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

ID 683872
Date 10/15/2021
Public

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4. Implementing the F-Tile Reference and System PLL Clocks Intel® FPGA IP

The F-Tile Reference and System PLL Clocks Intel® FPGA IP is required IP for F-tile PMA/FEC Direct PHY designs.

F-Tile Reference and System PLL Clocks Intel® FPGA IP Overview

The F-Tile Reference and System PLL Clocks Intel® FPGA IP performs three main functions, each described below:

  • Configures the reference clock for FHT PMA:
    • Enable the FHT Common PLLs and select the reference clock source for FHT common PLL
    • Specify the FHT reference clock frequency
  • Configures the reference clock for FGT PMA:
    • Enable FGT reference clocks and specify the reference clock frequency
    • To enable FGT CDR Output (RX recovered clock output)
  • Configures the system PLL:
    • Enable system PLL and specify the mode
    • Specify the reference clock source and frequency for system PLL

The F-Tile Reference and System PLL Clocks Intel® FPGA IP must always connect to the F-Tile PMA/FEC Direct PHY Intel® FPGA IP or protocol IPs. You cannot compile or simulate the F-Tile Reference and System PLL Clocks Intel® FPGA IP as a standalone IP. You must enable at least one system PLL because this is a requirement for F-tile configuration to pass successfully. Enabling at least one system PLL is required even when the data path is using PMA clocking mode.

When you use the system PLL only for F-tile configuration (that is, when all lanes use the PMA clocking mode) the following guidelines apply:

  • The system PLL output must be unconnected.
  • If not using FGT PMA, the reference clock to system PLL is not necessary (that is, you do not need to connect the reference clock); however, if you connect a reference clock, the configuration completes faster.
  • If using FGT PMA, the reference clock to system PLL is necessary (that is, you must connect the reference clock), and the clock must be stable and available before releasing the reset.

When you instantiate multiple interfaces or protocol-based IP cores within a single F-tile, you must use only one instance of the F-Tile Reference and System PLL Clocks Intel® FPGA IP to configure the following:

  • All reference clocks for FGT PMA (up to 10) and FHT PMA (up to 2) that are required to implement those multiple interfaces within a single F-tile.
  • All FHT common PLLs (up to 2) that are required to implement those multiple interfaces within a single F-tile.
  • All System PLLs (up to 3) that are required to implement those multiple interfaces within a single F-tile.
  • All reference clocks for system PLLs (up to 8, shared with FGT PMA) that are required to implement those multiple interfaces within a single F-tile.
Note: At least one system PLL must be enabled. All system PLLs cannot be disabled.

When you design multiple interfaces or protocols based IP cores within a single F-tile, you can only use three System PLLs. For example, you can use one System PLL for PCIe and two for Ethernet and other protocols. However, there are other use cases where you can use all three for various interfaces within the Ethernet and PMA-Direct digital blocks. As there are only three System PLLs, multiple interfaces or protocol-based IP cores with different line rates may have to share a System PLL. While sharing a System PLL, the interface with the highest line rate determines the system PLL frequency, and the interfaces with the lower line rates must be overclocked.