Time Stamp Features

Time-Stamping and Time Synchronization

Intel® PAC
Napatech SmartNIC
User Guide

In this section

This section describes a number of time stamp features supported by the SmartNICs.

The time stamp clock

A SmartNIC maintains a time stamp clock, which is used for precise time-stamping of frames received on the Ethernet ports of the SmartNIC. Received frames are time-stamped either when the first byte is received or when the last byte is received depending on the setting of the TimestampMethod configuration parameter in the ntservice.ini file (see Specifying the Time Stamp Method). This setting also determines if the first or the last byte of a frame is transmitted according to the time stamp in the packet descriptor.
Note: Start-of-frame time-stamping does not apply to NT40E3-4-PTP SmartNICs running on the capture/replay image, to NT40A01-4×10/1-SLB SmartNICs nor to the Intel® Programmable Acceleration Card with Intel® Arria® 10 GX FPGA.
Note: Using different settings of TimestampMethod for capturing data and later for transmitting the same data, will result in inaccuracies.

The time stamp clock is also used for time-stamping statistics data blocks transferred to the host memory. This enables the host application to correlate received frame data with statistics information.

The time stamp clock is driven by a local clock oscillator, and the internal resolution is 1 ns. The time stamp clock can either be free-running or be adjusted according to another reference clock.

Time stamps in packet descriptors

The standard packet descriptor, the dynamic packet descriptors and the PCAP packet descriptor contain the time stamp (see DN-1128). The time stamp in the standard packet descriptor can be retrieved using the NT_NET_GET_PKT_TIMESTAMP macro (see DN-0449).