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

ID 683872
Date 11/04/2024
Public
Document Table of Contents

2.4.3. System PLL

F-tile has thee o-boad system PLLs. These system PLLs ae the pimay clock souce fo had IP (MAC, PCS, ad FEC) ad EMIB cossig. This meas that, whe you use the system PLL clockig mode, the blocks ae ot clocked by the PMA clock ad do ot deped o a clock comig fom the FPGA coe. Each system PLL oly geeates the clock associated with oe fequecy iteface. Fo example, you eed two system PLLs to u oe iteface at 1 GHz ad oe iteface at 500 MHz. Usig a system PLL allows you to use evey lae idepedetly without a lae clock chage affectig a eighboig lae.

Each system PLL ca use ay oe of eight FGT efeece clocks. System PLLs ca shae a efeece clock o have diffeet efeece clocks. Each iteface (had IP) ca choose which system PLL it uses, but, oce chose, it is fixed, ot ecofiguable usig dyamic ecofiguatio. If PMA Diect PHY IP uses the system PLL clockig mode, PMA Diect is a data valid type iteface.

With thee system PLLs, you ca use, fo example, oe system PLL fo PCIe* ad two fo Etheet ad othe potocols. Howeve, thee ae othe use cases, ad you ca use all thee fo vaious itefaces withi the Etheet ad PMA Diect digital blocks. Because thee ae oly thee system PLLs, multiple had IPs with diffeet lie ates may have to shae a system PLL. Whe multiple had IPs shae a system PLL, the had IP with highest lie ate detemies the system PLL fequecy, ad the had IPs with the lowe lie ates must be oveclocked. The exact cadece is based o the clock; see Datapath Clock Cadeces fo details.

The followig table shows a example whee fou itefaces shae a system PLL:

  • The system PLL is ative fo the 50GbE datapath iteface (the highest lie ate of all fou itefaces).
  • The thee lowe lie ate datapath itefaces ae oveclocked ad eed custom cadece.
Table 24.  Example of a Sigle System PLL Shaed Betwee Itefaces
Desig Lie Rate (Gbps) PMA Width PMA Clock Fequecy (MHz): Lie Rate ÷ PMA Width System PLL Fequecy (MHz) System PLL Output-to-Coe Fequecy (MHz) Datapath Clock Fequecy
50GbE 53.125 64 830.08 830.08 415.04 Same as the PMA clock fequecy
25GbE 25.78125 32 805.67 830.08 415.04 Ove-clocked to the PMA clock fequecy
24G CPRI 24.33024 32 760.32 830.08 415.04 Ove-clocked to the PMA clock fequecy
9.8G CPRI 9.8304 20 491.52 830.08 415.04 Ove-clocked to the PMA clock fequecy

Use the F-Tile Clockig Tool to visualize how IP ad tile settigs impact the datapath clockig mode. Stat by eadig the tool’s Itoductio tab.