[linux-dvb] Re: Couple of frontend questions

[Christian Schuld <chris@sonnengesicht.de>]

Hi,

Am Freitag, 27. Februar 2004 15:24 schrieb Andrew de Quincey:
> The problem with that suggestion is that the AFC could be large for a
> number of reasons, one of which might be the LNB drifting. Others are: the
> frequency might have been slightly misspecified initially, the tuner might
> just not have "wanted" to tune to the frequency at a low AFC that time..
> (yuck, analogue things), momentary noise. I'm sure there are others.
>
> If only frontends had a bit you could read which said when the cable was
> plugged in. But as they don't, we have to assume the worst case, and that
> the LNB has drifted, and start zigzagging.
>
> We could always stop zigzagging after a few seconds if we don't get a lock,
> and assume its a cable unplug. But again, you might have the combination of
> LNB drift AND cable unplugging. Perhaps we should just keep zigzagging.
>
> If the frontend is plugged back in later, then the zigzag will quickly come
> round and lock on correctly again.
>
> Whatever happens, you're going to lose some data.

Please keep the users of motorized dishes in mind. The time between tuning and 
getting lock is in worst case (when the dish must be moved form far east to 
far west) about a minute.
Zigzag works most of the times, but leads to locks on the wrong satellites, 
too. Besides that it makes the installation of such a rotorized dish much 
more complicated, because observing signal strength and SNR to find a new 
satellite is more difficult when zigzagging changes freq/sr/fec all the time.

So I vote for a way to disable zigzagging completely, may be via a sysfs 
interface? It would be nice for tuning the zigzigging parameters, too.

-- 
Viele Grüße
Christian



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