Virtex-5 RocketIO GTP Transceiver User Guide
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
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
w
aits MAX SKE
W
cycles
b
efore
triggering
b
onding, gi
v
ing the sla
v
e time to
recei
v
e the se
qu
ence as
w
ell. The message
to perform channel
b
onding is sent
u
sing
the CHBO
N
DO port.
The CHA
N
_BO
N
D_LE
V
EL setting of the Master
determines ho
w
many cycles later the
b
onding
operation is exec
u
ted. At this time, the Sla
v
e
Elastic B
u
ffer pointers are mo
v
ed so the
o
u
tp
u
t is deske
w
ed.
Master
Recei
v
es CB
Se
qu
ence
Master
Elastic
B
u
ffer
Sla
v
e
Elastic
B
u
ffer
Master
Elastic
B
u
ffer
Sla
v
e
Elastic
B
u
ffer
Master
Elastic
B
u
ffer
Sla
v
e
Elastic
B
u
ffer
UG196_c7_30_092606
Sla
v
e’s
N
e
w
Elastic
B
u
ffer Read Pointer
D1
D2
D3
D4
D5
D6
D7
SEQ1
D1
D2
D3
D4
D5
D6
D7
D0
D4
D5
D6
D7
SEQ1
D8
D9
D10
D4
D5
D6
D7
SEQ1
D8
D9
D3
D5
D6
D7
SEQ1
D8
D9
D10
D11
D5
D6
D7
SEQ1
D9
D10
D11
D4
Содержание Virtex-5 RocketIO GTP
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Страница 312: ...312 www xilinx com Virtex 5 RocketIO GTP Transceiver User Guide UG196 v1 3 May 25 2007 Appendix E Low Latency Design R...