Method and apparatus for synchronization of slave clock to master clock
Existing synchronization methods can be inefficient in hardware-assisted implementations because of the effects of various jittery events. Thus, a method and an apparatus are provided to synchronize a slave device's clock to a master device's clock for a hardware-assisted implementation. The method can include the receipt of three messages. Time differences are determined based on a time extracted from two of the messages and a time of receipt of a different one of the messages. The slave device's clock can be adjusted based on these time differences. Thus, this method, which can include a dynamic weighted average to compute and implement the synchronization, can synchronize the clock of the slave device to the clock of the master device in a faster time interval.
1. A method to synchronize a clock of a slave device to a clock of a master device, the method comprising:
receiving a first message;
extracting a first time from the first message;
receiving a second message and a third message;
determining a second time that indicates a reception of the second message;
extracting a third time from the third message;
determining a first difference between the first time and the third time;
determining a second difference between the second time and the first time; and
adjusting a frequency of the clock of the slave device, based on the first difference and the second difference, to synchronize with the clock of the master device.
2. The method according to claim 1 , further comprising:
receiving a fourth message prior to the first message;
determining a fourth time that indicates a reception of the fourth message;
determining a third difference, based on the first message and the fourth message; and
adjusting a time of the clock of the slave device, based on the third difference.
3. The method according to claim 2 , wherein the fourth message is a Sync message, and the fourth time is a SyncEventIngressTimestamp.
4. The method according to claim 1 , further comprising:
determining a rate ratio, based on the first difference, the second difference, and a previous rate ratio; and
adjusting the frequency of the clock of the slave device, based on the rate ratio.
5. The method according to claim 1 , further comprising:
determining a rate ratio, based on the second difference; and
adjusting the frequency of the clock of the slave device, based on the rate ratio.
6. The method according to claim 5 , wherein the rate ratio is decreased if the second difference is greater than zero.
7. The method according to claim 1 , wherein the first message is a FollowUp message, the second message is a Sync message, the third message is a FollowUp message, the first time is a time indicated in a preciseOriginTimestamp, the second time is a SyncEventIngressTimestamp, and the third time is a time indicated in a preciseOriginTimestamp.
8. An apparatus to synchronize a clock of a slave device to a clock of a master device, the apparatus comprising:
at least one interface that receives a first message, a second message, and a third message; and
at least one processor that extracts a first time from the first message, determines a second time that indicates a reception of the second message, and extracts a third time from the third message, wherein
the at least one processor is configured to determine a first difference between the first time and the third time, to determine a second difference between the second time and the first time, and to adjust a frequency of the clock of the slave device, based on the first difference and the second difference, to synchronize with the clock of the master device.
9. The apparatus according to claim 8 , wherein the at least one interface receives a fourth message prior to the first message, the at least one processor determines a fourth time that indicates a reception of the fourth message, and the at least one processor is further configured to determine a third difference, based on the first message and the fourth message, and to adjust a time of the clock of the slave device, based on the third difference.
10. The apparatus according to claim 9 , wherein the first message is a FollowUp message, the second message is a Sync message, the third message is a FollowUp message, the first time is a time indicated in a preciseOriginTimestamp, the second time is a SyncEventIngressTimestamp, the third time is a time indicated in a preciseOriginTimestamp, the fourth message is a Sync message, and the fourth time is a SyncEventIngressTimestamp.
11. The apparatus according to claim 8 , wherein the at least one processor is further configured to determine a rate ratio based on the first difference, the second difference, and a previous rate ratio, and to adjust the frequency of the clock of the slave device, based on the rate ratio.
12. The apparatus according to claim 8 , wherein the at least one processor is further configured to determine a rate ratio, based on the second difference, and to adjust the frequency of the clock of the slave device, based on the rate ratio.
13. The apparatus according to claim 12 , wherein the rate ratio is decreased if the second difference is greater than zero.
14. The apparatus according to claim 12 , wherein the rate ratio is increased if the second difference is less than zero.
15. An apparatus to synchronize a clock of a slave device to a clock of a master device, the apparatus comprising:
externally interfacing means for receiving a first message, a second message, and a third message; and
processing means for extracting a first time from the first message, for determining a second time that indicates a reception of the second message, and for extracting a third time from the third message, wherein
the processing means determines a first difference between the first time and the third time, determines a second difference between the second time and the first time, and adjusts a frequency of the clock of the slave device, based on the first difference and the second difference, for synchronizing with the clock of the master device.
16. The apparatus according to claim 15 , wherein the externally interfacing means receives a fourth message prior to the first message, the processing means determines a fourth time that indicates a reception of the fourth message, determines a third difference, based on the first message and the fourth message, and adjusts a time of the clock of the slave device, based on the third difference.
17. The apparatus according to claim 15 , wherein the processing means determines a rate ratio, based on the first difference, the second difference, and a previous rate ratio, and adjusts the frequency of the clock of the slave device, based on the rate ratio.
18. The apparatus according to claim 15 , wherein the processing means determines a rate ratio, based on the second difference, and adjusts the frequency of the clock of the slave device, based on the rate ratio.
19. The apparatus according to claim 18 , wherein the rate ratio is decreased if the second difference is greater than zero.
20. The apparatus according to claim 18 , wherein the rate ratio is increased if the second difference is less than zero.