On 03.11.2013 13:31, Mauro Carvalho Chehab wrote:
Em Wed, 23 Oct 2013 00:57:47 +0200
Ralph Metzler <rjkm@xxxxxxxxxxxxxx> escreveu:
I am wondering if anybody looked into API extensions for DVB-C2 yet?
Obviously, we need some more modulations, guard intervals, etc.
even if the demod I use does not actually let me set those (only auto).
But I do need to set the PLP and slice ID.
I currently set them (8 bit each) by combining them into the 32 bit
stream_id (DTV_STREAM_ID parameter).
I don't like the idea of combining them into a single field. One of the
reasons is that we may have endianness issues.
So, IMHO, the better is to add a new property for slice ID.
I tried to understand what that data slice is. So what I understand, it
is layer to group PLPs, in order to get one wide OFDM channel as OFDM is
more efficient when channel bw increases.
So, in order to tune "stream" channel on DVB-C2 system, you *must* know
(in a order from radio channel to upper layers):
frequency
bandwidth
slice ID
PLP ID
Is that right?
I wonder if PLP IDs are defined so that there could not be overlapping
PLP IDs in a system... But if not, then defining slice ID is likely
needed. And if and when slice ID is needed to know before PLP ID, it is
even impossible to resolve slice ID from PLP ID.
By using the stream id like this and not having (or being able) to set
the rest of the new parameters I only have to add SYS_DVBC2 to the delivery systems
right now. But the new parameters should be added for completeness and if we want to
be able to scan we will need calls to read out L1 signalling information.
I didn't have time yet to dig into DVB-C2 API, but I think that the better
is to add full support to all modulation types, guard intervals, etc, even
knowing that most modern demods work fine on auto mode those days.
As you said, scan should be able to read out L1 signaling information.
Also, as we're starting to talk about modulator drivers, all those properties
should be specified on the modulator.
So, it makes sense to add a patch there extending the API (both
documentation and frontend.h) to fully support DVB C2.
regards
Antti
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