F-tile Architecture and PMA and FEC Direct PHY IP User Guide

ID 683872
Date 12/15/2021
Public

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2.3.1.3. FHT PMA Loopback Modes

Loopback modes are design-for-test features that verify different blocks of the PMA. FHT PMAs have loopback modes to debug different blocks of the PMA.

Note: PMA-receiver-to-transmitter reverse serial loopback is not supported.
Figure 42. FHT Loopback Modes
  • A PMA-transmitter-to-receiver internal serial loopback
  • B PMA-transmitter-to-receiver digital parallel loopback
  • C PMA-receiver-to-transmitter reverse parallel loopback

PMA-Transmitter-to-Receiver Internal Serial Loopback

The internal serial loopback path sets the CDR to recover data from the serializer instead of the receiver serial input pin. The transmitter buffer sends data normally, but internal serial loopback takes the data before the buffer. It is implemented completely on the PMA and does not require any connector on the serial path.

The FHT lane also supports external connectivity to connect the transmitter differential outputs to the receiver differential inputs.

  • Mission mode is an external connection where the data source is something other than the FHT transmitter.
  • External connectivity supports, for example, a bit-error rate tester (BERT) or another device's transmitter providing data to the FHT receiver.

PMA-Transmitter-to-Receiver Digital Parallel Loopback

In a digital parallel loopback path, the parallel data stream of the transmitter is looped back as the parallel data input stream for the receiver.

PMA-Receiver-to-Transmitter Reverse Parallel Loopback

The reverse parallel loopback path sets the transmitter buffer to transmit data fed directly from the CDR recovered data. From an external instrument, data is fed to the receiver buffer, and the deserialized parallel data stream of the receiver is looped back as the parallel data input stream for the transmitter.

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