Stratix V Device Handbook: Volume 2: Transceivers

ID 683779
Date 11/23/2021
Document Table of Contents

5.2. PIPE Reverse Parallel Loopback

For debugging, the PIPE Reverse Parallel Loopback option uses parallel data through the rate match FIFO, transmitter serializer, and the tx_serial_data port path.

PIPE reverse parallel loopback is only available in the PCIe® configuration for Gen1 and Gen2 data rates. The following figure shows the received serial data passing through the receiver CDR, deserializer, word aligner, and rate match FIFO buffer. The parallel data from the rate match FIFO is then looped back to the transmitter serializer and transmitted out through the tx_serial_data port. The received data is also available to the FPGA fabric through the rx_parallel_data signal.

PIPE reverse parallel loopback is compliant with the PCIe 2.0 specification. To enable this loopback configuration, assert the tx_detectrxloopback signal.

Note: PIPE reverse parallel loopback is the only loopback option supported in the PCIe configuration. PIPE reverse parallel loopback is not supported in the GT channels of Stratix V GT devices.
Note: For more information, refer to the "PCI Express Reverse Parallel Loopback" section in the Transceiver Configurations in Stratix V Devices chapter.
Figure 161. PIPE Reverse Parallel Loopback Configuration Datapath