Intel Gigabit Ethernet Controllers ユーザーズマニュアル
Software Developer’s Manual
187
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:
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
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).
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
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
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
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,
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
configure the specific Energy-Detect mode of behavior for the PHY.