>Hi, > >thanks for your answer. I feel I'm getting closer, but >I still haven't figured it out completely ;-/ Let's hope that this answer helps ... (Manu will post a more detailed mail concerning the same things) >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? Yes. > >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? 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. > > >> -- 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? Sorry, I wasn't correct. Most of the tuning params are retrieved from satellite_delivery_system_descriptor. S2_satellite_delivery_system_descriptor is used to know which mode is used (NBC-BS or BC). In the BC mode it's used for retrieving hp and lp stream ids too (see above). > >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"? Yes. >- S2 descriptor only for BC or non-BS modes? It is used only in BC mode. However it's needed to know which mode is used. > >------------------------------------------------ > >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.) Yes, for NBC-BS S2_satellite_delivery_system_descriptor isn't used, but see above. > >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 Yes. > - are there *multiple* S1 descriptors in the NIT for > this frequency, one with modulation_system S1 and > one for S2? As far as we understood, there is only one for S1 and one for S2 in BC, and just S1 in NBC-BS. > - 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? To select hp and lp stream, you use sismis / stream_id (see above). > >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? Multiple streams are distinguished by different modcods. I don't know anything about the descriptors in this case ... > > >Thanks, >Johannes Christoph _______________________________________________ linux-dvb@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
