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The Packetizer breaks stream frames in to smaller frames called packets. Each packet contains an 8 byte header as follows:
| Byte | Bits | Name | Description |
|---|---|---|---|
| 0 | 3:0 | Version | The packetizer protocol version. Should be 0. |
| 0 | 7:4 | FrameNumber[3:0] | Increments with each frame. Used to track missing frames. |
| 1 | 7:0 | FrameNumber[11:4] |
| 2 | 7:0 | PacketNumber[7:0] | Resets to 0 with each new frame |
| 3 | 7:0 | PacketNumber[15:8] |
| 4 | 7:0 | PacketNumber[23:16] |
| 5 | 7:0 | TDest | TDEST of AXI-Stream frame |
| 6 | 7:0 | TID | TID of AXI-Stream frame |
| 7 | 7:0 | TUserFirst | TUSER of first transaction of the AXI-Stream frame |
Packet Tail
Each packet also has a 1 byte tail appended:
| Byte | Bits | Name | Description |
|---|---|---|---|
| 0 | 6:0 | TUserLast | TUSER of of transaction of the AXI-Stream frame. Only valid if EOF=1 |
| 0 | 7 | EOF | Indicates that this is the last packet of a frame. |
Notes
- We steal the MSB of tUserLast to indicate EOF. EOF=0 indicates that there are more packets left in the frame.
- Having tUserLast/EOF in a tail allows the packetizer to function in streaming fashion and not have to buffer each packet worth of data in a FIFO.
- TDest, TId and TUserFirst are placed in the header of every packet, even though they don’t change after the first packet of the frame.
- TUserLast data is only valid if the EOF bit is 1
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