CPRI Intel® FPGA IP User Guide

ID 683595
Date 4/04/2022
Public

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Document Table of Contents

5.18. LOOPBACK Register

Table 72.  LOOPBACK Register at Offset 0x44
Bits Field Name Type Value on Reset Description
31:11 Reserved UR0 21'b0
10:8 loop_reversed RW 3'b0 Testing reverse loopback mode. If you turn on Enable parallel reversed loopback paths in the CPRI parameter editor, this register field specifies the parts of the CPRI frame that are sent on the reverse loopback path. If you do not turn on this parameter, you should leave this register field at its default value of 3'b0.

For standard testing, you would turn on these loopback modes in a CPRI RE slave only.

This field has the following valid values:

  • 3'b000: No loopback.
  • 3'b001: Full CPRI frame loopback. Incoming CPR data and control words are sent back as-is in outgoing CPR communication.
  • 3'b010: I/Q data loopback. Incoming CPRI data are sent back in outgoing CPRI communication; control words are generated locally.
  • 3'b011: Fast control and management loopback. Incoming CPRI fast control and management (Ethernet) control and data words are sent back in outgoing CPRI communication; remaining data and control words are generated locally.
  • 3'b100: Fast control and management and VS loopback. Incoming CPRI fast control and management (Ethernet) and vendor-specific control words are sent back in outgoing CPRI communication; data and remaining control words are generated locally.
7:2 Reserved UR0 6'b0
1:0 loop_forward RW 2'b0 Testing forward loopback mode. If you turn on Enable transceiver PMA serial forward loopback path or Enable parallel forward loopback paths in the CPRI parameter editor, this register field specifies the loopback path that is currently active. If you do not turn on either of these parameters, you should leave this register field at its default value of 2'b0.

This field has the following valid values:

  • 2'b00: No loopback.
  • 2'b01: Transceiver PMA loopback path is active. This path does not exercise the transceiver PCS. This option is available only if you turn on Enable transceiver PMA serial forward loopback path .
  • 2'b10: Active loopback path includes extended delay measurement logic but does not exercise the transceiver. This option is available only if you turn on Enable parallel forward loopback paths.
  • 2'b11: Active loopback path includes framing and deframing logic, but does not exercise the extended delay measurement logic and does not exercise the transceiver. This option is available only if you turn on Enable parallel forward loopback paths.