1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3.. _frontend-properties: 4 5************** 6Property types 7************** 8 9Tuning into a Digital TV physical channel and starting decoding it 10requires changing a set of parameters, in order to control the tuner, 11the demodulator, the Linear Low-noise Amplifier (LNA) and to set the 12antenna subsystem via Satellite Equipment Control - SEC (on satellite 13systems). The actual parameters are specific to each particular digital 14TV standards, and may change as the digital TV specs evolves. 15 16In the past (up to DVB API version 3 - DVBv3), the strategy used was to have a 17union with the parameters needed to tune for DVB-S, DVB-C, DVB-T and 18ATSC delivery systems grouped there. The problem is that, as the second 19generation standards appeared, the size of such union was not big 20enough to group the structs that would be required for those new 21standards. Also, extending it would break userspace. 22 23So, the legacy union/struct based approach was deprecated, in favor 24of a properties set approach. On such approach, 25:ref:`FE_GET_PROPERTY and FE_SET_PROPERTY <FE_GET_PROPERTY>` are used 26to setup the frontend and read its status. 27 28The actual action is determined by a set of dtv_property cmd/data pairs. 29With one single ioctl, is possible to get/set up to 64 properties. 30 31This section describes the new and recommended way to set the frontend, 32with supports all digital TV delivery systems. 33 34.. note:: 35 36 1. On Linux DVB API version 3, setting a frontend was done via 37 struct :c:type:`dvb_frontend_parameters`. 38 39 2. Don't use DVB API version 3 calls on hardware with supports 40 newer standards. Such API provides no support or a very limited 41 support to new standards and/or new hardware. 42 43 3. Nowadays, most frontends support multiple delivery systems. 44 Only with DVB API version 5 calls it is possible to switch between 45 the multiple delivery systems supported by a frontend. 46 47 4. DVB API version 5 is also called *S2API*, as the first 48 new standard added to it was DVB-S2. 49 50**Example**: in order to set the hardware to tune into a DVB-C channel 51at 651 kHz, modulated with 256-QAM, FEC 3/4 and symbol rate of 5.217 52Mbauds, those properties should be sent to 53:ref:`FE_SET_PROPERTY <FE_GET_PROPERTY>` ioctl: 54 55 :ref:`DTV_DELIVERY_SYSTEM <DTV-DELIVERY-SYSTEM>` = SYS_DVBC_ANNEX_A 56 57 :ref:`DTV_FREQUENCY <DTV-FREQUENCY>` = 651000000 58 59 :ref:`DTV_MODULATION <DTV-MODULATION>` = QAM_256 60 61 :ref:`DTV_INVERSION <DTV-INVERSION>` = INVERSION_AUTO 62 63 :ref:`DTV_SYMBOL_RATE <DTV-SYMBOL-RATE>` = 5217000 64 65 :ref:`DTV_INNER_FEC <DTV-INNER-FEC>` = FEC_3_4 66 67 :ref:`DTV_TUNE <DTV-TUNE>` 68 69The code that would that would do the above is show in 70:ref:`dtv-prop-example`. 71 72.. code-block:: c 73 :caption: Example: Setting digital TV frontend properties 74 :name: dtv-prop-example 75 76 #include <stdio.h> 77 #include <fcntl.h> 78 #include <sys/ioctl.h> 79 #include <linux/dvb/frontend.h> 80 81 static struct dtv_property props[] = { 82 { .cmd = DTV_DELIVERY_SYSTEM, .u.data = SYS_DVBC_ANNEX_A }, 83 { .cmd = DTV_FREQUENCY, .u.data = 651000000 }, 84 { .cmd = DTV_MODULATION, .u.data = QAM_256 }, 85 { .cmd = DTV_INVERSION, .u.data = INVERSION_AUTO }, 86 { .cmd = DTV_SYMBOL_RATE, .u.data = 5217000 }, 87 { .cmd = DTV_INNER_FEC, .u.data = FEC_3_4 }, 88 { .cmd = DTV_TUNE } 89 }; 90 91 static struct dtv_properties dtv_prop = { 92 .num = 6, .props = props 93 }; 94 95 int main(void) 96 { 97 int fd = open("/dev/dvb/adapter0/frontend0", O_RDWR); 98 99 if (!fd) { 100 perror ("open"); 101 return -1; 102 } 103 if (ioctl(fd, FE_SET_PROPERTY, &dtv_prop) == -1) { 104 perror("ioctl"); 105 return -1; 106 } 107 printf("Frontend set\\n"); 108 return 0; 109 } 110 111.. attention:: While it is possible to directly call the Kernel code like the 112 above example, it is strongly recommended to use 113 `libdvbv5 <https://linuxtv.org/docs/libdvbv5/index.html>`__, as it 114 provides abstraction to work with the supported digital TV standards and 115 provides methods for usual operations like program scanning and to 116 read/write channel descriptor files. 117 118.. toctree:: 119 :maxdepth: 1 120 121 fe_property_parameters 122 frontend-stat-properties 123 frontend-property-terrestrial-systems 124 frontend-property-cable-systems 125 frontend-property-satellite-systems 126 frontend-header 127