On Sun, 2008-11-23 at 09:55 -0500, Andy Walls wrote: > On Sun, 2008-11-23 at 09:29 -0500, Andy Walls wrote: > > On Sun, 2008-11-23 at 12:25 +0100, Levente Novák wrote: > > > Does somebody know how to interpret the register dump of the cx25840 > > > (and also how to set a register to a given value)? Some of the registers > > > are clearly different during a static OSD capture and a dynamic one > > > (when the tape is being played). > > > > Sorry. Your previous mail got lost in my inbox. I'm feeling rather > > under the weather right now and a US holiday is coming up this week, so > > I'm probably not going to look at it soon. > > > > If you want to take a look at it, the data sheet is here: > > > > http://dl.ivtvdriver.org/datasheets/video/cx25840.pdf > > > > The registers definitions are near the back of the document. The video > > processing registers are usually in the 0x400-0x4ff range. The Analog > > front end registers are usually in the 0x100-0x1ff range. > > > > Register 0x488 in particular has the current state of the Analog Front > > End's (AFE) Variable Gain Amplifier (VGA) and the Digital Front End's > > (DFE) Automatic Gain Control (AGC). If the VGA is near the top of it's > > range, then you have a weak analog signal or one that is fooling the VGA > > into thinking that it is weak - this can cause sync problems. > > > Static case: reg 0x488 = 0x26 => Gain = 1.375 = +2.77 dB > Dynamic case: reg 0x488 = 0x19 => Gain = 0.78125 = -2.14 dB > > So there's a total of 4.91 dB difference between the 2 cases' VGA gain > setting for this measurement . > > I would suspect the "static" case signal may be varying - you should > collect some more data points for that case to see how wide of a change > the automatic VGA setting is experiencing. > > You could also experiment with turning off the VGA_AUTO_EN setting and > setting the VGA gain to some fixed value. That way you can "see" the > signal visually presented on the screen without the AFE trying to > compensate for time varying effects going on with the overall signal. > > Registers 0x48d-0x48e also have some threshold settings for the VGA > automatic gain loop for making declarations of horizontal sync > acquisition and loss. Tweaking those may help. I'd try setting the > track range lower to see if I could get the VGA gain algorithm to be a > little more reactive to changes. >
Thanks Andy, I will run some experiments. BTW, is there some kind of tool under Windows which would permit to compare the register values set from within Windows with those under Linux? Regards, Levente _______________________________________________ ivtv-users mailing list [email protected] http://ivtvdriver.org/mailman/listinfo/ivtv-users
