Packets¶

S-Link uses packets to communicate between application layers on each side.

There are two type of packets in S-Link, short packets and long packets. These packet types lean heavily on the CSI/DSI packet definitions due to their simplicity as well as flexible packet lengths.

Short Packets¶

Short Packet Structure¶

Short packets are 32bits in size and are generally used for intra-link communication and small data payloads. They comprise of the following:

Data ID [7:0] - Denotes packet type. Data Id’s 0x0 - 0x1f are short packets. 0x20 - 0xff are long packets
Payload [23:8] - Optional payload for short packets
ECC [31:24] - ECC used for packet error correction/detection.

Long Packets¶

Long Packet Structure¶

Long Packets have varying sizes dependent on the payload size. They compromise of a 4byte packet header and 2byte CRC. The make up of a long packet is defined by the following:

Data ID [7:0] - Denotes packet type. Data Id’s 0x0 - 0x1f are short packets. 0x20 - 0xff are long packets
Word Count [23:8] - Number of bytes for this long packet
ECC [31:24] - ECC used for packet error correction/detection. Same ECC as short packets
Payload - Application specific payload
CRC - CRC generated on the payload data.

Note

A future revision of S-Link may allow the CRC to be bypassed/disabled to allow more bandwidth.

Reserved Data IDs¶

Several data ids are reserved for S-Link internal use and/or S-Link communication. The applicaiton layer shall not use the following data ids for application-specific data transfer.

Note

The applicaiton layer can optionally use some of these for communicating to the other S-Link controller. This is indicated by the table under the “App can use” column.

This is allowed so hardware can perform attribute checks/updates.

Data ID	Packet Type	App can use?	Description
Short Packets
0x00/0x01	NOP	N	No Operation/IDLE packet that is used to keep the link alive but conveys no data
Long Packets
0xf0-0xff	RESERVED		Reserved for future use