A Video Interface Protocol for FPGA-Based Video Applications

The concepts behind the Avalon Streaming (Avalon-ST) Video Interface protocol, an open interface from Altera.

By Suhel Dhanani, Senior Manager, DSP, Altera

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Video/Imaging DesignWire
(11/4/2010 1:30:07 AM)

Control Data Packet – Definitions

The control data packets are used to configure the VIP functions so they correctly process the video data packets that follow. Control data packets contain the width, height, and interlacing information. The width and height, 16 bits each, are the dimensions of the video data packets that follow. The width refers to the width in pixels of the lines of a frame. The height refers to the number of lines in a frame or field. For example a 1080i field would have width of 1920 pixels and height of 540 pixels, and a 1080p frame would have width of 1920 pixels and height of 1080 pixels.

There are the two main components to the interlacing bits. The two most significant bits are used to indicate whether the next video packet is progressive or interlaced. The two least significant bits have different meaning, depending on whether the next video packet is progressive or not. The detailed encodings are listed in Figure 3.
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Figure 3. Video control data format

Other details for the control packets are:

  • A control data packet must immediately precede every video data packet
  • All VIP functions either pass on a control data packet or generate a new one before each video data packet
  • If the function receives more than one control data packet before a video data packet, it uses the parameters from the last received control data packet. And if it receives none, it will keep the settings from the last control data packet received.

Ancillary Data Packets

Ancillary data packets send ancillary packets between the VIP functions. These ancillary data packets are typically placed between a control data packet and a video data packet and contain information that describes the video data packet, for example active format description codes.

Summary

The Avalon-ST and Avalon-MM specifications are in the public domain and are fully defined in a specifications document that is available on the web. Customers can use this spec to build their own custom video functions and plug-and-play their custom IP with the Video Design Framework.

About the author:
Suhel Dhanani is a Senior Manager in Altera’s software, embedded and DSP marketing group. Mr. Dhanani is responsible for DSP product marketing. He has over 15 years of industry experience in semiconductors — with both large companies such as Xilinx and VLSI Technology as well as with Silicon Valley startups including Anadigm and Tabula. Mr. Dhanani has completed a graduate certificate in Management Science from Stanford University and holds M.S.E.E. and M.B.A. degrees from Arizona State University.

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