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Software Developer’s Manual 191
PHY Functionality and Features
11.3 Cable Length Detection (copper only)
In 100/1000 Mbps operation, the Ethernet controller PHY attempts to indicate the approximate
length of the CAT 5 cable attached. The estimated cable length is reported as one of the following
ranges:
• <= 50 m
• 50 – 80 m
• 80 – 110 m
• 110 – 140 m
• >= 140 m
The estimated cable length can be obtained by reading the PHY Specific Status Register bits 9:7.
11.4 PHY Power Management (copper only)
The Ethernet controller PHY supports power-management based on either link status, MAC
power-state, or both. During link-down states, the PHY utilizes its energy-detection capabilities to
consume the least amount of power while still being capable of resuming link-up automatically. the
Ethernet controller can be configured to automatically reduce PHY power during certain MAC D3
states by re-negotiating a low-speed link (the default behavior, but this can be disabled).
11.4.1 Link Down – Energy Detect (copper only)
When the link is operational and the Ethernet controller PHY detects loss of link, it initiates an
Auto-Negotiation session. Failing to re-establish link via auto-negotiation, the PHY reverts to an
Energy Detect power-down state. Following link loss, the PHY monitors receive energy on the
wire. If the PHY detects energy on the wire, it starts to initiate Auto-Negotiation sending FLPs for
five seconds. If at the end of five seconds the Auto-Negotiation has not completed, then the PHY
stops sending FLPs and returns to monitoring receive energy. While monitoring receive energy, the
PHY sends out a single 10 Mbps NLP (Normal Link Pulse) every one second in an attempt to wake
up a connected device.
The above behavior is considered to be an advanced Energy-Detect (Energy Detect+) mode of
PHY operation. The PHY can also be configured for a regular Energy Detect mode, which behaves
similarly, except does not send out NLPs while monitoring receive energy. In this configuration,
the Ethernet controller PHY can be woken by a connected device, but does not wake up the
connected device itself.
The PHY Specific Control Register bits 9 and 8 described in Section 13.4.7.1.13 are used to
configure the specific Energy-Detect mode of behavior for the PHY.