F-Tile Triple-Speed Ethernet Intel® FPGA IP User Guide

ID 741328
Date 10/07/2024
Public
Document Table of Contents

8.4. Clocking Scheme of MAC with 2XTBI PCS and Embedded PMA

The following is the clocking scheme of the design that contains MAC with 2XTBI and embedded PMA on F-Tile :
  • 2XTBI PCS runs on 125 MHz and 62.5 MHz clocks while the same 125 MHz clock is used by MAC.
  • The 125 MHz and 62.5 MHz clocks must be synchronous, in which their rising edges must align and must have 0 ppm and phase shift.
  • The F-Tile Direct PHY are the embedded PMAs in this variant. The tx_clkout and rx_clkout on the F-Tile Direct PHY are used as clock sources for 2XTBI PCS tbi2x_tx_clk and tbi2x_rx_clk.
  • Logic is implemented in the PCS block for clock rate matching by default regardless whether the ENABLE_SGMII option is selected. Therefore, the 125 MHz and 62.5 MHz clocks do not need to be at 0 ppm in comparison with tx_clkout and rx_clkout, which are usually provided by external SERDES.
  • The F-Tile Direct PHY transceivers are driven by the 156.25 MHz clock.
  • The reference clock input to the F-Tile Direct PHY, tx_pll_refclk_link and rx_cdr_refclk_link, should be driven by the 156.25 MHz system PLL output.
Table 101.  Clock Signals Visible at Top-Level DesignClock signals that are visible at the top-level design for each possible configuration.
Clocks Configurations 18
MAC and 2XTBI PCS with PMA 2XTBI PCS Only
clk Yes N/A
reg_clk No Yes
ff_tx_clk Yes N/A
ff_rx_clk Yes N/A
tx_clk_125 Yes Yes
rx_clk_125 Yes Yes
tx_clk_62_5 Yes Yes
rx_clk_62_5 Yes Yes
tbi2x_tx_clk No Yes
tbi2x_rx_clk No Yes
tx_pll_refclk_link 19 Yes N/A
rx_cdr_refclk_link 19 Yes N/A
Figure 79. Clock Connectivity in MAC with 2XTBI PCS and Embedded PMA (F-Tile)
Notes to Clock Connectivity in MAC with 2XTBI PCS and Embedded PMA (F-Tile):
  1. Altera recommends that the rx_clk_125, tx_clk_125, rx_clk_62_5, and tx_clk_62_5 share the same clock source.
  2. Therefore, Altera recommends you use one IOPLL with two output clocks to get the 125 MHz and 62.5 MHz clocks and connect to both the TX and RX datapaths.
  3. rx_clkout and tx_clkout are output clocks generated by the F-Tile transceiver Direct PHY and internally connected to tbi2x_rx_clk and tbi2x_tx_clk in the variant MAC with 2XTBI and embedded PMA.
  4. The reg_clk clock is internally connected to clk in the variant MAC with 2XTBI and embedded PMA. Refer to Register Interface Signals for more information about reg_clk.
  5. Altera recommends 156.25 MHz frequency for this clock source when the F-Tile Reference and System PLL Clocks is used to drive the Triple-Speed Ethernet IP only.

When you enable dynamic reconfiguration, System PLL clock is selected for the datapath clocking mode. TX and RX FIFO is introduced between PCS and PMA via the F-Tile 2XTBI terminator block.

Figure 80. MAC with 2XTBI PCS and Embedded PMA (F-Tile) with F-Tile Transceiver Dynamic Reconfiguration Enabled Functional Block Diagram
  1. In system PLL mode, the tx_clkout and rx_clkout is SYSPLL clock frequency divided by 2. In PMA mode, the tx_clkout and rx_clkout is the PMA clock frequency.
  2. tx_clkout2 and rx_clkout2 coming from PMA to terminator is 62.5 MHz in SYSPLL & PMA Mode.
18 Yes indicates that the clock is visible at the top-level design.

No indicates that the clock is not visible at the top-level design.

N/A indicates that the clock is not applicable for the given configuration.

19 Clock signals of F-Tile transceiver Direct PHY.