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UG155 March 24, 2008
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Appendix F

Debugging Guide
This appendix provides assistance for debugging the core within a system. For additional
help, contact Xilinx by submitting a WebCase at support.xilinx.com/.

General Checks

Ensure that all the timing constraints for the core were met d uring Place and Route.
Does it wor k in timing s imulation? If problems a re seen in hard ware but not i n timing
simulation, this could indicate a PCB issue.
Ensure that all clock sources are clean. If using DCMs in the design, ensure that all
DCMs have obtained lock by monitoring the LOCKED port.

Problems with the MDIO

Ensure that the MDIO is driven properly. See “MDIO Management Interface,” page
115 for detailed information about performing MDIO transactions.
Check that the mdc clock is running and that the frequency is 2.5 MHz or less.
Read from a configuration register that does not have all 0s as a default. If all 0s are
read back, the read was unsuccessful. Check that the PHYAD field placed into the
MDIO frame matches the value placed on the phyad[4:0] port of the core.

Problems with Data Reception or Transmission

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.
“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. 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 “Startup Sequencing,”
page 197 for more information.