A condition is detected to cause a component having physical layer
circuitry with a transmitter and a receiver to enter a testing state. The
transmitter transmits a pre-selected data pattern while comparing data
received by the receiver to the pre-selected data pattern during a first
phase of the testing state. The transmitter transmits data received by
the receiver without comparing the data received by the receiver to the
pre-selected data pattern during a second phase of the testing state.