When no data is being received or transmitted:
- Ensure that a valid link has been established between the core and its link partner, either by auto-negotiation or manual configuration: status_vector[0] and status_vector[1] should both be High. If no link has been established, see the topics discussed in the next section.
- 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. For an external GMII, the PHY will be electrically isolated from the GMII; for an internal GMII, it will behave as if it is isolated. This results in no data transfer across the GMII. See Start-up Sequencing for more information.
If data is being transmitted and received between the core and its link partner, but with a high rate of packet loss, see Special Design Considerations.