3.4.1 Loopback Modes

Loopback operations are embedded within the XCVR and are commonly used in debug practice. These loop backs can be tested solely within the device by sending and receiving on-chip or can test real-data to and from the system side. For information, see Loopback.

For example, by placing the transceiver into EQ Far-End loopback, a system can drive data into the Rx and send it back directly onto the Tx. In this case, the system is passing the serial data stream within the input and output buffers. Change the Signal Integrity panel settings to find the optimal setting to match the system.

In the Loopback Modes tab, select the targeted lane to test under Transceiver Hierarchy, select EQ-FAR END and then click Apply to monitor the system performance from the far-end. Adjust the signal integrity setting to optimize the Rx and Tx performance of the transceiver. The following figure shows the loopback modes of the Debug TRANSCEIVER.

Note: The Apply button is enabled when you make a selection for any parameter.
Figure 3-5. Loopback Modes—Far-end Example

Similarly, the user can also continue to test a deeper path into the XCVR path using CDR Far-end loopback. In this manner, the same system data stream would pass from the input buffer through the Rx PMA and the parallel data stream would be routed back through a pathway to the Tx PMA to the output buffer.