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.
Please check section below on Stride and Height align.
The following config options should be enabled in order to build Xilinx Multi-Scaler driver
To check if the options are enabled run the following:
petalinux-config -c kernel
When the GUI opens, you can use '/' to search for each config.
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).
# ls /dev/ | grep video
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.
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 an example using Gstreamer. You can open Multiple channels by running v4l2videoNconvert process in parallel. **Note Gstreamer plugins may change, please refer to Gstreamer documentation for the latest information on using Gstreamer plugins
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
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 :
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.
The gstreamer plugins mentioned on this page are developed for Proof of Concept and testing some limited featured only. This plugins are not tested for all possible resolutions, video formats etc. Customers may need to develop their own plugins by using these plugins as example.