[linux-dvb] Re: Problems with Frontend API

[rolf.siebrecht@t-online.de (Rolf Siebrecht)]

Hi!

On Thu, 15 Nov 2001, davep wrote:
> > I tried to read the signal strength via the FE_READ_SIGNAL_STRENGTH
> > command,
> > but I get 0 as result every time, even if the tuning was successful. Has
> > anyone tried
> > this with better results ?
> >
> > I call it like this inside the zap_to function in szap.c :
> >
> > long int strength = -1;
> > ...
> > result =3D ioctl(fefd,FE_READ_SIGNAL_STRENGTH,&strength);
> >
> > I'm using a WinDVB-S card,
> 
> I've noticed the same with my WinTV Nova-T card. Also FE_READ_SNR returns 
> zero and FE_READ_BER returns random-looking garbage.

Look at the various demodulator modules:

L64781.c returns a fixed front.nest == 0.
VES1820.c returns front.nest == 0.
stv0299.c returns front.afc == 0, front.agc == 0, front.vber == 0.
tda8083.c returns f.afc==0, f.agc==0, f.sync==0, f.nest==0, f.vber==0.
Only VES1893.c seems to return true register values for the whole set of
parameters.

So, dependent on the DVB card type you have you may experience
unreasonable results for the some of the FE_READ commands.

BER is derived from front.vber.
SIGNAL    - " -     front.agc.
SNR       - " -     front.nest.

To derive SIGNAL a dvb-0.9.x driver makes other computations than a 0.8.x
driver.

You must always keep in mind if measurements achieved at different times
and by different utilities are comparable at all.


Bye,
     Rolf



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