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

ID 683872
Date 4/07/2025
Public
Document Table of Contents

4.6.1.1. How to Determine the TX PLL Your FGT Channel is Using

Within each FGT PMA, there are three TX PLLs which can be used to clock the transmit data. These TX PLLs are Fast, Medium and Slow and generally refer to the speed of your transmit link. In order to determine which TX PLL your FGT PMA is using, perform the following steps:
  1. Open the <project_directory>/<design_name>.syn.rpt file.
  2. Search on the following strings:
    1. _synth_lc_fast_en
    2. _synth_lc_med_en
    3. _synth_lc_slow_en
  3. You can determine which TX PLL is enabled for your channel by locating a string similar to the one below:
    ; z1577b_u_ux_quad_3__ux2_synth_lc_fast_en                         ; enable
    In the example above, the Quad3, Channel 2 is using the Fast TX PLL
In a dynamic reconfiguration design, when data rate changes, the corresponding TX PLL type might change as well. In order to determine which TX PLL your FGT PMA is currently using, perform the following steps:
  1. Calculate Fout frequency.

    Fout = Datarate / 2 (NRZ modulation) or Fout = Datarate / 4 (PAM4 modulation).

    For example, for a 53.125 Gbps PAM4 modulation design, the Fout = 13.28125 GHz

  2. Retrieve L counter value. Read register 0x47808[25:20] 47:
    • Value 0: L counter is 1
    • Value 1: L counter is 2
    • Value 2: L counter is 4
    • Value 3: L counter is 8
  3. Calculate the VCO frequency.

    VCO = Fout * L counter

  4. Determine FGT TX PLL type based on VCO frequency:
    • Slow: VCO <= 10.5 GHz
    • Medium: 10.5 GHz < VCO <= 12.5 GHz
    • Fast: VCO > 12.5 GHz
47 0x47808 is the address for lane 0. For the offset calculation of other lanes, refer to FGT PMA Register Address Range 0x40000 to 0x48000