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Software Developer’s Manual 187
PHY Functionality and Features
PHY Functionality and Features 11
11.1 Auto-Negotiation
Auto-Negotiation between the PCI/PCI-X Family of Gigabit Ethernet Controllers and its link
partner is performed by the PHY. Under normal, expected operating conditions, the MAC
automatically establishes common speed and duplex settings via the PHY. This section details PHY
configuration features involved in the auto-negotiation process.
11.1.1 Overview
Auto-Negotiation by the PHY is initiated upon any of the following conditions:
• Power-up reset (copper and fiber)
• PHY detects loss of link (copper and fiber)
• PHY detects re-appearance of energy on the link (copper and fiber)
• MAC control of PHY power-management is enabled (CTRL.EN_PHY_PWR_MGMT = 1b
and MAC transitions to low power state (D3) where continued PHY operation required for
wakeup/manageability (copper and fiber)
• PHY hardware reset asserted using the MAC CTRL.PHY_RST bit (copper only)
• PHY soft-reset initiated via the PHY Control Register (bit 15, copper only)
• Explicit Auto-Negotiation Re-Start initiated via the PHY Control Register (bit 9, copper only)
• Explicit transition of PHY from internal IEEE power-down to normal mode via the PHY
Control Register (bit 11, copper only)
• Explicit transition of PHY from internal IEEE power-down to normal mode via the PHY
Control Register by setting CTRL.LRST = 1 and TXCW.ANE = 1 (fiber only)
Hardware defaults for the PHY configurations enable the PHY to advertise its full 1000BASE-T
and 1000BASE-X capability, and to auto-negotiate to the best possible operation
1
without any
software intervention required. If the remote device does not have Auto-Negotiation capability, the
Ethernet controller PHY uses the parallel detect function to determine the speed of the remote
device for 100BASE-TX and 10BASE-T modes. Under certain circumstances, it might be
desirable to configure auto-negotiation options to restrict certain behavior. For example, operate in
half-duplex mode only.
2
Note: Any PHY auto-negotiation options configured by software are only persistent while the LAN
power (indicated by LAN_PWR_GOOD) remains available. Following a complete loss of power,
the PHY reverts to auto-negotiation using its hardware-defaults.
1. 1000 half-duplex not supported.
2. TXCW and RXCW registers are used for fiber auto-negotiation advertising. For fiber, the MAC can be forced to 1000 full-duplex when
connected to a non-auto-negotiating fiber switch.