Chbondi, Chbondo; Rxclkcorcnt, Rxlossofsync; Troubleshooting; Crc (Cyclic Redundancy Check) - Xilinx RocketIO User Manual

CRC (Cyclic Redundancy Check)

CHBONDI,
CHBONDO
These two 4-bit ports are used by the Master MGT to control its clock correction and channel
bonding, as well as those of any Slaves bonded to it. CHBONDO of the Master is connected to
CHBONDI of a SLAVE_1_HOP. The signal is then daisy-chained from SLAVE_1_HOP
CHBONDO to a SLAVE_2_HOPS CHBONDI. See
Table 2-18, page
RXCLKCORCNT port. These four bits allow the Master to control when the Slaves perform clock
correction. This keeps channels from going out of sync if, for instance, one Slave repeated a CCS
while another skipped.
RXCLKCORCNT,
RXLOSSOFSYNC
These signals are mainly used for clock correction. However, they can convey some information
relevant to channel bonding as well. Refer to
page

Troubleshooting

Factors that influence channel bonding include:
•
•
There are several possibilities that could cause unsuccessful channel bonding:
•
•
•
CRC (Cyclic Redundancy Check)

Overview

Cyclic Redundancy Check (CRC) is a procedure to detect errors in the received data. The RocketIO
transceiver CRC logic supports the 32-bit invariant CRC calculation used by Infiniband, Fibre
Channel, and Gigabit Ethernet.

CRC Operation

On the transmitter side, the CRC logic recognizes where the CRC bytes should be inserted and
replaces four placeholder bytes at the tail of a data packet with the computed CRC. For Gigabit
RocketIO™ Transceiver User Guide
UG024 (v2.3.2) June 24, 2004
Note:
The Slave's RXCLKCORCNT will go to 101 regardless of whether the channel bonding
was successful or not. To determine if channel bonding was successful, check both this signal
and RXCLKCORCNT.
80, for examples. The three least significant bits correlate to the value of the
78.
Skew between Master and Slave CBS arrival time, both Master-lags-Slave and Slave-lags-
Master cases. The larger the separation, the larger CHAN_BOND_WAIT needs to be.
Arrival time between consecutive CBSs. The smaller the separation is between consecutive
CBSs, the smaller CHAN_BOND_WAIT needs to be set to ensure that the Master aligns to the
intended sequence instead of the one after or the one before.
Slave's CBS lagging the master by too much. Essentially, the Slave does not see a CBS when
CHBONDO is asserted.
Master CBS lags the slave by too much. In this case, the slave's CBS sequence has exceeded
CHAN_BOND_LIMIT and has expired.
CBS sequences appear more frequently than CHAN_BOND_LIMIT allows, causing the Slave
to align to a CBS before or after the expected one.
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Figure 4-1 and Figure 4-2, page
"RXCLKCORCNT" and "RXLOSSOFSYNC,"
R
120, and
83