The offset-based scheme also supports synchronized transmit of frames on multiple ports
on multiple SmartNICs.
Synchronizing SmartNICs for transmit on time stamp
If the transmission time is to be synchronized across ports on multiple SmartNICs, the
SmartNICs must be time-synchronized to ensure a common notion of time.
Also, time stamps in the sequences of frames to be transmitted on different ports must be
based on a common notion of time. If this is not the case, frames will be transmitted with
the correct relative distance on each port, however, asynchronously across ports.
Example configuration
The following figure shows a configuration in which a host application is transmitting
frames on two SmartNICs.
Figure. Synchronized transmit on multiple SmartNICs
Calculating the offset
The synchronized start is obtained by writing a common constant offset ∆ to the offset
register for each port used. The time stamp of the first frame is used as the reference for
calculating the common offset value, similarly to the calculation for transmit on time stamp
on a single port. The additional offset TD part of ∆ must be large enough to
allow all the ports to be initialized and for allowing the frames scheduled for transmission
to be placed in the transmit buffer system of all the SmartNICs, so that all ports are ready
for transmission when the transmit time for the first frame occurs, as illustrated in the
following figure.
Figure. Example of synchronized transmit of frame sequence on multiple ports