autoneg_enable
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 to 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.