124 www.xilinx.com Virtex-6 FPGA GTX Transceivers User GuideUG366 (v2.5) January 17, 2011Chapter 2: Shared Transceiver Featuresand then compared to check for errors. Figure 2-10 illustrates a loopback test configurationwith four different loopback modes.Loopback test modes fall into two broad categories:• Near-end loopback modes loop transmit data back in the transceiver closest to thetraffic generator.• Far-end loopback modes loop received data back in the transceiver at the far end ofthe link.Loopback testing can be used either during development or in deployed equipment forfault isolation. The traffic patterns used can be either application traffic patterns orspecialized pseudo-random bit sequences. Each GTX transceiver has a built-in PRBSgenerator and checker.Each GTX transceiver features several loopback modes to facilitate testing:• Near-End PCS Loopback (path 1 in Figure 2-10)• Near-End PMA Loopback (path 2 in Figure 2-10)• Far-End PMA Loopback (path 3 in Figure 2-10)• Far-End PCS Loopback (path 4 in Figure 2-10)Ports and AttributesTable 2-16 defines the loopback ports.X-Ref Target - Figure 2-10Figure 2-10: Loopback Testing OverviewRX-PMARX-PCSTX-PMATX-PCSRX-PMA RX-PCSTX-PMA TX-PCSNear-End GTXLink Near-End Test Structures Link Far-End Test StructuresTest LogicUG366_c2_07_081109Far-End GTXTrafficCheckerTrafficGenerator1 432www.BDTIC.com/XILINX
