Date: Tue, 27 Apr 1999 06:58:14 +0100 From: Roger Hardiman <roger@cs.strath.ac.uk> To: Juha.Nurmela@quicknet.inet.fi Cc: multimedia@FreeBSD.ORG Subject: Re: brooktree driver problems?? Message-ID: <372551F6.E328D2A0@cs.strath.ac.uk> References: <Pine.BSF.4.05.9904260715220.22043-100000@pena.oh5nxo.ampr.org>
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Juha I agree that the bktr_intr() codes attempt to work out if the interrupt was ODD or EVEN is a bit of a cludge and we should be modifying the risc program to use the special signal bits. I found all this recently when writing the VBI support for teletext capture. > I got so confused about the even/odd things. > Does VRE _follow_ even field ? Yes it does. The bt878 datasheet contradicts itself but I wrote a test to find the real meaning. VRE is at the END of the even field. VRO is at the end of the odd field. > Which field produces the first visible scanline ? In PAL, the odd field is transmitted first, then the even. So a RISC program should be grab to odd data buffer, check for VRO, grab to even data, check for VRE > Circles in still pictures look correct but moving objects > generate an effect which led me to think the fields are > from differing frames (maybe this is just the way television works ?) The fields (odd and even) are "sampled" in the camera 1/50th of a second appart. On a real TV, the phosphor from the odd lines has faded away before the even lines are drawn. Of course this does not happen on a VGA screen, so you see each moving object in two positions. > Can we get vbi data without the corresponding field of pixel data ? Not sure what you mean, but I have preliminary VBI capture on my site now. http://telepresence.dmem.strath.ac.uk/bt848 Do you mean "get VBI from even and odd fields, but just video from the odd field?" If so, in theory yes. But the RISC program I wrote did not work right. I kept getting interrputs due to an error in executing the RISC program. Bye Roger To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-multimedia" in the body of the message
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