This page gives an overview of Xilinx Multi-Scaler driver, which is available as part of the Xilinx Linux distribution.
The driver is part of the V4L2 Memory to Memory framework.
The Multi-Scaler driver generates up to eight scaled output images from a single or multiple (up to eight) external video and/or graphics sources. Video scaling is the process of converting an input color image of dimensions Xin pixels by Yin lines to an output color image of dimensions Xout pixels by Yout lines. This IP also capable of doing color space conversion. Multi-Scaler IP reads the input images from the memory addresses and writes the scaled output images to the destination memory addresses.
The Multi-scaler works in a sequential way, i.e. the input of the first channel scaled first and then the 2nd input gets scaled and so no up to the maximum channels configured in HwReg_num_outs. When all channels (configured) get scaled, IP generates the interrupt and ready for next processing.
Multi-Scaler converts and scales video frames between a great variety of video formats. For more supported formats please visit IP Product guide.
Xilinx-multiscaler creates a device node per channel and can be accessed from user-space via standard V4L2 system calls. Even though the devices created by driver looks like independent nodes but as multi-scaler IP has one scaler inside and works in sequential manner these nodes/devices are not independent. For more details see limitation section.
HW IP features
- Memory mapped AXI4 Interface
- Supports maximum 8 outputs
- Supports spatial resolutions from 64 × 64 up to 7680 × 4320
- Supports one, two, or four pixel-width
- Supports RGB, YUV 444, YUV 422, YUV 420
- Supports 8-bit and 10-bit per color component on memory interface
- Supports semi-planar memory formats next to packed memory formats
- Dynamically configurable source and destination buffer addresses
- Supports 6, 8, 10, and 12 taps in both H and V domains
- Supports 64 phases
- Supports 8K 30 fps depending on the device family
Missing Features / Known Issues / Limitations in Driver
- Tested 64 × 64 up to 1920 × 1080.
- 10-bit per color component is not tested.
- As hardware processes all channels in sequential order, the driver has limitation to add only the next immediate channel.
Example: Channels 0,1,2,3 are streaming, then the user can stream on immediate next channel 4.
If user adds stream for channel 6 when channels 0,1,2,3 are running, then driver does not start 6th channel and does not return any error.
If any intermediate channel stops the streaming, the streaming continues for only channels before the stopped channel.
In this case if channel 0,1,2,3,4 are running and channel 3 stops, then the streaming for channels 0,1,2 will continue and driver stop processing 4th channel without any error indications.
A channel is not processed by the driver, if all channel with lower channel number are not queueing the buffers.
E.g. If 0,1,2,3 channels were being processed by driver and channel 1 didn't queue any buffers, then channel 2 and 3 won't be processed but channel 0 will continue.
- The driver is tested with YUY2, NV16, NV12, RGB, GRAY8, UYVY and BGR Gstreamer formats only.
- Stride and height align issue. Please check here.
The following config options should be enabled in order to build Xilinx Multi-Scaler driver
The driver is available at,
Device Tree Binding
The device tree node will be automatically generated, if the core is configured in the HW design, using the Device Tree BSP.
Steps to generate device-tree is documented here,
And a sample binding is shown below and the description of DT property is documented here
A reference design for testing is as below
Multi-Scaler driver creates a video device per channel, which can be visual in /dev directory.
The device names are /dev/videoN to /dev/videoN+8 where N starts from the next available video device to the maximum number of devices the IP is configured (xlnx, max-chan in DT).
Multi-Scaler is tested with the generic gstreamer v4l2videotransform plugin which maps device node to v4l2videoNconvert elements. Where N is the number of device node.
Below is the steps to get the proper gstreamer element for the Multi-Scaler.
Find the Multi-Scaler devices
Gstreamer device name for Multi-Scaler is xm2msc (Xilinx memory to memory video multi-scaler).
In below example the IP is configured for 8 channels.
N-N Use Case:
Multi-Scaler is tested with the generic gstreamer v4l2videotransform elements which is part of gst-plugins-good. So no extra library required to run N:N use case.
In below image, it is represented a basic test scenario where multiple v4l2videoNconvert elements are launched as different process opening different node of Multi-Scale. The input for the v4l2videoNconvert is frames of different format and different resolutions and the output is given to filesink which stores the scaled and converted frames in a file.
Commands to test
Below command is used to test Multi-Scaler with Gstreamer. You can open Multiple channels by running v4l2videoNconvert process in parallel.
1 to N Use Case:
Multi-Scaler's 1 to N use case is tested with the xlnxabrscaler plugin.
In below image, it is represented a basic test scenario where single input given to xlnxabrscaler elements which opens different node of Multi-Scaler. The output is given to filesink which stores the scaled and converted frames in files.
Commands to test
For 1 to N Use Case, run commands mention in debugging section.
Mapping table between Gstreamer string and Xilinx Multi-Scaler Supported Formats
Replace the format string in above command with below Gstreamer strings, to test different supported formats
Enable Dynamic Debugging in kernel.
Run below commands to enable logs on console
Stride and Height Alignment
Multiple IPs required aligned stride and height to work properly, but till now there is no way to share this information with Multi-Scaler plugin and driver.
Multi-Scaler driver has implemented a mechanism to provide stride and height align values per channel for both output and capture pads, at run-time. This is temporary fix. Once the stride and height alignment support added to plugin, this change will be reverted.
Filesrc -> Decoder -> Multi-Scaler -> filesink
As decoder require 256 align byteperline and 64 align lines per frame, so the setting before running gstreamer pipe are :
And then run :
Filesrc -> Decoder -> Multi-Scaler -> DP kmssink
And the run:
videotestsrc -> Multi-Scaler -> filesink
videotestsrc -> Multi-Scaler0 -> filesink
Filesrc -> Decoder -> Multi-Scaler1 -> DP kmssink
Gstreamer plugins enumerate all the channel/video devices for each of gst command. So, there might be chances that starting all channels with different gst process at same time do not allow the actual process to open the device and the process dedicated for the device does not start. For example, if all channels are opened immediately in a script, all the gst process open and close all the devices for all the channels and if somehow gst process 1 opens channel 2 and at same time if process 2 open channel 2, the 2nd process do not get the channel 2 and returns, despite the process 1 do not require the channel 2 and close the channel 2 afterwards. Adding sleep after every enumeration is required to make all applications work properly.
- No changes
- Support VB2_USERPTR IO mode
- Added support for Pixels per clock
- Add support for formats having contiguous buffers for two planes. (NV12, NV16, XV20, XV15)
- Clock framework support
- Hack support for stride and height alignment required for VCU decoder
- 144e268 v4l: xilinx: multi-scaler: Set channel parameters to default values
- 54b31ac v4l: xilinx: multi-scaler: Fix precedence error
- 1fa95a9 media: xilinx: multi-scaler: Support stride and height alignment
- 0dce6af media: xilinx: multi-scaler: Add clock framework support
- f280f6a media: xilinx: multi-scaler: Add support for formats having contiguous buffers for two planes.
- b30b1e media: xilinx: multi-scaler: Align width to pixels per clock
- 68bbe2 media: xilinx: multi-scaler: Add extra padding bytes after each row of pixels
- fc81159 media: xilinx: multi-scaler: Replace dev_info with dev_dbg if all jobs are not ready
- 2e2ece media: xilinx: multi-scaler: support VB2_USERPTR IO mode