15. i.MX Video Capture Driver

15.1. Introduction

The Freescale i.MX5/6 contains an Image Processing Unit (IPU), which handles the flow of image frames to and from capture devices and display devices.

For image capture, the IPU contains the following internal subunits:

  • Image DMA Controller (IDMAC)
  • Camera Serial Interface (CSI)
  • Image Converter (IC)
  • Sensor Multi-FIFO Controller (SMFC)
  • Image Rotator (IRT)
  • Video De-Interlacing or Combining Block (VDIC)

The IDMAC is the DMA controller for transfer of image frames to and from memory. Various dedicated DMA channels exist for both video capture and display paths. During transfer, the IDMAC is also capable of vertical image flip, 8x8 block transfer (see IRT description), pixel component re-ordering (for example UYVY to YUYV) within the same colorspace, and even packed <–> planar conversion. It can also perform a simple de-interlacing by interleaving even and odd lines during transfer (without motion compensation which requires the VDIC).

The CSI is the backend capture unit that interfaces directly with camera sensors over Parallel, BT.656/1120, and MIPI CSI-2 busses.

The IC handles color-space conversion, resizing (downscaling and upscaling), horizontal flip, and 90/270 degree rotation operations.

There are three independent “tasks” within the IC that can carry out conversions concurrently: pre-process encoding, pre-process viewfinder, and post-processing. Within each task, conversions are split into three sections: downsizing section, main section (upsizing, flip, colorspace conversion, and graphics plane combining), and rotation section.

The IPU time-shares the IC task operations. The time-slice granularity is one burst of eight pixels in the downsizing section, one image line in the main processing section, one image frame in the rotation section.

The SMFC is composed of four independent FIFOs that each can transfer captured frames from sensors directly to memory concurrently via four IDMAC channels.

The IRT carries out 90 and 270 degree image rotation operations. The rotation operation is carried out on 8x8 pixel blocks at a time. This operation is supported by the IDMAC which handles the 8x8 block transfer along with block reordering, in coordination with vertical flip.

The VDIC handles the conversion of interlaced video to progressive, with support for different motion compensation modes (low, medium, and high motion). The deinterlaced output frames from the VDIC can be sent to the IC pre-process viewfinder task for further conversions. The VDIC also contains a Combiner that combines two image planes, with alpha blending and color keying.

In addition to the IPU internal subunits, there are also two units outside the IPU that are also involved in video capture on i.MX:

  • MIPI CSI-2 Receiver for camera sensors with the MIPI CSI-2 bus interface. This is a Synopsys DesignWare core.
  • Two video multiplexers for selecting among multiple sensor inputs to send to a CSI.

For more info, refer to the latest versions of the i.MX5/6 reference manuals [1] and [2].

15.2. Features

Some of the features of this driver include:

  • Many different pipelines can be configured via media controller API, that correspond to the hardware video capture pipelines supported in the i.MX.
  • Supports parallel, BT.565, and MIPI CSI-2 interfaces.
  • Concurrent independent streams, by configuring pipelines to multiple video capture interfaces using independent entities.
  • Scaling, color-space conversion, horizontal and vertical flip, and image rotation via IC task subdevs.
  • Many pixel formats supported (RGB, packed and planar YUV, partial planar YUV).
  • The VDIC subdev supports motion compensated de-interlacing, with three motion compensation modes: low, medium, and high motion. Pipelines are defined that allow sending frames to the VDIC subdev directly from the CSI. There is also support in the future for sending frames to the VDIC from memory buffers via a output/mem2mem devices.
  • Includes a Frame Interval Monitor (FIM) that can correct vertical sync problems with the ADV718x video decoders.

15.3. Entities

15.4. imx6-mipi-csi2

This is the MIPI CSI-2 receiver entity. It has one sink pad to receive the MIPI CSI-2 stream (usually from a MIPI CSI-2 camera sensor). It has four source pads, corresponding to the four MIPI CSI-2 demuxed virtual channel outputs. Multpiple source pads can be enabled to independently stream from multiple virtual channels.

This entity actually consists of two sub-blocks. One is the MIPI CSI-2 core. This is a Synopsys Designware MIPI CSI-2 core. The other sub-block is a “CSI-2 to IPU gasket”. The gasket acts as a demultiplexer of the four virtual channels streams, providing four separate parallel buses containing each virtual channel that are routed to CSIs or video multiplexers as described below.

On i.MX6 solo/dual-lite, all four virtual channel buses are routed to two video multiplexers. Both CSI0 and CSI1 can receive any virtual channel, as selected by the video multiplexers.

On i.MX6 Quad, virtual channel 0 is routed to IPU1-CSI0 (after selected by a video mux), virtual channels 1 and 2 are hard-wired to IPU1-CSI1 and IPU2-CSI0, respectively, and virtual channel 3 is routed to IPU2-CSI1 (again selected by a video mux).

15.5. ipuX_csiY_mux

These are the video multiplexers. They have two or more sink pads to select from either camera sensors with a parallel interface, or from MIPI CSI-2 virtual channels from imx6-mipi-csi2 entity. They have a single source pad that routes to a CSI (ipuX_csiY entities).

On i.MX6 solo/dual-lite, there are two video mux entities. One sits in front of IPU1-CSI0 to select between a parallel sensor and any of the four MIPI CSI-2 virtual channels (a total of five sink pads). The other mux sits in front of IPU1-CSI1, and again has five sink pads to select between a parallel sensor and any of the four MIPI CSI-2 virtual channels.

On i.MX6 Quad, there are two video mux entities. One sits in front of IPU1-CSI0 to select between a parallel sensor and MIPI CSI-2 virtual channel 0 (two sink pads). The other mux sits in front of IPU2-CSI1 to select between a parallel sensor and MIPI CSI-2 virtual channel 3 (two sink pads).

15.6. ipuX_csiY

These are the CSI entities. They have a single sink pad receiving from either a video mux or from a MIPI CSI-2 virtual channel as described above.

This entity has two source pads. The first source pad can link directly to the ipuX_vdic entity or the ipuX_ic_prp entity, using hardware links that require no IDMAC memory buffer transfer.

When the direct source pad is routed to the ipuX_ic_prp entity, frames from the CSI can be processed by one or both of the IC pre-processing tasks.

When the direct source pad is routed to the ipuX_vdic entity, the VDIC will carry out motion-compensated de-interlace using “high motion” mode (see description of ipuX_vdic entity).

The second source pad sends video frames directly to memory buffers via the SMFC and an IDMAC channel, bypassing IC pre-processing. This source pad is routed to a capture device node, with a node name of the format “ipuX_csiY capture”.

Note that since the IDMAC source pad makes use of an IDMAC channel, it can do pixel reordering within the same colorspace. For example, the sink pad can take UYVY2X8, but the IDMAC source pad can output YUYV2X8. If the sink pad is receiving YUV, the output at the capture device can also be converted to a planar YUV format such as YUV420.

It will also perform simple de-interlace without motion compensation, which is activated if the sink pad’s field type is an interlaced type, and the IDMAC source pad field type is set to none.

This subdev can generate the following event when enabling the second IDMAC source pad:

  • V4L2_EVENT_IMX_FRAME_INTERVAL_ERROR

The user application can subscribe to this event from the ipuX_csiY subdev node. This event is generated by the Frame Interval Monitor (see below for more on the FIM).

15.7. Cropping in ipuX_csiY

The CSI supports cropping the incoming raw sensor frames. This is implemented in the ipuX_csiY entities at the sink pad, using the crop selection subdev API.

The CSI also supports fixed divide-by-two downscaling indepently in width and height. This is implemented in the ipuX_csiY entities at the sink pad, using the compose selection subdev API.

The output rectangle at the ipuX_csiY source pad is the same as the compose rectangle at the sink pad. So the source pad rectangle cannot be negotiated, it must be set using the compose selection API at sink pad (if /2 downscale is desired, otherwise source pad rectangle is equal to incoming rectangle).

To give an example of crop and /2 downscale, this will crop a 1280x960 input frame to 640x480, and then /2 downscale in both dimensions to 320x240 (assumes ipu1_csi0 is linked to ipu1_csi0_mux):

media-ctl -V “‘ipu1_csi0_mux’:2[fmt:UYVY2X8/1280x960]” media-ctl -V “‘ipu1_csi0’:0[crop:(0,0)/640x480]” media-ctl -V “‘ipu1_csi0’:0[compose:(0,0)/320x240]”

15.8. Frame Skipping in ipuX_csiY

The CSI supports frame rate decimation, via frame skipping. Frame rate decimation is specified by setting the frame intervals at sink and source pads. The ipuX_csiY entity then applies the best frame skip setting to the CSI to achieve the desired frame rate at the source pad.

The following example reduces an assumed incoming 60 Hz frame rate by half at the IDMAC output source pad:

media-ctl -V “‘ipu1_csi0’:0[fmt:UYVY2X8/640x480@1/60]” media-ctl -V “‘ipu1_csi0’:2[fmt:UYVY2X8/640x480@1/30]”

15.9. Frame Interval Monitor in ipuX_csiY

The adv718x decoders can occasionally send corrupt fields during NTSC/PAL signal re-sync (too little or too many video lines). When this happens, the IPU triggers a mechanism to re-establish vertical sync by adding 1 dummy line every frame, which causes a rolling effect from image to image, and can last a long time before a stable image is recovered. Or sometimes the mechanism doesn’t work at all, causing a permanent split image (one frame contains lines from two consecutive captured images).

From experiment it was found that during image rolling, the frame intervals (elapsed time between two EOF’s) drop below the nominal value for the current standard, by about one frame time (60 usec), and remain at that value until rolling stops.

While the reason for this observation isn’t known (the IPU dummy line mechanism should show an increase in the intervals by 1 line time every frame, not a fixed value), we can use it to detect the corrupt fields using a frame interval monitor. If the FIM detects a bad frame interval, the ipuX_csiY subdev will send the event V4L2_EVENT_IMX_FRAME_INTERVAL_ERROR. Userland can register with the FIM event notification on the ipuX_csiY subdev device node. Userland can issue a streaming restart when this event is received to correct the rolling/split image.

The ipuX_csiY subdev includes custom controls to tweak some dials for FIM. If one of these controls is changed during streaming, the FIM will be reset and will continue at the new settings.

  • V4L2_CID_IMX_FIM_ENABLE

Enable/disable the FIM.

  • V4L2_CID_IMX_FIM_NUM

How many frame interval measurements to average before comparing against the nominal frame interval reported by the sensor. This can reduce noise caused by interrupt latency.

  • V4L2_CID_IMX_FIM_TOLERANCE_MIN

If the averaged intervals fall outside nominal by this amount, in microseconds, the V4L2_EVENT_IMX_FRAME_INTERVAL_ERROR event is sent.

  • V4L2_CID_IMX_FIM_TOLERANCE_MAX

If any intervals are higher than this value, those samples are discarded and do not enter into the average. This can be used to discard really high interval errors that might be due to interrupt latency from high system load.

  • V4L2_CID_IMX_FIM_NUM_SKIP

How many frames to skip after a FIM reset or stream restart before FIM begins to average intervals.

  • V4L2_CID_IMX_FIM_ICAP_CHANNEL
  • V4L2_CID_IMX_FIM_ICAP_EDGE

These controls will configure an input capture channel as the method for measuring frame intervals. This is superior to the default method of measuring frame intervals via EOF interrupt, since it is not subject to uncertainty errors introduced by interrupt latency.

Input capture requires hardware support. A VSYNC signal must be routed to one of the i.MX6 input capture channel pads.

V4L2_CID_IMX_FIM_ICAP_CHANNEL configures which i.MX6 input capture channel to use. This must be 0 or 1.

V4L2_CID_IMX_FIM_ICAP_EDGE configures which signal edge will trigger input capture events. By default the input capture method is disabled with a value of IRQ_TYPE_NONE. Set this control to IRQ_TYPE_EDGE_RISING, IRQ_TYPE_EDGE_FALLING, or IRQ_TYPE_EDGE_BOTH to enable input capture, triggered on the given signal edge(s).

When input capture is disabled, frame intervals will be measured via EOF interrupt.

15.10. ipuX_vdic

The VDIC carries out motion compensated de-interlacing, with three motion compensation modes: low, medium, and high motion. The mode is specified with the menu control V4L2_CID_DEINTERLACING_MODE. It has two sink pads and a single source pad.

The direct sink pad receives from an ipuX_csiY direct pad. With this link the VDIC can only operate in high motion mode.

When the IDMAC sink pad is activated, it receives from an output or mem2mem device node. With this pipeline, it can also operate in low and medium modes, because these modes require receiving frames from memory buffers. Note that an output or mem2mem device is not implemented yet, so this sink pad currently has no links.

The source pad routes to the IC pre-processing entity ipuX_ic_prp.

15.11. ipuX_ic_prp

This is the IC pre-processing entity. It acts as a router, routing data from its sink pad to one or both of its source pads.

It has a single sink pad. The sink pad can receive from the ipuX_csiY direct pad, or from ipuX_vdic.

This entity has two source pads. One source pad routes to the pre-process encode task entity (ipuX_ic_prpenc), the other to the pre-process viewfinder task entity (ipuX_ic_prpvf). Both source pads can be activated at the same time if the sink pad is receiving from ipuX_csiY. Only the source pad to the pre-process viewfinder task entity can be activated if the sink pad is receiving from ipuX_vdic (frames from the VDIC can only be processed by the pre-process viewfinder task).

15.12. ipuX_ic_prpenc

This is the IC pre-processing encode entity. It has a single sink pad from ipuX_ic_prp, and a single source pad. The source pad is routed to a capture device node, with a node name of the format “ipuX_ic_prpenc capture”.

This entity performs the IC pre-process encode task operations: color-space conversion, resizing (downscaling and upscaling), horizontal and vertical flip, and 90/270 degree rotation. Flip and rotation are provided via standard V4L2 controls.

Like the ipuX_csiY IDMAC source, it can also perform simple de-interlace without motion compensation, and pixel reordering.

15.13. ipuX_ic_prpvf

This is the IC pre-processing viewfinder entity. It has a single sink pad from ipuX_ic_prp, and a single source pad. The source pad is routed to a capture device node, with a node name of the format “ipuX_ic_prpvf capture”.

It is identical in operation to ipuX_ic_prpenc, with the same resizing and CSC operations and flip/rotation controls. It will receive and process de-interlaced frames from the ipuX_vdic if ipuX_ic_prp is receiving from ipuX_vdic.

Like the ipuX_csiY IDMAC source, it can perform simple de-interlace without motion compensation. However, note that if the ipuX_vdic is included in the pipeline (ipuX_ic_prp is receiving from ipuX_vdic), it’s not possible to use simple de-interlace in ipuX_ic_prpvf, since the ipuX_vdic has already carried out de-interlacing (with motion compensation) and therefore the field type output from ipuX_ic_prp can only be none.

15.14. Capture Pipelines

The following describe the various use-cases supported by the pipelines.

The links shown do not include the backend sensor, video mux, or mipi csi-2 receiver links. This depends on the type of sensor interface (parallel or mipi csi-2). So these pipelines begin with:

sensor -> ipuX_csiY_mux -> …

for parallel sensors, or:

sensor -> imx6-mipi-csi2 -> (ipuX_csiY_mux) -> …

for mipi csi-2 sensors. The imx6-mipi-csi2 receiver may need to route to the video mux (ipuX_csiY_mux) before sending to the CSI, depending on the mipi csi-2 virtual channel, hence ipuX_csiY_mux is shown in parenthesis.

15.15. Unprocessed Video Capture:

Send frames directly from sensor to camera device interface node, with no conversions, via ipuX_csiY IDMAC source pad:

-> ipuX_csiY:2 -> ipuX_csiY capture

15.16. IC Direct Conversions:

This pipeline uses the preprocess encode entity to route frames directly from the CSI to the IC, to carry out scaling up to 1024x1024 resolution, CSC, flipping, and image rotation:

-> ipuX_csiY:1 -> 0:ipuX_ic_prp:1 -> 0:ipuX_ic_prpenc:1 ->
ipuX_ic_prpenc capture

15.17. Motion Compensated De-interlace:

This pipeline routes frames from the CSI direct pad to the VDIC entity to support motion-compensated de-interlacing (high motion mode only), scaling up to 1024x1024, CSC, flip, and rotation:

-> ipuX_csiY:1 -> 0:ipuX_vdic:2 -> 0:ipuX_ic_prp:2 ->
0:ipuX_ic_prpvf:1 -> ipuX_ic_prpvf capture

15.18. Usage Notes

To aid in configuration and for backward compatibility with V4L2 applications that access controls only from video device nodes, the capture device interfaces inherit controls from the active entities in the current pipeline, so controls can be accessed either directly from the subdev or from the active capture device interface. For example, the FIM controls are available either from the ipuX_csiY subdevs or from the active capture device.

The following are specific usage notes for the Sabre* reference boards:

15.19. SabreLite with OV5642 and OV5640

This platform requires the OmniVision OV5642 module with a parallel camera interface, and the OV5640 module with a MIPI CSI-2 interface. Both modules are available from Boundary Devices:

https://boundarydevices.com/product/nit6x_5mp https://boundarydevices.com/product/nit6x_5mp_mipi

Note that if only one camera module is available, the other sensor node can be disabled in the device tree.

The OV5642 module is connected to the parallel bus input on the i.MX internal video mux to IPU1 CSI0. It’s i2c bus connects to i2c bus 2.

The MIPI CSI-2 OV5640 module is connected to the i.MX internal MIPI CSI-2 receiver, and the four virtual channel outputs from the receiver are routed as follows: vc0 to the IPU1 CSI0 mux, vc1 directly to IPU1 CSI1, vc2 directly to IPU2 CSI0, and vc3 to the IPU2 CSI1 mux. The OV5640 is also connected to i2c bus 2 on the SabreLite, therefore the OV5642 and OV5640 must not share the same i2c slave address.

The following basic example configures unprocessed video capture pipelines for both sensors. The OV5642 is routed to ipu1_csi0, and the OV5640, transmitting on MIPI CSI-2 virtual channel 1 (which is imx6-mipi-csi2 pad 2), is routed to ipu1_csi1. Both sensors are configured to output 640x480, and the OV5642 outputs YUYV2X8, the OV5640 UYVY2X8:

# Setup links for OV5642
media-ctl -l "'ov5642 1-0042':0 -> 'ipu1_csi0_mux':1[1]"
media-ctl -l "'ipu1_csi0_mux':2 -> 'ipu1_csi0':0[1]"
media-ctl -l "'ipu1_csi0':2 -> 'ipu1_csi0 capture':0[1]"
# Setup links for OV5640
media-ctl -l "'ov5640 1-0040':0 -> 'imx6-mipi-csi2':0[1]"
media-ctl -l "'imx6-mipi-csi2':2 -> 'ipu1_csi1':0[1]"
media-ctl -l "'ipu1_csi1':2 -> 'ipu1_csi1 capture':0[1]"
# Configure pads for OV5642 pipeline
media-ctl -V "'ov5642 1-0042':0 [fmt:YUYV2X8/640x480 field:none]"
media-ctl -V "'ipu1_csi0_mux':2 [fmt:YUYV2X8/640x480 field:none]"
media-ctl -V "'ipu1_csi0':2 [fmt:AYUV32/640x480 field:none]"
# Configure pads for OV5640 pipeline
media-ctl -V "'ov5640 1-0040':0 [fmt:UYVY2X8/640x480 field:none]"
media-ctl -V "'imx6-mipi-csi2':2 [fmt:UYVY2X8/640x480 field:none]"
media-ctl -V "'ipu1_csi1':2 [fmt:AYUV32/640x480 field:none]"

Streaming can then begin independently on the capture device nodes “ipu1_csi0 capture” and “ipu1_csi1 capture”. The v4l2-ctl tool can be used to select any supported YUV pixelformat on the capture device nodes, including planar.

15.20. SabreAuto with ADV7180 decoder

On the SabreAuto, an on-board ADV7180 SD decoder is connected to the parallel bus input on the internal video mux to IPU1 CSI0.

The following example configures a pipeline to capture from the ADV7180 video decoder, assuming NTSC 720x480 input signals, with Motion Compensated de-interlacing. Pad field types assume the adv7180 outputs “interlaced”. $outputfmt can be any format supported by the ipu1_ic_prpvf entity at its output pad:

# Setup links
media-ctl -l "'adv7180 3-0021':0 -> 'ipu1_csi0_mux':1[1]"
media-ctl -l "'ipu1_csi0_mux':2 -> 'ipu1_csi0':0[1]"
media-ctl -l "'ipu1_csi0':1 -> 'ipu1_vdic':0[1]"
media-ctl -l "'ipu1_vdic':2 -> 'ipu1_ic_prp':0[1]"
media-ctl -l "'ipu1_ic_prp':2 -> 'ipu1_ic_prpvf':0[1]"
media-ctl -l "'ipu1_ic_prpvf':1 -> 'ipu1_ic_prpvf capture':0[1]"
# Configure pads
media-ctl -V "'adv7180 3-0021':0 [fmt:UYVY2X8/720x480]"
media-ctl -V "'ipu1_csi0_mux':2 [fmt:UYVY2X8/720x480 field:interlaced]"
media-ctl -V "'ipu1_csi0':1 [fmt:AYUV32/720x480 field:interlaced]"
media-ctl -V "'ipu1_vdic':2 [fmt:AYUV32/720x480 field:none]"
media-ctl -V "'ipu1_ic_prp':2 [fmt:AYUV32/720x480 field:none]"
media-ctl -V "'ipu1_ic_prpvf':1 [fmt:$outputfmt field:none]"

Streaming can then begin on the capture device node at “ipu1_ic_prpvf capture”. The v4l2-ctl tool can be used to select any supported YUV or RGB pixelformat on the capture device node.

This platform accepts Composite Video analog inputs to the ADV7180 on Ain1 (connector J42).

15.21. SabreSD with MIPI CSI-2 OV5640

Similarly to SabreLite, the SabreSD supports a parallel interface OV5642 module on IPU1 CSI0, and a MIPI CSI-2 OV5640 module. The OV5642 connects to i2c bus 1 and the OV5640 to i2c bus 2.

The device tree for SabreSD includes OF graphs for both the parallel OV5642 and the MIPI CSI-2 OV5640, but as of this writing only the MIPI CSI-2 OV5640 has been tested, so the OV5642 node is currently disabled. The OV5640 module connects to MIPI connector J5 (sorry I don’t have the compatible module part number or URL).

The following example configures a direct conversion pipeline to capture from the OV5640, transmitting on MIPI CSI-2 virtual channel 1. $sensorfmt can be any format supported by the OV5640. $sensordim is the frame dimension part of $sensorfmt (minus the mbus pixel code). $outputfmt can be any format supported by the ipu1_ic_prpenc entity at its output pad:

# Setup links
media-ctl -l "'ov5640 1-003c':0 -> 'imx6-mipi-csi2':0[1]"
media-ctl -l "'imx6-mipi-csi2':2 -> 'ipu1_csi1':0[1]"
media-ctl -l "'ipu1_csi1':1 -> 'ipu1_ic_prp':0[1]"
media-ctl -l "'ipu1_ic_prp':1 -> 'ipu1_ic_prpenc':0[1]"
media-ctl -l "'ipu1_ic_prpenc':1 -> 'ipu1_ic_prpenc capture':0[1]"
# Configure pads
media-ctl -V "'ov5640 1-003c':0 [fmt:$sensorfmt field:none]"
media-ctl -V "'imx6-mipi-csi2':2 [fmt:$sensorfmt field:none]"
media-ctl -V "'ipu1_csi1':1 [fmt:AYUV32/$sensordim field:none]"
media-ctl -V "'ipu1_ic_prp':1 [fmt:AYUV32/$sensordim field:none]"
media-ctl -V "'ipu1_ic_prpenc':1 [fmt:$outputfmt field:none]"

Streaming can then begin on “ipu1_ic_prpenc capture” node. The v4l2-ctl tool can be used to select any supported YUV or RGB pixelformat on the capture device node.

15.22. Known Issues

  1. When using 90 or 270 degree rotation control at capture resolutions near the IC resizer limit of 1024x1024, and combined with planar pixel formats (YUV420, YUV422p), frame capture will often fail with no end-of-frame interrupts from the IDMAC channel. To work around this, use lower resolution and/or packed formats (YUYV, RGB3, etc.) when 90 or 270 rotations are needed.

15.23. File list

drivers/staging/media/imx/ include/media/imx.h include/linux/imx-media.h

15.25. Authors

Copyright (C) 2012-2017 Mentor Graphics Inc.