Documentation/driver-api/media/drivers/vidtv.rst - linux - Git at Google

 .. SPDX-License-Identifier: GPL-2.0

 ================================
 vidtv: Virtual Digital TV driver
 ================================

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

 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 reponsible 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.

 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

 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.

 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.

 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
 	<https://tsduck.io/streams/brazil-isdb-tb/TS1globo.ts>`_.

 	A good way to visualize the structure of streams is by using
 	`DVBInspector <https://sourceforge.net/projects/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.

 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
 <https://linuxtv.org/wiki/index.php/V4l-utils>`_.

 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.

 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
 <https://www.linuxtv.org/wiki/index.php/Dvb-fe-tool>`_.

 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
 <https://git.linuxtv.org/dtv-scan-tables.git>`_.

 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 <https://www.linuxtv.org/wiki/index.php/Dvbscan>`_.

 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

 .. [1] In this example, it records 10 seconds with all program ID's stored
        at the music.ts file.


 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
 <https://www.linuxtv.org/wiki/index.php/Dvbv5-zap>`_.
 See also: `zap <https://www.linuxtv.org/wiki/index.php/Zap>`_.


 What can still be improved in vidtv
 -----------------------------------

 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.

 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/


 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.

 Functions and structs used within vidtv
 ---------------------------------------

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_bridge.h

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_channel.h

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_demod.h

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_encoder.h

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_mux.h

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_pes.h

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_psi.h

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_s302m.h

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_ts.h

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_tuner.h

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_common.c

 .. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_tuner.c
	.. SPDX-License-Identifier: GPL-2.0

	================================
	vidtv: Virtual Digital TV driver
	================================

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

	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 reponsible 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.

	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

	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.

	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.

	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
	<https://tsduck.io/streams/brazil-isdb-tb/TS1globo.ts>`_.

	A good way to visualize the structure of streams is by using
	`DVBInspector <https://sourceforge.net/projects/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.

	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
	<https://linuxtv.org/wiki/index.php/V4l-utils>`_.

	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.

	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
	<https://www.linuxtv.org/wiki/index.php/Dvb-fe-tool>`_.

	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
	<https://git.linuxtv.org/dtv-scan-tables.git>`_.

	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 <https://www.linuxtv.org/wiki/index.php/Dvbscan>`_.

	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

	.. [1] In this example, it records 10 seconds with all program ID's stored
	at the music.ts file.


	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
	<https://www.linuxtv.org/wiki/index.php/Dvbv5-zap>`_.
	See also: `zap <https://www.linuxtv.org/wiki/index.php/Zap>`_.


	What can still be improved in vidtv
	-----------------------------------

	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.

	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/


	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.

	Functions and structs used within vidtv
	---------------------------------------

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_bridge.h

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_channel.h

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_demod.h

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_encoder.h

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_mux.h

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_pes.h

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_psi.h

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_s302m.h

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_ts.h

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_tuner.h

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_common.c

	.. kernel-doc:: drivers/media/test-drivers/vidtv/vidtv_tuner.c