Communication device, cascaded network and internal synchronization method
A communication device comprising at least one communication port called reception port and another communication port called forward port, each communication port being associated with a respective clock, the communication device being further configured for computing an offset between the respective clocks associated with the reception and forward ports, and synchronizing the respective clocks based on the computed offset.
1. A communication device comprising one communication port called reception port and another communication port called forward port, one of the communication ports being set as a master port, each communication port being associated with a respective clock, the communication device being further configured for:
computing an offset between the respective clocks associated with the reception and forward ports; and
synchronizing the respective clocks based on the computed offset;
wherein the communication device is further configured for computing a residence time as the amount of time elapsed between reception of a message at the reception port and forward of this message at the forward port, the residence time being equal to:
TS egress −TS ingress +clockOffset initial
when the respective clocks are cadenced by the same oscillator, and the residence time being equal to:
TS egress −TS ingress +clockOffset discipline −offsetAdjustment discipline
when the respective clocks are each cadenced by a respective independent oscillator,
where:
TS ingress is an ingress timestamp at reception time;
TS egress is an egress timestamp at forward time; and
clockOffset initial is the clock offset at start-up between the clocks associated with the reception port and the forward port;
clockOffset discipline is the clock offset at a processing time between the clocks associated with the reception port and the forward port; and
offsetAdjustment discipline is the clock adjustment applied to the clocks associated with the reception port and the forward port at the processing time,
wherein the processing time is a time of a last application of a process applied between the master port and the other communication ports during runtime of the communication device for maintaining the synchronization of the clocks associated with the communication ports, the process taking into account the computed offset.
2. The communication device of claim 1 , wherein the respective clocks are cadenced by the same oscillator and the communication device is further configured for performing the following steps from start-up and during runtime of the communication device:
adjusting the clock associated with the master port with the Grand Master clock of a system comprising the communication device;
applying a same adjustment to all the other clocks associated with the other communication ports.
3. The communication device of claim 1 , wherein the respective clocks are each cadenced by a respective independent oscillator and wherein the communication device is further configured for applying a process between the master port and the other communication ports during runtime of the communication device for maintaining the synchronization of the clocks associated with the communication ports, the process taking into account the computed offset.
4. The communication device of claim 3 , wherein the process comprises:
computing a clock adjustment to apply to the respective clocks based on the computed offset;
adjusting the respective clocks with the computed clock adjustment.
5. The communication device of claim 3 , wherein the process comprises:
upon PPS interrupt, computing a clock adjustment to apply to the respective clocks based on a timestamp associated with the PPS interrupt;
adjusting the respective clocks with the computed clock adjustment.
6. The communication device of claim 3 , wherein the communication device is further configured for launching a process running a PTP stack for synchronizing clock associated with the master port with the Grand Master clock of a system comprising the communication device.
7. A method for internal synchronization of a communication device comprising one communication port called reception port and another communication port called forward port, one of the communication ports being set as a master port, each communication port being associated with a respective clock, the method comprising the following steps:
computing an offset existing between the respective clocks associated with the communication ports; and
synchronizing the respective clocks based on the computed offset;
wherein the method further comprises computing a residence time as the amount of time elapsed between reception of a message at the reception port and forward of this message at the forward port,
the residence time being equal to:
TS egress −TS ingress +clockOffset initial
when the respective clocks are cadenced by the same oscillator,
and the residence time being equal to:
TS egress −TS ingress +clockOffset discipline −offsetAdjustment discipline
when the respective clocks are each cadenced by a respective independent oscillator;
where:
TS ingress is an ingress timestamp at reception time;
TS egress is an egress timestamp at forward time; and
clockOffset initial is the clock offset at start-up between the clocks associated with the reception port and the forward port;
clockOffset discipline is the clock offset at a processing time between the clocks associated with the reception port and the forward port; and
offsetAdjustment discipline is the clock adjustment applied to the clocks associated with the reception port and the forward port at the processing time,
wherein the processing time is a time of a last application of a process applied between the master port and the other communication ports during runtime of the communication device for maintaining the synchronization of the clocks associated with the communication ports, the process taking into account the computed offset.
8. The method of claim 7 , wherein the respective clocks are cadenced by the same oscillator, the method comprising the following steps at start-up:
adjusting the clock associated with the master port with the Grand Master clock of a system comprising the communication device;
applying a same adjustment to all the other clocks associated with the other communication ports.
9. The method of claim 7 , wherein the respective clocks are each cadenced by a respective independent oscillator, the method further comprising applying a process between the master port and the other communication ports during runtime of the communication device for maintaining the synchronization of the clocks associated with the communication ports, the process taking into account the computed offset.
10. The method of claim 9 , wherein the process comprises:
computing a clock adjustment to apply to the respective clocks based on the computed offset;
adjusting the respective clocks with the computed clock adjustment.
11. The method of claim 9 , wherein the process comprises:
upon PPS interrupt, computing a clock adjustment to apply to the respective clocks based on a timestamp associated with the PPS interrupt;
adjusting the respective clocks with the computed clock adjustment.
12. The method of claim 9 , further comprising launching a process running a PTP stack for synchronizing clock associated with the master port with the Grand Master clock of a system comprising the communication device.
13. A cascaded network comprising at least two communication devices according to claim 1 .