GTS Transceiver PHY User Guide: Agilex™ 3 FPGAs and SoCs

ID 848344
Date 8/04/2025
Public
Document Table of Contents

3.8.1. Implementing PMA Direct Mode with TX Core FIFO in Elastic Configuration

To implement the PMA Direct mode with TX or RX core FIFO in elastic configuration, there is a working range for the TX user clock division value.
Figure 45. TX User Clock Setting

For the minimum TX user clock division value calculation, you must use the following formula:

User Clock Frequency = 2 x Word Clock Frequency

TX User Minimum TX User Clock Division Value = VCO Frequency / User Clock

Following is an example of the minimum TX user clock division value calculation for 10.3125 Gbps with a PMA width of 32 bits:
  1. Word Frequency = 10.3125G / 32 = 322.265625 MHz
  2. Calculate the maximum user clock for the minimum clock division value:

    322.265625 MHz x 2 = 644.53125 MHz

  3. Clock Division Value (Minimum) = 10312.5 MHz / 644.53125 MHz = 16
For the maximum TX user clock division value, the TX user clock must be less than the word clock frequency. With the same example as above at 10.3125 Gbps and a PMA width of 32 bits:
  1. Word Frequency = 10.3125G / 32 = 322.265625 MHz
  2. Using a TX user clock div value of 32:

    User Clock = 10.3125G / 32 = 322.265625 MHz

  3. Using a TX user clock div value of 33:

    User Clock = 10.3125G / 33 = 312.5 MHz, which does not work

Therefore, for PMA Direct mode with TX or RX core interface FIFO in elastic configuration, the working range for the TX user clock division value at 10.3125 Gbps with a PMA width of 32 bits is between 16 — 32.