Method and apparatus for transmit time timestamping

A network device, comprising:

• a network interface configured to transmit packets via a network link that is external to the network device;
• timestamp circuitry configured to modify a packet that is to be transmitted by the network interface by embedding a future timestamp in the packet to generate a timestamped packet that is formatted for transmission with the embedded future timestamp via the network link that is external to the network device, the future timestamp associated with a transmit time at which the timestamped packet is to be transmitted by the network interface, the transmit time occurring after the timestamp circuitry embeds the future timestamp in the packet, the timestamp circuitry further configured to generate timing information that is outside of the timestamped packet and that includes the transmit time;
• one or more circuitry stages configured to i) receive the timestamped packet, and ii) synchronize passage of the timestamped packet through the one or more circuitry stages with passage of the timing information through the one or more circuitry stages;
• and
• time gating circuitry that includes, or is coupled to, a clock circuit that maintains a first time clock, the time gating circuitry configured to i) receive the timestamped packet and the timing information from the one or more circuitry stages, ii) determine when a current time indicated by the clock circuit reaches the transmit time that is included in the timing information, iii) hold the timestamped packet from proceeding to the network interface prior to the current time reaching the transmit time, and iv) release the timestamped packet, embedded with the future timestamp that is associated with the transmit time, in response to the current time reaching the transmit time so that the timestamped packet, embedded with the future timestamp that is associated with the transmit time, is transmitted by the network interface at the transmit time via the network link that is external to the network device, the future timestamp being embedded in the packet to indicate to a receiving device that receives the packet via the network link a time at which the timestamped packet was transmitted by the network device to enable the receiving device to synchronize a second time clock of the receiving device to the first time clock.