Intel PCI User Manual

165

STATUS.ASDV [9:8], provides the results of speed status indication for diagnostics purposes 
regardless of whether the Auto-Speed Detection feature is enabled. This function is initiated with a 

write to the CTRL_EXT.ASDCHK bit. See 

 for details.

With the CTRL register configure as CTRL.FRCSPD = 0, the speed is reconfigured automatically 

each time a new linkup event is detected. This configuration is recommended why the PHY is 
configured for Auto-Negotiation.

The duplex configuration of the link is also resolved during the Auto-Negotiation process. As 
previously mentioned, the Ethernet controller supports both full- and half-duplex operation in 

internal PHY mode. When the PHY asserts its link signal to the MAC, it also communicates the 

duplex setting.

Software can override the duplex setting via the CTRL.FD bit when the CTRL.FRCDPLX (force 
duplex) bit is set. If CTRL.FRCDPLX is 0b, the CTRL.FD bit is ignored.

The software driver is required under some circumstances to read from, or write to, the MII 
management registers in the PHY. These accesses are performed via the MDIC registers. The MII 

registers allow the software driver to have direct control over the PHY’s operation, which includes:

•

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

•

Extended capabilities

The standard set of PHY management registers can be found in the IEEE P802.3ab standard.

Forcing link in GMII/MII mode requires the software driver to configure both the MAC and the 

PHY in a consistent manner with respect to each other as well as the link partner. After 
initialization, the software driver configures the desired modes in the MAC, then accesses the PHY 

MII registers to set the PHY to the same configuration.

In internal PHY mode, setting the CTRL.SLU bit forces a link up condition in the MAC. The 

duplex setting at this point should be forced by software on the CTRL.FD bit.