Altera SerialLite II Protocol - Manual (Page 38)

38 Altera Corporation
SerialLite II Protocol Reference Manual
Data Link Layer Description
Figure 2–16. User Packet Encapsulation
Notes to Figure 2–16 :
(1) IDL is required to align the control words to the proper location.
(2) The CRC is optional.
Figure 2–17 shows an example of packet activity during transmission.
Idle refers to the transmitted IDL characters when data is unavailable.
Figure 2–17. Sample Packet Activity
Note to Figure 2–17 :
(1) The CRCs are optional.
Link Management Packets
The link management packets (LMP) are optional and provide two link
control mechanisms: flow control and retry-on-error.
The link management packets are generated and processed in the Data
Link layer and are not intended to be accessible by the user interface. Link
management packets can nest within a user data or priority packet. See
“Nesting Packets” on page 2–42 for more information.
Link Management Packet Identification
The SerialLite II protocol identifies link management packets by
prepending the start-of-link management packet symbol (SLP) to the
payload, as shown in
Figure 2–18 on page 2–39 .
User Packet
User Packet
[IDL] SDP1 EGP1 SDP2 EGP2
[IDL]
CRC User Packet
(2) (1)
Idle Data Packet Idle Data Packet Idle Priority Packet Idle Idle Data Packet
SDP Data Payload EGP CRC SPP Priority Payload EGP CRC (1) (1)