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author | holger <devnull@localhost> | 2002-10-10 15:59:05 -0300 |
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committer | holger <devnull@localhost> | 2002-10-10 15:59:05 -0300 |
commit | ab85b007da42f42856a775d8cff97332093f5b34 (patch) | |
tree | 7ea0b240dd39132663eafbaca11b6dc54fc2cc94 /dvb-spec/dvbapi/intro.tex | |
parent | aed2950af0b53026e245705b265059ee9a439e1f (diff) | |
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diff --git a/dvb-spec/dvbapi/intro.tex b/dvb-spec/dvbapi/intro.tex deleted file mode 100644 index 1d859fadb..000000000 --- a/dvb-spec/dvbapi/intro.tex +++ /dev/null @@ -1,183 +0,0 @@ -\chapter{Introduction} -%\addcontentsline{toc}{part}{Introduction} -%\chaptermark{Introduction} -\section{What you need to know} -The reader of this document is required to have some knowledge in the -area of digital video broadcasting (DVB) and should be familiar with -part I of ISO/IEC 13818, i.e you should know what a -program/transport stream (PS/TS) is and what is meant by a packetized elementary -stream (PES) or an I-frame. - -It is also necessary to know how to access unix/linux devices and how -to use ioctl calls. This also includes the knowledge of C or C++. -\section{History} - -The first API for DVB cards we used at Convergence in late 1999 -was an extension of the Video4Linux API which was primarily -developed for frame grabber cards. -As such it was not really well suited to be used for DVB cards and -their new features like recording MPEG streams and filtering several -section and PES data streams at the same time. - -In early 2000, we were approached by Nokia with a proposal for a new -standard Linux DVB API. -As a commitment to the development of terminals based on open standards, -Nokia and Convergence made it available to all Linux developers and -published it on \texttt{http://www.linuxtv.org/} in September 2000. -Convergence is the maintainer of the Linux DVB API. -Together with the LinuxTV community (i.e. you, the reader of this document), -the Linux DVB API will be constantly reviewed and improved upon. -With the Linux driver for the Siemens/Hauppauge DVB PCI card Convergence -provides a first implementation of the Linux DVB API. - - -\section{Overview} - -\begin{figure}[htbp] - \begin{center} - \includegraphics{dvbstb.ps} - \caption{Components of a DVB card/STB} - \label{fig:dvbstb} - \end{center} -\end{figure} - - -A DVB PCI card or DVB set-top-box (STB) usually consists of the following -main hardware components: -\begin{itemize} -\item Frontend consisting of tuner and DVB demodulator - -Here the raw signal reaches the DVB hardware from a satellite dish or antenna -or directly from cable. The frontend down-converts and demodulates -this signal into an MPEG transport stream (TS). - -\item SEC for controlling external hardware like LNBs and antennas - -This part of the hardware can send signals back through the satellite -cable to control the polarization of the LNB, to switch between -different LNBs or even to control the movements of a dish rotor. - - -\item Conditional Access (CA) hardware like CI adapters and smartcard slots - -The complete TS is passed through the CA hardware. Programs to which -the user has access (controlled by the smart card) are decoded in real -time and re-inserted into the TS. - -\item Demultiplexer which filters the incoming DVB stream - -The demultiplexer splits the TS into its components like audio and video -streams. Besides usually several of such audio and video streams it also -contains data streams with information about the programs offered in this -or other streams of the same provider. - -\item MPEG2 audio and video decoder - -The main targets of the demultiplexer are the MPEG2 audio and video -decoders. After decoding the pass on the uncompressed audio -and video to the computer screen or (through a PAL/NTSC encoder) to -a TV set. -\end{itemize} -Figure \ref{fig:dvbstb} shows a crude schematic of the control and data flow -between those components. - -On a DVB PCI card not all of these have to be present since some -functionality can be provided by the main CPU of the PC (e.g. MPEG picture -and sound decoding) or is not needed (e.g. for data-only uses like -``internet over satellite''). -Also not every card or STB provides conditional access hardware. - -\section{Linux DVB Devices} - -The Linux DVB API lets you control these hardware components -through currently six Unix-style character devices for -video, audio, frontend, SEC, demux and CA. -The video and audio devices control the MPEG2 decoder hardware, -the frontend device the tuner and the DVB demodulator. -External hardware like DiSEqC switches and rotors can be controlled -through the SEC device. -The demux device gives you control over the PES and section filters -of the hardware. If the hardware does not support filtering these filters -can be implemented in software. -Finally, the CA device controls all the conditional access capabilities -of the hardware. It can depend on the individual security requirements -of the platform, if and how many of the CA functions are made available -to the application through this device. - -All devices can be found in the \texttt{/dev} tree under -\texttt{/dev/ost}, where OST stands for Open Standards Terminal. -The individual devices are called -\begin{itemize} -\item \texttt{/dev/ost/audio}, -\item \texttt{/dev/ost/video}, -\item \texttt{/dev/ost/frontend}, -\item \texttt{/dev/ost/sec}, -\item \texttt{/dev/ost/demux}, -\item \texttt{/dev/ost/ca}, -\end{itemize} -but we will omit the ``\texttt{/dev/ost/}'' in the further dicussion of -these devices. - -If more than one card is present in the system the other cards -can be accessed through the corresponding devices with the -card's number appended. \texttt{/dev/ost/demux0} (which -is identical to \texttt{/dev/ost/demux}) would, e.g., control the -demultiplexer of the first card, while \texttt{/dev/ost/demux1} -would control the demultiplexer of the second card, and so on. - -More details about the data structures and function calls of -all the devices are described in the following chapters. - - -\section{DVB Devices with Devfs} - -Recent Linux kernel versions support a special file system called -\textsl{devfs} which is a replacement for the traditional -device directory. -With devfs a Linux DVB driver will only create those device file entries -which actually exist. -It also makes dealing with more complex DVB hardware much easier. -The device structure described above is not well suited to deal -with multiple DVB cards with more than one frontend or demultiplexer. -Consider, e.g., two DVB cards, one with two frontends and -one demultiplexer, the other with one frontend and two demultiplexers. -If we just assign them consecutive numbers, there would be a demultiplexer -and a frontend which do not belong to the same card but have -the same number. - -With \textsl{devfs} we propose a different scheme for the device names. -The root directory for all DVB cards will be \texttt{/dev/dvb}. -Each card gets assigned a sub-directory with the name \texttt{/dev/card0}, -\texttt{/dev/card1}, etc. -The files created in these sub-directories will correspond directly to the -hardware actually present on the card. -Thus, if the first card has one QAM frontend, one demultiplexer -and otherwise no other hardware, -only \texttt{/dev/dvb/card0/qamfe0} and \texttt{/dev/dvb/card0/demux0} -will be created. -When a second DVB-S card with one frontend (including SEC) device, -two demultiplexers and an MPEG2 audio/video decoder is added, the -complete \texttt{/dev/dvb} tree will look like this: - -\begin{verbatim} -/dev/dvb/card0/frontend0 - demux0 - -/dev/dvb/card1/video0 - audio0 - demux0 - demux1 - frontend0 - sec0 -\end{verbatim} - - -\section{Using the Devices} - -\dots - - -%%% Local Variables: -%%% mode: latex -%%% TeX-master: "dvbapi" -%%% End: |