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[media] DocBook: Improve the description of the properties API 

Make the text clearer about what the properties API does.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
This commit is contained in:
Mauro Carvalho Chehab 2015-05-26 11:04:14 -03:00
parent 277dfcb4e0
commit e4aa18d33c
1 changed files with 32 additions and 5 deletions
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37
Documentation/DocBook/media/dvb/dvbproperty.xml
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@ -1,8 +1,35 @@
<section id="FE_GET_SET_PROPERTY">
<title><constant>FE_GET_PROPERTY/FE_SET_PROPERTY</constant></title>
<para>This section describes the DVB version 5 extension of the DVB-API, also
called "S2API", as this API were added to provide support for DVB-S2. It was
designed to be able to replace the old frontend API. Yet, the DISEQC and
<section id="frontend-properties">
<title>DVB Frontend properties</title>
<para>Tuning into a Digital TV physical channel and starting decoding it
requires to change a set of parameters, in order to control the
tuner, the demodulator, the Linear Low-noise Amplifier (LNA) and to set the
antena subsystem via Satellite Equipment Control (SEC), on satellital
systems. The actual parameters are specific to each particular digital
TV standards, and may change as the digital TV specs evolutes.</para>
<para>In the past, the strategy used were to have an union with the parameters
needed to tune for DVB-S, DVB-C, DVB-T and ATSC delivery systems grouped
there. The problem is that, as the second generation standards appeared,
those structs were not big enough to contain the additional parameters.
Also, the union didn't have any space left to be expanded without breaking
userspace. So, the decision was to deprecate the legacy union/struct based
approach, in favor of a properties set approach.</para>
<para>By using a properties set, it is now possible to extend and support any
digital TV without needing to redesign the API</para>
<para>Example: with the properties based approach, in order to set the tuner
to a DVB-C channel at 651 kHz, modulated with 256-QAM, FEC 3/4 and symbol
rate of 5.217 Mbauds, those properties should be sent to
<link linkend="FE_GET_PROPERTY"><constant>FE_SET_PROPERTY</constant></link> ioctl:</para>
<itemizedlist>
<listitem>DTV_FREQUENCY = 651000000</listitem>
<listitem>DTV_MODULATION = QAM_256</listitem>
<listitem>DTV_INVERSION = INVERSION_AUTO</listitem>
<listitem>DTV_SYMBOL_RATE = 5217000</listitem>
<listitem>DTV_INNER_FEC = FEC_3_4</listitem>
<listitem>DTV_TUNE</listitem>
</itemizedlist>
<para>NOTE: This section describes the DVB version 5 extension of the DVB-API,
also called "S2API", as this API were added to provide support for DVB-S2. It
was designed to be able to replace the old frontend API. Yet, the DISEQC and
the capability ioctls weren't implemented yet via the new way.</para>
<para>The typical usage for the <constant>FE_GET_PROPERTY/FE_SET_PROPERTY</constant>
API is to replace the ioctl's were the <link linkend="dvb-frontend-parameters">