F-Tile Ethernet Intel® FPGA Hard IP User Guide

ID 683023
Date 4/03/2023

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4.4.4. RX Virtual Lane Offset Calculation for No FEC Variants

  1. Lock the RX PCS.

    The RX PCS must be fully aligned before extracting VL Offset data. Wait for o_rx_pcs_fully_aligned to be asserted.

  2. Read the VL data for each of the Local Virtual Lanes (VL):

    Perform the read operation from o_rx_pcs_status[mode] register via CSR interface. This returns VL data field data for all 20 virtual lanes.

  3. Set the Physical Lanes for each Remote Virtual Lane:
    Step through the data provided by each Local Virtual lane:
    • Each lane provides a REMOTE_VL and a LOCAL_PL value.

    For each of the 20 possible Remote virtual lanes, set PL[REMOTE_VL] = LOCAL_PL.

    For example, if you read Local Virtual lane 12, and get back REMOTE_VL = 5, LOCAL_PL = 2, that means the data for Virtual lane 5 from the link partner is coming in on our Physical lane 2. You store that as PL[5] = 2.

  4. Calculate the Virtual Lane Offsets for each of the Remote Virtual Lanes in bits:
    For 100GE rate:
    Virtual Lane Offset = sync_pulse to last AM  
       = gb_33_66_occupancy + gb_66_110_occupancy + blk_align_occupancy
       + am_detect_occupancy + am_count - local_lane_adjust
    For 50GE-2 rate:
    Virtual Lane Offset = sync_pulse to last AM  
      = gb_33_66_occupancy + sep50_occupancy + blk_align_occupancy
      + am_detect_occupancy + am_count - local_lane_adjust
  5. Apply shifts to the offsets for REMOTE_VLs {18..19} to account for the mii_am/mii_data reordering that happens in the PCS MII Decoder. This step is applicable for 50GE-2 and 100GE rates only.
    • Generate vl_offset_bits shifted for each of the REMOTE_VLs.
    • When using RX PTP on data from the RX PCS, shift the times for REMOTE_VLs 18 to 19 by -330 bits:
      vl_offset_bits_shifted[REMOTE_VL] = vl_offset_bits[REMOTE_VL] -330 for REMOTE_VL == {18..19}
      vl_offset_bits_shifted[REMOTE_VL] = vl_offset_bits[REMOTE_VL] for REMOTE_VL == {0..17}

      This shift accounts for a shift that is applied by the RX PCS to incoming data.

      For example, if vl_offset_bits[18] == 887, set vl_offset_bits_shifted[18] to 557. If vl_offset_bits[17] == 887, set vl_offset_bits_shifted[17] to 887.

    Note: For 50GE-2 rates, follow same instructions except only apply the shifting to VL3.
  6. Convert the vl_offset_bits to VL_OFFSET (in ns):
    For each REMOTE_VL, VL_OFFSET[REMOTE_VL] = vl_offset_bits_shifted[REMOTE_VL] * RX_UI