127 lines
3.7 KiB
ReStructuredText
127 lines
3.7 KiB
ReStructuredText
.. Permission is granted to copy, distribute and/or modify this
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.. document under the terms of the GNU Free Documentation License,
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.. Version 1.1 or any later version published by the Free Software
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.. Foundation, with no Invariant Sections, no Front-Cover Texts
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.. and no Back-Cover Texts. A copy of the license is included at
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.. Documentation/media/uapi/fdl-appendix.rst.
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..
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.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
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.. c:type:: dvb_frontend_parameters
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*******************
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frontend parameters
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*******************
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The kind of parameters passed to the frontend device for tuning depend
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on the kind of hardware you are using.
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The struct ``dvb_frontend_parameters`` uses a union with specific
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per-system parameters. However, as newer delivery systems required more
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data, the structure size weren't enough to fit, and just extending its
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size would break the existing applications. So, those parameters were
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replaced by the usage of
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:ref:`FE_GET_PROPERTY/FE_SET_PROPERTY <FE_GET_PROPERTY>`
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ioctl's. The new API is flexible enough to add new parameters to
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existing delivery systems, and to add newer delivery systems.
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So, newer applications should use
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:ref:`FE_GET_PROPERTY/FE_SET_PROPERTY <FE_GET_PROPERTY>`
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instead, in order to be able to support the newer System Delivery like
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DVB-S2, DVB-T2, DVB-C2, ISDB, etc.
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All kinds of parameters are combined as a union in the
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``dvb_frontend_parameters`` structure:
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.. code-block:: c
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struct dvb_frontend_parameters {
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uint32_t frequency; /* (absolute) frequency in Hz for QAM/OFDM */
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/* intermediate frequency in kHz for QPSK */
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fe_spectral_inversion_t inversion;
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union {
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struct dvb_qpsk_parameters qpsk;
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struct dvb_qam_parameters qam;
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struct dvb_ofdm_parameters ofdm;
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struct dvb_vsb_parameters vsb;
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} u;
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};
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In the case of QPSK frontends the ``frequency`` field specifies the
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intermediate frequency, i.e. the offset which is effectively added to
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the local oscillator frequency (LOF) of the LNB. The intermediate
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frequency has to be specified in units of kHz. For QAM and OFDM
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frontends the ``frequency`` specifies the absolute frequency and is
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given in Hz.
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.. c:type:: dvb_qpsk_parameters
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QPSK parameters
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===============
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For satellite QPSK frontends you have to use the ``dvb_qpsk_parameters``
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structure:
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.. code-block:: c
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struct dvb_qpsk_parameters {
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uint32_t symbol_rate; /* symbol rate in Symbols per second */
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fe_code_rate_t fec_inner; /* forward error correction (see above) */
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};
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.. c:type:: dvb_qam_parameters
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QAM parameters
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==============
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for cable QAM frontend you use the ``dvb_qam_parameters`` structure:
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.. code-block:: c
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struct dvb_qam_parameters {
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uint32_t symbol_rate; /* symbol rate in Symbols per second */
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fe_code_rate_t fec_inner; /* forward error correction (see above) */
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fe_modulation_t modulation; /* modulation type (see above) */
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};
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.. c:type:: dvb_vsb_parameters
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VSB parameters
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==============
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ATSC frontends are supported by the ``dvb_vsb_parameters`` structure:
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.. code-block:: c
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struct dvb_vsb_parameters {
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fe_modulation_t modulation; /* modulation type (see above) */
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};
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.. c:type:: dvb_ofdm_parameters
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OFDM parameters
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===============
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DVB-T frontends are supported by the ``dvb_ofdm_parameters`` structure:
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.. code-block:: c
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struct dvb_ofdm_parameters {
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fe_bandwidth_t bandwidth;
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fe_code_rate_t code_rate_HP; /* high priority stream code rate */
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fe_code_rate_t code_rate_LP; /* low priority stream code rate */
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fe_modulation_t constellation; /* modulation type (see above) */
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fe_transmit_mode_t transmission_mode;
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fe_guard_interval_t guard_interval;
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fe_hierarchy_t hierarchy_information;
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};
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