Low Latency 50G Ethernet Intel® FPGA IP User Guide: Stratix® 10 Devices

ID 683675
Date 4/09/2024
Public
Document Table of Contents

2.5.2. Adding the Transceiver PLL

The Low Latency 50G Ethernet IP core requires one TX transceiver PLLs that are not part of the IP core, to compile and to function correctly in hardware. On Stratix® 10 devices, only the ATX PLL supports the required data rate.

The transceiver PLLs you configure are physically present on the device, but the Low Latency 50G Ethernet IP core does not configure and connect them.

Figure 5. PLL Configuration Example for Low Latency 50G Ethernet IP Core Variation
To configure ATX PLL:
  • Set VCCR_GXB and VCCT_GXB supply voltage for the Transceiver to 1_1V.
  • Set Primary PLL clock output buffer to GXT clock output buffer.
  • Turn on Enable GXT local clock output port (tx_serial_clk_gxt).
  • Set GXT output clock source to Local ATX PLL.
  • Set PLL output frequency to 12890.625 MHz. The transceiver performs dual edge clocking, using both the rising and falling edges of the input clock from the PLL. Therefore, this PLL output frequency setting supports a 25.78125 Gbps data rate through the transceiver.
  • Set PLL auto mode reference clock frequency to the value you specified for the PHY reference frequency parameter.

When you generate an Low Latency 50G Ethernet IP core, the software also generates the HDL code for an ATX PLL. However, the HDL code for the Low Latency 50G Ethernet IP core does not instantiate the ATX PLL. If you choose to use the ATX PLL provided with the Low Latency 50G Ethernet IP core, you must instantiate and connect the instances of the ATX PLL with the Low Latency 50G Ethernet IP core in user logic.

If you generate your own ATX PLL, you must ensure its file name differs from the PLL provided with the IP core.
Note: If your design includes multiple instances of the Low Latency 50G Ethernet IP core, do not use the ATX PLL HDL code provided with the IP core. Instead, generate new ATX PLL IP cores to connect in your design.