When no data is being received or transmitted on a channel:
• Ensure that a valid link has been established between the core and its link partner, either by Auto-Negotiation or Manual Configuration; status_vector_chx[0] and status_vector_chx[1] should both be High. If no link has been established, see the topics discussed in the next section.
° Problems with Auto-Negotiation
° Problems in Obtaining a Link (Auto-Negotiation Disabled)
Note: Transmission through the core is not allowed unless a link has been established. This behavior can be overridden by setting the Unidirectional Enable bit.
• Ensure that the Isolate state has been disabled.
By default, the Isolate state is enabled after power-up. In the PHY mode, the PHY is electrically isolated from the GMII; for an internal GMII, it behaves as if it is isolated. This results in no data transfer across the GMII.