Re: STV0299: reading property DTV_FREQUENCY -- what am I expected to get?

[Antti Palosaari <crope@xxxxxx>]

On 08/14/2012 11:53 AM, Reinhard Nissl wrote:
> Hi,
>
> it seems that my 9 years old LNBs got some drift over time, as tuning
> takes quite a while until I get a lock. So I thought I could compensate
> this offset by adjusting VDR's diseqc.conf.
>
> Therefore I first hacked some logging into VDR's tuner code to read and
> output the above mentioned property once it got a lock after tuning. As
> VDR's EPG scanner travels over all transponders when idle, I get offset
> values for all transponders and can then try to find some average offset
> to put into diseqc.conf.
>
> So here are several "travel" results for a single transponder ordered by
> Delta:
>
> Sat.    Pol.    Band    Freq (MHz) Set    Freq (MHz) Get    Delta (MHz)
> S13,0E    H    H    11938    11930,528    -7,472
> S13,0E    H    H    11938    11936,294    -1,706
> S13,0E    H    H    11938    11938,917    0,917
> S13,0E    H    H    11938    11939,158    1,158
> S13,0E    H    H    11938    11939,906    1,906
> S13,0E    H    H    11938    11939,965    1,965
> S13,0E    H    H    11938    11940,029    2,029
> S13,0E    H    H    11938    11940,032    2,032
> S13,0E    H    H    11938    11940,103    2,103
> S13,0E    H    H    11938    11940,112    2,112
> S13,0E    H    H    11938    11940,167    2,167
> S13,0E    H    H    11938    11941,736    3,736
> S13,0E    H    H    11938    11941,736    3,736
> S13,0E    H    H    11938    11941,736    3,736
> S13,0E    H    H    11938    11942,412    4,412
> S13,0E    H    H    11938    11943,604    5,604
> S13,0E    H    H    11938    11943,604    5,604
> S13,0E    H    H    11938    11943,604    5,604
> S13,0E    H    H    11938    11945,472    7,472
> S13,0E    H    H    11938    11945,472    7,472
> S13,0E    H    H    11938    11945,472    7,472
> S13,0E    H    H    11938    11945,472    7,472
> S13,0E    H    H    11938    11945,472    7,472
> S13,0E    H    H    11938    11945,472    7,472
> S13,0E    H    H    11938    11945,472    7,472
> S13,0E    H    H    11938    11945,777    7,777
> S13,0E    H    H    11938    11945,777    7,777
> S13,0E    H    H    11938    11945,777    7,777
> S13,0E    H    H    11938    11945,777    7,777
>
> I really wonder why Delta varies that much, and there are other
> transponders in the same band which have no larger deltas then 3 MHz.
>
> So is it at all possible to determine LNB drift in that way?
>
> My other device, a STB0899, always reports the set frequency. So it
> seems driver dependent whether it reports the actually locked frequency
> found by the zig-zag-algorithm or just the set frequency to tune to.

That is tricky part. I recently explained that too when Mauro added 
get_afc() callback:
http://www.spinics.net/lists/linux-media/msg51308.html

It should return actual frequency frontend is tuned (I am not sure about 
DVB-S as there is IF/LNB). But the way DVBv5 API is implemented, using 
cache, you never know if it is same value you set or some real value 
tuner is listening. You can never trust APIv5 get values - those are 1) 
just same you have set or 2) those could be values updated by driver.

> Thanks in advance for any replies.
>
> Bye.

regards
Antti


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