Altera SerialLite II Protocol - Manual (Page 64)

64 Altera Corporation
SerialLite II Protocol Reference Manual
Data Link Layer Description
Effect of Link Management Packet Corruption
If a flow control link management packet is corrupted, it is discarded and
the near transmitter continues to send data. The data may overrun the far
receiver FIFO buffers. Buffer overrun triggers a link error and initiates the
link initialization process of
“Link Initialization and Training” .
Retry-on-Error (Optional)
Implementation of the retry-on-error mechanism is optional for the
priority port.
The priority port always transfers segments in the order they were
received and retransmits them in the required order. The segment ID
associated with each priority packet segment ensures this sequence is
maintained.
For the purposes of this specification, the link consists of a near
transmitter sending the priority packets to a far receiver and a far
transmitter sending link management packets to the near receiver.
Retry-on-error is a mechanism that allows the far end to request
retransmission of segments when an error is detected by the far receiver.
This mechanism requires the far transmitter to acknowledge every
segment received. There are two types of acknowledgement:
■ ACK: The received segment is good and error-free.
■ NACK: The received segment contains an error. If the retry-on-error
option is enabled, retransmit all segments starting from the segment
with errors. (If the retry-on-error option is not enabled, raise a data
error.)
If the retry-on-error option is not enabled, all segments are transmitted
without any acknowledgements from the receiver.
Retry-on-Error Link Management Packet Format
Table 2–22 specifies the retry-on-error packet format, and Table 2–23
specifies the retry-on-error packet parameter values.
Table 2–22. Retry-On-Error Packet Format
Bit[23:20] Bit[19:16] Bit[15:12] Bit[11:8]
Link packet type Link packet parameter
0x2 CLASS Reserved = 0x0 SID