Patent ID: 8761031

Claim:
An apparatus comprising: an input port and an output port to connect to a device via an in-band interconnect comprising one or more point-to-point differential links, wherein each link of the one or more point-to-point differential links includes a plurality of lanes; a receiver to receive a first signal from the in-band interconnect through the input port; a transmitter to send a second signal onto the in-band interconnect through the output port; and a control circuitry to: detect a loopback request from the first signal; enter a loopback mode upon detecting the loopback request, wherein some but not all lanes of the plurality of lanes in the link enter the loopback state based on the loopback request; transmit at least a portion of the first signal through the transmitter back to the device over the in-band interconnect; detect an indicator to end the loopback mode from a signal received from the device by the receiver after entering the loopback mode; and exit the loopback mode based at least in part on detecting the indicator to end the loopback mode; and adjust output voltage level and timing for the transmitter based at least in part on information in the loopback request, wherein the control circuitry to adjust output voltage level and timing until a miscompare is generated indicating a boundary of the voltage level and timing.