>On Thu, May 25, 2006, christophpfister@xxxxxxxxxxx wrote:
>> >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?
>>
>> Yes.
>
>I'm trying to spell out what your proposal means:
>
>- during scan you get the value of backwards_compatibility_indicator
> and store it (NBC is default if there is no S2 descriptor)
>- for tuning you pass the value of backwards_compatibility_indicator
> verbatim to the API in the obc_mode field
>
>IOW: The demod hw/fw has a seperate BC mode which is enabled
>by DVBFE_OBC_ON.
Yes.
>
>Do I get you correctly? Because while I think it isn't wrong,
>it contradicts what you say below:
>
>> sismis and stream_id are only used in backward compatible mode.
>> In the mis mode both hp and lp streams are received, whereas in sis mode
>> stream_id is used to select hp or lp stream.
>
>I just read EN 302 307 annex F *again*, and it contains two
>totally different BC modes (again, a lot of guesswork done
>by me, please correct and/or amend):
>
>- layered modulation: one DVB-S and one DVB-S2 signal are just mixed
> together and broadcast on the same transponder
> ("asynchronously combined on the same radio-frequency channel");
> i.e. a DVB-S receiver will just see a DVB-S signal (the DVB-S2
> signal will appear as additonal noise); a DVB-S2 receiver will
> just see a DVB-S2 signal; in our API one would select the
> stream via DVBFE_DELSYS_DVBS vs. DVBFE_DELSYS_DVBS2
> ("this operational mode does not require any specific tool
> in the DVB-S.2 specification")
>
> remember the framing of DVB-S and DVB-S2 is totally differernt,
> in DVB-S2 mode the demod will just not sync to a DVB-S signal
Yes. But don't worry about about layered modulation (that's just a way to
transmit two *independent* streams on the same frequency).
So the card really behaves as there would be only one stream (DVB-S when
you select DVBFE_DELSYS_DVBS or DVB-S2 NBC-BS (please let us not argue about
that) when you select DVBFE_DELSYS_DVBS2).
So even if layered modulation would be used (which is quite unlikely), we
aren't affected by it at all.
>
>- hierarchical modulation: one DVB-S and one DVB-S2 signal are
> combined via a hierarchical mapper; the DVB-S2 signal
> is _SIS_ (note that the hierarchical mapper is located *after*
> PL header insertion); a DVB-S receiver will only see the
> DVB-S stream; a DVB-S2 receiver will see the DVB-S2 stream,
> however to do so it needs to be set in a special BC mode
> (because of the "asymmetric 8PSK constellation");
> again our API would use DVBFE_DELSYS_DVBS vs. DVBFE_DELSYS_DVBS2
> to select HP vs. LP stream, but also needs the obc_mode flag.
That's not quite correct. While a DVB-S device receives only the HP stream,
a DVB-S2 device receives *both* streams.
So the most used mode is MIS. The stream_id is used in this case to select
either the lp or the hp stream.
>
>To summarize: BC modes don't use MIS and stream_id, but
>a dedicated modulation mode (layered or hierarchical).
>DVBFE_DELSYS_DVBS vs. DVBFE_DELSYS_DVBS2 selects the
>HP vs. LP stream, for hierarchical modulation the DVB-S2
>demod needs to be set in a dedicated mode. In our API
>I would use a boolean "hierarchical_modulation" to
>enable this mode.
>
>I think this matches the LOWP_EN bit in the HW registers
>which Manu mentioned in his reply.
See above. The SISMIS is only used in backward compatible mode.
(Well SISMIS is retrieved from S2 descriptor which is in turn only provided
if not mode != NBC-BS (means mode == BC)).
>
>
>> >- NBC-BS == "normative broadcast mode"?
>>
>> Yes.
>
>After sleeping it over, I think NBC-BS and
>"normative broadcast mode" are not equivalent.
>DVB-S2 NBC-BS has mandatory and optional parts
>(EN 302 307 table 1), and "normative broadcast mode"
>means "the mandatory parts of NBC-BS only".
>
>I.e. MIS is optional and thus nor part of
>"normative broadcast mode". Thus what EN 300 468
>means to say is: "If you only use the mandatory parts
>of NBC-BS you don't need the S2 descriptor".
>
>
>Johannes
NBC-BS doesn't need the S2 descriptor (as explained earlier).
But still NBC-BS == "normative broadcast mode", e.g. because the backward
compatible mode isn't the same as normative broadcast mode.
Christoph
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