[linux-dvb] Re: Couple of frontend questions

[Andrew de Quincey <adq_dvb@lidskialf.net>]

On Friday 27 February 2004 12:15, Johannes Stezenbach wrote:
> Andrew de Quincey wrote:
> > I would suggest the following is done:
> >
> > FE_RESET ioctl. Change to FE_POLL. The frontends which use this only once
> > to kick off tuning will be changed so that they just do this as part of
> > FE_SET_FRONTEND, which is really how it should be anyway.
> >
> > FE_CAN_CLEAN_SETUP. Remove this completely.
> >
> > Add FE_NEEDS_POLL. If this is set, the FE_POLL internal ioctl will be
> > issued during tuning. So only the ves1x93 frontend will currently have
> > this set, and it will use it to reset the signal acquisition algorithms.
> >
> > FE_CAN_RECOVER. Change name to FE_CAN_COMPENSATE_DRIFT. Same semantics as
> > FE_CAN_RECOVER, but a clearer name.
>
> FE_CAN_COMPENSATE_DRIFT is a bit misleading. I think FE_CAN_RECOVER
> means that if you unplug the antenna cable and replug it, the
> frontend will resynchronize itself without manual intervention.
> You'd think that every frontend should be able to do this, but...

Oh right. At the moment, the new code doesn't start a zigzag scan if 
FE_CAN_RECOVER is set. But is this the right behaviour? If FE_CAN_RECOVER 
means it can recover from the cable being unplugged, that doesn't necessarily 
mean it doesn't need to have the zigzag scan for LNB drift, because we can't 
tell the difference between the two.

So in that case, is there any point in having FE_CAN_RECOVER? To ensure it 
works, we have to do a zigzag scan anyway. 

I _suppose_ you could just do one zigzag scan if FE_CAN_RECOVER is set. If 
that fails, then you assume the cable has been unplugged, and stop 
zigzagging. But I don't like that; that could easily fail if for some reason 
the first zigzag scan failed to lock on (e.g. the old noisy signal lock time 
problem) and there really WAS LNB drift.

> > What do you think? I won't actually do any of this until after you've
> > done that release, to save you some hassle (sorry about checking the
> > dvb_frontend changes in immediately BTW; I should have thought first).
>
> If you have patches just post them to the list so I can test them.

Sure.


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