Auto-Negotiation Description - 3.3 English

40G/50G High Speed Ethernet Subsystem v3.3 Product Guide (PG211)
Document ID
PG211
Release Date
2023-11-01
Version
3.3 English
autoneg_enable
When the autoneg_enable input signal is set to a 1, auto-negotiation begins automatically at power-up, or if the carrier signal is lost, or if the input restart_negotiation signal is cycled from a 0 to a 1. All of the 'ability' input signals and the two input signals PAUSE and ASM_DIR are tied Low or High to indicate the capability of the hardware. The nonce_seed[7:0] input must be set to a unique value for every instance of the auto-negotiator. The AN IP does not function if the nonce_seed is set to 0. This is important to guarantee that no deadlocks occur at power-up. If two link partners connected together attempt to auto-negotiate with their nonce_seed[7:0] inputs set to the same value, the auto-negotiation fails continuously. The pseudo_sel input is an arbitrary selection that is used to select the polynomial of the random bit generator in bit position 49 of the DME pages used during auto-negotiation. Any selection on this input is valid and does not result in any adverse behavior.
Link Control
When auto-negotiation has begun, the various 'link control' signals are activated, depending on the disposition of the corresponding 'Ability' inputs for those links. Subsequently, the corresponding 'link status' signals are monitored by the AN IP hardware for an indication of the state of the various links that can be connected. If particular links are unused, the corresponding link control outputs are unconnected, and the corresponding link-status inputs should be tied Low. During this time, the AN IP hardware sets up a communication link with the link partner and uses this link to negotiate the capabilities of the connection.
Autoneg Complete
When Auto-Negotiation is complete, the autoneg_complete output signal is asserted. In addition to this, the output signal an_fec_enable is asserted if the Forward Error Correction hardware is to be used; the output signal tx_pause_en is asserted if the transmitter hardware is allowed to generate PAUSE control packets, the output signal rx_pause_en is asserted if the receiver hardware is allowed to detect PAUSE control packets, and the output link control of the selected link is set to its mission mode value (bin)11.
Important: The autoneg complete signal is not asserted until rx_status is received from the PCS. That means that, where link training is included, the autoneg_complete output signal is not asserted until after link training has completed and rx_status is High.