3.2. Digital TV Frontend kABI¶

3.2.1. 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/.

3.2.1.1. Demodulator driver¶

The demodulator driver is responsible for talking with the decoding part of the hardware. Such driver should implement dvb_frontend_ops, which 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 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 DVBv5 statistics 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.

The include/media/dvb_frontend.c has a kernel thread which is responsible for tuning the device. It supports multiple algorithms to detect a channel, as defined at enum dvbfe_algo().

The algorithm to be used is obtained via .get_frontend_algo. If the driver doesn’t fill its field at struct 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 + Δ, f - Δ, f + 2 x Δ, f - 2 x Δ 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 dvb_frontend_ops.

3.2.1.2. 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 dvb_register_frontend(), in order to register the new frontend at the subsystem. At device detach/removal, the bridge driver should call dvb_unregister_frontend() to remove the frontend from the core and then dvb_frontend_detach() to free the memory allocated by the frontend drivers.

The drivers should also call dvb_frontend_suspend() as part of their handler for the device_driver.suspend(), and dvb_frontend_resume() as part of their handler for device_driver.resume().

A few other optional functions are provided to handle some special cases.

3.2.2. Digital TV Frontend statistics¶

3.2.2.1. Introduction¶

Digital TV frontends provide a range of statistics 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 1.

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;

1

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.

3.2.2.2. Groups of statistics¶

There are several groups of statistics currently supported:

Signal strength (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 2.
Drivers should try to make it available all the times, as these statistics can be used when adjusting an antenna position and to check for troubles at the cabling.

2: On a few devices, the gain keeps floating if there is no carrier. On such devices, strength report should check first if carrier is detected at the tuner (FE_HAS_CARRIER, see fe_status), and otherwise return the lowest possible value.

Carrier Signal to Noise ratio (DTV_STAT_CNR)

Signal to Noise ratio for the main carrier.
Signal to Noise measurement depends on the device. On some hardware, it 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 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 fe_status).

Having it available after inner FEC is more common.

Bit counts post-FEC (DTV_STAT_POST_ERROR_BIT_COUNT and DTV_STAT_POST_TOTAL_BIT_COUNT)

Those counters measure the number of bits and bit 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 fe_status).

Bit counts pre-FEC (DTV_STAT_PRE_ERROR_BIT_COUNT and DTV_STAT_PRE_TOTAL_BIT_COUNT)

Those counters measure the number of bits and bit 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 fe_status).

Block counts (DTV_STAT_ERROR_BLOCK_COUNT and DTV-STAT_TOTAL_BLOCK_COUNT)

Those counters measure the number of blocks and block 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 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,
};

3.2.2.3. Statistics collection¶

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:

3.2.2.3.1. 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;
}

3.2.2.3.2. 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 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.

3.2.3. Digital TV Frontend functions and types¶

struct dvb_frontend_tune_settings¶: parameters to adjust frontend tuning

Definition:

struct dvb_frontend_tune_settings {
    int min_delay_ms;
    int step_size;
    int max_drift;
};

Members

min_delay_ms: minimum delay for tuning, in ms
step_size: step size between two consecutive frequencies
max_drift: maximum drift

NOTE

step_size is in Hz, for terrestrial/cable or kHz for satellite

struct dvb_tuner_info¶: Frontend name and min/max ranges/bandwidths

Definition:

struct dvb_tuner_info {
    char name[128];
    u32 frequency_min_hz;
    u32 frequency_max_hz;
    u32 frequency_step_hz;
    u32 bandwidth_min;
    u32 bandwidth_max;
    u32 bandwidth_step;
};

Members

name: name of the Frontend
frequency_min_hz: minimal frequency supported in Hz
frequency_max_hz: maximum frequency supported in Hz
frequency_step_hz: frequency step in Hz
bandwidth_min: minimal frontend bandwidth supported
bandwidth_max: maximum frontend bandwidth supported
bandwidth_step: frontend bandwidth step

struct analog_parameters¶: Parameters to tune into an analog/radio channel

Definition:

struct analog_parameters {
    unsigned int frequency;
    unsigned int mode;
    unsigned int audmode;
    u64 std;
};

Members

frequency: Frequency used by analog TV tuner (either in 62.5 kHz step, for TV, or 62.5 Hz for radio)
mode: Tuner mode, as defined on enum v4l2_tuner_type
audmode: Audio mode as defined for the rxsubchans field at videodev2.h, e. g. V4L2_TUNER_MODE_*
std: TV standard bitmap as defined at videodev2.h, e. g. V4L2_STD_*

Description

Hybrid tuners should be supported by both V4L2 and DVB APIs. This struct contains the data that are used by the V4L2 side. To avoid dependencies from V4L2 headers, all enums here are declared as integers.

enum dvbfe_algo¶: defines the algorithm used to tune into a channel

Constants

DVBFE_ALGO_HW: Hardware Algorithm - Devices that support this algorithm do everything in hardware and no software support is needed to handle them. Requesting these devices to LOCK is the only thing required, device is supposed to do everything in the hardware.
DVBFE_ALGO_SW: Software Algorithm - These are dumb devices, that require software to do everything
DVBFE_ALGO_CUSTOM: Customizable Agorithm - Devices having this algorithm can be customized to have specific algorithms in the frontend driver, rather than simply doing a software zig-zag. In this case the zigzag maybe hardware assisted or it maybe completely done in hardware. In all cases, usage of this algorithm, in conjunction with the search and track callbacks, utilizes the driver specific algorithm.
DVBFE_ALGO_RECOVERY: Recovery Algorithm - These devices have AUTO recovery capabilities from LOCK failure

enum dvbfe_search¶: search callback possible return status

Constants

DVBFE_ALGO_SEARCH_SUCCESS

The frontend search algorithm completed and returned successfully

DVBFE_ALGO_SEARCH_ASLEEP

The frontend search algorithm is sleeping

DVBFE_ALGO_SEARCH_FAILED

The frontend search for a signal failed

DVBFE_ALGO_SEARCH_INVALID

The frontend search algorithm was probably supplied with invalid parameters and the search is an invalid one

DVBFE_ALGO_SEARCH_AGAIN

The frontend search algorithm was requested to search again

DVBFE_ALGO_SEARCH_ERROR

The frontend search algorithm failed due to some error

struct dvb_tuner_ops¶: Tuner information and callbacks

Definition:

struct dvb_tuner_ops {
    struct dvb_tuner_info info;
    void (*release)(struct dvb_frontend *fe);
    int (*init)(struct dvb_frontend *fe);
    int (*sleep)(struct dvb_frontend *fe);
    int (*suspend)(struct dvb_frontend *fe);
    int (*resume)(struct dvb_frontend *fe);
    int (*set_params)(struct dvb_frontend *fe);
    int (*set_analog_params)(struct dvb_frontend *fe, struct analog_parameters *p);
    int (*set_config)(struct dvb_frontend *fe, void *priv_cfg);
    int (*get_frequency)(struct dvb_frontend *fe, u32 *frequency);
    int (*get_bandwidth)(struct dvb_frontend *fe, u32 *bandwidth);
    int (*get_if_frequency)(struct dvb_frontend *fe, u32 *frequency);
#define TUNER_STATUS_LOCKED 1;
#define TUNER_STATUS_STEREO 2;
    int (*get_status)(struct dvb_frontend *fe, u32 *status);
    int (*get_rf_strength)(struct dvb_frontend *fe, u16 *strength);
    int (*get_afc)(struct dvb_frontend *fe, s32 *afc);
    int (*calc_regs)(struct dvb_frontend *fe, u8 *buf, int buf_len);
    int (*set_frequency)(struct dvb_frontend *fe, u32 frequency);
    int (*set_bandwidth)(struct dvb_frontend *fe, u32 bandwidth);
};

Members

info: embedded struct dvb_tuner_info with tuner properties
release: callback function called when frontend is detached. drivers should free any allocated memory.
init: callback function used to initialize the tuner device.
sleep: callback function used to put the tuner to sleep.
suspend: callback function used to inform that the Kernel will suspend.
resume: callback function used to inform that the Kernel is resuming from suspend.
set_params: callback function used to inform the tuner to tune into a digital TV channel. The properties to be used are stored at struct dvb_frontend.dtv_property_cache. The tuner demod can change the parameters to reflect the changes needed for the channel to be tuned, and update statistics. This is the recommended way to set the tuner parameters and should be used on newer drivers.
set_analog_params: callback function used to tune into an analog TV channel on hybrid tuners. It passes analog_parameters to the driver.
set_config: callback function used to send some tuner-specific parameters.
get_frequency: get the actual tuned frequency
get_bandwidth: get the bandwidth used by the low pass filters
get_if_frequency: get the Intermediate Frequency, in Hz. For baseband, should return 0.
get_status: returns the frontend lock status
get_rf_strength: returns the RF signal strength. Used mostly to support analog TV and radio. Digital TV should report, instead, via DVBv5 API (struct dvb_frontend.dtv_property_cache).
get_afc: Used only by analog TV core. Reports the frequency drift due to AFC.
calc_regs: callback function used to pass register data settings for simple tuners. Shouldn’t be used on newer drivers.
set_frequency: Set a new frequency. Shouldn’t be used on newer drivers.
set_bandwidth: Set a new frequency. Shouldn’t be used on newer drivers.

NOTE

frequencies used on get_frequency and set_frequency are in Hz for terrestrial/cable or kHz for satellite.

struct analog_demod_info¶: Information struct for analog TV part of the demod

Definition:

struct analog_demod_info {
    char *name;
};

Members

name: Name of the analog TV demodulator

struct analog_demod_ops¶: Demodulation information and callbacks for analog TV and radio

Definition:

struct analog_demod_ops {
    struct analog_demod_info info;
    void (*set_params)(struct dvb_frontend *fe, struct analog_parameters *params);
    int (*has_signal)(struct dvb_frontend *fe, u16 *signal);
    int (*get_afc)(struct dvb_frontend *fe, s32 *afc);
    void (*tuner_status)(struct dvb_frontend *fe);
    void (*standby)(struct dvb_frontend *fe);
    void (*release)(struct dvb_frontend *fe);
    int (*i2c_gate_ctrl)(struct dvb_frontend *fe, int enable);
    int (*set_config)(struct dvb_frontend *fe, void *priv_cfg);
};

Members

info: pointer to struct analog_demod_info
set_params: callback function used to inform the demod to set the demodulator parameters needed to decode an analog or radio channel. The properties are passed via struct analog_params.
has_signal: returns 0xffff if has signal, or 0 if it doesn’t.
get_afc: Used only by analog TV core. Reports the frequency drift due to AFC.
tuner_status: callback function that returns tuner status bits, e. g. TUNER_STATUS_LOCKED and TUNER_STATUS_STEREO.
standby: set the tuner to standby mode.
release: callback function called when frontend is detached. drivers should free any allocated memory.
i2c_gate_ctrl: controls the I2C gate. Newer drivers should use I2C mux support instead.
set_config: callback function used to send some tuner-specific parameters.

struct dvb_frontend_internal_info¶: Frontend properties and capabilities

Definition:

struct dvb_frontend_internal_info {
    char name[128];
    u32 frequency_min_hz;
    u32 frequency_max_hz;
    u32 frequency_stepsize_hz;
    u32 frequency_tolerance_hz;
    u32 symbol_rate_min;
    u32 symbol_rate_max;
    u32 symbol_rate_tolerance;
    enum fe_caps caps;
};

Members

name: Name of the frontend
frequency_min_hz: Minimal frequency supported by the frontend.
frequency_max_hz: Minimal frequency supported by the frontend.
frequency_stepsize_hz: All frequencies are multiple of this value.
frequency_tolerance_hz: Frequency tolerance.
symbol_rate_min: Minimal symbol rate, in bauds (for Cable/Satellite systems).
symbol_rate_max: Maximal symbol rate, in bauds (for Cable/Satellite systems).
symbol_rate_tolerance: Maximal symbol rate tolerance, in ppm (for Cable/Satellite systems).
caps: Capabilities supported by the frontend, as specified in enum fe_caps.

struct dvb_frontend_ops¶: Demodulation information and callbacks for ditialt TV

Definition:

struct dvb_frontend_ops {
    struct dvb_frontend_internal_info info;
    u8 delsys[MAX_DELSYS];
    void (*detach)(struct dvb_frontend *fe);
    void (*release)(struct dvb_frontend* fe);
    void (*release_sec)(struct dvb_frontend* fe);
    int (*init)(struct dvb_frontend* fe);
    int (*sleep)(struct dvb_frontend* fe);
    int (*suspend)(struct dvb_frontend *fe);
    int (*resume)(struct dvb_frontend *fe);
    int (*write)(struct dvb_frontend* fe, const u8 buf[], int len);
    int (*tune)(struct dvb_frontend* fe,bool re_tune,unsigned int mode_flags,unsigned int *delay, enum fe_status *status);
    enum dvbfe_algo (*get_frontend_algo)(struct dvb_frontend *fe);
    int (*set_frontend)(struct dvb_frontend *fe);
    int (*get_tune_settings)(struct dvb_frontend* fe, struct dvb_frontend_tune_settings* settings);
    int (*get_frontend)(struct dvb_frontend *fe, struct dtv_frontend_properties *props);
    int (*read_status)(struct dvb_frontend *fe, enum fe_status *status);
    int (*read_ber)(struct dvb_frontend* fe, u32* ber);
    int (*read_signal_strength)(struct dvb_frontend* fe, u16* strength);
    int (*read_snr)(struct dvb_frontend* fe, u16* snr);
    int (*read_ucblocks)(struct dvb_frontend* fe, u32* ucblocks);
    int (*diseqc_reset_overload)(struct dvb_frontend* fe);
    int (*diseqc_send_master_cmd)(struct dvb_frontend* fe, struct dvb_diseqc_master_cmd* cmd);
    int (*diseqc_recv_slave_reply)(struct dvb_frontend* fe, struct dvb_diseqc_slave_reply* reply);
    int (*diseqc_send_burst)(struct dvb_frontend *fe, enum fe_sec_mini_cmd minicmd);
    int (*set_tone)(struct dvb_frontend *fe, enum fe_sec_tone_mode tone);
    int (*set_voltage)(struct dvb_frontend *fe, enum fe_sec_voltage voltage);
    int (*enable_high_lnb_voltage)(struct dvb_frontend* fe, long arg);
    int (*dishnetwork_send_legacy_command)(struct dvb_frontend* fe, unsigned long cmd);
    int (*i2c_gate_ctrl)(struct dvb_frontend* fe, int enable);
    int (*ts_bus_ctrl)(struct dvb_frontend* fe, int acquire);
    int (*set_lna)(struct dvb_frontend *);
    enum dvbfe_search (*search)(struct dvb_frontend *fe);
    struct dvb_tuner_ops tuner_ops;
    struct analog_demod_ops analog_ops;
};

Members

info: embedded struct dvb_tuner_info with tuner properties
delsys: Delivery systems supported by the frontend
detach: callback function called when frontend is detached. drivers should clean up, but not yet free the struct dvb_frontend allocation.
release: callback function called when frontend is ready to be freed. drivers should free any allocated memory.
release_sec: callback function requesting that the Satellite Equipment Control (SEC) driver to release and free any memory allocated by the driver.
init: callback function used to initialize the tuner device.
sleep: callback function used to put the tuner to sleep.
suspend: callback function used to inform that the Kernel will suspend.
resume: callback function used to inform that the Kernel is resuming from suspend.
write: callback function used by some demod legacy drivers to allow other drivers to write data into their registers. Should not be used on new drivers.
tune: callback function used by demod drivers that use DVBFE_ALGO_HW to tune into a frequency.
get_frontend_algo: returns the desired hardware algorithm.
set_frontend: callback function used to inform the demod to set the parameters for demodulating a digital TV channel. The properties to be used are stored at struct dvb_frontend.dtv_property_cache. The demod can change the parameters to reflect the changes needed for the channel to be decoded, and update statistics.
get_tune_settings: callback function
get_frontend: callback function used to inform the parameters actuall in use. The properties to be used are stored at struct dvb_frontend.dtv_property_cache and update statistics. Please notice that it should not return an error code if the statistics are not available because the demog is not locked.
read_status: returns the locking status of the frontend.
read_ber: legacy callback function to return the bit error rate. Newer drivers should provide such info via DVBv5 API, e. g. set_frontend;/get_frontend, implementing this callback only if DVBv3 API compatibility is wanted.
read_signal_strength: legacy callback function to return the signal strength. Newer drivers should provide such info via DVBv5 API, e. g. set_frontend/get_frontend, implementing this callback only if DVBv3 API compatibility is wanted.
read_snr: legacy callback function to return the Signal/Noise rate. Newer drivers should provide such info via DVBv5 API, e. g. set_frontend/get_frontend, implementing this callback only if DVBv3 API compatibility is wanted.
read_ucblocks: legacy callback function to return the Uncorrected Error Blocks. Newer drivers should provide such info via DVBv5 API, e. g. set_frontend/get_frontend, implementing this callback only if DVBv3 API compatibility is wanted.
diseqc_reset_overload: callback function to implement the FE_DISEQC_RESET_OVERLOAD() ioctl (only Satellite)
diseqc_send_master_cmd: callback function to implement the FE_DISEQC_SEND_MASTER_CMD() ioctl (only Satellite).
diseqc_recv_slave_reply: callback function to implement the FE_DISEQC_RECV_SLAVE_REPLY() ioctl (only Satellite)
diseqc_send_burst: callback function to implement the FE_DISEQC_SEND_BURST() ioctl (only Satellite).
set_tone: callback function to implement the FE_SET_TONE() ioctl (only Satellite).
set_voltage: callback function to implement the FE_SET_VOLTAGE() ioctl (only Satellite).
enable_high_lnb_voltage: callback function to implement the FE_ENABLE_HIGH_LNB_VOLTAGE() ioctl (only Satellite).
dishnetwork_send_legacy_command: callback function to implement the FE_DISHNETWORK_SEND_LEGACY_CMD() ioctl (only Satellite). Drivers should not use this, except when the DVB core emulation fails to provide proper support (e.g. if set_voltage takes more than 8ms to work), and when backward compatibility with this legacy API is required.
i2c_gate_ctrl: controls the I2C gate. Newer drivers should use I2C mux support instead.
ts_bus_ctrl: callback function used to take control of the TS bus.
set_lna: callback function to power on/off/auto the LNA.
search: callback function used on some custom algo search algos.
tuner_ops: pointer to struct dvb_tuner_ops
analog_ops: pointer to struct analog_demod_ops

struct dtv_frontend_properties¶: contains a list of properties that are specific to a digital TV standard.

Definition:

struct dtv_frontend_properties {
    u32 frequency;
    enum fe_modulation      modulation;
    enum fe_sec_voltage     voltage;
    enum fe_sec_tone_mode   sectone;
    enum fe_spectral_inversion inversion;
    enum fe_code_rate       fec_inner;
    enum fe_transmit_mode   transmission_mode;
    u32 bandwidth_hz;
    enum fe_guard_interval  guard_interval;
    enum fe_hierarchy       hierarchy;
    u32 symbol_rate;
    enum fe_code_rate       code_rate_HP;
    enum fe_code_rate       code_rate_LP;
    enum fe_pilot           pilot;
    enum fe_rolloff         rolloff;
    enum fe_delivery_system delivery_system;
    enum fe_interleaving    interleaving;
    u8 isdbt_partial_reception;
    u8 isdbt_sb_mode;
    u8 isdbt_sb_subchannel;
    u32 isdbt_sb_segment_idx;
    u32 isdbt_sb_segment_count;
    u8 isdbt_layer_enabled;
    struct {
        u8 segment_count;
        enum fe_code_rate   fec;
        enum fe_modulation  modulation;
        u8 interleaving;
    } layer[3];
    u32 stream_id;
    u32 scrambling_sequence_index;
    u8 atscmh_fic_ver;
    u8 atscmh_parade_id;
    u8 atscmh_nog;
    u8 atscmh_tnog;
    u8 atscmh_sgn;
    u8 atscmh_prc;
    u8 atscmh_rs_frame_mode;
    u8 atscmh_rs_frame_ensemble;
    u8 atscmh_rs_code_mode_pri;
    u8 atscmh_rs_code_mode_sec;
    u8 atscmh_sccc_block_mode;
    u8 atscmh_sccc_code_mode_a;
    u8 atscmh_sccc_code_mode_b;
    u8 atscmh_sccc_code_mode_c;
    u8 atscmh_sccc_code_mode_d;
    u32 lna;
    struct dtv_fe_stats     strength;
    struct dtv_fe_stats     cnr;
    struct dtv_fe_stats     pre_bit_error;
    struct dtv_fe_stats     pre_bit_count;
    struct dtv_fe_stats     post_bit_error;
    struct dtv_fe_stats     post_bit_count;
    struct dtv_fe_stats     block_error;
    struct dtv_fe_stats     block_count;
};

Members

frequency: frequency in Hz for terrestrial/cable or in kHz for Satellite
modulation: Frontend modulation type
voltage: SEC voltage (only Satellite)
sectone: SEC tone mode (only Satellite)
inversion: Spectral inversion
fec_inner: Forward error correction inner Code Rate
transmission_mode: Transmission Mode
bandwidth_hz: Bandwidth, in Hz. A zero value means that userspace wants to autodetect.
guard_interval: Guard Interval
hierarchy: Hierarchy
symbol_rate: Symbol Rate
code_rate_HP: high priority stream code rate
code_rate_LP: low priority stream code rate
pilot: Enable/disable/autodetect pilot tones
rolloff: Rolloff factor (alpha)
delivery_system: FE delivery system (e. g. digital TV standard)
interleaving: interleaving
isdbt_partial_reception: ISDB-T partial reception (only ISDB standard)
isdbt_sb_mode: ISDB-T Sound Broadcast (SB) mode (only ISDB standard)
isdbt_sb_subchannel: ISDB-T SB subchannel (only ISDB standard)
isdbt_sb_segment_idx: ISDB-T SB segment index (only ISDB standard)
isdbt_sb_segment_count: ISDB-T SB segment count (only ISDB standard)
isdbt_layer_enabled: ISDB Layer enabled (only ISDB standard)
layer: ISDB per-layer data (only ISDB standard)
layer.segment_count: Segment Count;
layer.fec: per layer code rate;
layer.modulation: per layer modulation;
layer.interleaving: per layer interleaving.
stream_id: If different than zero, enable substream filtering, if hardware supports (DVB-S2 and DVB-T2).
scrambling_sequence_index: Carries the index of the DVB-S2 physical layer scrambling sequence.
atscmh_fic_ver: Version number of the FIC (Fast Information Channel) signaling data (only ATSC-M/H)
atscmh_parade_id: Parade identification number (only ATSC-M/H)
atscmh_nog: Number of MH groups per MH subframe for a designated parade (only ATSC-M/H)
atscmh_tnog: Total number of MH groups including all MH groups belonging to all MH parades in one MH subframe (only ATSC-M/H)
atscmh_sgn: Start group number (only ATSC-M/H)
atscmh_prc: Parade repetition cycle (only ATSC-M/H)
atscmh_rs_frame_mode: Reed Solomon (RS) frame mode (only ATSC-M/H)
atscmh_rs_frame_ensemble: RS frame ensemble (only ATSC-M/H)
atscmh_rs_code_mode_pri: RS code mode pri (only ATSC-M/H)
atscmh_rs_code_mode_sec: RS code mode sec (only ATSC-M/H)
atscmh_sccc_block_mode: Series Concatenated Convolutional Code (SCCC) Block Mode (only ATSC-M/H)
atscmh_sccc_code_mode_a: SCCC code mode A (only ATSC-M/H)
atscmh_sccc_code_mode_b: SCCC code mode B (only ATSC-M/H)
atscmh_sccc_code_mode_c: SCCC code mode C (only ATSC-M/H)
atscmh_sccc_code_mode_d: SCCC code mode D (only ATSC-M/H)
lna: Power ON/OFF/AUTO the Linear Now-noise Amplifier (LNA)
strength: DVBv5 API statistics: Signal Strength
cnr: DVBv5 API statistics: Signal to Noise ratio of the (main) carrier
pre_bit_error: DVBv5 API statistics: pre-Viterbi bit error count
pre_bit_count: DVBv5 API statistics: pre-Viterbi bit count
post_bit_error: DVBv5 API statistics: post-Viterbi bit error count
post_bit_count: DVBv5 API statistics: post-Viterbi bit count
block_error: DVBv5 API statistics: block error count
block_count: DVBv5 API statistics: block count

NOTE

derivated statistics like Uncorrected Error blocks (UCE) are calculated on userspace.

Description

Only a subset of the properties are needed for a given delivery system. For more info, consult the media_api.html with the documentation of the Userspace API.

struct dvb_frontend¶: Frontend structure to be used on drivers.

Definition:

struct dvb_frontend {
    struct kref refcount;
    struct dvb_frontend_ops ops;
    struct dvb_adapter *dvb;
    void *demodulator_priv;
    void *tuner_priv;
    void *frontend_priv;
    void *sec_priv;
    void *analog_demod_priv;
    struct dtv_frontend_properties dtv_property_cache;
#define DVB_FRONTEND_COMPONENT_TUNER 0;
#define DVB_FRONTEND_COMPONENT_DEMOD 1;
    int (*callback)(void *adapter_priv, int component, int cmd, int arg);
    int id;
    unsigned int exit;
};

Members

refcount: refcount to keep track of struct dvb_frontend references
ops: embedded struct dvb_frontend_ops
dvb: pointer to struct dvb_adapter
demodulator_priv: demod private data
tuner_priv: tuner private data
frontend_priv: frontend private data
sec_priv: SEC private data
analog_demod_priv: Analog demod private data
dtv_property_cache: embedded struct dtv_frontend_properties
callback: callback function used on some drivers to call either the tuner or the demodulator.
id: Frontend ID
exit: Used to inform the DVB core that the frontend thread should exit (usually, means that the hardware got disconnected.

int dvb_register_frontend(struct dvb_adapter *dvb, struct dvb_frontend *fe)¶: Registers a DVB frontend at the adapter

Parameters

struct dvb_adapter *dvb: pointer to struct dvb_adapter
struct dvb_frontend *fe: pointer to struct dvb_frontend

Description

Allocate and initialize the private data needed by the frontend core to manage the frontend and calls dvb_register_device() to register a new frontend. It also cleans the property cache that stores the frontend parameters and selects the first available delivery system.

int dvb_unregister_frontend(struct dvb_frontend *fe)¶: Unregisters a DVB frontend

Parameters

struct dvb_frontend *fe: pointer to struct dvb_frontend

Description

Stops the frontend kthread, calls dvb_unregister_device() and frees the private frontend data allocated by dvb_register_frontend().

NOTE

This function doesn’t frees the memory allocated by the demod, by the SEC driver and by the tuner. In order to free it, an explicit call to dvb_frontend_detach() is needed, after calling this function.

void dvb_frontend_detach(struct dvb_frontend *fe)¶: Detaches and frees frontend specific data

Parameters

struct dvb_frontend *fe: pointer to struct dvb_frontend

Description

This function should be called after dvb_unregister_frontend(). It calls the SEC, tuner and demod release functions: dvb_frontend_ops.release_sec, dvb_frontend_ops.tuner_ops.release, dvb_frontend_ops.analog_ops.release and dvb_frontend_ops.release.

If the driver is compiled with CONFIG_MEDIA_ATTACH, it also decreases the module reference count, needed to allow userspace to remove the previously used DVB frontend modules.

int dvb_frontend_suspend(struct dvb_frontend *fe)¶: Suspends a Digital TV frontend

Parameters

struct dvb_frontend *fe: pointer to struct dvb_frontend

Description

This function prepares a Digital TV frontend to suspend.

In order to prepare the tuner to suspend, if dvb_frontend_ops.tuner_ops.suspend() is available, it calls it. Otherwise, it will call dvb_frontend_ops.tuner_ops.sleep(), if available.

It will also call dvb_frontend_ops.suspend() to put the demod to suspend, if available. Otherwise it will call dvb_frontend_ops.sleep().

The drivers should also call dvb_frontend_suspend() as part of their handler for the device_driver.suspend().

int dvb_frontend_resume(struct dvb_frontend *fe)¶: Resumes a Digital TV frontend

Parameters

struct dvb_frontend *fe: pointer to struct dvb_frontend

Description

This function resumes the usual operation of the tuner after resume.

In order to resume the frontend, it calls the demod dvb_frontend_ops.resume() if available. Otherwise it calls demod dvb_frontend_ops.init().

If dvb_frontend_ops.tuner_ops.resume() is available, It, it calls it. Otherwise,t will call dvb_frontend_ops.tuner_ops.init(), if available.

Once tuner and demods are resumed, it will enforce that the SEC voltage and tone are restored to their previous values and wake up the frontend’s kthread in order to retune the frontend.

The drivers should also call dvb_frontend_resume() as part of their handler for the device_driver.resume().

void dvb_frontend_reinitialise(struct dvb_frontend *fe)¶: forces a reinitialisation at the frontend

Parameters

struct dvb_frontend *fe: pointer to struct dvb_frontend

Description

Calls dvb_frontend_ops.init() and dvb_frontend_ops.tuner_ops.init(), and resets SEC tone and voltage (for Satellite systems).

NOTE

Currently, this function is used only by one driver (budget-av). It seems to be due to address some special issue with that specific frontend.

void dvb_frontend_sleep_until(ktime_t *waketime, u32 add_usec)¶: Sleep for the amount of time given by add_usec parameter

Parameters

ktime_t *waketime: pointer to struct ktime_t
u32 add_usec: time to sleep, in microseconds

Description

This function is used to measure the time required for the FE_DISHNETWORK_SEND_LEGACY_CMD() ioctl to work. It needs to be as precise as possible, as it affects the detection of the dish tone command at the satellite subsystem.

Its used internally by the DVB frontend core, in order to emulate FE_DISHNETWORK_SEND_LEGACY_CMD() using the dvb_frontend_ops.set_voltage() callback.

NOTE

it should not be used at the drivers, as the emulation for the legacy callback is provided by the Kernel. The only situation where this should be at the drivers is when there are some bugs at the hardware that would prevent the core emulation to work. On such cases, the driver would be writing a dvb_frontend_ops.dishnetwork_send_legacy_command() and calling this function directly.

The Linux Kernel

Contents

This Page

3.2. Digital TV Frontend kABI¶

3.2.1. Digital TV Frontend¶

3.2.1.1. Demodulator driver¶

3.2.1.2. Attaching frontend driver to the bridge driver¶

3.2.2. Digital TV Frontend statistics¶

3.2.2.1. Introduction¶

3.2.2.2. Groups of statistics¶

3.2.2.3. Statistics collection¶

3.2.2.3.1. if the driver have a bit that indicates when a collected data is ready¶

3.2.2.3.2. If the driver doesn’t provide a statistics available check bit¶

3.2.3. Digital TV Frontend functions and types¶