Re: SYS_DVBS vs. SYS_DVBS2

[Josef Wolf <jw@raven.inka.de>]

Thanks for your response, Mauro!

On Wed, Dec 19, 2018 at 09:22:11AM -0200, Mauro Carvalho Chehab wrote:
> Em Wed, 19 Dec 2018 11:28:46 +0100
> Josef Wolf <jw@raven.inka.de> escreveu:

> > I would like to know how to know whether for a specific program SYS_DVBS or
> > SYS_DVBS2 should be specified to the FE_SET_PROPERTY ioctl() call.
> 
> This is not specific to a program. It affects the hole transponder. Either
> the transponder is DVB-S or DVB-S2.

Yes, I'm aware of it. In my question I meant: when I want to tune to some
program, I need to set the SYS_DVBx property in addition to the other tuning
parameters (like frequency, polarization, FEC etc/pp)

> > Is this somehow broadcasted in some PAT/PMT tables?
> 
> It is at the NAT tables. They contain all needed information to properly
> tune into the transponders. There are different tables, depending if the
> transponder is -S or -S2.

OK.

> > Or is it possible to simple always specify SYS_DVBS2 and the kernel will
> > manage the backwards compatibilities when a DVB-S transponder is specified in
> > the tuning parameters?
> 
> The Kernel can't and shouldn't guess the tuning parameters. It depends
> on userspace to parse the NAT tables and get it right.

It is pretty much obvois to me that the kernel can't guess tuning parameters
like diseqc-sequence, polarity, frequency and symrate. This is because the
kernel needs those parameters to get a signal at all.

But, on the other side, there are lots of parameters that the kernel (or
hardware?) _can_ guess: INVERSION_AUTO, FEC_AUTO, QAM_AUTO just to name some.

So what' so special about SYS_DVBS/SYS_DVBS2 that it has to be handled
differently from those other parameters?

-- 
Josef Wolf
jw@raven.inka.de