diff options
Diffstat (limited to 'Documentation/media/uapi/dvb/dvb-frontend-parameters.rst')
-rw-r--r-- | Documentation/media/uapi/dvb/dvb-frontend-parameters.rst | 119 |
1 files changed, 119 insertions, 0 deletions
diff --git a/Documentation/media/uapi/dvb/dvb-frontend-parameters.rst b/Documentation/media/uapi/dvb/dvb-frontend-parameters.rst new file mode 100644 index 0000000..16cb581 --- /dev/null +++ b/Documentation/media/uapi/dvb/dvb-frontend-parameters.rst @@ -0,0 +1,119 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _dvb-frontend-parameters: + +******************* +frontend parameters +******************* + +The kind of parameters passed to the frontend device for tuning depend +on the kind of hardware you are using. + +The struct ``dvb_frontend_parameters`` uses an union with specific +per-system parameters. However, as newer delivery systems required more +data, the structure size weren't enough to fit, and just extending its +size would break the existing applications. So, those parameters were +replaced by the usage of +:ref:`FE_GET_PROPERTY/FE_SET_PROPERTY <FE_GET_PROPERTY>` +ioctl's. The new API is flexible enough to add new parameters to +existing delivery systems, and to add newer delivery systems. + +So, newer applications should use +:ref:`FE_GET_PROPERTY/FE_SET_PROPERTY <FE_GET_PROPERTY>` +instead, in order to be able to support the newer System Delivery like +DVB-S2, DVB-T2, DVB-C2, ISDB, etc. + +All kinds of parameters are combined as an union in the +FrontendParameters structure: + + +.. code-block:: c + + struct dvb_frontend_parameters { + uint32_t frequency; /* (absolute) frequency in Hz for QAM/OFDM */ + /* intermediate frequency in kHz for QPSK */ + fe_spectral_inversion_t inversion; + union { + struct dvb_qpsk_parameters qpsk; + struct dvb_qam_parameters qam; + struct dvb_ofdm_parameters ofdm; + struct dvb_vsb_parameters vsb; + } u; + }; + +In the case of QPSK frontends the ``frequency`` field specifies the +intermediate frequency, i.e. the offset which is effectively added to +the local oscillator frequency (LOF) of the LNB. The intermediate +frequency has to be specified in units of kHz. For QAM and OFDM +frontends the ``frequency`` specifies the absolute frequency and is +given in Hz. + + +.. _dvb-qpsk-parameters: + +QPSK parameters +=============== + +For satellite QPSK frontends you have to use the ``dvb_qpsk_parameters`` +structure: + + +.. code-block:: c + + struct dvb_qpsk_parameters { + uint32_t symbol_rate; /* symbol rate in Symbols per second */ + fe_code_rate_t fec_inner; /* forward error correction (see above) */ + }; + + +.. _dvb-qam-parameters: + +QAM parameters +============== + +for cable QAM frontend you use the ``dvb_qam_parameters`` structure: + + +.. code-block:: c + + struct dvb_qam_parameters { + uint32_t symbol_rate; /* symbol rate in Symbols per second */ + fe_code_rate_t fec_inner; /* forward error correction (see above) */ + fe_modulation_t modulation; /* modulation type (see above) */ + }; + + +.. _dvb-vsb-parameters: + +VSB parameters +============== + +ATSC frontends are supported by the ``dvb_vsb_parameters`` structure: + + +.. code-block:: c + + struct dvb_vsb_parameters { + fe_modulation_t modulation; /* modulation type (see above) */ + }; + + +.. _dvb-ofdm-parameters: + +OFDM parameters +=============== + +DVB-T frontends are supported by the ``dvb_ofdm_parameters`` structure: + + +.. code-block:: c + + struct dvb_ofdm_parameters { + fe_bandwidth_t bandwidth; + fe_code_rate_t code_rate_HP; /* high priority stream code rate */ + fe_code_rate_t code_rate_LP; /* low priority stream code rate */ + fe_modulation_t constellation; /* modulation type (see above) */ + fe_transmit_mode_t transmission_mode; + fe_guard_interval_t guard_interval; + fe_hierarchy_t hierarchy_information; + }; |