[linux-dvb] DVB-S2 and other (new) modulation standards

Felix Domke tmbinc at elitedvb.net
Wed Nov 23 00:25:25 CET 2005


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Johannes Stezenbach wrote:
> Maybe we should finally rename FE_QPSK etc. and dvb_qpsk_parameters etc.
> to FE_TYPE_DVB_S etc. and dvb_tuning_parameters_dvb_t etc.,
> and provide backwards compat #defines for "old" apps?
> This wouldn't create binary compatibilty problems.
YES. please.

That would stop the endless questions about "but - DVB-T be QAM, too?
Which structure is the right one?" A modulation just does not describe
the important things - it's the standard.

A standard much better matches a structure definition than a modulation.

Each new standard would require a new struct, which is fine then.

> How about enum fe_rolloff_flag from Marcel's posting?
It would be part of that new dvb_qpsk2_parameters-struct, which should
then be renamed to dvb_dvbs2_parameters, yes.

Does changing the size breaks binary compatibility? The usercopy just
has to copy the correct size, depending on the selected standard.

The alternative would be FE_SET_FRONTEND_DVBS, FE_SET_FRONTEND_DVBC, ...

I don't like the current that a parameter external to the
FE_SET_FRONTEND call determines which parts of the
dvb_frontend_parameters are used. For example, strace could never
properly decode a FE_SET_FRONTEND - but i agree that adding IOCTLs might
not be the best.

>>This method would also catch the DVB-S/DVB-T-combi frontends which
>>lately appeared here. One could set the STANDARD, and the frontend would
>>change it's complete personality (probably including other FE_CAN_-caps,
>>changing the frequency_min/max/..-limits etc.). A frontend could decide
>>to stop supporting SEC commands when switched to DVB-T mode etc.
> Hm. How do we handle dvb_frontend_info.type?
It should change after a FE_SET_STANDARD.

The allowed standards should be in the capabilities-list.

It would be backward compatible - applications not selecting a certain
standard would use the default standard. Dual-Mode-Frontends would
default to either DVB-S, oder -T or whatever. There could be a tool to
change the mode. DVB-S2 would simply be not possible without the new
FE_SET_STANDARD, as the default would be DVB-S.

Felix
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