The operational mode of the egress timestamping function is determined by the settings on the 1588 command port. The information contained within the command port indicates one of the following:
- No operation: the frame is not a PTP frame and no timestamp action should be taken.
- Two-step operation is required and a tag value (user-sequence ID) is provided as part of the command field; the frame should be timestamped, and the timestamp made available to the client logic, along with the provided tag value for the frame. The additional MAC transmitter ports provide this function.