Data Sheet

Interconnects—Ethernet Controller I210

• Software asks the MAC to attempt to auto-detect the PHY speed from the PHY-to-MAC RX_CLK,

then programs the MAC speed accordingly

• MAC automatically detects and sets the link speed of the MAC based on PHY indications by using

the PHY's internal PHY-to-MAC speed indication (SPD_IND)

Aspects of these methods are discussed in the sections that follow.

3.7.4.4.2.1 Forcing MAC Speed

There might be circumstances when the software device driver must forcibly set the link speed of the

MAC. This can occur when the link is manually configured. To force the MAC speed, the software device

driver must set the CTRL.FRCSPD (force-speed) bit to 1b and then write the speed bits in the Device

Control register (CTRL.SPEED) to the desired speed setting. Refer to Section 8.2.1 for details.

Note: Forcing the MAC speed using CTRL.FRCSPD overrides all other mechanisms for configuring

the MAC speed and can yield non-functional links if the MAC and PHY are not operating at the

same speed/configuration.

When forcing the I210 to a specific speed configuration, the software device driver must also ensure

the PHY is configured to a speed setting consistent with MAC speed settings. This implies that software

must access the PHY registers to either force the PHY speed or to read the PHY status register bits that

indicate link speed of the PHY.

Note: Forcing speed settings by CTRL.SPEED can also be accomplished by setting the

CTRL_EXT.SPD_BYPS bit. This bit bypasses the MAC's internal clock switching logic and

enables the software device driver complete control of when the speed setting takes place.

The CTRL.FRCSPD bit uses the MAC's internal clock switching logic, which does delay the

effect of the speed change.

3.7.4.4.2.2 Using Internal PHY Direct Link-Speed Indication

The I210’s internal PHY provides a direct internal indication of its speed to the MAC (SPD_IND). When

using the internal PHY, the most direct method for determining the PHY link speed and either manually

or automatically configuring the MAC speed is based on these direct speed indications.

For MAC speed to be set/determined from these direct internal indications from the PHY, the MAC must

be configured such that CTRL.ASDE and CTRL.FRCSPD are both 0b (both auto-speed detection and

forced-speed override disabled). After configuring the Device Control register, MAC speed is re-

configured automatically each time the PHY indicates a new link-up event to the MAC.

When MAC speed is neither forced nor auto-sensed by the MAC, the current MAC speed setting and the

speed indicated by the PHY is reflected in the Device Status register bits STATUS.SPEED.

3.7.4.4.3 MAC Full-/Half- Duplex Resolution

The duplex configuration of the link is also resolved by the PHY during the auto-negotiation process.

The I210’s internal PHY provides an internal indication to the MAC of the resolved duplex configuration

using an internal full-duplex indication (FDX).

When using the internal PHY, this internal duplex indication is normally sampled by the MAC each time

the PHY indicates the establishment of a good link (LINK indication). The PHY's indicated duplex

configuration is applied in the MAC and reflected in the MAC Device Status register (STATUS.FD).

Software can override the duplex setting of the MAC 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 and the PHY's internal

duplex indication is applied.