Xilinx Virtex-5 RocketIO GTP User Manual

Virtex-5 RocketIO GTP Transceiver User Guide www.xilinx.com 181
UG196 (v1.3) May 25, 2007
Configurable Channel Bonding (Lane Deskew)
R
Setting the Maximum Skew
When the master receives a channel bonding sequence, it does not trigger channel bonding
immediately. Several more bytes must arrive in case the slaves have more latency. This
wait time effectively becomes the maximum skew the buffer can handle. If the skew is
greater than this wait time, the slaves might not receive the sequence by the time the
master triggers channel bonding (see Figure 7-33).
Figure 7-33 shows two FIFOs, one for the master and one for the slave. If the slave is
behind the master, the master must wait several cycles before triggering channel bonding,
otherwise the slow slave will not have the channel bonding sequence in its buffer.
CHAN_BOND_1_MAX_SKEW and CHAN_BOND_2_MAX_SKEW are used to set the
maximum skew allowed for channel bonding sequences 1 and 2, respectively. The
maximum skew range is 1 to 14. The channel bond skew must be set no higher than the
minimum distance allowed between channel bonding sequences in the datastream. This
minimum distance is determined by the protocol being used.
Precedence between Channel Bonding and Clock Correction
The clock correction (see “Configurable Clock Correction,” page 168) and channel bonding
circuits both perform operations on the pointers of the RX elastic buffer. Normally, the two
circuits work together without conflict, except when clock correction events and channel
bonding events occur simultaneously. In this case, one of the two circuits must take
precedence. To make clock correction a higher priority than channel bonding,
CLK_COR_PRECEDENCE must be set to TRUE. To make channel bonding a higher
priority, CLK_COR_PRECEDENCE must be set to FALSE.
Figure 7-33: Channel Bonding Example (MAX_SKEW = 2 and Master CHAN_BOND_LEVEL = 1)
The Master waits MAX SKEW cycles before
triggering bonding, giving the slave time to
receive the sequence as well. The message
to perform channel bonding is sent using
the CHBONDO port.
The CHAN_BOND_LEVEL setting of the Master
determines how many cycles later the bonding
operation is executed. At this time, the Slave
Elastic Buffer pointers are moved so the
output is deskewed.
Master
Receives CB
Sequence
Master
Elastic
Buffer
Slave
Elastic
Buffer
Master
Elastic
Buffer
Slave
Elastic
Buffer
Master
Elastic
Buffer
Slave
Elastic
Buffer
UG196_c7_30_092606
Slave’s New Elastic
Buffer Read Pointer
D1D2D3D4D5D6D7SEQ1
D1D2D3D4D5D6D7 D0
D4D5D6D7SEQ1D8D9D10
D4D5D6D7SEQ1D8D9 D3
D5D6D7SEQ1D8D9D10D11
D5D6D7SEQ1D9D10D11 D4

Xilinx Virtex-5 RocketIO GTP Specifications

General

Brand	Xilinx
Model	Virtex-5 RocketIO GTP
Category	Transceiver
Language	English