82575 Ethernet Controller Design Guide

3.6.2Smartspeed

SmartSpeed is an enhancement to auto-negotiation that allows the PHY to react to network conditions that are preventing a 1000BASE-T link, such as cable problems. These problems may allow auto-negotiation to complete, but then inhibit completion of the training phase. Normally, if a 1000BASE-T link fails, the PHY returns to the auto- negotiation state with the same speed settings indefinitely.

With SmartSpeed enabled, after a configurable number (1-5, Register 27.8:6) of failed attempts, the PHY automatically downgrades the highest ability it advertises to the next lower speed: from 1000 to 100 to 10. Once a link is established, and if it is later broken, the PHY automatically upgrades the capabilities advertised to the original setting. This allows the PHY to automatically recover once the problem is corrected.

3.6.2.1Using SmartSpeed

SmartSpeed is enabled by setting PHYREG.16.7 = 1. When SmartSpeed downgrades the PHY advertised capabilities, it sets Bit PHYREG.19.5. When link is established, its speed is indicated in PHYREG.17.15:14. SmartSpeed automatically resets the highest- level auto-negotiation abilities advertised, if the link is established and then lost for more than two seconds.

Number of failed attempts allowed is configured by Register 27.8:6.

Note: When SmartSpeed is enabled, the M/S (Master-Slave) resolution is not given seven attempts to try to resolve M/S status (see IEEE 802.3 clause 40.5.2), this is because SmartSpeed will downgrade the link after five attempts.

Note: The time to link with Smart Speed in most cases is approximately 2.5 seconds, in other cases it could take more than 2.5 seconds, depending on configuration and other factors.

3.6.3Flow Control

Flow control allows congested nodes to pause traffic. Flow control is essentially a MAC- to-MAC function. MACs indicate their ability to implement flow control during auto- negotiation. This ability is communicated through two bits in the auto-negotiation registers (PHYREG.4.10 and PHYREG.4.11).

Prior to auto-negotiation, the MAC indicates its flow control capabilities via PHYREG.4.10 (Pause) and PHYREG.4.10 (ASM_DIR). After auto-negotiation, the link partner's flow control capabilities are indicated in PHYREG.5.10 and PHYREG.5.11.

There are two forms of flow control that can be established via auto-negotiation: symmetric and asymmetric. Symmetric flow control is for point-to-point links; asymmetric for hub-to-end-node connections. Symmetric flow control allows either node to flow-control the other. Asymmetric flow-control allows a repeater or switch to flow-control a DTE, but not vice versa.

It is the responsibility of the MAC to implement the correct function. The PHY merely allows the two MACs to communicate their abilities to each other.

3.6.4Low-Power Link Up

Normally, PHY speed negotiation tries to establish a link at the highest possible speed. The PHY supports an additional mode of operation, where the PHY drives to establish a link at a low speed. The link-up process allows a link to come up at the lowest possible speed in cases where power is valued over performance. Different behavior is defined for the D0 state and the other non-D0 states.

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Intel 317698-001 manual Smartspeed, Flow Control, Low-Power Link Up, Using SmartSpeed
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317698-001 specifications

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