Commit 7e397561 authored by Jonathan Corbet's avatar Jonathan Corbet
Browse files

Remove videobook.tmpl



This document describes the long-deprecated V4L1 interface.  In-tree, it
can only serve to encourage developers to write drivers to the wrong API.
Remove it in favor of the V4L2 documentation which must surely show up
someday.
Acked-by: default avatarAlan Cox <alan@redhat.com>
Acked-by: default avatarMauro Carvalho Chehab <mchehab@infradead.org>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 58bae1f5
......@@ -6,7 +6,7 @@
# To add a new book the only step required is to add the book to the
# list of DOCBOOKS.
DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \
DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml \
kernel-hacking.xml kernel-locking.xml deviceiobook.xml \
procfs-guide.xml writing_usb_driver.xml networking.xml \
kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \
......
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
<book id="V4LGuide">
<bookinfo>
<title>Video4Linux Programming</title>
<authorgroup>
<author>
<firstname>Alan</firstname>
<surname>Cox</surname>
<affiliation>
<address>
<email>alan@redhat.com</email>
</address>
</affiliation>
</author>
</authorgroup>
<copyright>
<year>2000</year>
<holder>Alan Cox</holder>
</copyright>
<legalnotice>
<para>
This documentation is free software; you can redistribute
it and/or modify it under the terms of the GNU General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later
version.
</para>
<para>
This program is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the GNU General Public License for more details.
</para>
<para>
You should have received a copy of the GNU General Public
License along with this program; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
MA 02111-1307 USA
</para>
<para>
For more details see the file COPYING in the source
distribution of Linux.
</para>
</legalnotice>
</bookinfo>
<toc></toc>
<chapter id="intro">
<title>Introduction</title>
<para>
Parts of this document first appeared in Linux Magazine under a
ninety day exclusivity.
</para>
<para>
Video4Linux is intended to provide a common programming interface
for the many TV and capture cards now on the market, as well as
parallel port and USB video cameras. Radio, teletext decoders and
vertical blanking data interfaces are also provided.
</para>
</chapter>
<chapter id="radio">
<title>Radio Devices</title>
<para>
There are a wide variety of radio interfaces available for PC's, and these
are generally very simple to program. The biggest problem with supporting
such devices is normally extracting documentation from the vendor.
</para>
<para>
The radio interface supports a simple set of control ioctls standardised
across all radio and tv interfaces. It does not support read or write, which
are used for video streams. The reason radio cards do not allow you to read
the audio stream into an application is that without exception they provide
a connection on to a soundcard. Soundcards can be used to read the radio
data just fine.
</para>
<sect1 id="registerradio">
<title>Registering Radio Devices</title>
<para>
The Video4linux core provides an interface for registering devices. The
first step in writing our radio card driver is to register it.
</para>
<programlisting>
static struct video_device my_radio
{
"My radio",
VID_TYPE_TUNER,
radio_open.
radio_close,
NULL, /* no read */
NULL, /* no write */
NULL, /* no poll */
radio_ioctl,
NULL, /* no special init function */
NULL /* no private data */
};
</programlisting>
<para>
This declares our video4linux device driver interface. The VID_TYPE_ value
defines what kind of an interface we are, and defines basic capabilities.
</para>
<para>
The only defined value relevant for a radio card is VID_TYPE_TUNER which
indicates that the device can be tuned. Clearly our radio is going to have some
way to change channel so it is tuneable.
</para>
<para>
We declare an open and close routine, but we do not need read or write,
which are used to read and write video data to or from the card itself. As
we have no read or write there is no poll function.
</para>
<para>
The private initialise function is run when the device is registered. In
this driver we've already done all the work needed. The final pointer is a
private data pointer that can be used by the device driver to attach and
retrieve private data structures. We set this field "priv" to NULL for
the moment.
</para>
<para>
Having the structure defined is all very well but we now need to register it
with the kernel.
</para>
<programlisting>
static int io = 0x320;
int __init myradio_init(struct video_init *v)
{
if(!request_region(io, MY_IO_SIZE, "myradio"))
{
printk(KERN_ERR
"myradio: port 0x%03X is in use.\n", io);
return -EBUSY;
}
if(video_device_register(&amp;my_radio, VFL_TYPE_RADIO)==-1) {
release_region(io, MY_IO_SIZE);
return -EINVAL;
}
return 0;
}
</programlisting>
<para>
The first stage of the initialisation, as is normally the case, is to check
that the I/O space we are about to fiddle with doesn't belong to some other
driver. If it is we leave well alone. If the user gives the address of the
wrong device then we will spot this. These policies will generally avoid
crashing the machine.
</para>
<para>
Now we ask the Video4Linux layer to register the device for us. We hand it
our carefully designed video_device structure and also tell it which group
of devices we want it registered with. In this case VFL_TYPE_RADIO.
</para>
<para>
The types available are
</para>
<table frame="all" id="Device_Types"><title>Device Types</title>
<tgroup cols="3" align="left">
<tbody>
<row>
<entry>VFL_TYPE_RADIO</entry><entry>/dev/radio{n}</entry><entry>
Radio devices are assigned in this block. As with all of these
selections the actual number assignment is done by the video layer
accordijng to what is free.</entry>
</row><row>
<entry>VFL_TYPE_GRABBER</entry><entry>/dev/video{n}</entry><entry>
Video capture devices and also -- counter-intuitively for the name --
hardware video playback devices such as MPEG2 cards.</entry>
</row><row>
<entry>VFL_TYPE_VBI</entry><entry>/dev/vbi{n}</entry><entry>
The VBI devices capture the hidden lines on a television picture
that carry further information like closed caption data, teletext
(primarily in Europe) and now Intercast and the ATVEC internet
television encodings.</entry>
</row><row>
<entry>VFL_TYPE_VTX</entry><entry>/dev/vtx[n}</entry><entry>
VTX is 'Videotext' also known as 'Teletext'. This is a system for
sending numbered, 40x25, mostly textual page images over the hidden
lines. Unlike the /dev/vbi interfaces, this is for 'smart' decoder
chips. (The use of the word smart here has to be taken in context,
the smartest teletext chips are fairly dumb pieces of technology).
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
We are most definitely a radio.
</para>
<para>
Finally we allocate our I/O space so that nobody treads on us and return 0
to signify general happiness with the state of the universe.
</para>
</sect1>
<sect1 id="openradio">
<title>Opening And Closing The Radio</title>
<para>
The functions we declared in our video_device are mostly very simple.
Firstly we can drop in what is basically standard code for open and close.
</para>
<programlisting>
static int users = 0;
static int radio_open(struct video_device *dev, int flags)
{
if(users)
return -EBUSY;
users++;
return 0;
}
</programlisting>
<para>
At open time we need to do nothing but check if someone else is also using
the radio card. If nobody is using it we make a note that we are using it,
then we ensure that nobody unloads our driver on us.
</para>
<programlisting>
static int radio_close(struct video_device *dev)
{
users--;
}
</programlisting>
<para>
At close time we simply need to reduce the user count and allow the module
to become unloadable.
</para>
<para>
If you are sharp you will have noticed neither the open nor the close
routines attempt to reset or change the radio settings. This is intentional.
It allows an application to set up the radio and exit. It avoids a user
having to leave an application running all the time just to listen to the
radio.
</para>
</sect1>
<sect1 id="ioctlradio">
<title>The Ioctl Interface</title>
<para>
This leaves the ioctl routine, without which the driver will not be
terribly useful to anyone.
</para>
<programlisting>
static int radio_ioctl(struct video_device *dev, unsigned int cmd, void *arg)
{
switch(cmd)
{
case VIDIOCGCAP:
{
struct video_capability v;
v.type = VID_TYPE_TUNER;
v.channels = 1;
v.audios = 1;
v.maxwidth = 0;
v.minwidth = 0;
v.maxheight = 0;
v.minheight = 0;
strcpy(v.name, "My Radio");
if(copy_to_user(arg, &amp;v, sizeof(v)))
return -EFAULT;
return 0;
}
</programlisting>
<para>
VIDIOCGCAP is the first ioctl all video4linux devices must support. It
allows the applications to find out what sort of a card they have found and
to figure out what they want to do about it. The fields in the structure are
</para>
<table frame="all" id="video_capability_fields"><title>struct video_capability fields</title>
<tgroup cols="2" align="left">
<tbody>
<row>
<entry>name</entry><entry>The device text name. This is intended for the user.</entry>
</row><row>
<entry>channels</entry><entry>The number of different channels you can tune on
this card. It could even by zero for a card that has
no tuning capability. For our simple FM radio it is 1.
An AM/FM radio would report 2.</entry>
</row><row>
<entry>audios</entry><entry>The number of audio inputs on this device. For our
radio there is only one audio input.</entry>
</row><row>
<entry>minwidth,minheight</entry><entry>The smallest size the card is capable of capturing
images in. We set these to zero. Radios do not
capture pictures</entry>
</row><row>
<entry>maxwidth,maxheight</entry><entry>The largest image size the card is capable of
capturing. For our radio we report 0.
</entry>
</row><row>
<entry>type</entry><entry>This reports the capabilities of the device, and
matches the field we filled in in the struct
video_device when registering.</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Having filled in the fields, we use copy_to_user to copy the structure into
the users buffer. If the copy fails we return an EFAULT to the application
so that it knows it tried to feed us garbage.
</para>
<para>
The next pair of ioctl operations select which tuner is to be used and let
the application find the tuner properties. We have only a single FM band
tuner in our example device.
</para>
<programlisting>
case VIDIOCGTUNER:
{
struct video_tuner v;
if(copy_from_user(&amp;v, arg, sizeof(v))!=0)
return -EFAULT;
if(v.tuner)
return -EINVAL;
v.rangelow=(87*16000);
v.rangehigh=(108*16000);
v.flags = VIDEO_TUNER_LOW;
v.mode = VIDEO_MODE_AUTO;
v.signal = 0xFFFF;
strcpy(v.name, "FM");
if(copy_to_user(&amp;v, arg, sizeof(v))!=0)
return -EFAULT;
return 0;
}
</programlisting>
<para>
The VIDIOCGTUNER ioctl allows applications to query a tuner. The application
sets the tuner field to the tuner number it wishes to query. The query does
not change the tuner that is being used, it merely enquires about the tuner
in question.
</para>
<para>
We have exactly one tuner so after copying the user buffer to our temporary
structure we complain if they asked for a tuner other than tuner 0.
</para>
<para>
The video_tuner structure has the following fields
</para>
<table frame="all" id="video_tuner_fields"><title>struct video_tuner fields</title>
<tgroup cols="2" align="left">
<tbody>
<row>
<entry>int tuner</entry><entry>The number of the tuner in question</entry>
</row><row>
<entry>char name[32]</entry><entry>A text description of this tuner. "FM" will do fine.
This is intended for the application.</entry>
</row><row>
<entry>u32 flags</entry>
<entry>Tuner capability flags</entry>
</row>
<row>
<entry>u16 mode</entry><entry>The current reception mode</entry>
</row><row>
<entry>u16 signal</entry><entry>The signal strength scaled between 0 and 65535. If
a device cannot tell the signal strength it should
report 65535. Many simple cards contain only a
signal/no signal bit. Such cards will report either
0 or 65535.</entry>
</row><row>
<entry>u32 rangelow, rangehigh</entry><entry>
The range of frequencies supported by the radio
or TV. It is scaled according to the VIDEO_TUNER_LOW
flag.</entry>
</row>
</tbody>
</tgroup>
</table>
<table frame="all" id="video_tuner_flags"><title>struct video_tuner flags</title>
<tgroup cols="2" align="left">
<tbody>
<row>
<entry>VIDEO_TUNER_PAL</entry><entry>A PAL TV tuner</entry>
</row><row>
<entry>VIDEO_TUNER_NTSC</entry><entry>An NTSC (US) TV tuner</entry>
</row><row>
<entry>VIDEO_TUNER_SECAM</entry><entry>A SECAM (French) TV tuner</entry>
</row><row>
<entry>VIDEO_TUNER_LOW</entry><entry>
The tuner frequency is scaled in 1/16th of a KHz
steps. If not it is in 1/16th of a MHz steps
</entry>
</row><row>
<entry>VIDEO_TUNER_NORM</entry><entry>The tuner can set its format</entry>
</row><row>
<entry>VIDEO_TUNER_STEREO_ON</entry><entry>The tuner is currently receiving a stereo signal</entry>
</row>
</tbody>
</tgroup>
</table>
<table frame="all" id="video_tuner_modes"><title>struct video_tuner modes</title>
<tgroup cols="2" align="left">
<tbody>
<row>
<entry>VIDEO_MODE_PAL</entry><entry>PAL Format</entry>
</row><row>
<entry>VIDEO_MODE_NTSC</entry><entry>NTSC Format (USA)</entry>
</row><row>
<entry>VIDEO_MODE_SECAM</entry><entry>French Format</entry>
</row><row>
<entry>VIDEO_MODE_AUTO</entry><entry>A device that does not need to do
TV format switching</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The settings for the radio card are thus fairly simple. We report that we
are a tuner called "FM" for FM radio. In order to get the best tuning
resolution we report VIDEO_TUNER_LOW and select tuning to 1/16th of KHz. Its
unlikely our card can do that resolution but it is a fair bet the card can
do better than 1/16th of a MHz. VIDEO_TUNER_LOW is appropriate to almost all
radio usage.
</para>
<para>
We report that the tuner automatically handles deciding what format it is
receiving - true enough as it only handles FM radio. Our example card is
also incapable of detecting stereo or signal strengths so it reports a
strength of 0xFFFF (maximum) and no stereo detected.
</para>
<para>
To finish off we set the range that can be tuned to be 87-108Mhz, the normal
FM broadcast radio range. It is important to find out what the card is
actually capable of tuning. It is easy enough to simply use the FM broadcast
range. Unfortunately if you do this you will discover the FM broadcast
ranges in the USA, Europe and Japan are all subtly different and some users
cannot receive all the stations they wish.
</para>
<para>
The application also needs to be able to set the tuner it wishes to use. In
our case, with a single tuner this is rather simple to arrange.
</para>
<programlisting>
case VIDIOCSTUNER:
{
struct video_tuner v;
if(copy_from_user(&amp;v, arg, sizeof(v)))
return -EFAULT;
if(v.tuner != 0)
return -EINVAL;
return 0;
}
</programlisting>
<para>
We copy the user supplied structure into kernel memory so we can examine it.
If the user has selected a tuner other than zero we reject the request. If
they wanted tuner 0 then, surprisingly enough, that is the current tuner already.
</para>
<para>
The next two ioctls we need to provide are to get and set the frequency of
the radio. These both use an unsigned long argument which is the frequency.
The scale of the frequency depends on the VIDEO_TUNER_LOW flag as I
mentioned earlier on. Since we have VIDEO_TUNER_LOW set this will be in
1/16ths of a KHz.
</para>
<programlisting>
static unsigned long current_freq;
case VIDIOCGFREQ:
if(copy_to_user(arg, &amp;current_freq,
sizeof(unsigned long))
return -EFAULT;
return 0;
</programlisting>
<para>
Querying the frequency in our case is relatively simple. Our radio card is
too dumb to let us query the signal strength so we remember our setting if
we know it. All we have to do is copy it to the user.
</para>
<programlisting>
case VIDIOCSFREQ:
{
u32 freq;
if(copy_from_user(arg, &amp;freq,
sizeof(unsigned long))!=0)
return -EFAULT;
if(hardware_set_freq(freq)&lt;0)
return -EINVAL;
current_freq = freq;
return 0;
}
</programlisting>
<para>
Setting the frequency is a little more complex. We begin by copying the
desired frequency into kernel space. Next we call a hardware specific routine
to set the radio up. This might be as simple as some scaling and a few
writes to an I/O port. For most radio cards it turns out a good deal more
complicated and may involve programming things like a phase locked loop on
the card. This is what documentation is for.
</para>
<para>
The final set of operations we need to provide for our radio are the
volume controls. Not all radio cards can even do volume control. After all
there is a perfectly good volume control on the sound card. We will assume
our radio card has a simple 4 step volume control.
</para>
<para>
There are two ioctls with audio we need to support
</para>
<programlisting>
static int current_volume=0;
case VIDIOCGAUDIO:
{
struct video_audio v;
if(copy_from_user(&amp;v, arg, sizeof(v)))
return -EFAULT;
if(v.audio != 0)
return -EINVAL;
v.volume = 16384*current_volume;
v.step = 16384;
strcpy(v.name, "Radio");
v.mode = VIDEO_SOUND_MONO;
v.balance = 0;
v.base = 0;
v.treble = 0;
if(copy_to_user(arg. &amp;v, sizeof(v)))
return -EFAULT;
return 0;
}
</programlisting>
<para>
Much like the tuner we start by copying the user structure into kernel
space. Again we check if the user has asked for a valid audio input. We have
only input 0 and we punt if they ask for another input.
</para>
<para>
Then we fill in the video_audio structure. This has the following format
</para>
<table frame="all" id="video_audio_fields"><title>struct video_audio fields</title>
<tgroup cols="2" align="left">
<tbody>
<row>
<entry>audio</entry><entry>The input the user wishes to query</entry>
</row><row>
<entry>volume</entry><entry>The volume setting on a scale of 0-65535</entry>
</row><row>
<entry>base</entry><entry>The base level on a scale of 0-65535</entry>
</row><row>
<entry>treble</entry><entry>The treble level on a scale of 0-65535</entry>
</row><row>
<entry>flags</entry><entry>The features this audio device supports
</entry>
</row><row>
<entry>name</entry><entry>A text name to display to the user. We picked
"Radio" as it explains things quite nicely.</entry>
</row><row>
<entry>mode</entry><entry>The current reception mode for the audio
We report MONO because our card is too stupid to know if it is in
mono or stereo.
</entry>
</row><row>
<entry>balance</entry><entry>The stereo balance on a scale of 0-65535, 32768 is
middle.</entry>
</row><row>
<entry>step</entry><entry>The step by which the volume control jumps. This is
used to help make it easy for applications to set
slider behaviour.</entry>
</row>
</tbody>
</tgroup>
</table>
<table frame="all" id="video_audio_flags"><title>struct video_audio flags</title>
<tgroup cols="2" align="left">
<tbody>
<row>
<entry>VIDEO_AUDIO_MUTE</entry><entry>The audio is currently muted. We
could fake this in our driver but we
choose not to bother.</entry>
</row><row>
<entry>VIDEO_AUDIO_MUTABLE</entry><entry>The input has a mute option</entry>
</row><row>
<entry>VIDEO_AUDIO_TREBLE</entry><entry>The input has a treble control</entry>
</row><row>
<entry>VIDEO_AUDIO_BASS</entry><entry>The input has a base control</entry>
</row>
</tbody>
</tgroup>
</table>
<table frame="all" id="video_audio_modes"><title>struct video_audio modes</title>
<tgroup cols="2" align="left">
<tbody>