Exceptions

Feature Set N-ANL11

Platform
Intel® PAC
Napatech SmartNIC
Content Type
Feature Description

If the SmartNIC time is incorrect or the frames have erroneous time stamps, the relative time of the frames cannot be preserved, or the port may appear blocked.

Scheduled time of transmission in the past

As soon as the next frame scheduled for transmission fulfills the transmit condition, the frame will be transmitted. Usually, for example for replay of captured traffic, the SmartNIC time T >> TPx for all frames, since the time stamp of captured frames will always be in the past. However, if the SmartNIC time is incorrect or if the frames have erroneous time stamps, it may be the case that the transmit condition for all frames is always true.

In that case, the frames will be transmitted in correct sequence; however, as the frames will be transmitted as fast as possible, the relative time of the frames cannot be preserved.

Scheduled time of transmission in the far distant future

Until the transmit condition is fulfilled for the next frame scheduled for transmission, no frames are transmitted. If the scheduled time of transmission of the next frame to transmit lies in the far distant future, no frames will be transmitted for a very long period of time. Consequently, the port may appear blocked.

Monitoring

No exception handling is implemented in hardware; instead information is provided to allow the host application to monitor transmission on time stamp. The information is updated each time a frame is transmitted on time stamp, and is available from an Info stream as port info:
Field Description
NtInfoPort_v9_s.maxPktDelayedNs

The maximum difference in ns between the scheduled and the actual transmission time of a frame since start of ntservice.

This register allows the host application software to verify that transmission is not falling behind.

NtInfoPort_v9_s.nextPktNs

The difference in ns between the current SmartNIC time and the scheduled transmission time of the next frame.

This register allows the host application software to verify that time stamps are not in the far distant future.