1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2
3 .. c:type:: dvb_frontend_parameters
4
5 *******************
6 frontend parameters
7 *******************
8
9 The kind of parameters passed to the frontend device for tuning depend
10 on the kind of hardware you are using.
11
12 The struct ``dvb_frontend_parameters`` uses a union with specific
13 per-system parameters. However, as newer delivery systems required more
14 data, the structure size weren't enough to fit, and just extending its
15 size would break the existing applications. So, those parameters were
16 replaced by the usage of
17 :ref:`FE_GET_PROPERTY/FE_SET_PROPERTY <FE_GET_PROPERTY>`
18 ioctl's. The new API is flexible enough to add new parameters to
19 existing delivery systems, and to add newer delivery systems.
20
21 So, newer applications should use
22 :ref:`FE_GET_PROPERTY/FE_SET_PROPERTY <FE_GET_PROPERTY>`
23 instead, in order to be able to support the newer System Delivery like
24 DVB-S2, DVB-T2, DVB-C2, ISDB, etc.
25
26 All kinds of parameters are combined as a union in the
27 ``dvb_frontend_parameters`` structure:
28
29
30 .. code-block:: c
31
32 struct dvb_frontend_parameters {
33 uint32_t frequency; /* (absolute) frequency in Hz for QAM/OFDM */
34 /* intermediate frequency in kHz for QPSK */
35 fe_spectral_inversion_t inversion;
36 union {
37 struct dvb_qpsk_parameters qpsk;
38 struct dvb_qam_parameters qam;
39 struct dvb_ofdm_parameters ofdm;
40 struct dvb_vsb_parameters vsb;
41 } u;
42 };
43
44 In the case of QPSK frontends the ``frequency`` field specifies the
45 intermediate frequency, i.e. the offset which is effectively added to
46 the local oscillator frequency (LOF) of the LNB. The intermediate
47 frequency has to be specified in units of kHz. For QAM and OFDM
48 frontends the ``frequency`` specifies the absolute frequency and is
49 given in Hz.
50
51
52 .. c:type:: dvb_qpsk_parameters
53
54 QPSK parameters
55 ===============
56
57 For satellite QPSK frontends you have to use the ``dvb_qpsk_parameters``
58 structure:
59
60
61 .. code-block:: c
62
63 struct dvb_qpsk_parameters {
64 uint32_t symbol_rate; /* symbol rate in Symbols per second */
65 fe_code_rate_t fec_inner; /* forward error correction (see above) */
66 };
67
68
69 .. c:type:: dvb_qam_parameters
70
71 QAM parameters
72 ==============
73
74 for cable QAM frontend you use the ``dvb_qam_parameters`` structure:
75
76
77 .. code-block:: c
78
79 struct dvb_qam_parameters {
80 uint32_t symbol_rate; /* symbol rate in Symbols per second */
81 fe_code_rate_t fec_inner; /* forward error correction (see above) */
82 fe_modulation_t modulation; /* modulation type (see above) */
83 };
84
85
86 .. c:type:: dvb_vsb_parameters
87
88 VSB parameters
89 ==============
90
91 ATSC frontends are supported by the ``dvb_vsb_parameters`` structure:
92
93
94 .. code-block:: c
95
96 struct dvb_vsb_parameters {
97 fe_modulation_t modulation; /* modulation type (see above) */
98 };
99
100
101 .. c:type:: dvb_ofdm_parameters
102
103 OFDM parameters
104 ===============
105
106 DVB-T frontends are supported by the ``dvb_ofdm_parameters`` structure:
107
108
109 .. code-block:: c
110
111 struct dvb_ofdm_parameters {
112 fe_bandwidth_t bandwidth;
113 fe_code_rate_t code_rate_HP; /* high priority stream code rate */
114 fe_code_rate_t code_rate_LP; /* low priority stream code rate */
115 fe_modulation_t constellation; /* modulation type (see above) */
116 fe_transmit_mode_t transmission_mode;
117 fe_guard_interval_t guard_interval;
118 fe_hierarchy_t hierarchy_information;
119 };
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