CSI

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CSI on mainline Linux with v4l2

The CSI (CMOS Sensor Interface) hardware block is partially supported in mainline Linux. Support for the hardware block found on A31 and later generations is already upstream, while the one found on A10/A20 is being worked on, as of 2019/04/12.

Currently parallel and BT.656 (embedded sync) interfaces are supported. MIPI CSI-2 is not.

The mainline driver uses v4l2 with the sub-device API and media controller API.

Kernel config options

To enable the driver, please first check if you have the VIDEO_DEV, MEDIA_CONTROLLER and VIDEO_V4L2_SUBDEV_API Kconfig options enabled.

Then once you enable V4L_PLATFORM_DRIVERS you should be able to enable VIDEO_SUN6I_CSI for the A31 CSI driver. For the A10/A20 CSI driver, enable VIDEO_SUN4I_CSI. (Provided you have the patches applied.)

Userspace configuration

It is recommended to use an up-to-date version of v4l-utils, as older versions, such as the one in Debian Stable (1.12.x) has some bugs, and doesn't understand all formats or knobs.

The usage of the media controller and sub-device API means configuration of the capture options is slightly complicated. The media-ctl and v4l2-ctl are used.

If you are using buildroot, enable BR2_PACKAGE_LIBV4L and BR2_PACKAGE_LIBV4L_UTILS in the make menuconfig to be able to use media-ctl and v4l2-ctl. media-ctl source and development have been moved to v4l-utils since June 2014.

Media bus and capture formats

To see the current settings of the media bus, use 

$ media-ctl --print-topology

Media controller API version 5.1.0

Media device information
------------------------
driver          sun6i-csi
model           Allwinner Video Capture Device
serial
bus info
hw revision     0x0
driver version  5.1.0

Device topology
- entity 1: sun6i-csi (1 pad, 1 link)
            type Node subtype V4L flags 0
            device node name /dev/video0
        pad0: Sink
                <- "ov5640 1-003c":0 [ENABLED,IMMUTABLE]

- entity 5: ov5640 1-003c (1 pad, 1 link)
            type V4L2 subdev subtype Sensor flags 0
            device node name /dev/v4l-subdev0
        pad0: Source
                [fmt:UYVY8_2X8/640x480 field:none]
                -> "sun6i-csi":0 [ENABLED,IMMUTABLE]

On systems with the Cedrus driver enabled, the media device may not be the default one, in which case you should use 

$ media-ctl --device /dev/mediaN --print-topology

To set the capture format (including the bus format and capture size), you specify the properties of the source pad. 

$ media-ctl --set-v4l2 '"ov5640 1-003c":0[fmt:UYVY8_2X8/720x480]'

Here the entity name "ov5640 1-003c" can also be replaced with the entity ID 5.

This configures a capture size of 720x480 pixels with the UYVY8_2X8 bus format, which is YUV 4:2:0. See Media Bus Formats for a list and description of formats.

The capture resolution specified here must match what is requested by the capture application, otherwise the kernel driver will report an error and refuse to capture.

Sensor sub-device configuration

Sensors can have a number of control knobs that can be configured from userspace. These range from image orientation to power line frequency to test patterns.

To see the full list of control knobs along with menu item descriptions, use 

$ v4l2-ctl --list-ctrls-menus

User Controls

                       contrast (int)    : min=0 max=255 step=1 default=0 value=0 flags=slider
                     saturation (int)    : min=0 max=255 step=1 default=64 value=64 flags=slider
                            hue (int)    : min=0 max=359 step=1 default=0 value=0 flags=slider
        white_balance_automatic (bool)   : default=1 value=1 flags=update
                    red_balance (int)    : min=0 max=4095 step=1 default=0 value=0 flags=inactive, slider
                   blue_balance (int)    : min=0 max=4095 step=1 default=0 value=0 flags=inactive, slider
                       exposure (int)    : min=0 max=65535 step=1 default=0 value=885 flags=inactive, volatile
                 gain_automatic (bool)   : default=1 value=1 flags=update
                           gain (int)    : min=0 max=1023 step=1 default=0 value=248 flags=inactive, volatile
                horizontal_flip (bool)   : default=0 value=0
                  vertical_flip (bool)   : default=0 value=0
           power_line_frequency (menu)   : min=0 max=3 default=1 value=1
                                0: Disabled
                                1: 50 Hz
                                2: 60 Hz
                                3: Auto

Camera Controls

                  auto_exposure (menu)   : min=0 max=1 default=0 value=0 flags=update
                                0: Auto Mode
                                1: Manual Mode

Image Processing Controls

                   test_pattern (menu)   : min=0 max=4 default=0 value=0
                                0: Disabled
                                1: Color bars
                                2: Color bars w/ rolling bar
                                3: Color squares
                                4: Color squares w/ rolling bar

Note that if the system has multiple video devices, you may need to specify which one to use: 

$ v4l2-ctl --device=/dev/videoN --list-ctrls-menus

To set an option, use 

$ v4l2-ctl --set-ctrl=vertical_flip=1

Or multiple options at once 

$ v4l2-ctl --set-ctrl=power_line_frequency=2,vertical_flip=1,horizontal_flip=1

Capturing Images

FFMpeg

FFMpeg supports capturing from v4l2 devices. However it does not support configuration of the media bus or sub-devices. Please use the commands shown in the previous sections instead.

To capture from the first video device, use 

$ ffmpeg -s WxH -i /dev/video0 output.mjpg

This captures and encodes a video of W by H pixels from the first video device to an M-JPEG file.

Note that W and H must match what you previously set with media-ctl. The system default is 640x480.

If you also specified a different bus format, such as JPEG_1X8, you will need to tell FFMpeg as well, using 

$ ffmpeg -input_format mjpeg -s WxH -i /dev/video0 output.mjpg


Caveats / TODOs

JPEG media bus format buffers

The JPEG media bus format support in the driver does not trim the returned buffer. In other words, the full buffer is passed back to userspace, with trailing zeros. This means the user will end up with enormous JPEG files without post-processing.

There are already several JPEG parsers in the kernel. A proposal was made to combine and generalize them, which could then be used in our CSI driver to detect the end of the JPEG stream. This has not been implemented yet.

MIPI CSI-2

While a few Allwinner SoCs support MIPI CSI-2, details on the hardware is sparse. No one has attempted to support this yet.

BSP kernel supported camera's sensors table

Vendor Part Number Pixels Type Specification Focus AVDD DOVDD DVDD AFVCC NOTE
OmniVision OV7670 0.3M Photo/Video 640*480@30fps
352*176@30fps
320*240@30fps
176*144@30fps		 Fixed focus 2.8 2.8 1.8 NC
OmniVision OV2655 2M Photo/Video 1600*1200
800*600@30fps
640*480@30fps		 Fixed focus 2.8 2.8 1.5 NC Basic image can fine tune the effect
OmniVision OV2643 2M Photo/Video 1600*1200
1280*760@30fps
640*480@30fps		 Fixed focus 2.8 2.8 1.5 NC Module FPC needs to be as short as possible
OmniVision OV3660 3M Photo/Video 2048*1536@5fps
1600*1200@5fps
1280*720@30fps
640*480@30fps		 Fixed focus 2.8 2.8 1.8 NC
OmniVision OV5640 5M Photo/Video 2592*1936@5fps
2048*1536@5fps
1600*1200@5fps
1280*960@5fps
1024*768@5fps
1920*1080@30fps
1280*720@30fps
640*480@30fps		 Fixed focus/Autofocus 2.8 2.8 1.5 2.8~3 1.OV5640 drive capability module selection FPC.
Need to be as short as possible.
2. Recommendation module model effects and auto-focus function is fine.
If the election of the other modules, and does not guarantee results.
OmniVision OV5647 5M Photo/Video 5M@15fps
1080p@30fps
720p@30fps		 Autofocus 2.8 2.8 1.5 2.8
Micron MT9V112 0.3M Photo/Video 640*480@30fps Fixed focus 2.8 2.8 1.8 NC
Micron MT9M112 1.3M Photo/Video 1280*1024@15fps
640*512@30fps		 Fixed focus 2.8 2.8 1.8 NC
Micron MT9M113 1.3M Photo/Video 1280*1024@15fps
640*512@30fps		 Fixed focus 2.8 2.8 1.8 NC
Micron MT9D112 1.3M Photo/Video 1600*1200@15fps
640*480@30fps		 Fixed focus 2.8 2.8 1.8 NC
Galaxy Core GC0307 0.3M Video 640*480@15fps Fixed focus 2.8 2.8 1.8 NC
Galaxy Core GC0308 0.3M Video 640*480@15fps Fixed focus 2.8 2.8 1.8 NC
Galaxy Core GC0309 0.3M Video 640*480@15fps Fixed focus 2.8 2.8 1.8 NC
Galaxy Core GC0329 0.3M Video 640*480@15fps Fixed focus 2.8 2.8 1.8 NC
Galaxy Core GT2005 2M Photo/Video 1600*1200@15fps
1280*720@15fps
800*600@30fps
640*480@30fps		 Fixed focus 2.8 2.8 1.8 NC
Galaxy Core GT2035 2M Photo/Video 1600*1200@2fps
1280*720@10fps
800*600@10fps
640*480@10fps		 Fixed focus 2.8 2.8 1.8 NC
Galaxy Core GC2015 2M Photo/Video 1600*1200@2fps
1280*1024@2fps
1024*768@2fps
800*600@8fps
640*480@8fps		 Fixed focus 2.8 2.8 2.8 NC
Hynix HI704 0.3M Video 640*480@20fps Fixed focus 2.8 2.8 2.8 NC I2C and other devices share may be a conflict
Hynix HI253 6M Photo/Video 1600*1200
1280*720@15fps
800*600@30fps
640*480@30fps
320*240@30fps		 Fixed focus/Autofocus 2.8 2.8 1.8 NC
SETi SIV121D 0.3M YUV 640x480@30fps Fixed focus 2.8 1.8/2.8 internal NC based on SIV121C datasheet
Superpix SP0838 0.3M Video 640*480@20fps Fixed focus 2.8 2.8 1.8 NC
Superpix SP2518 2M Video 1600*1200@15fps Fixed focus 2.8 2.8 1.8 NC
Samsung S5K4EC 5M Photo/Video 2560*[email protected]
2048*[email protected]
1920*1080@15fps
1280*720@30fps
640*480@30fps		 Autofocus 2.8 2.8 1.2 2.8~3
TOSHIBA T8ET5 5M Video 5M@15fps
2048*[email protected]
1080p@30fps
720p@30fps		 Autofocus 2.8 2.8 1.5 2.8

Reference

*[1] Allwinnertech Wiki

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