Low Latency Ethernet 10G MAC Intel® FPGA IP User Guide: Agilex™ 5 FPGAs and SoCs

ID 813663
Date 4/01/2024
Public
Document Table of Contents

6.10.2. Calculating Deterministic Latency

Note: Please refer to the configuration registers of Multirate PHY IP for more information on the registers used in the Deterministic Latency calculation.
Table 43.  Deterministic Latency Parameter Description
Item Value Description
sampling_clk_period

4.375ns (10M/100M/1G/2.5G)

Period for sampling clock of 228.571 MHz for 1G/2.5G.

UI period
  • 0.8ns (10M/100M/1G)
  • 0.32ns (2.5G)

Unit interval. Indicates bit time of one serial bit for specific speed. For 2.5G, the line rate is 3.125Gbps and hence UI = 0.32ns (=1/3.125G). For 1G/10M/100M, the line rate is 1.25G. UI are calculated accordingly.

parallel_clk 20 UI Period for 1 parallel clock cycle.
tx_delay (TxDL)

Read from EFIFO-DL register

[0x19:0x18] – [20:0]

TX delay value in sampling_clk cycles, fixed point format Q13.8.

Bit [20:8] is integer, bit [7:0] is fractional.

Example: tx_delay = 0x27F4,

Bit [20:8] = 0x27 = 39,

Bit [7:0] = 0xF4 = 244/2^8 = 0.953125,

Hence, tx_delay = 39.953125 clock cycles.

rx_delay (RxDL)

Read from EFIFO-DL register

[0x1B:0x1A] – [20:0]

RX delay value in sampling_clk cycles, fixed point format Q13.8.

Bit [20:8] is integer, bit [7:0] is fractional.

TX PMA Delay
  • For 1G/2.5G:

    Simulation: 49

    Hardware: 49

TX PMA delay in the number of UI. Multiply by UI period to convert to nanoseconds and fractional nanoseconds format.

RX PMA Delay
  • For 1G/2.5G:

    Simulation: 67.5

    Hardware: 67.5

RX PMA delay in the number of UI. Multiply by UI period to convert to nanoseconds and fractional nanoseconds format.

To calculate the TX and RX latency for 1G/2.5G:
TX Latency = TxDL * (sampling_clock_period in ns)
RX Latency = RxDL * (sampling_clock_period in ns)