Data Sheet

Ethernet Controller I210 —Interconnects
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3.7.4.4.4 Using PHY Registers
The software device driver might be required under some circumstances to read from, or write to, the
MII management registers in the PHY. These accesses are performed via the MDIC register (refer to
Section 8.2.4). The MII registers enable the software device driver to have direct control over the PHY's
operation, which can include:
• Resetting the PHY
• Setting preferred link configuration for advertisement during the auto-negotiation process
• Restarting the auto-negotiation process
• Reading auto-negotiation status from the PHY
• Forcing the PHY to a specific link configuration
The set of PHY management registers required for all PHY devices can be found in the IEEE P802.3ab
standard.
3.7.4.4.5 Comments Regarding Forcing Link
Forcing link in GMII/MII mode (internal PHY) requires the software device driver to configure both the
MAC and PHY in a consistent manner with respect to each other as well as the link partner. After
initialization, the software device driver configures the desired modes in the MAC, then accesses the
PHY registers to set the PHY to the same configuration.
Before enabling the link, the speed and duplex settings of the MAC can be forced by software using the
CTRL.FRCSPD, CTRL.FRCDPX, CTRL.SPEED, and CTRL.FD bits. After the PHY and MAC have both been
configured, the software device driver should write a 1b to the CTRL.SLU bit.
3.7.4.5 Loss of Signal/Link Status Indication
For all modes of operation, a LOS/LINK signal provides an indication of physical link status to the MAC.
When the MAC is configured for optical SerDes mode, the input reflects loss-of-signal connection from
the optics. In backplane mode, where there is no LOS external indication, an internal indication from
the SerDes receiver can be used. In SFP systems the LOS indication from the SFP can be used. In
internal PHY mode, this signal from the PHY indicates whether the link is up or down; typically indicated
after successful auto-negotiation. Assuming that the MAC has been configured with CTRL.SLU=1b, the
MAC status bit STATUS.LU, when read, generally reflects whether the PHY or SerDes has link (except
under forced-link setup where even the PHY link indication might have been forced).
When the link indication from the PHY is de-asserted or the loss-of-signal asserted from the SerDes, the
MAC considers this to be a transition to a link-down situation (such as cable unplugged, loss of link
partner, etc.). If the Link Status Change (LSC) interrupt is enabled, the MAC generates an interrupt to
be serviced by the software device driver.
3.7.5 Ethernet Flow Control (FC)
The I210 supports flow control as defined in 802.3x as well as the specific operation of asymmetrical
flow control defined by 802.3z.
Flow control is implemented as a means of reducing the possibility of receive packet buffer overflows,
which result in the dropping of received packets, and allows for local controlling of network congestion
levels. This can be accomplished by sending an indication to a transmitting station of a nearly full
receive buffer condition at a receiving station.