Video and Image Processing Suite User Guide

ID 683416
Date 2/12/2021

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2.2.1. Avalon-ST Video Control Packets

A control packet is identified when the low nibble of the first symbol is set to decimal 15 (0xF). The Avalon-ST Video protocol further defines that any other symbol data transmitted in the first cycle (or beat) of the transmission is ignored.

An Avalon-ST Video control packet comprises the identifier nibble, and 9 other nibbles which indicate the height, width and interlacing information of any subsequent Avalon-ST Video packets.

Figure 5. Avalon-ST Video Control PacketThe figure below shows the structure of a control packet in an Avalon-ST Video configuration of two 10 bit symbols (color planes) per pixel and two pixels in parallel. Observe the symbol-alignment of the control packet nibbles; the remaining bits in each symbol are undefined.
Note: Most VIP IP cores do not drive the empty signal for control packets because extra data is always ignored. Nevertheless, a value of two indicating that the last pixel of the final beat is invalid would be tolerated.
Table 7.  Avalon-ST Video Control Packet Nibble DecodingThe Height and Width are given in pixels and the Interlacing nibble is decoded.
Nibble Description
D0 Width[15:12]
D1 Width[11:8]
D2 Width[7:4]
D3 Width[3:0]
D4 Height[15:12]
D5 Height[11:8]
D6 Height[7:4]
D7 Height[3:0]
D8 Interlacing[3:0]

When the Interlacing nibble indicates an interlaced field, the height nibble gives the height of the individual fields and not that of the equivalent whole frame—for example, a control packet for 1080i video would show a height of 540, not 1080.

Table 8.  Avalon-ST Video Control Packet Interlaced Nibble Decoding
Interlaced/Progressive Interlacing[3] Interlacing[2] Interlacing[1] Interlacing[0] Description
Interlaced 1 1 0 0 Interlaced F1 field, paired with the following F0 field
0 1 Interlaced F1 field, paired with the preceding F0 field
1 x Interlaced F1 field, pairing don’t care
0 0 0 Interlaced F0 field, paired with the preceding F1 field
0 1 Interlaced F0 field, paired with the following F1 field
1 x Interlaced F0 field, pairing don’t care
Progressive 0 x 0 1 Progressive frame, deinterlaced from an f1 field
0 0 Progressive frame, deinterlaced from an f0 field
1 x Progressive frame

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