Flow Control Parameters; Interpacket Gap Parameters; Table 4-3 Read-Write Flow Control Parameters Values And Descriptions; Table 4-4 Read-Write Interpacket Gap Parameter Values And Descriptions - Sun Microsystems GigabitEthernet FC-AL/P Combination Adapter Installation Manual

Flow Control Parameters

The GEM ASIC is capable of sourcing (transmitting) and terminating (receiving)
pause frames conforming to the IEEE 802.3x Frame Based Link Level Flow Control
Protocol. In response to received flow control frames, the GEM can slow down its
transmit rate. On the other hand, GEM is capable of sourcing flow control frames,
requesting the link partner to slow down, provided that the link partner supports
this feature. By default, the driver advertises Receive PAUSE capability, during
autonegotiation.
TABLE 4-3
Parameter
adv_pauseTX
adv_pauseRX
For normal operations, the driver doesn't need to source flow control frames.
However, if the adapter is operating on a slow bus (for instance, a 33-MHz PCI bus
slot), and there is a lot of frame reception activity, there could be a performance
degradation due to Receive FIFO overflow. If the link partner is capable of
terminating PAUSE flow control frames, the performance of the adapter could be
improved by enabling adv_pauseTX and restarting autonegotiation.

Interpacket Gap Parameters

The GEM ASIC supports the programmable Interpacket Gap (IPG) parameters ipg1
and ipg2. The total IPG is the sum of ipg1 and ipg2. The total IPG is 0.096
microseconds for the link speed of 1000 Mbps.
TABLE 4-4
TABLE 4-4
Parameter
ipg1
ipg2
By default, the driver sets ipg1 to 8-byte time and ipg2 to 4-byte time, which are
the standard values. (Byte time is the time it takes to transmit one byte on the link,
with a link speed of 1000 Mbps.)
30 Sun GigabitEthernet FC-AL/P Combination Adapter Installation Guide • March 2000
Read-Write Flow Control Parameters Values and Descriptions
Values Description
(on/off)
0, 1 Transmit PAUSE Capable (default: not capable)
0, 1 Receive Pause Capable (default: capable)
lists the default values and allowable values for the IPG parameters.
Read-Write Interpacket Gap Parameter Values and Descriptions
Values
(Byte-time)
0, 255
0, 255
Description
ipg1 = 8 (default at initialization)
ipg2 = 4 (default at initialization)