134 lines
4.6 KiB
ReStructuredText
134 lines
4.6 KiB
ReStructuredText
.. Permission is granted to copy, distribute and/or modify this
|
|
.. document under the terms of the GNU Free Documentation License,
|
|
.. Version 1.1 or any later version published by the Free Software
|
|
.. Foundation, with no Invariant Sections, no Front-Cover Texts
|
|
.. and no Back-Cover Texts. A copy of the license is included at
|
|
.. Documentation/userspace-api/media/fdl-appendix.rst.
|
|
..
|
|
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
|
|
|
|
.. _frontend-properties:
|
|
|
|
**************
|
|
Property types
|
|
**************
|
|
|
|
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 (up to DVB API version 3 - DVBv3), 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, the size of such union was not big
|
|
enough to group the structs that would be required for those new
|
|
standards. Also, extending it would break userspace.
|
|
|
|
So, the legacy union/struct based approach was deprecated, in favor
|
|
of a properties set approach. On such approach,
|
|
:ref:`FE_GET_PROPERTY and FE_SET_PROPERTY <FE_GET_PROPERTY>` are used
|
|
to setup the frontend and read its status.
|
|
|
|
The actual action is determined by a set of dtv_property cmd/data pairs.
|
|
With one single ioctl, is possible to get/set up to 64 properties.
|
|
|
|
This section describes the new and recommended way to set the frontend,
|
|
with supports all digital TV delivery systems.
|
|
|
|
.. note::
|
|
|
|
1. On Linux DVB API version 3, setting a frontend was done via
|
|
struct :c:type:`dvb_frontend_parameters`.
|
|
|
|
2. Don't use DVB API version 3 calls on hardware with supports
|
|
newer standards. Such API provides no support or a very limited
|
|
support to new standards and/or new hardware.
|
|
|
|
3. Nowadays, most frontends support multiple delivery systems.
|
|
Only with DVB API version 5 calls it is possible to switch between
|
|
the multiple delivery systems supported by a frontend.
|
|
|
|
4. DVB API version 5 is also called *S2API*, as the first
|
|
new standard added to it was DVB-S2.
|
|
|
|
**Example**: in order to set the hardware to tune into 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`.
|
|
|
|
.. code-block:: c
|
|
:caption: Example: Setting digital TV frontend properties
|
|
:name: dtv-prop-example
|
|
|
|
#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
|
|
|
|
fe_property_parameters
|
|
frontend-stat-properties
|
|
frontend-property-terrestrial-systems
|
|
frontend-property-cable-systems
|
|
frontend-property-satellite-systems
|
|
frontend-header
|