Triple-Speed Ethernet Intel® FPGA IP User Guide

ID 683402
Date 5/30/2022
Document Table of Contents 1000BASE-X Auto-Negotiation

When link synchronization is acquired, the PCS function starts sending a /C/ sequence (configuration sequence) to the link partner device with the advertised register set to 0x00. The sequence is sent for a time specified in the PCS link_timer register mapped in the PCS register space.

When the link_timer time expires, the PCS dev_ability register is advertised, with the ACK bit set to 0 for the link partner. The auto-negotiation state machine checks for three consecutive /C/ sequences received from the link partner.

The auto-negotiation state machine then sets the ACK bit to 1 in the advertised dev_ability register and checks if three consecutive /C/ sequences are received from the link partner with the ACK bit set to 1.

Auto-negotiation waits for the value configured in the link_timer register to ensure no more consecutive /C/sequences are received from the link partner. The auto-negotiation is successfully completed when three consecutive idle sequences are received after the link timer expires.

After auto-negotiation completes successfully, the user software reads both the dev_ability and partner_ability register and proceed to resolve priority for duplex mode and pause mode. If the design contains a MAC and PCS, the user software configures the MAC with a proper resolved pause mode by setting the PAUSE_IGNORE bit in command_config register. To disable pause frame generation based on the receive FIFO buffer level, you should set the rx_section_empty register accordingly.

Figure 29. Auto-Negotiation Activity (Simplified)

Once auto-negotiation completes successfully, the ability advertised by the link partner device is available in the partner_ability register and the AUTO_NEGOTIATION_COMPLETE bit in the status register is set to 1.

The PCS function restarts auto-negotiation when link synchronization is lost and reacquired, or when you set the RESTART_AUTO_NEGOTIATION bit in the PCS control register to 1.

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