Documentation/userspace-api/media/drivers/npcm-video.rst

Source file repositories/reference/linux-study-clean/Documentation/userspace-api/media/drivers/npcm-video.rst

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Documentation/userspace-api/media/drivers/npcm-video.rst
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Support Tooling And Documentation
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Support Tooling And Documentation: documentation
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Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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.. SPDX-License-Identifier: GPL-2.0

.. include:: <isonum.txt>

NPCM video driver
=================

This driver is used to control the Video Capture/Differentiation (VCD) engine
and Encoding Compression Engine (ECE) present on Nuvoton NPCM SoCs. The VCD can
capture a frame from digital video input and compare two frames in memory, and
the ECE can compress the frame data into HEXTILE format.

Driver-specific Controls
------------------------

V4L2_CID_NPCM_CAPTURE_MODE
~~~~~~~~~~~~~~~~~~~~~~~~~~

The VCD engine supports two modes:

- COMPLETE mode:

  Capture the next complete frame into memory.

- DIFF mode:

  Compare the incoming frame with the frame stored in memory, and updates the
  differentiated frame in memory.

Application can use ``V4L2_CID_NPCM_CAPTURE_MODE`` control to set the VCD mode
with different control values (enum v4l2_npcm_capture_mode):

- ``V4L2_NPCM_CAPTURE_MODE_COMPLETE``: will set VCD to COMPLETE mode.
- ``V4L2_NPCM_CAPTURE_MODE_DIFF``: will set VCD to DIFF mode.

V4L2_CID_NPCM_RECT_COUNT
~~~~~~~~~~~~~~~~~~~~~~~~

If using V4L2_PIX_FMT_HEXTILE format, VCD will capture frame data and then ECE
will compress the data into HEXTILE rectangles and store them in V4L2 video
buffer with the layout defined in Remote Framebuffer Protocol:
::

           (RFC 6143, https://www.rfc-editor.org/rfc/rfc6143.html#section-7.6.1)

           +--------------+--------------+-------------------+
           | No. of bytes | Type [Value] | Description       |
           +--------------+--------------+-------------------+
           | 2            | U16          | x-position        |
           | 2            | U16          | y-position        |
           | 2            | U16          | width             |
           | 2            | U16          | height            |
           | 4            | S32          | encoding-type (5) |
           +--------------+--------------+-------------------+
           |             HEXTILE rectangle data              |
           +-------------------------------------------------+

Application can get the video buffer through VIDIOC_DQBUF, and followed by
calling ``V4L2_CID_NPCM_RECT_COUNT`` control to get the number of HEXTILE
rectangles in this buffer.

References
----------
include/uapi/linux/npcm-video.h

**Copyright** |copy| 2022 Nuvoton Technologies

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