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Diffstat (limited to 'Documentation/media/kapi/dtv-core.rst')
| -rw-r--r-- | Documentation/media/kapi/dtv-core.rst | 443 |
1 files changed, 441 insertions, 2 deletions
diff --git a/Documentation/media/kapi/dtv-core.rst b/Documentation/media/kapi/dtv-core.rst index ff86bf0abeae..de9a228aca8a 100644 --- a/Documentation/media/kapi/dtv-core.rst +++ b/Documentation/media/kapi/dtv-core.rst @@ -1,6 +1,31 @@ Digital TV (DVB) devices ------------------------ +Digital TV devices are implemented by several different drivers: + +- A bridge driver that is responsible to talk with the bus where the other + devices are connected (PCI, USB, SPI), bind to the other drivers and + implement the digital demux logic (either in software or in hardware); + +- Frontend drivers that are usually implemented as two separate drivers: + + - A tuner driver that implements the logic with commands the part of the + hardware with is reponsible to tune into a digital TV transponder or + physical channel. The output of a tuner is usually a baseband or + Intermediate Frequency (IF) signal; + + - A demodulator driver (a.k.a "demod") that implements the logic with + commands the digital TV decoding hardware. The output of a demod is + a digital stream, with multiple audio, video and data channels typically + multiplexed using MPEG Transport Stream [#f1]_. + +On most hardware, the frontend drivers talk with the bridge driver using an +I2C bus. + +.. [#f1] Some standards use TCP/IP for multiplexing data, like DVB-H (an + abandoned standard, not used anymore) and ATSC version 3.0 current + proposals. Currently, the DVB subsystem doesn't implement those standards. + Digital TV Common functions --------------------------- @@ -55,8 +80,141 @@ 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 -drivers/media/dvb-core. +The header file for this API is named ``dvb_frontend.h`` and located in +``drivers/media/dvb-core``. + +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 ``drivers/media/dvb-core/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 ``drivers/media/dvb-core/dvb_frontend.c`` has a kernel thread with is +responsible for tuning the device. It supports multiple algoritms 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 @@ -74,6 +232,287 @@ 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 programable), 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:: drivers/media/dvb-core/dvb_frontend.h |