Hi,
thanks for your answer. I feel I'm getting closer, but
I still haven't figured it out completely ;-/
So, some more questions:
On Tue, May 23, 2006, christophpfister@xxxxxxxxxxx wrote:
> Those params are *all* needed for tuning (except the pad of course). Most
> of them should be self-explanatory. Just a note to the following ones:
>
> + enum dvbfe_obc_mode obc_mode;
>
> Needed to indicate in which mode the transponder is sending. But don't worry,
> this information is provided (see below).
Where does it come from? Is it the value of the
backwards_compatibility_indicator from
the S2 satellite delivery system descriptor?
I don't get the description in EN 300 468, which says
"set according to EN 302 307", but EN 302 307 doesn't
mention this flag at all...
(EN 302 307 contains a description of
"Backwards Compatible modes (optional)" in annex F,
however it's not obvious how it works and what
the relationship to the S2 descriptor is.)
> + enum dvbfe_sismis_flag sismis;
> + __u8 stream_id;
>
> If we set sismis to DVBFE_SISMIS_SINGLE, we have to specify which stream
> should be read. If sismis is set to DVBFE_SISMIS_MULTIPLE the stream_id is
> not used.
>
> -- How to retrieve needed values --
>
> The same way we do it for dvb-x / atsc right now. There is an initial tuning
> file containing the values for a first tune.
>
> Further channel data is retrieved from s2_satellite_delivery_system_descriptor.
I don't want to upset you, but this answer is a bit lame -- I'll try to
explain below why it doesn't further my understanding of the matter.
> Additionally the app has to set _only_ those fields:
>
> + enum dvbfe_sismis_flag sismis;
> + __u8 stream_id;
>
> Normally this is DVBFE_SISMIS_MULTIPLE as long as the app doesn't need special
> behaviour.
If the transmitter broadcasts MIS, I have to set a stream_id
(otherwise I'd get a garbage mix of multiple TS, right?).
Do I then have to set the sismis to DVBFE_SISMIS_MULTIPLE
(because it's MIS) or DVBFE_SISMIS_SINGLE (because I want
to filter out just one of them)?
EN 302 307 annex F talks about high and low priority streams
and hierarchical modulation. A previous version of
the API proposal consequently contained a way to select
the HP/LP stream. Has this been identified as unnecessary?
> -- Usage of this api --
>
> >- how to do service scan for DVB-S2
>
> Should be clear now. First do initial tune with the initial tuning file,
> then get service data from the s2_satellite_delivery_system_descriptor.
>
> >- what changes are necessary for channels.conf
>
> Well that shouldn't matter at this stage, otherwise we have the "chicken
> and egg" problem. But I think it's obvious: We add the params for modulation,
> fec, obc_mode and rolloff to channels.conf.
OK, these questions were not very clear. Let me rephrase:
Assuming VDR only cares about broadcast services (TV + radio),
is the s2_satellite_delivery_system_descriptor relevant
for VDR? All of it or just parts? And why?
EN 300 468 says: "This descriptor is only required if DVB-S2 is not used
in normative broadcast mode (NBC-BS). In normative broadcast
mode the satellite_delivery_system_descriptor is sufficient."
What does this mean?
- NBC-BS == "normative broadcast mode"?
- S2 descriptor only for BC or non-BS modes?
------------------------------------------------
OK, after reading through some parts of EN 302 307 and
EN 300 468 for the umpteenth time, here's how I currently
think it *might* work. Yeah, I'm still not sure, and there
are still holes for you to fill in, and hopefully you can
correct my mistakes:
1. DVB-S2 as used today: DVB-S2 is broadcast on dedicated
transponders in NBC mode; thus no S2 descriptor is
necessary, it is always SIS.
(NBC means an old DVB-S receiver cannot receive it.)
2. BC modes might be used, where a DVB-S and a DVB-S2
transmission are mixed together on the same transponder;
old DVB-S receivers will just see the DVB-S stream,
but DVB-S2 receivers can select either the DVB-S
or the DVB-S2 stream;
- an S2 descriptor must be present
- are there *multiple* S1 descriptors in the NIT for
this frequency, one with modulation_system S1 and
one for S2?
- do you select the HP/LP stream by passing the
backwards_compatibility_indicator? Or rather
by using DVBFE_DELSYS_DVBS vs. DVBFE_DELSYS_DVBS2?
Or even by setting the stream_id?
Or something else?
3. DVB-S2 also allows multiple streams in NBC-BS mode (I think)
(e.g. two TS with different levels of error protection
on the same transponder)
- contradicting EN 300 468 one needs the stream_id
from the S2 descriptor to select one of them
- are there multiple S2 descriptors for this
frequency, one for each stream_id?
Thanks,
Johannes
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