Markus Heiser | 5377d91 | 2016-06-30 15:18:56 +0200 | [diff] [blame^] | 1 | .. -*- coding: utf-8; mode: rst -*- |
| 2 | |
| 3 | .. _buffer: |
| 4 | |
| 5 | ******* |
| 6 | Buffers |
| 7 | ******* |
| 8 | |
| 9 | A buffer contains data exchanged by application and driver using one of |
| 10 | the Streaming I/O methods. In the multi-planar API, the data is held in |
| 11 | planes, while the buffer structure acts as a container for the planes. |
| 12 | Only pointers to buffers (planes) are exchanged, the data itself is not |
| 13 | copied. These pointers, together with meta-information like timestamps |
| 14 | or field parity, are stored in a struct :c:type:`struct v4l2_buffer`, |
| 15 | argument to the :ref:`VIDIOC_QUERYBUF <vidioc-querybuf>`, |
| 16 | :ref:`VIDIOC_QBUF <vidioc-qbuf>` and |
| 17 | :ref:`VIDIOC_DQBUF <vidioc-qbuf>` ioctl. In the multi-planar API, |
| 18 | some plane-specific members of struct :c:type:`struct v4l2_buffer`, |
| 19 | such as pointers and sizes for each plane, are stored in struct |
| 20 | :c:type:`struct v4l2_plane` instead. In that case, struct |
| 21 | :c:type:`struct v4l2_buffer` contains an array of plane structures. |
| 22 | |
| 23 | Dequeued video buffers come with timestamps. The driver decides at which |
| 24 | part of the frame and with which clock the timestamp is taken. Please |
| 25 | see flags in the masks ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` and |
| 26 | ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` in :ref:`buffer-flags`. These flags |
| 27 | are always valid and constant across all buffers during the whole video |
| 28 | stream. Changes in these flags may take place as a side effect of |
| 29 | :ref:`VIDIOC_S_INPUT <vidioc-g-input>` or |
| 30 | :ref:`VIDIOC_S_OUTPUT <vidioc-g-output>` however. The |
| 31 | ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` timestamp type which is used by e.g. on |
| 32 | mem-to-mem devices is an exception to the rule: the timestamp source |
| 33 | flags are copied from the OUTPUT video buffer to the CAPTURE video |
| 34 | buffer. |
| 35 | |
| 36 | |
| 37 | .. _v4l2-buffer: |
| 38 | |
| 39 | .. flat-table:: struct v4l2_buffer |
| 40 | :header-rows: 0 |
| 41 | :stub-columns: 0 |
| 42 | :widths: 1 1 1 2 |
| 43 | |
| 44 | |
| 45 | - .. row 1 |
| 46 | |
| 47 | - __u32 |
| 48 | |
| 49 | - ``index`` |
| 50 | |
| 51 | - |
| 52 | - Number of the buffer, set by the application except when calling |
| 53 | :ref:`VIDIOC_DQBUF <vidioc-qbuf>`, then it is set by the |
| 54 | driver. This field can range from zero to the number of buffers |
| 55 | allocated with the :ref:`VIDIOC_REQBUFS <vidioc-reqbufs>` ioctl |
| 56 | (struct :ref:`v4l2_requestbuffers <v4l2-requestbuffers>` |
| 57 | ``count``), plus any buffers allocated with |
| 58 | :ref:`VIDIOC_CREATE_BUFS <vidioc-create-bufs>` minus one. |
| 59 | |
| 60 | - .. row 2 |
| 61 | |
| 62 | - __u32 |
| 63 | |
| 64 | - ``type`` |
| 65 | |
| 66 | - |
| 67 | - Type of the buffer, same as struct |
| 68 | :ref:`v4l2_format <v4l2-format>` ``type`` or struct |
| 69 | :ref:`v4l2_requestbuffers <v4l2-requestbuffers>` ``type``, set |
| 70 | by the application. See :ref:`v4l2-buf-type` |
| 71 | |
| 72 | - .. row 3 |
| 73 | |
| 74 | - __u32 |
| 75 | |
| 76 | - ``bytesused`` |
| 77 | |
| 78 | - |
| 79 | - The number of bytes occupied by the data in the buffer. It depends |
| 80 | on the negotiated data format and may change with each buffer for |
| 81 | compressed variable size data like JPEG images. Drivers must set |
| 82 | this field when ``type`` refers to a capture stream, applications |
| 83 | when it refers to an output stream. If the application sets this |
| 84 | to 0 for an output stream, then ``bytesused`` will be set to the |
| 85 | size of the buffer (see the ``length`` field of this struct) by |
| 86 | the driver. For multiplanar formats this field is ignored and the |
| 87 | ``planes`` pointer is used instead. |
| 88 | |
| 89 | - .. row 4 |
| 90 | |
| 91 | - __u32 |
| 92 | |
| 93 | - ``flags`` |
| 94 | |
| 95 | - |
| 96 | - Flags set by the application or driver, see :ref:`buffer-flags`. |
| 97 | |
| 98 | - .. row 5 |
| 99 | |
| 100 | - __u32 |
| 101 | |
| 102 | - ``field`` |
| 103 | |
| 104 | - |
| 105 | - Indicates the field order of the image in the buffer, see |
| 106 | :ref:`v4l2-field`. This field is not used when the buffer |
| 107 | contains VBI data. Drivers must set it when ``type`` refers to a |
| 108 | capture stream, applications when it refers to an output stream. |
| 109 | |
| 110 | - .. row 6 |
| 111 | |
| 112 | - struct timeval |
| 113 | |
| 114 | - ``timestamp`` |
| 115 | |
| 116 | - |
| 117 | - For capture streams this is time when the first data byte was |
| 118 | captured, as returned by the :c:func:`clock_gettime()` function |
| 119 | for the relevant clock id; see ``V4L2_BUF_FLAG_TIMESTAMP_*`` in |
| 120 | :ref:`buffer-flags`. For output streams the driver stores the |
| 121 | time at which the last data byte was actually sent out in the |
| 122 | ``timestamp`` field. This permits applications to monitor the |
| 123 | drift between the video and system clock. For output streams that |
| 124 | use ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` the application has to fill |
| 125 | in the timestamp which will be copied by the driver to the capture |
| 126 | stream. |
| 127 | |
| 128 | - .. row 7 |
| 129 | |
| 130 | - struct :ref:`v4l2_timecode <v4l2-timecode>` |
| 131 | |
| 132 | - ``timecode`` |
| 133 | |
| 134 | - |
| 135 | - When ``type`` is ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` and the |
| 136 | ``V4L2_BUF_FLAG_TIMECODE`` flag is set in ``flags``, this |
| 137 | structure contains a frame timecode. In |
| 138 | :ref:`V4L2_FIELD_ALTERNATE <v4l2-field>` mode the top and |
| 139 | bottom field contain the same timecode. Timecodes are intended to |
| 140 | help video editing and are typically recorded on video tapes, but |
| 141 | also embedded in compressed formats like MPEG. This field is |
| 142 | independent of the ``timestamp`` and ``sequence`` fields. |
| 143 | |
| 144 | - .. row 8 |
| 145 | |
| 146 | - __u32 |
| 147 | |
| 148 | - ``sequence`` |
| 149 | |
| 150 | - |
| 151 | - Set by the driver, counting the frames (not fields!) in sequence. |
| 152 | This field is set for both input and output devices. |
| 153 | |
| 154 | - .. row 9 |
| 155 | |
| 156 | - :cspan:`3` |
| 157 | |
| 158 | In :ref:`V4L2_FIELD_ALTERNATE <v4l2-field>` mode the top and |
| 159 | bottom field have the same sequence number. The count starts at |
| 160 | zero and includes dropped or repeated frames. A dropped frame was |
| 161 | received by an input device but could not be stored due to lack of |
| 162 | free buffer space. A repeated frame was displayed again by an |
| 163 | output device because the application did not pass new data in |
| 164 | time. |
| 165 | |
| 166 | Note this may count the frames received e.g. over USB, without |
| 167 | taking into account the frames dropped by the remote hardware due |
| 168 | to limited compression throughput or bus bandwidth. These devices |
| 169 | identify by not enumerating any video standards, see |
| 170 | :ref:`standard`. |
| 171 | |
| 172 | - .. row 10 |
| 173 | |
| 174 | - __u32 |
| 175 | |
| 176 | - ``memory`` |
| 177 | |
| 178 | - |
| 179 | - This field must be set by applications and/or drivers in |
| 180 | accordance with the selected I/O method. See :ref:`v4l2-memory` |
| 181 | |
| 182 | - .. row 11 |
| 183 | |
| 184 | - union |
| 185 | |
| 186 | - ``m`` |
| 187 | |
| 188 | - .. row 12 |
| 189 | |
| 190 | - |
| 191 | - __u32 |
| 192 | |
| 193 | - ``offset`` |
| 194 | |
| 195 | - For the single-planar API and when ``memory`` is |
| 196 | ``V4L2_MEMORY_MMAP`` this is the offset of the buffer from the |
| 197 | start of the device memory. The value is returned by the driver |
| 198 | and apart of serving as parameter to the |
| 199 | :ref:`mmap() <func-mmap>` function not useful for applications. |
| 200 | See :ref:`mmap` for details |
| 201 | |
| 202 | - .. row 13 |
| 203 | |
| 204 | - |
| 205 | - unsigned long |
| 206 | |
| 207 | - ``userptr`` |
| 208 | |
| 209 | - For the single-planar API and when ``memory`` is |
| 210 | ``V4L2_MEMORY_USERPTR`` this is a pointer to the buffer (casted to |
| 211 | unsigned long type) in virtual memory, set by the application. See |
| 212 | :ref:`userp` for details. |
| 213 | |
| 214 | - .. row 14 |
| 215 | |
| 216 | - |
| 217 | - struct v4l2_plane |
| 218 | |
| 219 | - ``*planes`` |
| 220 | |
| 221 | - When using the multi-planar API, contains a userspace pointer to |
| 222 | an array of struct :ref:`v4l2_plane <v4l2-plane>`. The size of |
| 223 | the array should be put in the ``length`` field of this |
| 224 | :c:type:`struct v4l2_buffer` structure. |
| 225 | |
| 226 | - .. row 15 |
| 227 | |
| 228 | - |
| 229 | - int |
| 230 | |
| 231 | - ``fd`` |
| 232 | |
| 233 | - For the single-plane API and when ``memory`` is |
| 234 | ``V4L2_MEMORY_DMABUF`` this is the file descriptor associated with |
| 235 | a DMABUF buffer. |
| 236 | |
| 237 | - .. row 16 |
| 238 | |
| 239 | - __u32 |
| 240 | |
| 241 | - ``length`` |
| 242 | |
| 243 | - |
| 244 | - Size of the buffer (not the payload) in bytes for the |
| 245 | single-planar API. This is set by the driver based on the calls to |
| 246 | :ref:`VIDIOC_REQBUFS <vidioc-reqbufs>` and/or |
| 247 | :ref:`VIDIOC_CREATE_BUFS <vidioc-create-bufs>`. For the |
| 248 | multi-planar API the application sets this to the number of |
| 249 | elements in the ``planes`` array. The driver will fill in the |
| 250 | actual number of valid elements in that array. |
| 251 | |
| 252 | - .. row 17 |
| 253 | |
| 254 | - __u32 |
| 255 | |
| 256 | - ``reserved2`` |
| 257 | |
| 258 | - |
| 259 | - A place holder for future extensions. Drivers and applications |
| 260 | must set this to 0. |
| 261 | |
| 262 | - .. row 18 |
| 263 | |
| 264 | - __u32 |
| 265 | |
| 266 | - ``reserved`` |
| 267 | |
| 268 | - |
| 269 | - A place holder for future extensions. Drivers and applications |
| 270 | must set this to 0. |
| 271 | |
| 272 | |
| 273 | |
| 274 | .. _v4l2-plane: |
| 275 | |
| 276 | .. flat-table:: struct v4l2_plane |
| 277 | :header-rows: 0 |
| 278 | :stub-columns: 0 |
| 279 | :widths: 1 1 1 2 |
| 280 | |
| 281 | |
| 282 | - .. row 1 |
| 283 | |
| 284 | - __u32 |
| 285 | |
| 286 | - ``bytesused`` |
| 287 | |
| 288 | - |
| 289 | - The number of bytes occupied by data in the plane (its payload). |
| 290 | Drivers must set this field when ``type`` refers to a capture |
| 291 | stream, applications when it refers to an output stream. If the |
| 292 | application sets this to 0 for an output stream, then |
| 293 | ``bytesused`` will be set to the size of the plane (see the |
| 294 | ``length`` field of this struct) by the driver. Note that the |
| 295 | actual image data starts at ``data_offset`` which may not be 0. |
| 296 | |
| 297 | - .. row 2 |
| 298 | |
| 299 | - __u32 |
| 300 | |
| 301 | - ``length`` |
| 302 | |
| 303 | - |
| 304 | - Size in bytes of the plane (not its payload). This is set by the |
| 305 | driver based on the calls to |
| 306 | :ref:`VIDIOC_REQBUFS <vidioc-reqbufs>` and/or |
| 307 | :ref:`VIDIOC_CREATE_BUFS <vidioc-create-bufs>`. |
| 308 | |
| 309 | - .. row 3 |
| 310 | |
| 311 | - union |
| 312 | |
| 313 | - ``m`` |
| 314 | |
| 315 | - |
| 316 | - |
| 317 | |
| 318 | - .. row 4 |
| 319 | |
| 320 | - |
| 321 | - __u32 |
| 322 | |
| 323 | - ``mem_offset`` |
| 324 | |
| 325 | - When the memory type in the containing struct |
| 326 | :ref:`v4l2_buffer <v4l2-buffer>` is ``V4L2_MEMORY_MMAP``, this |
| 327 | is the value that should be passed to :ref:`mmap() <func-mmap>`, |
| 328 | similar to the ``offset`` field in struct |
| 329 | :ref:`v4l2_buffer <v4l2-buffer>`. |
| 330 | |
| 331 | - .. row 5 |
| 332 | |
| 333 | - |
| 334 | - unsigned long |
| 335 | |
| 336 | - ``userptr`` |
| 337 | |
| 338 | - When the memory type in the containing struct |
| 339 | :ref:`v4l2_buffer <v4l2-buffer>` is ``V4L2_MEMORY_USERPTR``, |
| 340 | this is a userspace pointer to the memory allocated for this plane |
| 341 | by an application. |
| 342 | |
| 343 | - .. row 6 |
| 344 | |
| 345 | - |
| 346 | - int |
| 347 | |
| 348 | - ``fd`` |
| 349 | |
| 350 | - When the memory type in the containing struct |
| 351 | :ref:`v4l2_buffer <v4l2-buffer>` is ``V4L2_MEMORY_DMABUF``, |
| 352 | this is a file descriptor associated with a DMABUF buffer, similar |
| 353 | to the ``fd`` field in struct :ref:`v4l2_buffer <v4l2-buffer>`. |
| 354 | |
| 355 | - .. row 7 |
| 356 | |
| 357 | - __u32 |
| 358 | |
| 359 | - ``data_offset`` |
| 360 | |
| 361 | - |
| 362 | - Offset in bytes to video data in the plane. Drivers must set this |
| 363 | field when ``type`` refers to a capture stream, applications when |
| 364 | it refers to an output stream. Note that data_offset is included |
| 365 | in ``bytesused``. So the size of the image in the plane is |
| 366 | ``bytesused``-``data_offset`` at offset ``data_offset`` from the |
| 367 | start of the plane. |
| 368 | |
| 369 | - .. row 8 |
| 370 | |
| 371 | - __u32 |
| 372 | |
| 373 | - ``reserved[11]`` |
| 374 | |
| 375 | - |
| 376 | - Reserved for future use. Should be zeroed by drivers and |
| 377 | applications. |
| 378 | |
| 379 | |
| 380 | |
| 381 | .. _v4l2-buf-type: |
| 382 | |
| 383 | .. flat-table:: enum v4l2_buf_type |
| 384 | :header-rows: 0 |
| 385 | :stub-columns: 0 |
| 386 | :widths: 3 1 4 |
| 387 | |
| 388 | |
| 389 | - .. row 1 |
| 390 | |
| 391 | - ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` |
| 392 | |
| 393 | - 1 |
| 394 | |
| 395 | - Buffer of a single-planar video capture stream, see |
| 396 | :ref:`capture`. |
| 397 | |
| 398 | - .. row 2 |
| 399 | |
| 400 | - ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` |
| 401 | |
| 402 | - 9 |
| 403 | |
| 404 | - Buffer of a multi-planar video capture stream, see |
| 405 | :ref:`capture`. |
| 406 | |
| 407 | - .. row 3 |
| 408 | |
| 409 | - ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` |
| 410 | |
| 411 | - 2 |
| 412 | |
| 413 | - Buffer of a single-planar video output stream, see |
| 414 | :ref:`output`. |
| 415 | |
| 416 | - .. row 4 |
| 417 | |
| 418 | - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`` |
| 419 | |
| 420 | - 10 |
| 421 | |
| 422 | - Buffer of a multi-planar video output stream, see :ref:`output`. |
| 423 | |
| 424 | - .. row 5 |
| 425 | |
| 426 | - ``V4L2_BUF_TYPE_VIDEO_OVERLAY`` |
| 427 | |
| 428 | - 3 |
| 429 | |
| 430 | - Buffer for video overlay, see :ref:`overlay`. |
| 431 | |
| 432 | - .. row 6 |
| 433 | |
| 434 | - ``V4L2_BUF_TYPE_VBI_CAPTURE`` |
| 435 | |
| 436 | - 4 |
| 437 | |
| 438 | - Buffer of a raw VBI capture stream, see :ref:`raw-vbi`. |
| 439 | |
| 440 | - .. row 7 |
| 441 | |
| 442 | - ``V4L2_BUF_TYPE_VBI_OUTPUT`` |
| 443 | |
| 444 | - 5 |
| 445 | |
| 446 | - Buffer of a raw VBI output stream, see :ref:`raw-vbi`. |
| 447 | |
| 448 | - .. row 8 |
| 449 | |
| 450 | - ``V4L2_BUF_TYPE_SLICED_VBI_CAPTURE`` |
| 451 | |
| 452 | - 6 |
| 453 | |
| 454 | - Buffer of a sliced VBI capture stream, see :ref:`sliced`. |
| 455 | |
| 456 | - .. row 9 |
| 457 | |
| 458 | - ``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT`` |
| 459 | |
| 460 | - 7 |
| 461 | |
| 462 | - Buffer of a sliced VBI output stream, see :ref:`sliced`. |
| 463 | |
| 464 | - .. row 10 |
| 465 | |
| 466 | - ``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY`` |
| 467 | |
| 468 | - 8 |
| 469 | |
| 470 | - Buffer for video output overlay (OSD), see :ref:`osd`. |
| 471 | |
| 472 | - .. row 11 |
| 473 | |
| 474 | - ``V4L2_BUF_TYPE_SDR_CAPTURE`` |
| 475 | |
| 476 | - 11 |
| 477 | |
| 478 | - Buffer for Software Defined Radio (SDR) capture stream, see |
| 479 | :ref:`sdr`. |
| 480 | |
| 481 | - .. row 12 |
| 482 | |
| 483 | - ``V4L2_BUF_TYPE_SDR_OUTPUT`` |
| 484 | |
| 485 | - 12 |
| 486 | |
| 487 | - Buffer for Software Defined Radio (SDR) output stream, see |
| 488 | :ref:`sdr`. |
| 489 | |
| 490 | |
| 491 | |
| 492 | .. _buffer-flags: |
| 493 | |
| 494 | .. flat-table:: Buffer Flags |
| 495 | :header-rows: 0 |
| 496 | :stub-columns: 0 |
| 497 | :widths: 3 1 4 |
| 498 | |
| 499 | |
| 500 | - .. row 1 |
| 501 | |
| 502 | - ``V4L2_BUF_FLAG_MAPPED`` |
| 503 | |
| 504 | - 0x00000001 |
| 505 | |
| 506 | - The buffer resides in device memory and has been mapped into the |
| 507 | application's address space, see :ref:`mmap` for details. |
| 508 | Drivers set or clear this flag when the |
| 509 | :ref:`VIDIOC_QUERYBUF <vidioc-querybuf>`, |
| 510 | :ref:`VIDIOC_QBUF <vidioc-qbuf>` or |
| 511 | :ref:`VIDIOC_DQBUF <vidioc-qbuf>` ioctl is called. Set by the |
| 512 | driver. |
| 513 | |
| 514 | - .. row 2 |
| 515 | |
| 516 | - ``V4L2_BUF_FLAG_QUEUED`` |
| 517 | |
| 518 | - 0x00000002 |
| 519 | |
| 520 | - Internally drivers maintain two buffer queues, an incoming and |
| 521 | outgoing queue. When this flag is set, the buffer is currently on |
| 522 | the incoming queue. It automatically moves to the outgoing queue |
| 523 | after the buffer has been filled (capture devices) or displayed |
| 524 | (output devices). Drivers set or clear this flag when the |
| 525 | ``VIDIOC_QUERYBUF`` ioctl is called. After (successful) calling |
| 526 | the ``VIDIOC_QBUF``\ ioctl it is always set and after |
| 527 | ``VIDIOC_DQBUF`` always cleared. |
| 528 | |
| 529 | - .. row 3 |
| 530 | |
| 531 | - ``V4L2_BUF_FLAG_DONE`` |
| 532 | |
| 533 | - 0x00000004 |
| 534 | |
| 535 | - When this flag is set, the buffer is currently on the outgoing |
| 536 | queue, ready to be dequeued from the driver. Drivers set or clear |
| 537 | this flag when the ``VIDIOC_QUERYBUF`` ioctl is called. After |
| 538 | calling the ``VIDIOC_QBUF`` or ``VIDIOC_DQBUF`` it is always |
| 539 | cleared. Of course a buffer cannot be on both queues at the same |
| 540 | time, the ``V4L2_BUF_FLAG_QUEUED`` and ``V4L2_BUF_FLAG_DONE`` flag |
| 541 | are mutually exclusive. They can be both cleared however, then the |
| 542 | buffer is in "dequeued" state, in the application domain so to |
| 543 | say. |
| 544 | |
| 545 | - .. row 4 |
| 546 | |
| 547 | - ``V4L2_BUF_FLAG_ERROR`` |
| 548 | |
| 549 | - 0x00000040 |
| 550 | |
| 551 | - When this flag is set, the buffer has been dequeued successfully, |
| 552 | although the data might have been corrupted. This is recoverable, |
| 553 | streaming may continue as normal and the buffer may be reused |
| 554 | normally. Drivers set this flag when the ``VIDIOC_DQBUF`` ioctl is |
| 555 | called. |
| 556 | |
| 557 | - .. row 5 |
| 558 | |
| 559 | - ``V4L2_BUF_FLAG_KEYFRAME`` |
| 560 | |
| 561 | - 0x00000008 |
| 562 | |
| 563 | - Drivers set or clear this flag when calling the ``VIDIOC_DQBUF`` |
| 564 | ioctl. It may be set by video capture devices when the buffer |
| 565 | contains a compressed image which is a key frame (or field), i. e. |
| 566 | can be decompressed on its own. Also known as an I-frame. |
| 567 | Applications can set this bit when ``type`` refers to an output |
| 568 | stream. |
| 569 | |
| 570 | - .. row 6 |
| 571 | |
| 572 | - ``V4L2_BUF_FLAG_PFRAME`` |
| 573 | |
| 574 | - 0x00000010 |
| 575 | |
| 576 | - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags predicted frames |
| 577 | or fields which contain only differences to a previous key frame. |
| 578 | Applications can set this bit when ``type`` refers to an output |
| 579 | stream. |
| 580 | |
| 581 | - .. row 7 |
| 582 | |
| 583 | - ``V4L2_BUF_FLAG_BFRAME`` |
| 584 | |
| 585 | - 0x00000020 |
| 586 | |
| 587 | - Similar to ``V4L2_BUF_FLAG_KEYFRAME`` this flags a bi-directional |
| 588 | predicted frame or field which contains only the differences |
| 589 | between the current frame and both the preceding and following key |
| 590 | frames to specify its content. Applications can set this bit when |
| 591 | ``type`` refers to an output stream. |
| 592 | |
| 593 | - .. row 8 |
| 594 | |
| 595 | - ``V4L2_BUF_FLAG_TIMECODE`` |
| 596 | |
| 597 | - 0x00000100 |
| 598 | |
| 599 | - The ``timecode`` field is valid. Drivers set or clear this flag |
| 600 | when the ``VIDIOC_DQBUF`` ioctl is called. Applications can set |
| 601 | this bit and the corresponding ``timecode`` structure when |
| 602 | ``type`` refers to an output stream. |
| 603 | |
| 604 | - .. row 9 |
| 605 | |
| 606 | - ``V4L2_BUF_FLAG_PREPARED`` |
| 607 | |
| 608 | - 0x00000400 |
| 609 | |
| 610 | - The buffer has been prepared for I/O and can be queued by the |
| 611 | application. Drivers set or clear this flag when the |
| 612 | :ref:`VIDIOC_QUERYBUF <vidioc-querybuf>`, |
| 613 | :ref:`VIDIOC_PREPARE_BUF <vidioc-qbuf>`, |
| 614 | :ref:`VIDIOC_QBUF <vidioc-qbuf>` or |
| 615 | :ref:`VIDIOC_DQBUF <vidioc-qbuf>` ioctl is called. |
| 616 | |
| 617 | - .. row 10 |
| 618 | |
| 619 | - ``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE`` |
| 620 | |
| 621 | - 0x00000800 |
| 622 | |
| 623 | - Caches do not have to be invalidated for this buffer. Typically |
| 624 | applications shall use this flag if the data captured in the |
| 625 | buffer is not going to be touched by the CPU, instead the buffer |
| 626 | will, probably, be passed on to a DMA-capable hardware unit for |
| 627 | further processing or output. |
| 628 | |
| 629 | - .. row 11 |
| 630 | |
| 631 | - ``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` |
| 632 | |
| 633 | - 0x00001000 |
| 634 | |
| 635 | - Caches do not have to be cleaned for this buffer. Typically |
| 636 | applications shall use this flag for output buffers if the data in |
| 637 | this buffer has not been created by the CPU but by some |
| 638 | DMA-capable unit, in which case caches have not been used. |
| 639 | |
| 640 | - .. row 12 |
| 641 | |
| 642 | - ``V4L2_BUF_FLAG_LAST`` |
| 643 | |
| 644 | - 0x00100000 |
| 645 | |
| 646 | - Last buffer produced by the hardware. mem2mem codec drivers set |
| 647 | this flag on the capture queue for the last buffer when the |
| 648 | :ref:`VIDIOC_QUERYBUF <vidioc-querybuf>` or |
| 649 | :ref:`VIDIOC_DQBUF <vidioc-qbuf>` ioctl is called. Due to |
| 650 | hardware limitations, the last buffer may be empty. In this case |
| 651 | the driver will set the ``bytesused`` field to 0, regardless of |
| 652 | the format. Any Any subsequent call to the |
| 653 | :ref:`VIDIOC_DQBUF <vidioc-qbuf>` ioctl will not block anymore, |
| 654 | but return an EPIPE error code. |
| 655 | |
| 656 | - .. row 13 |
| 657 | |
| 658 | - ``V4L2_BUF_FLAG_TIMESTAMP_MASK`` |
| 659 | |
| 660 | - 0x0000e000 |
| 661 | |
| 662 | - Mask for timestamp types below. To test the timestamp type, mask |
| 663 | out bits not belonging to timestamp type by performing a logical |
| 664 | and operation with buffer flags and timestamp mask. |
| 665 | |
| 666 | - .. row 14 |
| 667 | |
| 668 | - ``V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN`` |
| 669 | |
| 670 | - 0x00000000 |
| 671 | |
| 672 | - Unknown timestamp type. This type is used by drivers before Linux |
| 673 | 3.9 and may be either monotonic (see below) or realtime (wall |
| 674 | clock). Monotonic clock has been favoured in embedded systems |
| 675 | whereas most of the drivers use the realtime clock. Either kinds |
| 676 | of timestamps are available in user space via |
| 677 | :c:func:`clock_gettime(2)` using clock IDs ``CLOCK_MONOTONIC`` |
| 678 | and ``CLOCK_REALTIME``, respectively. |
| 679 | |
| 680 | - .. row 15 |
| 681 | |
| 682 | - ``V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC`` |
| 683 | |
| 684 | - 0x00002000 |
| 685 | |
| 686 | - The buffer timestamp has been taken from the ``CLOCK_MONOTONIC`` |
| 687 | clock. To access the same clock outside V4L2, use |
| 688 | :c:func:`clock_gettime(2)`. |
| 689 | |
| 690 | - .. row 16 |
| 691 | |
| 692 | - ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` |
| 693 | |
| 694 | - 0x00004000 |
| 695 | |
| 696 | - The CAPTURE buffer timestamp has been taken from the corresponding |
| 697 | OUTPUT buffer. This flag applies only to mem2mem devices. |
| 698 | |
| 699 | - .. row 17 |
| 700 | |
| 701 | - ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` |
| 702 | |
| 703 | - 0x00070000 |
| 704 | |
| 705 | - Mask for timestamp sources below. The timestamp source defines the |
| 706 | point of time the timestamp is taken in relation to the frame. |
| 707 | Logical 'and' operation between the ``flags`` field and |
| 708 | ``V4L2_BUF_FLAG_TSTAMP_SRC_MASK`` produces the value of the |
| 709 | timestamp source. Applications must set the timestamp source when |
| 710 | ``type`` refers to an output stream and |
| 711 | ``V4L2_BUF_FLAG_TIMESTAMP_COPY`` is set. |
| 712 | |
| 713 | - .. row 18 |
| 714 | |
| 715 | - ``V4L2_BUF_FLAG_TSTAMP_SRC_EOF`` |
| 716 | |
| 717 | - 0x00000000 |
| 718 | |
| 719 | - End Of Frame. The buffer timestamp has been taken when the last |
| 720 | pixel of the frame has been received or the last pixel of the |
| 721 | frame has been transmitted. In practice, software generated |
| 722 | timestamps will typically be read from the clock a small amount of |
| 723 | time after the last pixel has been received or transmitten, |
| 724 | depending on the system and other activity in it. |
| 725 | |
| 726 | - .. row 19 |
| 727 | |
| 728 | - ``V4L2_BUF_FLAG_TSTAMP_SRC_SOE`` |
| 729 | |
| 730 | - 0x00010000 |
| 731 | |
| 732 | - Start Of Exposure. The buffer timestamp has been taken when the |
| 733 | exposure of the frame has begun. This is only valid for the |
| 734 | ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type. |
| 735 | |
| 736 | |
| 737 | |
| 738 | .. _v4l2-memory: |
| 739 | |
| 740 | .. flat-table:: enum v4l2_memory |
| 741 | :header-rows: 0 |
| 742 | :stub-columns: 0 |
| 743 | :widths: 3 1 4 |
| 744 | |
| 745 | |
| 746 | - .. row 1 |
| 747 | |
| 748 | - ``V4L2_MEMORY_MMAP`` |
| 749 | |
| 750 | - 1 |
| 751 | |
| 752 | - The buffer is used for :ref:`memory mapping <mmap>` I/O. |
| 753 | |
| 754 | - .. row 2 |
| 755 | |
| 756 | - ``V4L2_MEMORY_USERPTR`` |
| 757 | |
| 758 | - 2 |
| 759 | |
| 760 | - The buffer is used for :ref:`user pointer <userp>` I/O. |
| 761 | |
| 762 | - .. row 3 |
| 763 | |
| 764 | - ``V4L2_MEMORY_OVERLAY`` |
| 765 | |
| 766 | - 3 |
| 767 | |
| 768 | - [to do] |
| 769 | |
| 770 | - .. row 4 |
| 771 | |
| 772 | - ``V4L2_MEMORY_DMABUF`` |
| 773 | |
| 774 | - 4 |
| 775 | |
| 776 | - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O. |
| 777 | |
| 778 | |
| 779 | |
| 780 | Timecodes |
| 781 | ========= |
| 782 | |
| 783 | The :c:type:`struct v4l2_timecode` structure is designed to hold a |
| 784 | :ref:`smpte12m` or similar timecode. (struct |
| 785 | :c:type:`struct timeval` timestamps are stored in struct |
| 786 | :ref:`v4l2_buffer <v4l2-buffer>` field ``timestamp``.) |
| 787 | |
| 788 | |
| 789 | .. _v4l2-timecode: |
| 790 | |
| 791 | .. flat-table:: struct v4l2_timecode |
| 792 | :header-rows: 0 |
| 793 | :stub-columns: 0 |
| 794 | :widths: 1 1 2 |
| 795 | |
| 796 | |
| 797 | - .. row 1 |
| 798 | |
| 799 | - __u32 |
| 800 | |
| 801 | - ``type`` |
| 802 | |
| 803 | - Frame rate the timecodes are based on, see :ref:`timecode-type`. |
| 804 | |
| 805 | - .. row 2 |
| 806 | |
| 807 | - __u32 |
| 808 | |
| 809 | - ``flags`` |
| 810 | |
| 811 | - Timecode flags, see :ref:`timecode-flags`. |
| 812 | |
| 813 | - .. row 3 |
| 814 | |
| 815 | - __u8 |
| 816 | |
| 817 | - ``frames`` |
| 818 | |
| 819 | - Frame count, 0 ... 23/24/29/49/59, depending on the type of |
| 820 | timecode. |
| 821 | |
| 822 | - .. row 4 |
| 823 | |
| 824 | - __u8 |
| 825 | |
| 826 | - ``seconds`` |
| 827 | |
| 828 | - Seconds count, 0 ... 59. This is a binary, not BCD number. |
| 829 | |
| 830 | - .. row 5 |
| 831 | |
| 832 | - __u8 |
| 833 | |
| 834 | - ``minutes`` |
| 835 | |
| 836 | - Minutes count, 0 ... 59. This is a binary, not BCD number. |
| 837 | |
| 838 | - .. row 6 |
| 839 | |
| 840 | - __u8 |
| 841 | |
| 842 | - ``hours`` |
| 843 | |
| 844 | - Hours count, 0 ... 29. This is a binary, not BCD number. |
| 845 | |
| 846 | - .. row 7 |
| 847 | |
| 848 | - __u8 |
| 849 | |
| 850 | - ``userbits``\ [4] |
| 851 | |
| 852 | - The "user group" bits from the timecode. |
| 853 | |
| 854 | |
| 855 | |
| 856 | .. _timecode-type: |
| 857 | |
| 858 | .. flat-table:: Timecode Types |
| 859 | :header-rows: 0 |
| 860 | :stub-columns: 0 |
| 861 | :widths: 3 1 4 |
| 862 | |
| 863 | |
| 864 | - .. row 1 |
| 865 | |
| 866 | - ``V4L2_TC_TYPE_24FPS`` |
| 867 | |
| 868 | - 1 |
| 869 | |
| 870 | - 24 frames per second, i. e. film. |
| 871 | |
| 872 | - .. row 2 |
| 873 | |
| 874 | - ``V4L2_TC_TYPE_25FPS`` |
| 875 | |
| 876 | - 2 |
| 877 | |
| 878 | - 25 frames per second, i. e. PAL or SECAM video. |
| 879 | |
| 880 | - .. row 3 |
| 881 | |
| 882 | - ``V4L2_TC_TYPE_30FPS`` |
| 883 | |
| 884 | - 3 |
| 885 | |
| 886 | - 30 frames per second, i. e. NTSC video. |
| 887 | |
| 888 | - .. row 4 |
| 889 | |
| 890 | - ``V4L2_TC_TYPE_50FPS`` |
| 891 | |
| 892 | - 4 |
| 893 | |
| 894 | - |
| 895 | |
| 896 | - .. row 5 |
| 897 | |
| 898 | - ``V4L2_TC_TYPE_60FPS`` |
| 899 | |
| 900 | - 5 |
| 901 | |
| 902 | - |
| 903 | |
| 904 | |
| 905 | |
| 906 | .. _timecode-flags: |
| 907 | |
| 908 | .. flat-table:: Timecode Flags |
| 909 | :header-rows: 0 |
| 910 | :stub-columns: 0 |
| 911 | :widths: 3 1 4 |
| 912 | |
| 913 | |
| 914 | - .. row 1 |
| 915 | |
| 916 | - ``V4L2_TC_FLAG_DROPFRAME`` |
| 917 | |
| 918 | - 0x0001 |
| 919 | |
| 920 | - Indicates "drop frame" semantics for counting frames in 29.97 fps |
| 921 | material. When set, frame numbers 0 and 1 at the start of each |
| 922 | minute, except minutes 0, 10, 20, 30, 40, 50 are omitted from the |
| 923 | count. |
| 924 | |
| 925 | - .. row 2 |
| 926 | |
| 927 | - ``V4L2_TC_FLAG_COLORFRAME`` |
| 928 | |
| 929 | - 0x0002 |
| 930 | |
| 931 | - The "color frame" flag. |
| 932 | |
| 933 | - .. row 3 |
| 934 | |
| 935 | - ``V4L2_TC_USERBITS_field`` |
| 936 | |
| 937 | - 0x000C |
| 938 | |
| 939 | - Field mask for the "binary group flags". |
| 940 | |
| 941 | - .. row 4 |
| 942 | |
| 943 | - ``V4L2_TC_USERBITS_USERDEFINED`` |
| 944 | |
| 945 | - 0x0000 |
| 946 | |
| 947 | - Unspecified format. |
| 948 | |
| 949 | - .. row 5 |
| 950 | |
| 951 | - ``V4L2_TC_USERBITS_8BITCHARS`` |
| 952 | |
| 953 | - 0x0008 |
| 954 | |
| 955 | - 8-bit ISO characters. |
| 956 | |
| 957 | |
| 958 | |
| 959 | |
| 960 | .. ------------------------------------------------------------------------------ |
| 961 | .. This file was automatically converted from DocBook-XML with the dbxml |
| 962 | .. library (https://github.com/return42/sphkerneldoc). The origin XML comes |
| 963 | .. from the linux kernel, refer to: |
| 964 | .. |
| 965 | .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook |
| 966 | .. ------------------------------------------------------------------------------ |