F-Tile Low Latency Ethernet 10G MAC Intel® FPGA IP User Guide

ID 720985
Date 5/18/2023
Public

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Document Table of Contents

7.9.2. Calculating Deterministic Latency

Note: Please refer to the configuration registers of Multi-rate 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 6.5ns Period for sampling clock (latency_sclk) of 153.846 MHz
UI period 0.0969696..ns Period for unit interval
bitslip_cnt Read from pcs_bitslip_cnt[6:0] Read from the Ethernet Reconfiguration Interface register (pcs_bitslip_cnt) at base 0x1000, register offset 0x110.
dlpulse_alignment Read from pcs_bitslip_cnt[7] Read from the Ethernet Reconfiguration Interface register (pcs_bitslip_cnt) at base 0x1000, register offset 0x110.
tx_delay (TxDL)

Read from PTP_DL_TX register

0x421[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 PTP_DL_RX register

0x422[20:0]

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

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

TX PMA Delay

Simulation: 80

Hardware: 79

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

RX PMA Delay

Simulation: 88

Hardware: 88

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:
TX Latency = TxDL * (sampling_clock_period in ns)
RX Latency = RxDL * (sampling_clock_period in ns) + (- bitslip_cnt - 33 * dlpulse_alignment) * (UI period in ns)