Functional Description - 2.6 English

1G/10G/25G Switching Ethernet Subsystem Product Guide (PG292)

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2.6 English


When the autoneg_enable input signal is set to 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 as well as 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 non-zero value for every instance of the auto-negotiator. This is important to guarantee that no dead-locks 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 used in bit position 49 of the DME pages used during auto-negotiation. Any selection on this input is valid and does not result in adverse behavior.

Link Control

When auto-negotiation begins, 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 ANIPC hardware for an indication of the state of the various links that are 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 ANIPC hardware sets up a communication link with the link partner and uses this link to negotiate the capabilities of the connection.

Auto-Negotiation Complete

When Auto-Negotiation is complete, the autoneg_complete output signal is asserted. In addition, 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.