider a few things: * why should the VRAM be cacheable in the first place, given that the video chipset is doing all sorts of things on it. * often both the grabber and the video board are on the same PCI bus. * every location is written by the grabber only once per frame. * one frame does not fit into 256K of cache --> we should not bother too much about the problem mentioned by Terry. Luigi
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