Documentation/driver-api/media/drivers/vidtv.rst

Source file repositories/reference/linux-study-clean/Documentation/driver-api/media/drivers/vidtv.rst

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Documentation/driver-api/media/drivers/vidtv.rst
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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.. 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 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.

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

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