F-Tile Ethernet Intel® FPGA Hard IP User Guide

ID 683023
Date 12/04/2023
Public
Document Table of Contents

4.4.6.2. RX UI Adjustment

  1. Request snapshot of initial RX TAM:
    csr_write (ptp_uim_tam_snapshot.rx_tam_snapshot, 1’b1)
  2. Read snapshotted initial TAM and counter values:
    rx_tam_0_31_0 = csr_read (ptp_rx_uim_tam_info0.tam_31_0[31:0])
    rx_tam_0_47_32 = csr_read (ptp_rx_uim_tam_info1.tam_47_32[15:0])
    rx_tam_0_cnt   = csr_read (ptp_rx_uim_tam_info1.tam_cnt[30:16])
    rx_tam_0_valid = csr_read (ptp_rx_uim_tam_info1.tam_valid[31])
    • If rx_tam_0_valid = 1, complete TAM by concatenating the initial TAM values:
      rx_tam_0 = {rx_tam_0_47_32, rx_tam_0_31_0};
    • If rx_tam_0_valid = 0, restart from Step1.
  3. Starting from time when step 1 is executed, wait for time duration as specified in the Minimum and Maximum Reference Time (TAM) Interval for UI Measurement (Hardware) section.
  4. Request snapshot of Nth RX TAM:
    csr_write (ptp_uim_tam_snapshot.rx_tam_snapshot, 1’b1)
  5. Read snapshotted Nth TAM and counter values:
    rx_tam_n_31_0  = csr_read (ptp_rx_uim_info0.tam_31_0[31:0])
    rx_tam_n_47_32 = csr_read (ptp_rx_uim_tam_info1.tam_47_32[15:0])
    rx_tam_n_cnt   = csr_read (ptp_rx_uim_tam_info1.tam_cnt[30:16])
    rx_tam_n_valid = csr_read (ptp_rx_uim_tam_info1.tam_valid[31])
    Form the TAM by concatenating snapshotted Nth TAM values:
    rx_tam_n = {rx_tam_n_47_32, rx_tam_n_31_0};
  6. Check if there was a large change to TOD value impacting TAM value:
    rx_tam_n_valid = csr_read (ptp_rx_uim_tam_info1.tam_valid[31])

    If rx_tam_n_valid = 0, restart Step 1. If you used rx_tam_n as a new rx_tam_0 and rx_tam_n_cnt as a new rx_tam_0_cnt, you can skip Step 1 and 2. Then, you can start the wait time in Step 3 when Step 4 executes.

  7. Calculation:
    1. Get TAM interval
      rx_tam_interval = <Refer to Reference Time Interval>
      rx_tam_interval_per_pl = rx_tam_interval / PL
    2. Calculate time elapsed:
      rx_tam_delta = 
         (rx_tam_n <= rx_tam_0) ? [(rx_tam_n + 10^9ns) – rx_tam_0] 
                                 : (rx_tam_n – rx_tam_0)
      Per Step 3, rx_tam_0 and rx_tam_n difference must be within the expected time range.
      • If rx_tam_delta (in ms) is lesser that the minimum time value specified by Time (ms) column of Table: Minimum and Maximum Reference Time (TAM) Interval Allowed for UI Measurement (Hardware Basic Mode) and Table: Minimum and Maximum Reference Time (TAM) Interval Allowed for UI Measurement (Hardware Advanced Mode) in the Minimum and Maximum Reference Time (TAM) Interval for UI Measurement (Hardware) section, discard the result and restart from Step 3.
      • If rx_tam_delta (in ms) is greater than the maximum value specified by Time (ms) column of Table: Minimum and Maximum Reference Time (TAM) Interval Allowed for UI Measurement (Hardware Basic Mode) and Table: Minimum and Maximum Reference Time (TAM) Interval Allowed for UI Measurement (Hardware Advanced Mode) in the Minimum and Maximum Reference Time (TAM) Interval for UI Measurement (Hardware) section, discard the result and restart from Step 1 or Step 3 by using rx_tam_n as a new rx_tam_0.
      Note: 10^9ns = 48’h 3B9A_CA00_0000
    3. Calculate TAM count value:
      rx_tam_cnt = (rx_tam_n_cnt < rx_tam_0_cnt) ? [(rx_tam_n_cnt + 2^15) – rx_tam_0_cnt] 
      									       : (rx_tam_n_cnt – rx_tam_0_cnt)
      Per Step 3, rx_tam_0 and rx_tam_n difference must be within the expected time range.
      • If rx_tam_cnt (in ms) is lesser that the minimum time value specified by Number of Count column of Table: Minimum and Maximum Reference Time (TAM) Interval Allowed for UI Measurement (Hardware Basic Mode) and Table: Minimum and Maximum Reference Time (TAM) Interval Allowed for UI Measurement (Hardware Advanced Mode) in the Minimum and Maximum Reference Time (TAM) Interval for UI Measurement (Hardware) section, discard the result and restart from Step 3.
      • If rx_tam_cnt (in ms) is greater than the maximum value specified by Number of Count column of Table: Minimum and Maximum Reference Time (TAM) Interval Allowed for UI Measurement (Hardware Basic Mode) and Table: Minimum and Maximum Reference Time (TAM) Interval Allowed for UI Measurement (Hardware Advanced Mode) in the Minimum and Maximum Reference Time (TAM) Interval for UI Measurement (Hardware) section, discard the result and restart from Step 1 or Step 3 by using rx_tam_n as a new rx_tam_0.
    4. Calculate UI value:
      rx_ui = (rx_tam_delta) / (rx_tam_cnt * rx_tam_interval_pl)
  8. Write the calculated UI value to IP:
    csr_write (rx_ptp_ui, rx_ui)

    Ensure the format is {4-bit nanoseconds, 28-bit fractional nanoseconds}.

  9. After first UI measurement, for every minimum TAM interval or longer duration, repeat step 1 to 8. This is to prevent time counter drift from the golden time-of-day in the system whenever the clock ppm changes.