120 lines
3.3 KiB
ReStructuredText
Executable file
120 lines
3.3 KiB
ReStructuredText
Executable file
.. -*- coding: utf-8; mode: rst -*-
|
|
|
|
.. c:type:: 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 a 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 a union in the
|
|
``dvb_frontend_parameters`` 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.
|
|
|
|
|
|
.. c:type:: 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) */
|
|
};
|
|
|
|
|
|
.. c:type:: 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) */
|
|
};
|
|
|
|
|
|
.. c:type:: 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) */
|
|
};
|
|
|
|
|
|
.. c:type:: 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;
|
|
};
|