[linux-dvb] DVB-S2 / Multiproto and future modulation support

Hans Werner HWerner4 at gmx.de
Wed Sep 10 18:12:22 CEST 2008

-------- Original-Nachricht --------
> Datum: Wed, 10 Sep 2008 17:10:19 +0200
> Von: Christophe Thommeret <hftom at free.fr>
> An: Steven Toth <stoth at hauppauge.com>
> CC: linux-dvb at linuxtv.org
> Betreff: Re: [linux-dvb] DVB-S2 / Multiproto and future modulation support

> Le Wednesday 10 September 2008 15:38:23 Steven Toth, vous avez écrit :
> > > Is this card able to deliver both S and T at the same time?
> >
> > No, the hardware can do S/S2 or T.
> > The driver in the S2API tree only has S/S2 enabled (for the time being).
> So, maybe we have to think a bit about how to add support for this kind of
> device.

Yes, absolutely, and I hope this can go in to S2API and the kernel. It would be a lie
to claim that linux supports the HVR4000 until this is done. Fortunately Steven
and Darron made experimental drivers which do this.

> I mean, if the driver provides different adapters/frontends (say 
> adapter0/frontend0 and adapter1/frontend0), a typical application will see
> these as separate devices, and then when a user watch a S channel, the app
> assumes that the T frontend is free while in fact it's not.
> For example, Kaffeine updates its channels list according to which
> channels 
> can be viewed (based on which frontends are free). So, if you are
> recording a 
> S channel, all channels on this freq are shown as available and all T 
> channels are also shown as available. But in the HVR4000 case, it's false,
> since the T tuner isn't free.
> Maybe a solution could be to have :
> - adapter0/frontend0 -> S/S2 tuner
> - adapter0/frontend1 -> T tuner

This is what the multifrontend (mfe) driver at http://dev.kewl.org/hauppauge does.
And Kaffeine is the only major DVB app which correctly finds the two frontends
and uses them correctly (well done!!). Or very nearly -- TV watching is perfect, but
the only slight problem happens when you are recording:

(1) record a DVB-T channel:
-->all DVB-T channels except those in same multiplex vanish from the available
channels list (correct)
-->no satellite channels vanish (incorrect)

(2) record a DVB-S channel;
-->all DVB-S channels except those on the same multiplex vanish from the available
channels list (correct)
-->no DVB-T channels vanish (incorrect)

It's a small problem, easily fixed I would think.

> So applications could know that these 2 frontends are exclusive.
> That would not require any API change, but would have to be a rule
> followed by 
> all drivers.

Yes, if we keep to that rule then only frontends which can operate truly
simultaneously should have a different adapter number.

Release early, release often.

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