Devin Heitmueller wrote: > On Tue, Jan 5, 2010 at 3:40 AM, Michael Rüttgers > <ich@xxxxxxxxxxxxxxxxxxxx> wrote: >> Hello, >> >> a year ago I bought a device named "Hama Video Editor", which was not >> (and is not yet) supported by the em28xx driver. >> So I played around with the card parameter and got the device basically >> working with card=38. >> Basically working means, that I had a distortion when capturing old >> VHS-Tapes from my old vcr. >> >> The problem can be seen here: >> http://www.michael-ruettgers.de/em28xx/test.avi >> >> A few weeks ago I started tracking down the reason for this issue with >> the help of Devin. >> Wondering, that the device works perfectly in Windows, I compared the >> i2c commands, that programmed the register of the tvp5150 in Windows. >> >> Finally I got the device working properly, setting the "TV/VCR" option >> in the register "Operation Mode Controls Register" at address 02h >> manually to "Automatic mode determined by the internal detection >> circuit. (default)": >> >> 000109: OUT: 000000 ms 107025 ms 40 02 00 00 b8 00 02 00 >>> 02 00 >> >> After programming this register, the distortion issue disappeared. >> >> So my conclusion was, that the TV/VCR detection mode is forced to >> TV-mode in the em28xx, which could have been verified by a look into the >> debug output using the parameter reg_debug=1: >> >> OUT: 40 02 00 00 b8 00 02 00 >>> 02 30 >> >> Bit 4, 5 are used for setting the TV/VCR mode: >> >> Description in the Spec: >>> TV/VCR mode >>> 00 = Automatic mode determined by the internal detection circuit. >> (default) >>> 01 = Reserved >>> 10 = VCR (nonstandard video) mode >>> 11 = TV (standard video) mode >>> With automatic detection enabled, unstable or nonstandard syncs on the >> input video forces the detector into the VCR >>> mode. This turns off the comb filters and turns on the chroma trap >> filter. >> >> Thus far the tvp5150 distortion issues when capturing from vcr. > > Mauro, > > I have been working with Michael on this issue and I did some research > into the history of this issue, and it seems like you introduced code > in rev 2900 which turns off the auto mode and forces the tvp5150 into > "TV mode" if using a composite input: > > http://linuxtv.org/hg/v4l-dvb/rev/e6c585a76c77 > > Could you provide any information on the rationale for this decision? > I would think that having it in auto mode would be the appropriate > default (which is what the Windows driver does), and then you would > force it to either TV or VCR mode only if absolutely necessary. > > The comb filter only gets disabled if the auto mode actually concludes > the device should be in VCR mode. Hence, there shouldn't be any > downside to having it in auto mode unless you have some reason to > believe the detection code is faulty or error-prone. > This is a very old patch, and I forgot the reasons why. On that time, only TV were working. I suspect the change were needed in order to get signal working at Svideo/composite entry on WinTV USB2. Probably, I tested Svideo/composite with an old VCR I used for tests on that time. > We can add a modprobe option to allow the user to force it into one > mode or the other, if someone finds a case where the detection logic > has issues. But forcing it into one particular mode by default > doesn't seem like the right approach. A modprobe option would be very bad, IMHO. If the problem is with some old VCR's, maybe the better is to add a control for it. For example, bttv driver has one such control: V4L2_CID_PRIVATE_VCR_HACK I agree that it makes sense to keep the autodetect mode on by default, but tests are needed to validade if this won't break support with other devices. Cheers, Mauro. -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
