Data Sheet

Ethernet Controller I210 —Interconnects
98
3.7.4.3.2 Forcing Link in SGMII Mode
In SGMII, forcing of the link cannot be done at the PCS level, only in the external PHY. The forced
speed and duplex settings are reflected by the SGMII auto-negotiation process; the MAC settings are
automatically done according to this functionality.
3.7.4.3.3 MAC Speed Resolution
The MAC speed and duplex settings are always set according to the SGMII auto-negotiation process.
3.7.4.4 Copper PHY Link Configuration
When operating with the internal PHY, link configuration is generally determined by PHY auto-
negotiation. The software device driver must intervene in cases where a successful link is not
negotiated or the designer desires to manually configure the link. The following sections discuss the
methods of link configuration for copper PHY operation.
3.7.4.4.1 PHY Auto-Negotiation (Speed, Duplex, Flow Control)
When using a copper PHY, the PHY performs the auto-negotiation function. The actual operational
details of this operation are described in the IEEE P802.3ab draft standard and are not included here.
Auto-negotiation provides a method for two link partners to exchange information in a systematic
manner in order to establish a link configuration providing the highest common level of functionality
supported by both partners. Once configured, the link partners exchange configuration information to
resolve link settings such as:
• Speed: - 10/100/1000 Mb/s
• Duplex: - Full or half
• Flow control operation
PHY specific information required for establishing the link is also exchanged.
Note: If flow control is enabled in the I210, the settings for the desired flow control behavior must
be set by software in the PHY registers and auto-negotiation restarted. After auto-negotiation
completes, the software device driver must read the PHY registers to determine the resolved
flow control behavior of the link and reflect these in the MAC register settings (CTRL.TFCE
and CTRL.RFCE).
Once PHY auto-negotiation completes, the PHY asserts a link indication (LINK) to the MAC.
Software must have set the Set Link Up bit in the Device Control register (CTRL.SLU) before
the MAC recognizes the LINK indication from the PHY and can consider the link to be up.
3.7.4.4.2 MAC Speed Resolution
For proper link operation, both the MAC and PHY must be configured for the same speed of link
operation. The speed of the link can be determined and set by several methods with the I210. These
include:
• Software-forced configuration of the MAC speed setting based on PHY indications, which might be
determined as follows:
— Software reads of PHY registers directly to determine the PHY's auto-negotiated speed
— Software reads the PHY's internal PHY-to-MAC speed indication (SPD_IND) using the MAC
STATUS.SPEED register