From owner-freebsd-multimedia Tue Dec 1 10:11:38 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id KAA26044 for freebsd-multimedia-outgoing; Tue, 1 Dec 1998 10:11:38 -0800 (PST) (envelope-from owner-freebsd-multimedia@FreeBSD.ORG) Received: from labinfo.iet.unipi.it (labinfo.iet.unipi.it [131.114.9.5]) by hub.freebsd.org (8.8.8/8.8.8) with SMTP id KAA26022 for ; Tue, 1 Dec 1998 10:11:33 -0800 (PST) (envelope-from luigi@labinfo.iet.unipi.it) Received: from localhost (luigi@localhost) by labinfo.iet.unipi.it (8.6.5/8.6.5) id RAA02548; Tue, 1 Dec 1998 17:01:32 +0100 From: Luigi Rizzo Message-Id: <199812011601.RAA02548@labinfo.iet.unipi.it> Subject: Re: BT848 adaptive AGC To: mmt-ref@tu-dresden.de Date: Tue, 1 Dec 1998 17:01:31 +0100 (MET) Cc: roger@cs.strath.ac.uk, multimedia@FreeBSD.ORG In-Reply-To: from "Christoph Fleck" at Dec 1, 98 03:38:23 pm X-Mailer: ELM [version 2.4 PL23] Content-Type: text Sender: owner-freebsd-multimedia@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org > Thanks a lot for your fast answer. > > > > Can the BT848 driver enable the adaptive AGC mode? > > > > The adaptive AGC could avoid this. > > > > I doubt it! ... > > The "CRUSH" bit is disabled by default (at least in my copy of the > > sources) because I found out that the adaptation process is one-way: > > it reduces the gain, but never brings it up again. So when you have > > bad signal (usually from the tuner) and the capture chip looks for > > sync pulses in the wrong place, the image turns rapidly black. > > I think you don't want this feature, anyways. > > I could not play with this option in the past. Is it even not useful on > very smooth videosignals? no it is not, because it is unidirectional and it only serves to avoid saturation on the ADC. > > yuv422_prog(), yuv12_prog() -- i am not sure if this is a mistake > > or it is intentional. You can easily try to disable it yourself by > > commenting out the three pairs of lines in the above functions. > > I am not yet looked at the code. A small prog to set the registers > at runtime could help me very much. invest 10 minutes, look at /sys/pci/brooktree848.c, find the 3 places where {e|o}_scloop are set and change the value to 0 (or comment out those lines). This is really the quickest way to do (after all you have only two possible values so it does not pay to modify/add some ioctl to do the same job). > If there is no solution by the software to freeze or even limit the restless > AGC, I probably try to build an external referencevoltage for manual adjusting > of gain control. But this should be the very last. nor very effective as if the problem is agc-related you'd have to track the input signal and understand how to defeat the agc... luigi To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-multimedia" in the body of the message