Data Sheet
Interconnects—Ethernet Controller I210
105
Note: The Flow Control Refresh Threshold mechanism does not work in the case of software-
initiated flow control. Therefore, it is the software’s responsibility to re-generate PAUSE
frames before expiration of the pause counter at the other partner's end.
The state of the CTRL.TFCE bit or the negotiated flow control configuration does not affect software
generated PAUSE frame transmission.
Note: Software sends an XON frame by programming a 0b in the PAUSE timer field of the FCTTV
register. Software generating an XON packet is not allowed while the hardware flow control
mechanism is active, as both use the FCTTV registers for different purposes.
XOFF transmission is not supported in 802.3x for half-duplex links. Software should not
initiate an XOFF or XON transmission if the I210 is configured for half-duplex operation.
When flow control is disabled, pause packets (XON, XOFF, and other FC) are not detected as
flow control packets and can be counted in a variety of counters (such as multicast).
3.7.5.4 IPG Control and Pacing
The I210 supports the following modes of controlling IPG duration:
• Fixed IPG - the IPG is extended by a fixed duration
3.7.5.4.1 Fixed IPG Extension
The I210 allows controlling of the IPG duration. The IPGT configuration field enables an extension of
IPG in 4-byte increments. One possible use of this capability is to enable inserting bytes into the
transmit packet after it has been transmitted by the I210 without violating the minimum IPG
requirements. For example, a security device connected in series to the I210 might add security
headers to transmit packets before the packets are transmitted on the network.
3.7.6 Loopback Support
3.7.6.1 General
The I210 supports the following types of internal loopback in the LAN interface:
• MAC Loopback (Point 1)
• PHY Loopback (Point 2)
• SerDes, SGMII or 1000BASE-KX Loopback (Point 3)
• External PHY Loopback (Point 4)
By setting the device to loopback mode, packets that are transmitted towards the line are looped back
to the host. The I210 is fully functional in these modes, just not transmitting data over the lines.
Figure 3-12 shows the points of loopback.