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diff --git a/Documentation/media/uapi/dvb/dvbproperty.rst b/Documentation/media/uapi/dvb/dvbproperty.rst new file mode 100644 index 000000000000..cd0511b06c2c --- /dev/null +++ b/Documentation/media/uapi/dvb/dvbproperty.rst @@ -0,0 +1,116 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _frontend-properties: + +DVB Frontend properties +======================= + +Tuning into a Digital TV physical channel and starting decoding it +requires changing a set of parameters, in order to control the tuner, +the demodulator, the Linear Low-noise Amplifier (LNA) and to set the +antenna subsystem via Satellite Equipment Control (SEC), on satellite +systems. The actual parameters are specific to each particular digital +TV standards, and may change as the digital TV specs evolves. + +In the past, the strategy used was to have a union with the parameters +needed to tune for DVB-S, DVB-C, DVB-T and ATSC delivery systems grouped +there. The problem is that, as the second generation standards appeared, +those structs were not big enough to contain the additional parameters. +Also, the union didn't have any space left to be expanded without +breaking userspace. So, the decision was to deprecate the legacy +union/struct based approach, in favor of a properties set approach. + +.. note:: On Linux DVB API version 3, setting a frontend were done via + :ref:`struct dvb_frontend_parameters <dvb-frontend-parameters>`. + This got replaced on version 5 (also called "S2API", as this API were + added originally_enabled to provide support for DVB-S2), because the + old API has a very limited support to new standards and new hardware. + This section describes the new and recommended way to set the frontend, + with suppports all digital TV delivery systems. + +Example: with the properties based approach, in order to set the tuner +to a DVB-C channel at 651 kHz, modulated with 256-QAM, FEC 3/4 and +symbol rate of 5.217 Mbauds, those properties should be sent to +:ref:`FE_SET_PROPERTY <FE_GET_PROPERTY>` ioctl: + +- :ref:`DTV_DELIVERY_SYSTEM <DTV-DELIVERY-SYSTEM>` = + SYS_DVBC_ANNEX_A + +- :ref:`DTV_FREQUENCY <DTV-FREQUENCY>` = 651000000 + +- :ref:`DTV_MODULATION <DTV-MODULATION>` = QAM_256 + +- :ref:`DTV_INVERSION <DTV-INVERSION>` = INVERSION_AUTO + +- :ref:`DTV_SYMBOL_RATE <DTV-SYMBOL-RATE>` = 5217000 + +- :ref:`DTV_INNER_FEC <DTV-INNER-FEC>` = FEC_3_4 + +- :ref:`DTV_TUNE <DTV-TUNE>` + +The code that would that would do the above is show in +:ref:`dtv-prop-example`. + +.. _dtv-prop-example: + +Example: Setting digital TV frontend properties +=============================================== + +.. code-block:: c + + #include <stdio.h> + #include <fcntl.h> + #include <sys/ioctl.h> + #include <linux/dvb/frontend.h> + + static struct dtv_property props[] = { + { .cmd = DTV_DELIVERY_SYSTEM, .u.data = SYS_DVBC_ANNEX_A }, + { .cmd = DTV_FREQUENCY, .u.data = 651000000 }, + { .cmd = DTV_MODULATION, .u.data = QAM_256 }, + { .cmd = DTV_INVERSION, .u.data = INVERSION_AUTO }, + { .cmd = DTV_SYMBOL_RATE, .u.data = 5217000 }, + { .cmd = DTV_INNER_FEC, .u.data = FEC_3_4 }, + { .cmd = DTV_TUNE } + }; + + static struct dtv_properties dtv_prop = { + .num = 6, .props = props + }; + + int main(void) + { + int fd = open("/dev/dvb/adapter0/frontend0", O_RDWR); + + if (!fd) { + perror ("open"); + return -1; + } + if (ioctl(fd, FE_SET_PROPERTY, &dtv_prop) == -1) { + perror("ioctl"); + return -1; + } + printf("Frontend set\\n"); + return 0; + } + +.. attention:: While it is possible to directly call the Kernel code like the + above example, it is strongly recommended to use + `libdvbv5 <https://linuxtv.org/docs/libdvbv5/index.html>`__, as it + provides abstraction to work with the supported digital TV standards and + provides methods for usual operations like program scanning and to + read/write channel descriptor files. + + +.. toctree:: + :maxdepth: 1 + + dtv-stats + dtv-fe-stats + dtv-property + dtv-properties + dvbproperty-006 + fe_property_parameters + frontend-stat-properties + frontend-property-terrestrial-systems + frontend-property-cable-systems + frontend-property-satellite-systems |