blob: 5fd72c4c33e352ba3edded10ee5ad27fc87f6d86 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
|
<refentry id="vidioc-enum-frameintervals">
<refmeta>
<refentrytitle>ioctl VIDIOC_ENUM_FRAMEINTERVALS</refentrytitle>
&manvol;
</refmeta>
<refnamediv>
<refname>VIDIOC_ENUM_FRAMEINTERVALS</refname>
<refpurpose>Enumerate frame intervals</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>ioctl</function></funcdef>
<paramdef>int <parameter>fd</parameter></paramdef>
<paramdef>int <parameter>request</parameter></paramdef>
<paramdef>struct v4l2_frmivalenum *<parameter>argp</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Arguments</title>
<variablelist>
<varlistentry>
<term><parameter>fd</parameter></term>
<listitem>
<para>&fd;</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>request</parameter></term>
<listitem>
<para>VIDIOC_ENUM_FRAMEINTERVALS</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>argp</parameter></term>
<listitem>
<para>Pointer to a &v4l2-frmivalenum; structure that
contains a pixel format and size and receives a frame interval.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<para>This ioctl allows applications to enumerate all frame
intervals that the device supports for the given pixel format and
frame size.</para>
<para>The supported pixel formats and frame sizes can be obtained
by using the &VIDIOC-ENUM-FMT; and &VIDIOC-ENUM-FRAMESIZES;
functions.</para>
<para>The return value and the content of the
<structfield>v4l2_frmivalenum.type</structfield> field depend on the
type of frame intervals the device supports. Here are the semantics of
the function for the different cases:</para>
<itemizedlist>
<listitem>
<para><emphasis role="bold">Discrete:</emphasis> The function
returns success if the given index value (zero-based) is valid. The
application should increase the index by one for each call until
<constant>EINVAL</constant> is returned. The `v4l2_frmivalenum.type`
field is set to `V4L2_FRMIVAL_TYPE_DISCRETE` by the driver. Of the
union only the `discrete` member is valid.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Step-wise:</emphasis> The function
returns success if the given index value is zero and
<constant>EINVAL</constant> for any other index value. The
<structfield>v4l2_frmivalenum.type</structfield> field is set to
<constant>V4L2_FRMIVAL_TYPE_STEPWISE</constant> by the driver. Of the
union only the <structfield>stepwise</structfield> member is
valid.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Continuous:</emphasis> This is a
special case of the step-wise type above. The function returns success
if the given index value is zero and <constant>EINVAL</constant> for
any other index value. The
<structfield>v4l2_frmivalenum.type</structfield> field is set to
<constant>V4L2_FRMIVAL_TYPE_CONTINUOUS</constant> by the driver. Of
the union only the <structfield>stepwise</structfield> member is valid
and the <structfield>step</structfield> value is set to 1.</para>
</listitem>
</itemizedlist>
<para>When the application calls the function with index zero, it
must check the <structfield>type</structfield> field to determine the
type of frame interval enumeration the device supports. Only for the
<constant>V4L2_FRMIVAL_TYPE_DISCRETE</constant> type does it make
sense to increase the index value to receive more frame
intervals.</para>
<para>Note that the order in which the frame intervals are
returned has no special meaning. In particular does it not say
anything about potential default frame intervals.</para>
<para>Applications can assume that the enumeration data does not
change without any interaction from the application itself. This means
that the enumeration data is consistent if the application does not
perform any other ioctl calls while it runs the frame interval
enumeration.</para>
</refsect1>
<refsect1>
<title>Notes</title>
<itemizedlist>
<listitem>
<para><emphasis role="bold">Frame intervals and frame
rates:</emphasis> The V4L2 API uses frame intervals instead of frame
rates. Given the frame interval the frame rate can be computed as
follows:<screen>frame_rate = 1 / frame_interval</screen></para>
</listitem>
</itemizedlist>
</refsect1>
<refsect1>
<title>Structs</title>
<para>In the structs below, <emphasis>IN</emphasis> denotes a
value that has to be filled in by the application,
<emphasis>OUT</emphasis> denotes values that the driver fills in. The
application should zero out all members except for the
<emphasis>IN</emphasis> fields.</para>
<table pgwide="1" frame="none" id="v4l2-frmival-stepwise">
<title>struct <structname>v4l2_frmival_stepwise</structname></title>
<tgroup cols="3">
&cs-str;
<tbody valign="top">
<row>
<entry>&v4l2-fract;</entry>
<entry><structfield>min</structfield></entry>
<entry>Minimum frame interval [s].</entry>
</row>
<row>
<entry>&v4l2-fract;</entry>
<entry><structfield>max</structfield></entry>
<entry>Maximum frame interval [s].</entry>
</row>
<row>
<entry>&v4l2-fract;</entry>
<entry><structfield>step</structfield></entry>
<entry>Frame interval step size [s].</entry>
</row>
</tbody>
</tgroup>
</table>
<table pgwide="1" frame="none" id="v4l2-frmivalenum">
<title>struct <structname>v4l2_frmivalenum</structname></title>
<tgroup cols="4">
<colspec colname="c1" />
<colspec colname="c2" />
<colspec colname="c3" />
<colspec colname="c4" />
<tbody valign="top">
<row>
<entry>__u32</entry>
<entry><structfield>index</structfield></entry>
<entry></entry>
<entry>IN: Index of the given frame interval in the
enumeration.</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>pixel_format</structfield></entry>
<entry></entry>
<entry>IN: Pixel format for which the frame intervals are
enumerated.</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>width</structfield></entry>
<entry></entry>
<entry>IN: Frame width for which the frame intervals are
enumerated.</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>height</structfield></entry>
<entry></entry>
<entry>IN: Frame height for which the frame intervals are
enumerated.</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>type</structfield></entry>
<entry></entry>
<entry>OUT: Frame interval type the device supports.</entry>
</row>
<row>
<entry>union</entry>
<entry></entry>
<entry></entry>
<entry>OUT: Frame interval with the given index.</entry>
</row>
<row>
<entry></entry>
<entry>&v4l2-fract;</entry>
<entry><structfield>discrete</structfield></entry>
<entry>Frame interval [s].</entry>
</row>
<row>
<entry></entry>
<entry>&v4l2-frmival-stepwise;</entry>
<entry><structfield>stepwise</structfield></entry>
<entry></entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>reserved[2]</structfield></entry>
<entry></entry>
<entry>Reserved space for future use.</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
<title>Enums</title>
<table pgwide="1" frame="none" id="v4l2-frmivaltypes">
<title>enum <structname>v4l2_frmivaltypes</structname></title>
<tgroup cols="3">
&cs-def;
<tbody valign="top">
<row>
<entry><constant>V4L2_FRMIVAL_TYPE_DISCRETE</constant></entry>
<entry>1</entry>
<entry>Discrete frame interval.</entry>
</row>
<row>
<entry><constant>V4L2_FRMIVAL_TYPE_CONTINUOUS</constant></entry>
<entry>2</entry>
<entry>Continuous frame interval.</entry>
</row>
<row>
<entry><constant>V4L2_FRMIVAL_TYPE_STEPWISE</constant></entry>
<entry>3</entry>
<entry>Step-wise defined frame interval.</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
&return-value;
</refsect1>
</refentry>
|
