aboutsummaryrefslogtreecommitdiffstats
path: root/Documentation/DocBook/media/v4l/common.xml
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/DocBook/media/v4l/common.xml')
-rw-r--r--Documentation/DocBook/media/v4l/common.xml47
1 files changed, 27 insertions, 20 deletions
diff --git a/Documentation/DocBook/media/v4l/common.xml b/Documentation/DocBook/media/v4l/common.xml
index 4101aeb5654..73c6847436c 100644
--- a/Documentation/DocBook/media/v4l/common.xml
+++ b/Documentation/DocBook/media/v4l/common.xml
@@ -464,14 +464,14 @@ The <structfield>type</structfield> field of the respective
<structfield>tuner</structfield> field contains the index number of
the tuner.</para>
- <para>Radio devices have exactly one tuner with index zero, no
+ <para>Radio input devices have exactly one tuner with index zero, no
video inputs.</para>
<para>To query and change tuner properties applications use the
&VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; ioctl, respectively. The
&v4l2-tuner; returned by <constant>VIDIOC_G_TUNER</constant> also
contains signal status information applicable when the tuner of the
-current video input, or a radio tuner is queried. Note that
+current video or radio input is queried. Note that
<constant>VIDIOC_S_TUNER</constant> does not switch the current tuner,
when there is more than one at all. The tuner is solely determined by
the current video input. Drivers must support both ioctls and set the
@@ -491,8 +491,17 @@ the modulator. The <structfield>type</structfield> field of the
respective &v4l2-output; returned by the &VIDIOC-ENUMOUTPUT; ioctl is
set to <constant>V4L2_OUTPUT_TYPE_MODULATOR</constant> and its
<structfield>modulator</structfield> field contains the index number
-of the modulator. This specification does not define radio output
-devices.</para>
+of the modulator.</para>
+
+ <para>Radio output devices have exactly one modulator with index
+zero, no video outputs.</para>
+
+ <para>A video or radio device cannot support both a tuner and a
+modulator. Two separate device nodes will have to be used for such
+hardware, one that supports the tuner functionality and one that supports
+the modulator functionality. The reason is a limitation with the
+&VIDIOC-S-FREQUENCY; ioctl where you cannot specify whether the frequency
+is for a tuner or a modulator.</para>
<para>To query and change modulator properties applications use
the &VIDIOC-G-MODULATOR; and &VIDIOC-S-MODULATOR; ioctl. Note that
@@ -555,7 +564,7 @@ automatically.</para>
<para>To query and select the standard used by the current video
input or output applications call the &VIDIOC-G-STD; and
&VIDIOC-S-STD; ioctl, respectively. The <emphasis>received</emphasis>
-standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), <emphasis>not</emphasis> an index into the standard enumeration.<footnote>
+standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), <emphasis>not</emphasis> an index into the standard enumeration.<footnote>
<para>An alternative to the current scheme is to use pointers
to indices as arguments of <constant>VIDIOC_G_STD</constant> and
<constant>VIDIOC_S_STD</constant>, the &v4l2-input; and
@@ -579,30 +588,28 @@ switch to a standard by &v4l2-std-id;.</para>
</footnote> Drivers must implement all video standard ioctls
when the device has one or more video inputs or outputs.</para>
- <para>Special rules apply to USB cameras where the notion of video
-standards makes little sense. More generally any capture device,
-output devices accordingly, which is <itemizedlist>
+ <para>Special rules apply to devices such as USB cameras where the notion of video
+standards makes little sense. More generally for any capture or output device
+which is: <itemizedlist>
<listitem>
<para>incapable of capturing fields or frames at the nominal
rate of the video standard, or</para>
</listitem>
<listitem>
- <para>where <link linkend="buffer">timestamps</link> refer
-to the instant the field or frame was received by the driver, not the
-capture time, or</para>
- </listitem>
- <listitem>
- <para>where <link linkend="buffer">sequence numbers</link>
-refer to the frames received by the driver, not the captured
-frames.</para>
+ <para>that does not support the video standard formats at all.</para>
</listitem>
</itemizedlist> Here the driver shall set the
<structfield>std</structfield> field of &v4l2-input; and &v4l2-output;
-to zero, the <constant>VIDIOC_G_STD</constant>,
+to zero and the <constant>VIDIOC_G_STD</constant>,
<constant>VIDIOC_S_STD</constant>,
<constant>VIDIOC_QUERYSTD</constant> and
<constant>VIDIOC_ENUMSTD</constant> ioctls shall return the
-&EINVAL;.<footnote>
+&ENOTTY;.<footnote>
+ <para>See <xref linkend="buffer" /> for a rationale.</para>
+ <para>Applications can make use of the <xref linkend="input-capabilities" /> and
+<xref linkend="output-capabilities"/> flags to determine whether the video standard ioctls
+are available for the device.</para>
+&ENOTTY;.
<para>See <xref linkend="buffer" /> for a rationale. Probably
even USB cameras follow some well known video standard. It might have
been better to explicitly indicate elsewhere if a device cannot live
@@ -617,9 +624,9 @@ up to normal expectations, instead of this exception.</para>
&v4l2-standard; standard;
if (-1 == ioctl (fd, &VIDIOC-G-STD;, &amp;std_id)) {
- /* Note when VIDIOC_ENUMSTD always returns EINVAL this
+ /* Note when VIDIOC_ENUMSTD always returns ENOTTY this
is no video device or it falls under the USB exception,
- and VIDIOC_G_STD returning EINVAL is no error. */
+ and VIDIOC_G_STD returning ENOTTY is no error. */
perror ("VIDIOC_G_STD");
exit (EXIT_FAILURE);