Altera SerialLite II Protocol - Manual (Page 58)

58 Altera Corporation
SerialLite II Protocol Reference Manual
Data Link Layer Description
Payload Error Protection (Optional)
SerialLite II optionally provides CRC error-checking coverage to data
and/or priority packets to protect against errors. Two CRC polynomials
are supported. The CRC covers all user data packet bytes and the IDL
characters (if needed), as shown in
Figure 2–35 .
Figure 2–35. CRC Coverage
IDL bytes are asserted to the end of the packet to align the EGP bytes to
the first lane. The CRC bytes immediately follow the two EGP bytes.
CRCs are only calculated over full columns of data to allow for an easier
implementation. When there is a gap between data bytes and the
EGP/EBP, the gap must be filled with IDL characters. IDL bytes are
replaced with all zeros and included in the CRC calculation. The CRC
calculation is only performed on full data columns and partial data
column padded with idles. The start and end of packet delimiters, idle
ordered sets, clock compensation ordered sets and link management
packets are not protected by the CRC.
Figures 2–36 and 2–37 show the use of no CRC, CRC-16, or CRC-32 for
both priority and data packets. The SPP is processed before the first data
byte arrives, and the SPP can occur on the same row as the EGP shown,
reducing the overhead.
Figure 2–36. CRC Alignment for Four Lanes
User Data Packet CRC EGP [IDL]
CRC Coverage
SDP
Time
D8
IDL
D12
D16
PD0
PD4
D0
D4
D9
IDL
D13
IDL
PD1
PD5
D1
D5
D10
SDP1
D14
IDL
PD2
PD6
D2
D6
D11
SDP2
D15
IDL
PD3
PD7
D3
D7
CRC1 CRC2 EG P1 EG P2
SPP1 SPP2 IDL IDL
Lane
# 0
Lane
# 1
Lane
# 2
Lane
# 3
CRC1 EG P1 CRC2 EG P2
IDL IDL
CRC-16
IDL IDL
CRC-16