Hard Processor System Technical Reference Manual: Agilex™ 3 SoCs

ID 848530
Date 6/23/2025
Public
Document Table of Contents

12.3.2.3. Clocks

Clocking requirements:
  • tx_pll_refclk signal is the TX path reference clock for the PMA PLL. It is used to generate the serial clock and the parallel data clocks. Altera recommends that you use 156.25 MHz frequency for the tx_pll_refclk signal. Altera also recommends using the same clock for rx_cdr_refclk.
  • For 8-bit GMII (MGBASE):
    • The GMII 8-bit adapter generates the gmii8b_tx_clkout clock signal. For 10M, the clock frequency is 2.5 MHz. For 100M (MII, 4-bit interface), the clock frequency is 25 MHz. For 1G, the clock frequency is 125 MHz.
    • The Hard Processor System (HPS) Ethernet Media Access Controller (MAC) drives the gmii8b_tx_clkin signal at the same frequency with the gmii8b_tx_clkout signal.
    • The refclk frequency for MRPHY_PLL is 62.5 MHz for 1G.
  • For 16-bit GMII (MGBASE), the transmit is clocked by tx_clkout. The PHY drives this clock to the MAC. The primary clock frequency for 1G is 62.5 MHz. For 10M and 100M, the primary clock frequency is 62.5 MHz with clock enable.
  • xgmii_tx_coreclkin and xgmii_rx_coreclkin are available in MGBASE (10G) only.
Note: When instantiating the 1G/2.5G/5G/10G Multirate Ethernet PHY IP in the design, you must follow the shared clocking consideration specified in the Shared Clocking Resources Between the GTS Transceiver Bank and HVIO Bank section of the GTS Transceiver PHY User Guide.
Table 368.  Clocking Specifications
Clock Signals 10M (MII) 100M (MII) 1G (GMII)
MGBASE (8-bit)

gmii8b_tx_clkin/gmii8b_tx_clkout

gmii8b_rx_clkin/gmii8b_rx_clkout

2.5 MHz

(4-bit interface)

25 MHz

(4-bit interface)

125 MHz

(8-bit interface)

Figure 308. 2.5G, 1G/2.5G, 1G/2.5G/10G (MGBASE) Clocking