System and method for synchronizing nodes in a network device

A method for synchronizing a plurality of nodes to a timing signal, the method comprising:

• receiving a timing signal from a timing source at an external input pad;
• transmitting the timing signal from the external input pad to a top-level measurement circuit;
• transmitting the timing signal from the external input pad to a plurality of nodes, wherein each of the plurality of nodes are connected by a daisy-chain network comprising a forward transmission path and a reverse transmission path connected at a midpoint and wherein neighboring nodes of the plurality of nodes are delay-balanced such that a propagation delay of the timing signal between two neighboring nodes over the forward transmission path is equal to a propagation delay of the timing signal between the two neighboring nodes over the reverse transmission path;
• receiving the transmitted timing signal at the top-level measurement circuit;
• receiving the transmitted timing signal at the plurality of nodes,;
• determining, at the top-level measurement circuit, a total round-trip delay of the timing signal over the daisy-chain network;
• estimating, at the top-level measurement circuit, a latency of the timing signal to the midpoint of the daisy-chain network as one half of the total round-trip delay;
• determining, at each of the plurality of nodes, a respective round-trip delay of the timing signal over the daisy-chain network
• estimating, for each of the plurality of nodes, a respective latency of the timing signal from the node to the midpoint of the daisy-chain network as one half of the respective round-trip delay;
• determining an expected latency between receiving the timing signal at the external input pad and receiving the timing signal at the top-level measurement circuit;
• calculating a respective timing offset for each of the plurality of nodes, wherein the respective timing offset is equal to a difference between the latency of the timing signal to the midpoint of the daisy-chain network and the respective latency of the timing signal from the node to the midpoint of the daisy-chain network, minus the expected latency between receiving the timing signal at the external input pad and transmitting the timing signal to the top-level measurement circuit;
• and
• adjusting a local time-of-day counter at each of the plurality of nodes based upon the respective timing offset of the node to synchronize the plurality of nodes to the timing signal.

A system for synchronizing a plurality of nodes to a timing signal, the system comprising:

• a plurality of nodes, each of the plurality of node comprising a respective measurement circuit;
• a daisy-chain network connecting each of the plurality of nodes, the daisy-chain network comprising a forward transmission path and a reverse transmission path connected at a midpoint;
• a top-level measurement circuit for receiving a timing signal transmitted over the forward transmission path, for receiving the timing signal over the reverse transmission path of the daisy-chain network, for determining a total round-trip delay of the timing signal over the daisy-chain network and for estimating a latency of the timing signal from the top- level measurement circuit to the midpoint of the daisy-chain network as one half of the total round-trip delay;
• the respective measurement circuit at each of the plurality of nodes for;
• receiving the timing signal transmitted over the forward transmission path and receiving the timing signal transmitted over the reverse transmission path of the daisy-chain network;
• determining a respective round-trip delay of the timing signal over the daisy-chain network;
• estimating a respective latency of the timing signal from the node to the midpoint of the daisy-chain network as one half of the respective round-trip delay;
• calculating a respective timing offset for each of the plurality of nodes, wherein the respective timing offset is equal to a difference between the estimated latency of the timing signal from the top-level measurement circuit to the midpoint of the daisy-chain network and the respective estimated latency of the timing signal from the node to the midpoint of the daisy-chain network;
• and
• adjusting a local time-of-day counter at each of the plurality of nodes based upon the respective calculated timing offset of the node to synchronize the plurality of nodes to the timing signal.

The system of claim 19, wherein the respective measurement circuit of each of the plurality of nodes is further for:

• sampling the local time-of-day counter on an edge of the timing signal received over the forward transmission path to generate a first local timestamp;
• sampling the local time-of-day counter on the edge of the timing signal received over the reverse transmission path to generate a second local timestamp;
• and
• calculating the difference between the first local timestamp and the second local timestamp to determine the respective node round-trip delay of the timing signal over the daisy-chain network.