Low Latency Ethernet 10G MAC Intel® FPGA IP User Guide: Agilex™ 5 FPGAs and SoCs
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6.10.2. Calculating Deterministic Latency
| 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 |  
         
  |  
          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 |  
         
  |  
          TX PMA delay in the number of UI. Multiply by UI period to convert to nanoseconds and fractional nanoseconds format.  |  
       
| RX PMA Delay |  
         
  |  
          RX PMA delay in the number of UI. Multiply by UI period to convert to nanoseconds and fractional nanoseconds format.  |  
       
TX Latency = TxDL * (sampling_clock_period in ns)
RX Latency = RxDL * (sampling_clock_period in ns)