SmartNIC Daisy Chain

Qualifying, Fine-Tuning and Troubleshooting Time Synchronization

Platform
Napatech SmartNIC
Content Type
Application Note
Capture Software Version
N-ANL11
N-ANL10
N-ANL9
Link™ Capture Software 12.11
Link™ Capture Software 12.10
Link™ Capture Software 12.9
Link™ Capture Software 12.8
Link™ Capture Software 12.7
Link™ Capture Software 12.6
Link™ Capture Software 12.5
Link™ Capture Software 12.4
Link™ Capture Software 12.3
Link™ Capture Software 12.2
Link™ Capture Software 12.1
Link™ Capture Software 12.0
Link™ Capture Software 11.9
Link™ Capture Software 11.8
Link™ Capture Software 11.7
Link™ Capture Software 11.6
Link™ Capture Software 11.5
Link™ Capture Software 11.4
Link™ Capture Software 11.3
Link™ Capture Software 11.2

Illustration

This figure shows a configuration with 3 NT SmartNICs, where one SmartNIC, SmartNIC #0, acts as a master for the two other SmartNICs. In this example the master SmartNIC is synchronized to OS time, but this is an optional configuration. See also DN-0985.

A configuration with 3 NT SmartNICs, where one SmartNIC, NT SmartNIC #0, acts as a master for the two other SmartNICs

The time stamp clock of SmartNIC #0 provided via the output time synchronization connector is used as reference for SmartNICs #1 and #2. SmartNICs #1 and #2 are both configured to repeat the NT-TS signal from the input time synchronization connector (TS Int1) to the output time synchronization connector (TS Int2), and to synchronize the SmartNIC time stamp clock to the NT-TS signal received on the input time synchronization connector.

The external time synchronization connectors on SmartNICs #1 and #2 are both configured to transmit a PPS signal, which in turn can be connected to the external time synchronization connector of SmartNIC #0.

If compensation for NT-TS propagation delay in the daisy chain is configured correctly, the monitoring tool should display an offset corresponding to the propagation delay in the external signal path.

In Qualifying Time Synchronization, PPS statistics are displayed for SmartNICs #1 and #2, first without compensation for propagation delay, next with compensation.

Propagation delay compensation

Compensation for the delay in the time synchronization cables and the daisy chain delay (TimeSyncTimeOffset) must be made for SmartNICs #1 and #2. A time synchronization cable length of 0.2 m is used for all internal cables, and it is assumed that all SmartNICs are NT20E2 SmartNICs.

The external time synchronization cable is assumed to be 1 m long, corresponding to a 5 ns delay. Output circuit delay contributes 6 ns, and input circuit delay contributes 26 ns. Thus, the delay in the external signal path is 37 ns.

See DN-0985 for details on delays.

ntservice.ini configuration

These ntservice.ini code lines configure the NT SmartNICs in the setup in Illustration.

[Adapter0]
TimeSyncConnectorExt1 = PpsIn
TimeSyncConnectorInt2 = NttsOut
TimeSyncReferencePriority = OsTime
[Adapter1]
TimeSyncConnectorExt1 = PpsOut
TimeSyncConnectorInt1 = NttsIn
TimeSyncConnectorInt2 = RepeatInt1
TimeSyncReferencePriority = Int1,OsTime
TimeSyncTimeOffset = 9
[Adapter2]
TimeSyncConnectorExt1 = PpsOut
TimeSyncConnectorInt1 = NttsIn
TimeSyncReferencePriority = Int1,OsTime
TimeSyncTimeOffset = 18

See DN-0449 for further information about ntservice.ini.