446 lines
15 KiB
ReStructuredText
446 lines
15 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
Digital TV Frontend kABI
|
|
------------------------
|
|
|
|
Digital TV Frontend
|
|
~~~~~~~~~~~~~~~~~~~
|
|
|
|
The Digital TV Frontend kABI defines a driver-internal interface for
|
|
registering low-level, hardware specific driver to a hardware independent
|
|
frontend layer. It is only of interest for Digital TV device driver writers.
|
|
The header file for this API is named ``dvb_frontend.h`` and located in
|
|
``include/media/``.
|
|
|
|
Demodulator driver
|
|
^^^^^^^^^^^^^^^^^^
|
|
|
|
The demodulator driver is responsible to talk with the decoding part of the
|
|
hardware. Such driver should implement :c:type:`dvb_frontend_ops`, with
|
|
tells what type of digital TV standards are supported, and points to a
|
|
series of functions that allow the DVB core to command the hardware via
|
|
the code under ``include/media/dvb_frontend.c``.
|
|
|
|
A typical example of such struct in a driver ``foo`` is::
|
|
|
|
static struct dvb_frontend_ops foo_ops = {
|
|
.delsys = { SYS_DVBT, SYS_DVBT2, SYS_DVBC_ANNEX_A },
|
|
.info = {
|
|
.name = "foo DVB-T/T2/C driver",
|
|
.caps = FE_CAN_FEC_1_2 |
|
|
FE_CAN_FEC_2_3 |
|
|
FE_CAN_FEC_3_4 |
|
|
FE_CAN_FEC_5_6 |
|
|
FE_CAN_FEC_7_8 |
|
|
FE_CAN_FEC_AUTO |
|
|
FE_CAN_QPSK |
|
|
FE_CAN_QAM_16 |
|
|
FE_CAN_QAM_32 |
|
|
FE_CAN_QAM_64 |
|
|
FE_CAN_QAM_128 |
|
|
FE_CAN_QAM_256 |
|
|
FE_CAN_QAM_AUTO |
|
|
FE_CAN_TRANSMISSION_MODE_AUTO |
|
|
FE_CAN_GUARD_INTERVAL_AUTO |
|
|
FE_CAN_HIERARCHY_AUTO |
|
|
FE_CAN_MUTE_TS |
|
|
FE_CAN_2G_MODULATION,
|
|
.frequency_min = 42000000, /* Hz */
|
|
.frequency_max = 1002000000, /* Hz */
|
|
.symbol_rate_min = 870000,
|
|
.symbol_rate_max = 11700000
|
|
},
|
|
.init = foo_init,
|
|
.sleep = foo_sleep,
|
|
.release = foo_release,
|
|
.set_frontend = foo_set_frontend,
|
|
.get_frontend = foo_get_frontend,
|
|
.read_status = foo_get_status_and_stats,
|
|
.tune = foo_tune,
|
|
.i2c_gate_ctrl = foo_i2c_gate_ctrl,
|
|
.get_frontend_algo = foo_get_algo,
|
|
};
|
|
|
|
A typical example of such struct in a driver ``bar`` meant to be used on
|
|
Satellite TV reception is::
|
|
|
|
static const struct dvb_frontend_ops bar_ops = {
|
|
.delsys = { SYS_DVBS, SYS_DVBS2 },
|
|
.info = {
|
|
.name = "Bar DVB-S/S2 demodulator",
|
|
.frequency_min = 500000, /* KHz */
|
|
.frequency_max = 2500000, /* KHz */
|
|
.frequency_stepsize = 0,
|
|
.symbol_rate_min = 1000000,
|
|
.symbol_rate_max = 45000000,
|
|
.symbol_rate_tolerance = 500,
|
|
.caps = FE_CAN_INVERSION_AUTO |
|
|
FE_CAN_FEC_AUTO |
|
|
FE_CAN_QPSK,
|
|
},
|
|
.init = bar_init,
|
|
.sleep = bar_sleep,
|
|
.release = bar_release,
|
|
.set_frontend = bar_set_frontend,
|
|
.get_frontend = bar_get_frontend,
|
|
.read_status = bar_get_status_and_stats,
|
|
.i2c_gate_ctrl = bar_i2c_gate_ctrl,
|
|
.get_frontend_algo = bar_get_algo,
|
|
.tune = bar_tune,
|
|
|
|
/* Satellite-specific */
|
|
.diseqc_send_master_cmd = bar_send_diseqc_msg,
|
|
.diseqc_send_burst = bar_send_burst,
|
|
.set_tone = bar_set_tone,
|
|
.set_voltage = bar_set_voltage,
|
|
};
|
|
|
|
.. note::
|
|
|
|
#) For satellite digital TV standards (DVB-S, DVB-S2, ISDB-S), the
|
|
frequencies are specified in kHz, while, for terrestrial and cable
|
|
standards, they're specified in Hz. Due to that, if the same frontend
|
|
supports both types, you'll need to have two separate
|
|
:c:type:`dvb_frontend_ops` structures, one for each standard.
|
|
#) The ``.i2c_gate_ctrl`` field is present only when the hardware has
|
|
allows controlling an I2C gate (either directly of via some GPIO pin),
|
|
in order to remove the tuner from the I2C bus after a channel is
|
|
tuned.
|
|
#) All new drivers should implement the
|
|
:ref:`DVBv5 statistics <dvbv5_stats>` via ``.read_status``.
|
|
Yet, there are a number of callbacks meant to get statistics for
|
|
signal strength, S/N and UCB. Those are there to provide backward
|
|
compatibility with legacy applications that don't support the DVBv5
|
|
API. Implementing those callbacks are optional. Those callbacks may be
|
|
removed in the future, after we have all existing drivers supporting
|
|
DVBv5 stats.
|
|
#) Other callbacks are required for satellite TV standards, in order to
|
|
control LNBf and DiSEqC: ``.diseqc_send_master_cmd``,
|
|
``.diseqc_send_burst``, ``.set_tone``, ``.set_voltage``.
|
|
|
|
.. |delta| unicode:: U+00394
|
|
|
|
The ``include/media/dvb_frontend.c`` has a kernel thread with is
|
|
responsible for tuning the device. It supports multiple algorithms to
|
|
detect a channel, as defined at enum :c:func:`dvbfe_algo`.
|
|
|
|
The algorithm to be used is obtained via ``.get_frontend_algo``. If the driver
|
|
doesn't fill its field at struct :c:type:`dvb_frontend_ops`, it will default to
|
|
``DVBFE_ALGO_SW``, meaning that the dvb-core will do a zigzag when tuning,
|
|
e. g. it will try first to use the specified center frequency ``f``,
|
|
then, it will do ``f`` + |delta|, ``f`` - |delta|, ``f`` + 2 x |delta|,
|
|
``f`` - 2 x |delta| and so on.
|
|
|
|
If the hardware has internally a some sort of zigzag algorithm, you should
|
|
define a ``.get_frontend_algo`` function that would return ``DVBFE_ALGO_HW``.
|
|
|
|
.. note::
|
|
|
|
The core frontend support also supports
|
|
a third type (``DVBFE_ALGO_CUSTOM``), in order to allow the driver to
|
|
define its own hardware-assisted algorithm. Very few hardware need to
|
|
use it nowadays. Using ``DVBFE_ALGO_CUSTOM`` require to provide other
|
|
function callbacks at struct :c:type:`dvb_frontend_ops`.
|
|
|
|
Attaching frontend driver to the bridge driver
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
Before using the Digital TV frontend core, the bridge driver should attach
|
|
the frontend demod, tuner and SEC devices and call
|
|
:c:func:`dvb_register_frontend()`,
|
|
in order to register the new frontend at the subsystem. At device
|
|
detach/removal, the bridge driver should call
|
|
:c:func:`dvb_unregister_frontend()` to
|
|
remove the frontend from the core and then :c:func:`dvb_frontend_detach()`
|
|
to free the memory allocated by the frontend drivers.
|
|
|
|
The drivers should also call :c:func:`dvb_frontend_suspend()` as part of
|
|
their handler for the :c:type:`device_driver`.\ ``suspend()``, and
|
|
:c:func:`dvb_frontend_resume()` as
|
|
part of their handler for :c:type:`device_driver`.\ ``resume()``.
|
|
|
|
A few other optional functions are provided to handle some special cases.
|
|
|
|
.. _dvbv5_stats:
|
|
|
|
Digital TV Frontend statistics
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Introduction
|
|
^^^^^^^^^^^^
|
|
|
|
Digital TV frontends provide a range of
|
|
:ref:`statistics <frontend-stat-properties>` meant to help tuning the device
|
|
and measuring the quality of service.
|
|
|
|
For each statistics measurement, the driver should set the type of scale used,
|
|
or ``FE_SCALE_NOT_AVAILABLE`` if the statistics is not available on a given
|
|
time. Drivers should also provide the number of statistics for each type.
|
|
that's usually 1 for most video standards [#f2]_.
|
|
|
|
Drivers should initialize each statistic counters with length and
|
|
scale at its init code. For example, if the frontend provides signal
|
|
strength, it should have, on its init code::
|
|
|
|
struct dtv_frontend_properties *c = &state->fe.dtv_property_cache;
|
|
|
|
c->strength.len = 1;
|
|
c->strength.stat[0].scale = FE_SCALE_NOT_AVAILABLE;
|
|
|
|
And, when the statistics got updated, set the scale::
|
|
|
|
c->strength.stat[0].scale = FE_SCALE_DECIBEL;
|
|
c->strength.stat[0].uvalue = strength;
|
|
|
|
.. [#f2] For ISDB-T, it may provide both a global statistics and a per-layer
|
|
set of statistics. On such cases, len should be equal to 4. The first
|
|
value corresponds to the global stat; the other ones to each layer, e. g.:
|
|
|
|
- c->cnr.stat[0] for global S/N carrier ratio,
|
|
- c->cnr.stat[1] for Layer A S/N carrier ratio,
|
|
- c->cnr.stat[2] for layer B S/N carrier ratio,
|
|
- c->cnr.stat[3] for layer C S/N carrier ratio.
|
|
|
|
.. note:: Please prefer to use ``FE_SCALE_DECIBEL`` instead of
|
|
``FE_SCALE_RELATIVE`` for signal strength and CNR measurements.
|
|
|
|
Groups of statistics
|
|
^^^^^^^^^^^^^^^^^^^^
|
|
|
|
There are several groups of statistics currently supported:
|
|
|
|
Signal strength (:ref:`DTV-STAT-SIGNAL-STRENGTH`)
|
|
- Measures the signal strength level at the analog part of the tuner or
|
|
demod.
|
|
|
|
- Typically obtained from the gain applied to the tuner and/or frontend
|
|
in order to detect the carrier. When no carrier is detected, the gain is
|
|
at the maximum value (so, strength is on its minimal).
|
|
|
|
- As the gain is visible through the set of registers that adjust the gain,
|
|
typically, this statistics is always available [#f3]_.
|
|
|
|
- Drivers should try to make it available all the times, as this statistics
|
|
can be used when adjusting an antenna position and to check for troubles
|
|
at the cabling.
|
|
|
|
.. [#f3] On a few devices, the gain keeps floating if no carrier.
|
|
On such devices, strength report should check first if carrier is
|
|
detected at the tuner (``FE_HAS_CARRIER``, see :c:type:`fe_status`),
|
|
and otherwise return the lowest possible value.
|
|
|
|
Carrier Signal to Noise ratio (:ref:`DTV-STAT-CNR`)
|
|
- Signal to Noise ratio for the main carrier.
|
|
|
|
- Signal to Noise measurement depends on the device. On some hardware, is
|
|
available when the main carrier is detected. On those hardware, CNR
|
|
measurement usually comes from the tuner (e. g. after ``FE_HAS_CARRIER``,
|
|
see :c:type:`fe_status`).
|
|
|
|
On other devices, it requires inner FEC decoding,
|
|
as the frontend measures it indirectly from other parameters (e. g. after
|
|
``FE_HAS_VITERBI``, see :c:type:`fe_status`).
|
|
|
|
Having it available after inner FEC is more common.
|
|
|
|
Bit counts post-FEC (:ref:`DTV-STAT-POST-ERROR-BIT-COUNT` and :ref:`DTV-STAT-POST-TOTAL-BIT-COUNT`)
|
|
- Those counters measure the number of bits and bit errors errors after
|
|
the forward error correction (FEC) on the inner coding block
|
|
(after Viterbi, LDPC or other inner code).
|
|
|
|
- Due to its nature, those statistics depend on full coding lock
|
|
(e. g. after ``FE_HAS_SYNC`` or after ``FE_HAS_LOCK``,
|
|
see :c:type:`fe_status`).
|
|
|
|
Bit counts pre-FEC (:ref:`DTV-STAT-PRE-ERROR-BIT-COUNT` and :ref:`DTV-STAT-PRE-TOTAL-BIT-COUNT`)
|
|
- Those counters measure the number of bits and bit errors errors before
|
|
the forward error correction (FEC) on the inner coding block
|
|
(before Viterbi, LDPC or other inner code).
|
|
|
|
- Not all frontends provide this kind of statistics.
|
|
|
|
- Due to its nature, those statistics depend on inner coding lock (e. g.
|
|
after ``FE_HAS_VITERBI``, see :c:type:`fe_status`).
|
|
|
|
Block counts (:ref:`DTV-STAT-ERROR-BLOCK-COUNT` and :ref:`DTV-STAT-TOTAL-BLOCK-COUNT`)
|
|
- Those counters measure the number of blocks and block errors errors after
|
|
the forward error correction (FEC) on the inner coding block
|
|
(before Viterbi, LDPC or other inner code).
|
|
|
|
- Due to its nature, those statistics depend on full coding lock
|
|
(e. g. after ``FE_HAS_SYNC`` or after
|
|
``FE_HAS_LOCK``, see :c:type:`fe_status`).
|
|
|
|
.. note:: All counters should be monotonically increased as they're
|
|
collected from the hardware.
|
|
|
|
A typical example of the logic that handle status and statistics is::
|
|
|
|
static int foo_get_status_and_stats(struct dvb_frontend *fe)
|
|
{
|
|
struct foo_state *state = fe->demodulator_priv;
|
|
struct dtv_frontend_properties *c = &fe->dtv_property_cache;
|
|
|
|
int rc;
|
|
enum fe_status *status;
|
|
|
|
/* Both status and strength are always available */
|
|
rc = foo_read_status(fe, &status);
|
|
if (rc < 0)
|
|
return rc;
|
|
|
|
rc = foo_read_strength(fe);
|
|
if (rc < 0)
|
|
return rc;
|
|
|
|
/* Check if CNR is available */
|
|
if (!(fe->status & FE_HAS_CARRIER))
|
|
return 0;
|
|
|
|
rc = foo_read_cnr(fe);
|
|
if (rc < 0)
|
|
return rc;
|
|
|
|
/* Check if pre-BER stats are available */
|
|
if (!(fe->status & FE_HAS_VITERBI))
|
|
return 0;
|
|
|
|
rc = foo_get_pre_ber(fe);
|
|
if (rc < 0)
|
|
return rc;
|
|
|
|
/* Check if post-BER stats are available */
|
|
if (!(fe->status & FE_HAS_SYNC))
|
|
return 0;
|
|
|
|
rc = foo_get_post_ber(fe);
|
|
if (rc < 0)
|
|
return rc;
|
|
}
|
|
|
|
static const struct dvb_frontend_ops ops = {
|
|
/* ... */
|
|
.read_status = foo_get_status_and_stats,
|
|
};
|
|
|
|
Statistics collect
|
|
^^^^^^^^^^^^^^^^^^
|
|
|
|
On almost all frontend hardware, the bit and byte counts are stored by
|
|
the hardware after a certain amount of time or after the total bit/block
|
|
counter reaches a certain value (usually programmable), for example, on
|
|
every 1000 ms or after receiving 1,000,000 bits.
|
|
|
|
So, if you read the registers too soon, you'll end by reading the same
|
|
value as in the previous reading, causing the monotonic value to be
|
|
incremented too often.
|
|
|
|
Drivers should take the responsibility to avoid too often reads. That
|
|
can be done using two approaches:
|
|
|
|
if the driver have a bit that indicates when a collected data is ready
|
|
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|
|
|
|
Driver should check such bit before making the statistics available.
|
|
|
|
An example of such behavior can be found at this code snippet (adapted
|
|
from mb86a20s driver's logic)::
|
|
|
|
static int foo_get_pre_ber(struct dvb_frontend *fe)
|
|
{
|
|
struct foo_state *state = fe->demodulator_priv;
|
|
struct dtv_frontend_properties *c = &fe->dtv_property_cache;
|
|
int rc, bit_error;
|
|
|
|
/* Check if the BER measures are already available */
|
|
rc = foo_read_u8(state, 0x54);
|
|
if (rc < 0)
|
|
return rc;
|
|
|
|
if (!rc)
|
|
return 0;
|
|
|
|
/* Read Bit Error Count */
|
|
bit_error = foo_read_u32(state, 0x55);
|
|
if (bit_error < 0)
|
|
return bit_error;
|
|
|
|
/* Read Total Bit Count */
|
|
rc = foo_read_u32(state, 0x51);
|
|
if (rc < 0)
|
|
return rc;
|
|
|
|
c->pre_bit_error.stat[0].scale = FE_SCALE_COUNTER;
|
|
c->pre_bit_error.stat[0].uvalue += bit_error;
|
|
c->pre_bit_count.stat[0].scale = FE_SCALE_COUNTER;
|
|
c->pre_bit_count.stat[0].uvalue += rc;
|
|
|
|
return 0;
|
|
}
|
|
|
|
If the driver doesn't provide a statistics available check bit
|
|
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|
|
|
|
A few devices, however, may not provide a way to check if the stats are
|
|
available (or the way to check it is unknown). They may not even provide
|
|
a way to directly read the total number of bits or blocks.
|
|
|
|
On those devices, the driver need to ensure that it won't be reading from
|
|
the register too often and/or estimate the total number of bits/blocks.
|
|
|
|
On such drivers, a typical routine to get statistics would be like
|
|
(adapted from dib8000 driver's logic)::
|
|
|
|
struct foo_state {
|
|
/* ... */
|
|
|
|
unsigned long per_jiffies_stats;
|
|
}
|
|
|
|
static int foo_get_pre_ber(struct dvb_frontend *fe)
|
|
{
|
|
struct foo_state *state = fe->demodulator_priv;
|
|
struct dtv_frontend_properties *c = &fe->dtv_property_cache;
|
|
int rc, bit_error;
|
|
u64 bits;
|
|
|
|
/* Check if time for stats was elapsed */
|
|
if (!time_after(jiffies, state->per_jiffies_stats))
|
|
return 0;
|
|
|
|
/* Next stat should be collected in 1000 ms */
|
|
state->per_jiffies_stats = jiffies + msecs_to_jiffies(1000);
|
|
|
|
/* Read Bit Error Count */
|
|
bit_error = foo_read_u32(state, 0x55);
|
|
if (bit_error < 0)
|
|
return bit_error;
|
|
|
|
/*
|
|
* On this particular frontend, there's no register that
|
|
* would provide the number of bits per 1000ms sample. So,
|
|
* some function would calculate it based on DTV properties
|
|
*/
|
|
bits = get_number_of_bits_per_1000ms(fe);
|
|
|
|
c->pre_bit_error.stat[0].scale = FE_SCALE_COUNTER;
|
|
c->pre_bit_error.stat[0].uvalue += bit_error;
|
|
c->pre_bit_count.stat[0].scale = FE_SCALE_COUNTER;
|
|
c->pre_bit_count.stat[0].uvalue += bits;
|
|
|
|
return 0;
|
|
}
|
|
|
|
Please notice that, on both cases, we're getting the statistics using the
|
|
:c:type:`dvb_frontend_ops` ``.read_status`` callback. The rationale is that
|
|
the frontend core will automatically call this function periodically
|
|
(usually, 3 times per second, when the frontend is locked).
|
|
|
|
That warrants that we won't miss to collect a counter and increment the
|
|
monotonic stats at the right time.
|
|
|
|
Digital TV Frontend functions and types
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. kernel-doc:: include/media/dvb_frontend.h
|