Chapter 3
Configuring Driver Parameters
33
Gigabit Link Clock Mastership Controls
The concept of link clock mastership was introduced with gigabit twisted-pair
technology. One side of the link is the master that provides the link clock and the
other is the slave that uses the link clock. Once this relationship is established, the
link is up, and data can be communicated. Two physical layer parameters control
whether your side is the master or the slave or whether mastership is negotiated
with the link partner.
Caution –
Do not adjust the link clock mastership parameters unless you clearly
understand the settings of the link partner. Incorrect link clock mastership
configuration results in link up failure.
Interpacket Gap Parameters
The
ce
device supports a programmable mode called
enable_ipg0
.
When an instance receives a packet with
enable_ipg0
set (the default), it adds an
additional time delay before transmitting the packet. This delay, set by the
ipg0
parameter, is in addition to the delay set by the
ipg1
and
ipg2
parameters. The
additional
ipg0
delay helps to reduce collisions.
If
enable_ipg0
is disabled, the value of
ipg0
is ignored and no additional delay is
set. Only the delays set by
ipg1
and
ipg2
will be used. Disable
enable_ipg0
if
other systems keep sending a large number of back-to-back packets. Systems that
have
enable_ipg0
set might not have enough time on the network.
TABLE 3-4
Forced Mode Parameter
Parameter
Description
master-cfg-enable
Determines whether or not during the auto-negotiation process
the link clock mastership is setup automatically.
master-cfg-value
• If the
master-cfg-enable
parameter is set then the
mastership is not set up automatically but depends on the value
of
master-cfg-value
. If the
master-cfg-value
is set then
the physical layer expects the local device to be the link master. If
it is not set then it expects the link partner to be the master.
• If Auto-negotiation is not enabled, then the value of
master-
cfg-enable
is ignored and the value of
master-cfg-value
is
key to the link clock mastership. If the
master-cfg-value
is
set, then the physical layer expects the local device to be the link
master. If the value is not set then it expects the link partner to
the master.
