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.
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
- 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.
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.
> >- 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
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