9.2.3. vidtv: Virtual Digital TV driver¶

Author: Daniel W. S. Almeida <dwlsalmeida@gmail.com>, June 2020.

9.2.3.1. Background¶

Vidtv is a virtual DVB driver that aims to serve as a reference for driver writers by serving as a template. It also validates the existing media DVB APIs, thus helping userspace application writers.

Currently, it consists of:

A fake tuner driver, which will report a bad signal quality if the chosen frequency is too far away from a table of valid frequencies for a particular delivery system.
A fake demod driver, which will constantly poll the fake signal quality returned by the tuner, simulating a device that can lose/reacquire a lock on the signal depending on the CNR levels.
A fake bridge driver, which is the module responsible for modprobing the fake tuner and demod modules and implementing the demux logic. This module takes parameters at initialization that will dictate how the simulation behaves.
Code responsible for encoding a valid MPEG Transport Stream, which is then passed to the bridge driver. This fake stream contains some hardcoded content. For now, we have a single, audio-only channel containing a single MPEG Elementary Stream, which in turn contains a SMPTE 302m encoded sine-wave. Note that this particular encoder was chosen because it is the easiest way to encode PCM audio data in a MPEG Transport Stream.

9.2.3.2. Building vidtv¶

vidtv is a test driver and thus is not enabled by default when compiling the kernel.

In order to enable compilation of vidtv:

Enable DVB_TEST_DRIVERS, then
Enable DVB_VIDTV

When compiled as a module, expect the following .ko files:

dvb_vidtv_tuner.ko
dvb_vidtv_demod.ko
dvb_vidtv_bridge.ko

9.2.3.3. Running vidtv¶

When compiled as a module, run:

modprobe vidtv

That's it! The bridge driver will initialize the tuner and demod drivers as part of its own initialization.

By default, it will accept the following frequencies:

474 MHz for DVB-T/T2/C;

11,362 GHz for DVB-S/S2.

For satellite systems, the driver simulates an universal extended LNBf, with frequencies at Ku-Band, ranging from 10.7 GHz to 12.75 GHz.

You can optionally define some command-line arguments to vidtv.

9.2.3.4. Command-line arguments to vidtv¶

Below is a list of all arguments that can be supplied to vidtv:

drop_tslock_prob_on_low_snr: Probability of losing the TS lock if the signal quality is bad. This probability be used by the fake demodulator driver to eventually return a status of 0 when the signal quality is not good.
recover_tslock_prob_on_good_snr:: Probability recovering the TS lock when the signal improves. This probability be used by the fake demodulator driver to eventually return a status of 0x1f when/if the signal quality improves.
mock_power_up_delay_msec: Simulate a power up delay. Default: 0.
mock_tune_delay_msec: Simulate a tune delay. Default 0.
vidtv_valid_dvb_t_freqs: Valid DVB-T frequencies to simulate, in Hz.
vidtv_valid_dvb_c_freqs: Valid DVB-C frequencies to simulate, in Hz.
vidtv_valid_dvb_s_freqs: Valid DVB-S/S2 frequencies to simulate at Ku-Band, in kHz.
max_frequency_shift_hz,: Maximum shift in HZ allowed when tuning in a channel.
si_period_msec: How often to send SI packets. Default: 40ms.
pcr_period_msec: How often to send PCR packets. Default: 40ms.
mux_rate_kbytes_sec: Attempt to maintain this bit rate by inserting TS null packets, if necessary. Default: 4096.
pcr_pid,: PCR PID for all channels. Default: 0x200.
mux_buf_sz_pkts,: Size for the mux buffer in multiples of 188 bytes.

9.2.3.5. vidtv internal structure¶

The kernel modules are split in the following way:

vidtv_tuner.[ch]: Implements a fake tuner DVB driver.
vidtv_demod.[ch]: Implements a fake demodulator DVB driver.
vidtv_bridge.[ch]: Implements a bridge driver.

The MPEG related code is split in the following way:

vidtv_ts.[ch]

Code to work with MPEG TS packets, such as TS headers, adaptation fields, PCR packets and NULL packets.

vidtv_psi.[ch]

This is the PSI generator. PSI packets contain general information about a MPEG Transport Stream. A PSI generator is needed so userspace apps can retrieve information about the Transport Stream and eventually tune into a (dummy) channel.

Because the generator is implemented in a separate file, it can be reused elsewhere in the media subsystem.

Currently vidtv supports working with 5 PSI tables: PAT, PMT, SDT, NIT and EIT.

The specification for PAT and PMT can be found in ISO 13818-1: Systems, while the specification for the SDT, NIT, EIT can be found in ETSI EN 300 468: Specification for Service Information (SI) in DVB systems.

It isn't strictly necessary, but using a real TS file helps when debugging PSI tables. Vidtv currently tries to replicate the PSI structure found in this file: TS1Globo.ts.

A good way to visualize the structure of streams is by using DVBInspector.

vidtv_pes.[ch]

Implements the PES logic to convert encoder data into MPEG TS packets. These can then be fed into a TS multiplexer and eventually into userspace.

vidtv_encoder.h

An interface for vidtv encoders. New encoders can be added to this driver by implementing the calls in this file.

vidtv_s302m.[ch]

Implements a S302M encoder to make it possible to insert PCM audio data in the generated MPEG Transport Stream. The relevant specification is available online as SMPTE 302M-2007: Television - Mapping of AES3 Data into MPEG-2 Transport Stream.

The resulting MPEG Elementary Stream is conveyed in a private stream with a S302M registration descriptor attached.

This shall enable passing an audio signal into userspace so it can be decoded and played by media software. The corresponding decoder in ffmpeg is located in 'libavcodec/s302m.c' and is experimental.

vidtv_channel.[ch]

Implements a 'channel' abstraction.

When vidtv boots, it will create some hardcoded channels:

Their services will be concatenated to populate the SDT.
Their programs will be concatenated to populate the PAT
Their events will be concatenated to populate the EIT
For each program in the PAT, a PMT section will be created
The PMT section for a channel will be assigned its streams.
Every stream will have its corresponding encoder polled in a loop to produce TS packets. These packets may be interleaved by the muxer and then delivered to the bridge.

vidtv_mux.[ch]

Implements a MPEG TS mux, loosely based on the ffmpeg implementation in "libavcodec/mpegtsenc.c"

The muxer runs a loop which is responsible for:

Keeping track of the amount of time elapsed since the last iteration.
Polling encoders in order to fetch 'elapsed_time' worth of data.
Inserting PSI and/or PCR packets, if needed.
Padding the resulting stream with NULL packets if necessary in order to maintain the chosen bit rate.
Delivering the resulting TS packets to the bridge driver so it can pass them to the demux.

9.2.3.6. Testing vidtv with v4l-utils¶

Using the tools in v4l-utils is a great way to test and inspect the output of vidtv. It is hosted here: v4l-utils Documentation.

From its webpage:

The v4l-utils are a series of packages for handling media devices.

It is hosted at http://git.linuxtv.org/v4l-utils.git, and packaged
on most distributions.

It provides a series of libraries and utilities to be used to
control several aspect of the media boards.

Start by installing v4l-utils and then modprobing vidtv:

modprobe dvb_vidtv_bridge

If the driver is OK, it should load and its probing code will run. This will pull in the tuner and demod drivers.

9.2.3.6.1. Using dvb-fe-tool¶

The first step to check whether the demod loaded successfully is to run:

$ dvb-fe-tool
Device Dummy demod for DVB-T/T2/C/S/S2 (/dev/dvb/adapter0/frontend0) capabilities:
    CAN_FEC_1_2
    CAN_FEC_2_3
    CAN_FEC_3_4
    CAN_FEC_4_5
    CAN_FEC_5_6
    CAN_FEC_6_7
    CAN_FEC_7_8
    CAN_FEC_8_9
    CAN_FEC_AUTO
    CAN_GUARD_INTERVAL_AUTO
    CAN_HIERARCHY_AUTO
    CAN_INVERSION_AUTO
    CAN_QAM_16
    CAN_QAM_32
    CAN_QAM_64
    CAN_QAM_128
    CAN_QAM_256
    CAN_QAM_AUTO
    CAN_QPSK
    CAN_TRANSMISSION_MODE_AUTO
DVB API Version 5.11, Current v5 delivery system: DVBC/ANNEX_A
Supported delivery systems:
    DVBT
    DVBT2
    [DVBC/ANNEX_A]
    DVBS
    DVBS2
Frequency range for the current standard:
From:            51.0 MHz
To:              2.15 GHz
Step:            62.5 kHz
Tolerance:       29.5 MHz
Symbol rate ranges for the current standard:
From:            1.00 MBauds
To:              45.0 MBauds

This should return what is currently set up at the demod struct, i.e.:

static const struct dvb_frontend_ops vidtv_demod_ops = {
        .delsys = {
                SYS_DVBT,
                SYS_DVBT2,
                SYS_DVBC_ANNEX_A,
                SYS_DVBS,
                SYS_DVBS2,
        },

        .info = {
                .name                   = "Dummy demod for DVB-T/T2/C/S/S2",
                .frequency_min_hz       = 51 * MHz,
                .frequency_max_hz       = 2150 * MHz,
                .frequency_stepsize_hz  = 62500,
                .frequency_tolerance_hz = 29500 * kHz,
                .symbol_rate_min        = 1000000,
                .symbol_rate_max        = 45000000,

                .caps = FE_CAN_FEC_1_2 |
                        FE_CAN_FEC_2_3 |
                        FE_CAN_FEC_3_4 |
                        FE_CAN_FEC_4_5 |
                        FE_CAN_FEC_5_6 |
                        FE_CAN_FEC_6_7 |
                        FE_CAN_FEC_7_8 |
                        FE_CAN_FEC_8_9 |
                        FE_CAN_QAM_16 |
                        FE_CAN_QAM_64 |
                        FE_CAN_QAM_32 |
                        FE_CAN_QAM_128 |
                        FE_CAN_QAM_256 |
                        FE_CAN_QAM_AUTO |
                        FE_CAN_QPSK |
                        FE_CAN_FEC_AUTO |
                        FE_CAN_INVERSION_AUTO |
                        FE_CAN_TRANSMISSION_MODE_AUTO |
                        FE_CAN_GUARD_INTERVAL_AUTO |
                        FE_CAN_HIERARCHY_AUTO,
        }

        ....

For more information on dvb-fe-tools check its online documentation here: dvb-fe-tool Documentation.

9.2.3.6.2. Using dvb-scan¶

In order to tune into a channel and read the PSI tables, we can use dvb-scan.

For this, one should provide a configuration file known as a 'scan file', here's an example:

[Channel]
FREQUENCY = 474000000
MODULATION = QAM/AUTO
SYMBOL_RATE = 6940000
INNER_FEC = AUTO
DELIVERY_SYSTEM = DVBC/ANNEX_A

Note

The parameters depend on the video standard you're testing.

Note

Vidtv is a fake driver and does not validate much of the information in the scan file. Just specifying 'FREQUENCY' and 'DELIVERY_SYSTEM' should be enough for DVB-T/DVB-T2. For DVB-S/DVB-C however, you should also provide 'SYMBOL_RATE'.

You can browse scan tables online here: dvb-scan-tables.

Assuming this channel is named 'channel.conf', you can then run:

$ dvbv5-scan channel.conf
dvbv5-scan ~/vidtv.conf
ERROR    command BANDWIDTH_HZ (5) not found during retrieve
Cannot calc frequency shift. Either bandwidth/symbol-rate is unavailable (yet).
Scanning frequency #1 330000000
    (0x00) Signal= -68.00dBm
Scanning frequency #2 474000000
Lock   (0x1f) Signal= -34.45dBm C/N= 33.74dB UCB= 0
Service Beethoven, provider LinuxTV.org: digital television

For more information on dvb-scan, check its documentation online here: dvb-scan Documentation.

9.2.3.6.3. Using dvb-zap¶

dvbv5-zap is a command line tool that can be used to record MPEG-TS to disk. The typical use is to tune into a channel and put it into record mode. The example below - which is taken from the documentation - illustrates that[1]:

$ dvbv5-zap -c dvb_channel.conf "beethoven" -o music.ts -P -t 10
using demux 'dvb0.demux0'
reading channels from file 'dvb_channel.conf'
tuning to 474000000 Hz
pass all PID's to TS
dvb_set_pesfilter 8192
dvb_dev_set_bufsize: buffer set to 6160384
Lock   (0x1f) Quality= Good Signal= -34.66dBm C/N= 33.41dB UCB= 0 postBER= 0 preBER= 1.05x10^-3 PER= 0
Lock   (0x1f) Quality= Good Signal= -34.57dBm C/N= 33.46dB UCB= 0 postBER= 0 preBER= 1.05x10^-3 PER= 0
Record to file 'music.ts' started
received 24587768 bytes (2401 Kbytes/sec)
Lock   (0x1f) Quality= Good Signal= -34.42dBm C/N= 33.89dB UCB= 0 postBER= 0 preBER= 2.44x10^-3 PER= 0

The channel can be watched by playing the contents of the stream with some player that recognizes the MPEG-TS format, such as mplayer or vlc.

By playing the contents of the stream one can visually inspect the workings of vidtv, e.g., to play a recorded TS file with:

$ mplayer music.ts

or, alternatively, running this command on one terminal:

$ dvbv5-zap -c dvb_channel.conf "beethoven" -P -r &

And, on a second terminal, playing the contents from DVR interface with:

$ mplayer /dev/dvb/adapter0/dvr0

For more information on dvb-zap check its online documentation here: dvb-zap Documentation. See also: zap.

9.2.3.7. What can still be improved in vidtv¶

9.2.3.7.1. Add debugfs integration¶

Although frontend drivers provide DVBv5 statistics via the .read_status call, a nice addition would be to make additional statistics available to userspace via debugfs, which is a simple-to-use, RAM-based filesystem specifically designed for debug purposes.

The logic for this would be implemented on a separate file so as not to pollute the frontend driver. These statistics are driver-specific and can be useful during tests.

The Siano driver is one example of a driver using debugfs to convey driver-specific statistics to userspace and it can be used as a reference.

This should be further enabled and disabled via a Kconfig option for convenience.

9.2.3.7.2. Add a way to test video¶

Currently, vidtv can only encode PCM audio. It would be great to implement a barebones version of MPEG-2 video encoding so we can also test video. The first place to look into is ISO 13818-2: Information technology — Generic coding of moving pictures and associated audio information — Part 2: Video, which covers the encoding of compressed video in MPEG Transport Streams.

This might optionally use the Video4Linux2 Test Pattern Generator, v4l2-tpg, which resides at:

drivers/media/common/v4l2-tpg/

9.2.3.7.3. Add white noise simulation¶

The vidtv tuner already has code to identify whether the chosen frequency is too far away from a table of valid frequencies. For now, this means that the demodulator can eventually lose the lock on the signal, since the tuner will report a bad signal quality.

A nice addition is to simulate some noise when the signal quality is bad by:

Randomly dropping some TS packets. This will trigger a continuity error if the continuity counter is updated but the packet is not passed on to the demux.
Updating the error statistics accordingly (e.g. BER, etc).
Simulating some noise in the encoded data.

9.2.3.8. Functions and structs used within vidtv¶

struct vidtv_dvb¶: Vidtv bridge state

Definition:

struct vidtv_dvb {
    struct platform_device *pdev;
    struct dvb_frontend *fe[NUM_FE];
    struct dvb_adapter adapter;
    struct dvb_demux demux;
    struct dmxdev dmx_dev;
    struct dmx_frontend dmx_fe[NUM_FE];
    struct i2c_adapter i2c_adapter;
    struct i2c_client *i2c_client_demod[NUM_FE];
    struct i2c_client *i2c_client_tuner[NUM_FE];
    u32 nfeeds;
    struct mutex feed_lock;
    bool streaming;
    struct vidtv_mux *mux;
#ifdef CONFIG_MEDIA_CONTROLLER_DVB;
    struct media_device mdev;
#endif ;
};

Members

pdev: The platform device. Obtained when the bridge is probed.
fe: The frontends. Obtained when probing the demodulator modules.
adapter: Represents a DTV adapter. See 'dvb_register_adapter'.
demux: The demux used by the dvb_dmx_swfilter_packets() call.
dmx_dev: Represents a demux device.
dmx_fe: The frontends associated with the demux.
i2c_adapter: The i2c_adapter associated with the bridge driver.
i2c_client_demod: The i2c_clients associated with the demodulator modules.
i2c_client_tuner: The i2c_clients associated with the tuner modules.
nfeeds: The number of feeds active.
feed_lock: Protects access to the start/stop stream logic/data.
streaming: Whether we are streaming now.
mux: The abstraction responsible for delivering MPEG TS packets to the bridge.
mdev: The media_device struct for media controller support.

struct vidtv_channel¶: A 'channel' abstraction

Definition:

struct vidtv_channel {
    char *name;
    u16 transport_stream_id;
    struct vidtv_psi_table_sdt_service *service;
    u16 program_num;
    struct vidtv_psi_table_pat_program *program;
    struct vidtv_psi_table_pmt_stream *streams;
    struct vidtv_encoder *encoders;
    struct vidtv_psi_table_eit_event *events;
    struct vidtv_channel *next;
};

Members

name: name of the channel
transport_stream_id: a number to identify the TS, chosen at will.
service: A _single_ service. Will be concatenated into the SDT.
program_num: The link between PAT, PMT and SDT.
program: A _single_ program with one or more streams associated with it. Will be concatenated into the PAT.
streams: A stream loop used to populate the PMT section for 'program'
encoders: A encoder loop. There must be one encoder for each stream.
events: Optional event information. This will feed into the EIT.
next: Optionally chain this channel.

Description

When vidtv boots, it will create some hardcoded channels. Their services will be concatenated to populate the SDT. Their programs will be concatenated to populate the PAT For each program in the PAT, a PMT section will be created The PMT section for a channel will be assigned its streams. Every stream will have its corresponding encoder polled to produce TS packets These packets may be interleaved by the mux and then delivered to the bridge

int vidtv_channel_si_init(struct vidtv_mux *m)¶: Init the PSI tables from the channels in the mux

Parameters

struct vidtv_mux *m: The mux containing the channels.

int vidtv_channels_init(struct vidtv_mux *m)¶: Init hardcoded, fake 'channels'.

Parameters

struct vidtv_mux *m: The mux to store the channels into.

struct vidtv_demod_cnr_to_qual_s¶: Map CNR values to a given combination of modulation and fec_inner

Definition:

struct vidtv_demod_cnr_to_qual_s {
    u32 modulation;
    u32 fec;
    u32 cnr_ok;
    u32 cnr_good;
};

Members

modulation: see enum fe_modulation
fec: see enum fe_fec_rate
cnr_ok: S/N threshold to consider the signal as OK. Below that, there's a chance of losing sync.
cnr_good: S/N threshold to consider the signal strong.

Description

This struct matches values for 'good' and 'ok' CNRs given the combination of modulation and fec_inner in use. We might simulate some noise if the signal quality is not too good.

The values were taken from libdvbv5.

struct vidtv_demod_config¶: Configuration used to init the demod

Definition:

struct vidtv_demod_config {
    u8 drop_tslock_prob_on_low_snr;
    u8 recover_tslock_prob_on_good_snr;
};

Members

drop_tslock_prob_on_low_snr: probability of losing the lock due to low snr
recover_tslock_prob_on_good_snr: probability of recovering when the signal improves

Description

The configuration used to init the demodulator module, usually filled by a bridge driver. For vidtv, this is filled by vidtv_bridge before the demodulator module is probed.

struct vidtv_demod_state¶: The demodulator state

Definition:

struct vidtv_demod_state {
    struct dvb_frontend frontend;
    struct vidtv_demod_config config;
    enum fe_status status;
    u16 tuner_cnr;
};

Members

frontend: The frontend structure allocated by the demod.
config: The config used to init the demod.
status: the demod status.
tuner_cnr: current S/N ratio for the signal carrier

struct vidtv_encoder¶: A generic encoder type.

Definition:

struct vidtv_encoder {
    enum vidtv_encoder_id id;
    char *name;
    u8 *encoder_buf;
    u32 encoder_buf_sz;
    u32 encoder_buf_offset;
    u64 sample_count;
    struct vidtv_access_unit *access_units;
    void *src_buf;
    u32 src_buf_sz;
    u32 src_buf_offset;
    bool is_video_encoder;
    void *ctx;
    __be16 stream_id;
    __be16 es_pid;
    void *(*encode)(struct vidtv_encoder *e);
    u32 (*clear)(struct vidtv_encoder *e);
    struct vidtv_encoder *sync;
    u32 sampling_rate_hz;
    void (*last_sample_cb)(u32 sample_no);
    void (*destroy)(struct vidtv_encoder *e);
    struct vidtv_encoder *next;
};

Members

id: So we can cast to a concrete implementation when needed.
name: Usually the same as the stream name.
encoder_buf: The encoder internal buffer for the access units.
encoder_buf_sz: The encoder buffer size, in bytes
encoder_buf_offset: Our byte position in the encoder buffer.
sample_count: How many samples we have encoded in total.
access_units: encoder payload units, used for clock references
src_buf: The source of raw data to be encoded, encoder might set a default if null.
src_buf_sz: size of src_buf.
src_buf_offset: Our position in the source buffer.
is_video_encoder: Whether this a video encoder (as opposed to audio)
ctx: Encoder-specific state.
stream_id: Examples: Audio streams (0xc0-0xdf), Video streams (0xe0-0xef).
es_pid: The TS PID to use for the elementary stream in this encoder.
encode: Prepare enough AUs for the given amount of time.
clear: Clear the encoder output.
sync: Attempt to synchronize with this encoder.
sampling_rate_hz: The sampling rate (or fps, if video) used.
last_sample_cb: Called when the encoder runs out of data.This is so the source can read data in a piecemeal fashion instead of having to provide it all at once.
destroy: Destroy this encoder, freeing allocated resources.
next: Next in the chain

struct vidtv_mux_timing¶: Timing related information

Definition:

struct vidtv_mux_timing {
    u64 start_jiffies;
    u64 current_jiffies;
    u64 past_jiffies;
    u64 clk;
    u64 pcr_period_usecs;
    u64 si_period_usecs;
};

Members

start_jiffies: The value of 'jiffies' when we started the mux thread.
current_jiffies: The value of 'jiffies' for the current iteration.
past_jiffies: The value of 'jiffies' for the past iteration.
clk: A 27Mhz clock from which we will drive the PCR. Updated proportionally on every iteration.
pcr_period_usecs: How often we should send PCR packets.
si_period_usecs: How often we should send PSI packets.

Description

This is used to decide when PCR or PSI packets should be sent. This will also provide storage for the clock, which is used to compute the value for the PCR.

struct vidtv_mux_si¶: Store the PSI context.

Definition:

struct vidtv_mux_si {
    struct vidtv_psi_table_pat *pat;
    struct vidtv_psi_table_pmt **pmt_secs;
    struct vidtv_psi_table_sdt *sdt;
    struct vidtv_psi_table_nit *nit;
    struct vidtv_psi_table_eit *eit;
};

Members

pat: The PAT in use by the muxer.
pmt_secs: The PMT sections in use by the muxer. One for each program in the PAT.
sdt: The SDT in use by the muxer.
nit: The NIT in use by the muxer.
eit: the EIT in use by the muxer.

Description

This is used to store the PAT, PMT sections and SDT in use by the muxer.

The muxer acquire these by looking into the hardcoded channels in vidtv_channel and then periodically sends the TS packets for them>

struct vidtv_mux_pid_ctx¶: Store the context for a given TS PID.

Definition:

struct vidtv_mux_pid_ctx {
    u16 pid;
    u8 cc;
    struct hlist_node h;
};

Members

pid: The TS PID.
cc: The continuity counter for this PID. It is incremented on every TS pack and it will wrap around at 0xf0. If the decoder notices a sudden jump in this counter this will trigger a discontinuity state.
h: This is embedded in a hash table, mapping pid -> vidtv_mux_pid_ctx

struct vidtv_mux¶: A muxer abstraction loosely based in libavcodec/mpegtsenc.c

Definition:

struct vidtv_mux {
    struct dvb_frontend *fe;
    struct device *dev;
    struct vidtv_mux_timing timing;
    u32 mux_rate_kbytes_sec;
    unsigned long pid_ctx[1 << ((3) - 1)];
    void (*on_new_packets_available_cb)(void *priv, u8 *buf, u32 npackets);
    u8 *mux_buf;
    u32 mux_buf_sz;
    u32 mux_buf_offset;
    struct vidtv_channel  *channels;
    struct vidtv_mux_si si;
    u64 num_streamed_pcr;
    u64 num_streamed_si;
    struct work_struct mpeg_thread;
    bool streaming;
    u16 pcr_pid;
    u16 transport_stream_id;
    u16 network_id;
    char *network_name;
    void *priv;
};

Members

fe: The frontend structure allocated by the muxer.
dev: pointer to struct device.
timing: Keeps track of timing related information.
mux_rate_kbytes_sec: The bit rate for the TS, in kbytes.
pid_ctx: A hash table to keep track of per-PID metadata.
on_new_packets_available_cb: A callback to inform of new TS packets ready.
mux_buf: A pointer to a buffer for this muxer. TS packets are stored there and then passed on to the bridge driver.
mux_buf_sz: The size for 'mux_buf'.
mux_buf_offset: The current offset into 'mux_buf'.
channels: The channels associated with this muxer.
si: Keeps track of the PSI context.
num_streamed_pcr: Number of PCR packets streamed.
num_streamed_si: The number of PSI packets streamed.
mpeg_thread: Thread responsible for the muxer loop.
streaming: whether 'mpeg_thread' is running.
pcr_pid: The TS PID used for the PSI packets. All channels will share the same PCR.
transport_stream_id: The transport stream ID
network_id: The network ID
network_name: The network name
priv: Private data.

struct vidtv_mux_init_args¶: Arguments used to inix the muxer.

Definition:

struct vidtv_mux_init_args {
    u32 mux_rate_kbytes_sec;
    void (*on_new_packets_available_cb)(void *priv, u8 *buf, u32 npackets);
    u32 mux_buf_sz;
    u64 pcr_period_usecs;
    u64 si_period_usecs;
    u16 pcr_pid;
    u16 transport_stream_id;
    struct vidtv_channel *channels;
    u16 network_id;
    char *network_name;
    void *priv;
};

Members

mux_rate_kbytes_sec: The bit rate for the TS, in kbytes.
on_new_packets_available_cb: A callback to inform of new TS packets ready.
mux_buf_sz: The size for 'mux_buf'.
pcr_period_usecs: How often we should send PCR packets.
si_period_usecs: How often we should send PSI packets.
pcr_pid: The TS PID used for the PSI packets. All channels will share the same PCR.
transport_stream_id: The transport stream ID
channels: an optional list of channels to use
network_id: The network ID
network_name: The network name
priv: Private data.

struct pes_header_write_args¶: Arguments to write a PES header.

Definition:

struct pes_header_write_args {
    void *dest_buf;
    u32 dest_offset;
    u32 dest_buf_sz;
    u32 encoder_id;
    bool send_pts;
    u64 pts;
    bool send_dts;
    u64 dts;
    u16 stream_id;
    u32 n_pes_h_s_bytes;
    u32 access_unit_len;
};

Members

dest_buf: The buffer to write into.
dest_offset: where to start writing in the dest_buffer.
dest_buf_sz: The size of the dest_buffer
encoder_id: Encoder id (see vidtv_encoder.h)
send_pts: Should we send PTS?
pts: PTS value to send.
send_dts: Should we send DTS?
dts: DTS value to send.
stream_id: The stream id to use. Ex: Audio streams (0xc0-0xdf), Video streams (0xe0-0xef).
n_pes_h_s_bytes: Padding bytes. Might be used by an encoder if needed, gets discarded by the decoder.
access_unit_len: The size of _one_ access unit (with any headers it might need)

struct pes_ts_header_write_args¶: Arguments to write a TS header.

Definition:

struct pes_ts_header_write_args {
    void *dest_buf;
    u32 dest_offset;
    u32 dest_buf_sz;
    u16 pid;
    u8 *continuity_counter;
    bool wrote_pes_header;
    u32 n_stuffing_bytes;
    u64 pcr;
};

Members

dest_buf: The buffer to write into.
dest_offset: where to start writing in the dest_buffer.
dest_buf_sz: The size of the dest_buffer
pid: The PID to use for the TS packets.
continuity_counter: Incremented on every new TS packet.
wrote_pes_header: Flag to indicate that the PES header was written
n_stuffing_bytes: Padding bytes. Might be used by an encoder if needed, gets discarded by the decoder.
pcr: counter driven by a 27Mhz clock.

struct pes_write_args¶: Arguments for the packetizer.

Definition:

struct pes_write_args {
    void *dest_buf;
    void *from;
    u32 access_unit_len;
    u32 dest_offset;
    u32 dest_buf_sz;
    u16 pid;
    u32 encoder_id;
    u8 *continuity_counter;
    u16 stream_id;
    bool send_pts;
    u64 pts;
    bool send_dts;
    u64 dts;
    u32 n_pes_h_s_bytes;
    u64 pcr;
};

Members

dest_buf: The buffer to write into.
from: A pointer to the encoder buffer containing one access unit.
access_unit_len: The size of _one_ access unit (with any headers it might need)
dest_offset: where to start writing in the dest_buffer.
dest_buf_sz: The size of the dest_buffer
pid: The PID to use for the TS packets.
encoder_id: Encoder id (see vidtv_encoder.h)
continuity_counter: Incremented on every new TS packet.
stream_id: The stream id to use. Ex: Audio streams (0xc0-0xdf), Video streams (0xe0-0xef).
send_pts: Should we send PTS?
pts: PTS value to send.
send_dts: Should we send DTS?
dts: DTS value to send.
n_pes_h_s_bytes: Padding bytes. Might be used by an encoder if needed, gets discarded by the decoder.
pcr: counter driven by a 27Mhz clock.

u32 vidtv_pes_write_into(struct pes_write_args *args)¶: Write a PES packet as MPEG-TS packets into a buffer.

Parameters

struct pes_write_args *args: The args to use when writing

Description

This function translate the ES data for one access unit from an encoder into MPEG TS packets. It does so by first encapsulating it with a PES header and then splitting it into TS packets.

The data is then written into the buffer pointed to by 'args.buf'

Return

The number of bytes written into the buffer. This is usually NOT equal to the size of the access unit, since we need space for PES headers, TS headers and padding bytes, if any.

struct psi_write_args¶: Arguments for the PSI packetizer.

Definition:

struct psi_write_args {
    void *dest_buf;
    void *from;
    size_t len;
    u32 dest_offset;
    u16 pid;
    bool new_psi_section;
    u8 *continuity_counter;
    bool is_crc;
    u32 dest_buf_sz;
    u32 *crc;
};

Members

dest_buf: The buffer to write into.
from: PSI data to be copied.
len: How much to write.
dest_offset: where to start writing in the dest_buffer.
pid: TS packet ID.
new_psi_section: Set when starting a table section.
continuity_counter: Incremented on every new packet.
is_crc: Set when writing the CRC at the end.
dest_buf_sz: The size of the dest_buffer
crc: a pointer to store the crc for this chunk

struct desc_write_args¶: Arguments in order to write a descriptor.

Definition:

struct desc_write_args {
    void *dest_buf;
    u32 dest_offset;
    struct vidtv_psi_desc *desc;
    u16 pid;
    u8 *continuity_counter;
    u32 dest_buf_sz;
    u32 *crc;
};

Members

dest_buf: The buffer to write into.
dest_offset: where to start writing in the dest_buffer.
desc: A pointer to the descriptor
pid: TS packet ID.
continuity_counter: Incremented on every new packet.
dest_buf_sz: The size of the dest_buffer
crc: a pointer to store the crc for this chunk

struct crc32_write_args¶: Arguments in order to write the CRC at the end of the PSI tables.

Definition:

struct crc32_write_args {
    void *dest_buf;
    u32 dest_offset;
    __be32 crc;
    u16 pid;
    u8 *continuity_counter;
    u32 dest_buf_sz;
};

Members

dest_buf: The buffer to write into.
dest_offset: where to start writing in the dest_buffer.
crc: the CRC value to write
pid: TS packet ID.
continuity_counter: Incremented on every new packet.
dest_buf_sz: The size of the dest_buffer

struct header_write_args¶: Arguments in order to write the common table header

Definition:

struct header_write_args {
    void *dest_buf;
    u32 dest_offset;
    struct vidtv_psi_table_header *h;
    u16 pid;
    u8 *continuity_counter;
    u32 dest_buf_sz;
    u32 *crc;
};

Members

dest_buf: The buffer to write into.
dest_offset: where to start writing in the dest_buffer.
h: a pointer to the header.
pid: TS packet ID.
continuity_counter: Incremented on every new packet.
dest_buf_sz: The size of the dest_buffer
crc: a pointer to store the crc for this chunk

void vidtv_psi_sdt_service_assign(struct vidtv_psi_table_sdt *sdt, struct vidtv_psi_table_sdt_service *service)¶: Assigns the service loop to the SDT.

Parameters

struct vidtv_psi_table_sdt *sdt: The SDT to assign to.
struct vidtv_psi_table_sdt_service *service: The service loop (one or more services)

Description

This will free the previous service loop in the table. This will assign ownership of the service loop to the table, i.e. the table will free this service loop when a call to its destroy function is made.

void vidtv_psi_desc_assign(struct vidtv_psi_desc **to, struct vidtv_psi_desc *desc)¶: Assigns a descriptor loop at some point

Parameters

struct vidtv_psi_desc **to: Where to assign this descriptor loop to
struct vidtv_psi_desc *desc: The descriptor loop that will be assigned.

Description

This will free the loop in 'to', if any.

void vidtv_pmt_desc_assign(struct vidtv_psi_table_pmt *pmt, struct vidtv_psi_desc **to, struct vidtv_psi_desc *desc)¶: Assigns a descriptor loop at some point in a PMT section.

Parameters

struct vidtv_psi_table_pmt *pmt: The PMT section that will contain the descriptor loop
struct vidtv_psi_desc **to: Where in the PMT to assign this descriptor loop to
struct vidtv_psi_desc *desc: The descriptor loop that will be assigned.

Description

This will free the loop in 'to', if any. This will assign ownership of the loop to the table, i.e. the table will free this loop when a call to its destroy function is made.

void vidtv_sdt_desc_assign(struct vidtv_psi_table_sdt *sdt, struct vidtv_psi_desc **to, struct vidtv_psi_desc *desc)¶: Assigns a descriptor loop at some point in a SDT.

Parameters

struct vidtv_psi_table_sdt *sdt: The SDT that will contain the descriptor loop
struct vidtv_psi_desc **to: Where in the PMT to assign this descriptor loop to
struct vidtv_psi_desc *desc: The descriptor loop that will be assigned.

Description

This will free the loop in 'to', if any. This will assign ownership of the loop to the table, i.e. the table will free this loop when a call to its destroy function is made.

void vidtv_psi_pat_program_assign(struct vidtv_psi_table_pat *pat, struct vidtv_psi_table_pat_program *p)¶: Assigns the program loop to the PAT.

Parameters

struct vidtv_psi_table_pat *pat: The PAT to assign to.
struct vidtv_psi_table_pat_program *p: The program loop (one or more programs)

Description

This will free the previous program loop in the table. This will assign ownership of the program loop to the table, i.e. the table will free this program loop when a call to its destroy function is made.

void vidtv_psi_pmt_stream_assign(struct vidtv_psi_table_pmt *pmt, struct vidtv_psi_table_pmt_stream *s)¶: Assigns the stream loop to the PAT.

Parameters

struct vidtv_psi_table_pmt *pmt: The PMT to assign to.
struct vidtv_psi_table_pmt_stream *s: The stream loop (one or more streams)

Description

This will free the previous stream loop in the table. This will assign ownership of the stream loop to the table, i.e. the table will free this stream loop when a call to its destroy function is made.

struct vidtv_psi_table_pmt **vidtv_psi_pmt_create_sec_for_each_pat_entry(struct vidtv_psi_table_pat *pat, u16 pcr_pid)¶: Create a PMT section for each program found in the PAT

Parameters

struct vidtv_psi_table_pat *pat: The PAT to look for programs.
u16 pcr_pid: packet ID for the PCR to be used for the program described in this PMT section

u16 vidtv_psi_pmt_get_pid(struct vidtv_psi_table_pmt *section, struct vidtv_psi_table_pat *pat)¶: Get the TS PID for a PMT section.

Parameters

struct vidtv_psi_table_pmt *section: The PMT section whose PID we want to retrieve.
struct vidtv_psi_table_pat *pat: The PAT table to look into.

Return

the TS PID for 'section'

void vidtv_psi_pat_table_update_sec_len(struct vidtv_psi_table_pat *pat)¶: Recompute and update the PAT section length.

Parameters

struct vidtv_psi_table_pat *pat: The PAT whose length is to be updated.

Description

This will traverse the table and accumulate the length of its components, which is then used to replace the 'section_length' field.

If section_length > MAX_SECTION_LEN, the operation fails.

void vidtv_psi_pmt_table_update_sec_len(struct vidtv_psi_table_pmt *pmt)¶: Recompute and update the PMT section length.

Parameters

struct vidtv_psi_table_pmt *pmt: The PMT whose length is to be updated.

Description

This will traverse the table and accumulate the length of its components, which is then used to replace the 'section_length' field.

If section_length > MAX_SECTION_LEN, the operation fails.

void vidtv_psi_sdt_table_update_sec_len(struct vidtv_psi_table_sdt *sdt)¶: Recompute and update the SDT section length.

Parameters

struct vidtv_psi_table_sdt *sdt: The SDT whose length is to be updated.

Description

This will traverse the table and accumulate the length of its components, which is then used to replace the 'section_length' field.

If section_length > MAX_SECTION_LEN, the operation fails.

struct vidtv_psi_pat_write_args¶: Arguments for writing a PAT table

Definition:

struct vidtv_psi_pat_write_args {
    char *buf;
    u32 offset;
    struct vidtv_psi_table_pat *pat;
    u32 buf_sz;
    u8 *continuity_counter;
};

Members

buf: The destination buffer.
offset: The offset into the destination buffer.
pat: A pointer to the PAT.
buf_sz: The size of the destination buffer.
continuity_counter: A pointer to the CC. Incremented on every new packet.

u32 vidtv_psi_pat_write_into(struct vidtv_psi_pat_write_args *args)¶: Write PAT as MPEG-TS packets into a buffer.

Parameters

struct vidtv_psi_pat_write_args *args: An instance of struct vidtv_psi_pat_write_args

Description

This function writes the MPEG TS packets for a PAT table into a buffer. Calling code will usually generate the PAT via a call to its init function and thus is responsible for freeing it.

Return

The number of bytes written into the buffer. This is NOT equal to the size of the PAT, since more space is needed for TS headers during TS encapsulation.

struct vidtv_psi_sdt_write_args¶: Arguments for writing a SDT table

Definition:

struct vidtv_psi_sdt_write_args {
    char *buf;
    u32 offset;
    struct vidtv_psi_table_sdt *sdt;
    u32 buf_sz;
    u8 *continuity_counter;
};

Members

buf: The destination buffer.
offset: The offset into the destination buffer.
sdt: A pointer to the SDT.
buf_sz: The size of the destination buffer.
continuity_counter: A pointer to the CC. Incremented on every new packet.

u32 vidtv_psi_sdt_write_into(struct vidtv_psi_sdt_write_args *args)¶: Write SDT as MPEG-TS packets into a buffer.

Parameters

struct vidtv_psi_sdt_write_args *args: an instance of struct vidtv_psi_sdt_write_args

Description

This function writes the MPEG TS packets for a SDT table into a buffer. Calling code will usually generate the SDT via a call to its init function and thus is responsible for freeing it.

Return

The number of bytes written into the buffer. This is NOT equal to the size of the SDT, since more space is needed for TS headers during TS encapsulation.

struct vidtv_psi_pmt_write_args¶: Arguments for writing a PMT section

Definition:

struct vidtv_psi_pmt_write_args {
    char *buf;
    u32 offset;
    struct vidtv_psi_table_pmt *pmt;
    u16 pid;
    u32 buf_sz;
    u8 *continuity_counter;
    u16 pcr_pid;
};

Members

buf: The destination buffer.
offset: The offset into the destination buffer.
pmt: A pointer to the PMT.
pid: Program ID
buf_sz: The size of the destination buffer.
continuity_counter: A pointer to the CC. Incremented on every new packet.
pcr_pid: The TS PID used for the PSI packets. All channels will share the same PCR.

u32 vidtv_psi_pmt_write_into(struct vidtv_psi_pmt_write_args *args)¶: Write PMT as MPEG-TS packets into a buffer.

Parameters

struct vidtv_psi_pmt_write_args *args: an instance of struct vidtv_psi_pmt_write_args

Description

This function writes the MPEG TS packets for a PMT section into a buffer. Calling code will usually generate the PMT section via a call to its init function and thus is responsible for freeing it.

Return

The number of bytes written into the buffer. This is NOT equal to the size of the PMT section, since more space is needed for TS headers during TS encapsulation.

struct vidtv_psi_table_pmt *vidtv_psi_find_pmt_sec(struct vidtv_psi_table_pmt **pmt_sections, u16 nsections, u16 program_num)¶: Finds the PMT section for 'program_num'

Parameters

struct vidtv_psi_table_pmt **pmt_sections: The sections to look into.
u16 nsections: The number of sections.
u16 program_num: The 'program_num' from PAT pointing to a PMT section.

Return

A pointer to the PMT, if found, or NULL.

struct vidtv_psi_table_transport¶: A entry in the TS loop for the NIT and/or other tables. See ETSI 300 468 section 5.2.1

Definition:

struct vidtv_psi_table_transport {
    __be16 transport_id;
    __be16 network_id;
    __be16 bitfield;
    struct vidtv_psi_desc *descriptor;
    struct vidtv_psi_table_transport *next;
};

Members

transport_id: The TS ID being described
network_id: The network_id that contains the TS ID
bitfield: Contains the descriptor loop length
descriptor: A descriptor loop
next: Pointer to the next entry

struct vidtv_psi_table_nit¶: A Network Information Table (NIT). See ETSI 300 468 section 5.2.1

Definition:

struct vidtv_psi_table_nit {
    struct vidtv_psi_table_header header;
    __be16 bitfield;
    struct vidtv_psi_desc *descriptor;
    __be16 bitfield2;
    struct vidtv_psi_table_transport *transport;
};

Members

header: A PSI table header
bitfield: Contains the network descriptor length
descriptor: A descriptor loop describing the network
bitfield2: Contains the transport stream loop length
transport: The transport stream loop

struct vidtv_psi_nit_write_args¶: Arguments for writing a NIT section

Definition:

struct vidtv_psi_nit_write_args {
    char *buf;
    u32 offset;
    struct vidtv_psi_table_nit *nit;
    u32 buf_sz;
    u8 *continuity_counter;
};

Members

buf: The destination buffer.
offset: The offset into the destination buffer.
nit: A pointer to the NIT
buf_sz: The size of the destination buffer.
continuity_counter: A pointer to the CC. Incremented on every new packet.

u32 vidtv_psi_nit_write_into(struct vidtv_psi_nit_write_args *args)¶: Write NIT as MPEG-TS packets into a buffer.

Parameters

struct vidtv_psi_nit_write_args *args: an instance of struct vidtv_psi_nit_write_args

Description

This function writes the MPEG TS packets for a NIT table into a buffer. Calling code will usually generate the NIT via a call to its init function and thus is responsible for freeing it.

Return

The number of bytes written into the buffer. This is NOT equal to the size of the NIT, since more space is needed for TS headers during TS encapsulation.

struct vidtv_psi_eit_write_args¶: Arguments for writing an EIT section

Definition:

struct vidtv_psi_eit_write_args {
    char *buf;
    u32 offset;
    struct vidtv_psi_table_eit *eit;
    u32 buf_sz;
    u8 *continuity_counter;
};

Members

buf: The destination buffer.
offset: The offset into the destination buffer.
eit: A pointer to the EIT
buf_sz: The size of the destination buffer.
continuity_counter: A pointer to the CC. Incremented on every new packet.

u32 vidtv_psi_eit_write_into(struct vidtv_psi_eit_write_args *args)¶: Write EIT as MPEG-TS packets into a buffer.

Parameters

struct vidtv_psi_eit_write_args *args: an instance of struct vidtv_psi_nit_write_args

Description

This function writes the MPEG TS packets for a EIT table into a buffer. Calling code will usually generate the EIT via a call to its init function and thus is responsible for freeing it.

Return

The number of bytes written into the buffer. This is NOT equal to the size of the EIT, since more space is needed for TS headers during TS encapsulation.

void vidtv_psi_eit_table_update_sec_len(struct vidtv_psi_table_eit *eit)¶: Recompute and update the EIT section length.

Parameters

struct vidtv_psi_table_eit *eit: The EIT whose length is to be updated.

Description

This will traverse the table and accumulate the length of its components, which is then used to replace the 'section_length' field.

If section_length > EIT_MAX_SECTION_LEN, the operation fails.

void vidtv_psi_eit_event_assign(struct vidtv_psi_table_eit *eit, struct vidtv_psi_table_eit_event *e)¶: Assigns the event loop to the EIT.

Parameters

struct vidtv_psi_table_eit *eit: The EIT to assign to.
struct vidtv_psi_table_eit_event *e: The event loop

Description

This will free the previous event loop in the table. This will assign ownership of the stream loop to the table, i.e. the table will free this stream loop when a call to its destroy function is made.

struct vidtv_s302m_ctx¶: s302m encoder context.

Definition:

struct vidtv_s302m_ctx {
    struct vidtv_encoder *enc;
    u32 frame_index;
    u32 au_count;
    int last_duration;
    unsigned int note_offset;
    enum musical_notes last_tone;
};

Members

enc: A pointer to the containing encoder structure.
frame_index: The current frame in a block
au_count: The total number of access units encoded up to now
last_duration: Duration of the tone currently being played
note_offset: Position at the music tone array
last_tone: Tone currently being played

struct vidtv_s302m_encoder_init_args¶: Args for the s302m encoder.

Definition:

struct vidtv_s302m_encoder_init_args {
    char *name;
    void *src_buf;
    u32 src_buf_sz;
    u16 es_pid;
    struct vidtv_encoder *sync;
    void (*last_sample_cb)(u32 sample_no);
    struct vidtv_encoder *head;
};

Members

name: A name to identify this particular instance
src_buf: The source buffer, encoder will default to a sine wave if this is NULL.
src_buf_sz: The size of the source buffer.
es_pid: The MPEG Elementary Stream PID to use.
sync: Attempt to synchronize audio with this video encoder, if not NULL.
last_sample_cb: A callback called when the encoder runs out of data.
head: Add to this chain

struct pcr_write_args¶: Arguments for the pcr_write_into function.

Definition:

struct pcr_write_args {
    void *dest_buf;
    u32 dest_offset;
    u16 pid;
    u32 buf_sz;
    u8 *continuity_counter;
    u64 pcr;
};

Members

dest_buf: The buffer to write into.
dest_offset: The byte offset into the buffer.
pid: The TS PID for the PCR packets.
buf_sz: The size of the buffer in bytes.
continuity_counter: The TS continuity_counter.
pcr: A sample from the system clock.

struct null_packet_write_args¶: Arguments for the null_write_into function

Definition:

struct null_packet_write_args {
    void *dest_buf;
    u32 dest_offset;
    u32 buf_sz;
    u8 *continuity_counter;
};

Members

dest_buf: The buffer to write into.
dest_offset: The byte offset into the buffer.
buf_sz: The size of the buffer in bytes.
continuity_counter: The TS continuity_counter.

u32 vidtv_ts_null_write_into(struct null_packet_write_args args)¶: Write a TS null packet into a buffer.

Parameters

struct null_packet_write_args args: the arguments to use when writing.

Description

This function will write a null packet into a buffer. This is usually used to pad TS streams.

Return

The number of bytes written into the buffer.

u32 vidtv_ts_pcr_write_into(struct pcr_write_args args)¶: Write a PCR packet into a buffer.

Parameters

struct pcr_write_args args: the arguments to use when writing.

Description

This function will write a PCR packet into a buffer. This is used to synchronize the clocks between encoders and decoders.

Return

The number of bytes written into the buffer.

struct vidtv_tuner_config¶: Configuration used to init the tuner.

Definition:

struct vidtv_tuner_config {
    struct dvb_frontend *fe;
    u32 mock_power_up_delay_msec;
    u32 mock_tune_delay_msec;
    u32 vidtv_valid_dvb_t_freqs[NUM_VALID_TUNER_FREQS];
    u32 vidtv_valid_dvb_c_freqs[NUM_VALID_TUNER_FREQS];
    u32 vidtv_valid_dvb_s_freqs[NUM_VALID_TUNER_FREQS];
    u8 max_frequency_shift_hz;
};

Members

fe: A pointer to the dvb_frontend structure allocated by vidtv_demod.
mock_power_up_delay_msec: Simulate a power-up delay.
mock_tune_delay_msec: Simulate a tune delay.
vidtv_valid_dvb_t_freqs: The valid DVB-T frequencies to simulate.
vidtv_valid_dvb_c_freqs: The valid DVB-C frequencies to simulate.
vidtv_valid_dvb_s_freqs: The valid DVB-S frequencies to simulate.
max_frequency_shift_hz: The maximum frequency shift in HZ allowed when tuning in a channel

Description

The configuration used to init the tuner module, usually filled by a bridge driver. For vidtv, this is filled by vidtv_bridge before the tuner module is probed.

u32 vidtv_memcpy(void *to, size_t to_offset, size_t to_size, const void *from, size_t len)¶: wrapper routine to be used by MPEG-TS generator, in order to avoid going past the output buffer.

Parameters

void *to: Starting element to where a MPEG-TS packet will be copied.
size_t to_offset: Starting position of the to buffer to be filled.
size_t to_size: Size of the to buffer.
const void *from: Starting element of the buffer to be copied.
size_t len: Number of elements to be copy from from buffer into to**+ **to_offset buffer.

Note

Real digital TV demod drivers should not have memcpy wrappers. We use it here because emulating MPEG-TS generation at kernelspace requires some extra care.

Return

Returns the number of bytes written

u32 vidtv_memset(void *to, size_t to_offset, size_t to_size, const int c, size_t len)¶: wrapper routine to be used by MPEG-TS generator, in order to avoid going past the output buffer.

Parameters

void *to: Starting element to set
size_t to_offset: Starting position of the to buffer to be filled.
size_t to_size: Size of the to buffer.
const int c: The value to set the memory to.
size_t len: Number of elements to be copy from from buffer into to**+ **to_offset buffer.

Note

Real digital TV demod drivers should not have memset wrappers. We use it here because emulating MPEG-TS generation at kernelspace requires some extra care.

Return

Returns the number of bytes written

struct vidtv_tuner_hardware_state¶: Simulate the tuner hardware status

Definition:

struct vidtv_tuner_hardware_state {
    bool asleep;
    u32 lock_status;
    u32 if_frequency;
    u32 tuned_frequency;
    u32 bandwidth;
};

Members

asleep: whether the tuner is asleep, i.e whether _sleep() or _suspend() was called.
lock_status: Whether the tuner has managed to lock on the requested frequency.
if_frequency: The tuner's intermediate frequency. Hardcoded for the purposes of simulation.
tuned_frequency: The actual tuned frequency.
bandwidth: The actual bandwidth.

Description

This structure is meant to simulate the status of the tuner hardware, as if we had a physical tuner hardware.

struct vidtv_tuner_dev¶: The tuner struct

Definition:

struct vidtv_tuner_dev {
    struct dvb_frontend *fe;
    struct vidtv_tuner_hardware_state hw_state;
    struct vidtv_tuner_config config;
};

Members

fe: A pointer to the dvb_frontend structure allocated by vidtv_demod
hw_state: A struct to simulate the tuner's hardware state as if we had a physical tuner hardware.
config: The configuration used to start the tuner module, usually filled by a bridge driver. For vidtv, this is filled by vidtv_bridge before the tuner module is probed.

The Linux Kernel

Contents

This Page

9.2.3. vidtv: Virtual Digital TV driver¶

9.2.3.1. Background¶

9.2.3.2. Building vidtv¶

9.2.3.3. Running vidtv¶

9.2.3.4. Command-line arguments to vidtv¶

9.2.3.5. vidtv internal structure¶

9.2.3.6. Testing vidtv with v4l-utils¶

9.2.3.6.1. Using dvb-fe-tool¶

9.2.3.6.2. Using dvb-scan¶

9.2.3.6.3. Using dvb-zap¶

9.2.3.7. What can still be improved in vidtv¶

9.2.3.7.1. Add debugfs integration¶

9.2.3.7.2. Add a way to test video¶

9.2.3.7.3. Add white noise simulation¶

9.2.3.8. Functions and structs used within vidtv¶