System and method for clock synchronization for USB sink device
View Patent ↗In a method for adaptive synchronization of a data sink device to a data source device coupled by a USB, data is received and stored in a buffer of the sink device at an average data rate representative of the data rate of the source device. A data level for the buffer is determined based on input packet size and output packet size. An accumulated data level for the buffer is compared with a threshold level. A clock frequency for the sink device is corrected when the accumulated data level exceeds the threshold level.
1. A method of adaptive synchronization of a data sink device to a data source device coupled by a USB, comprising the steps of:
receiving data at a buffer of said sink device at an average data rate representative of a data rate of said source device;
determining a data level for said buffer based on input packet size and output packet size;
comparing an accumulated data level for said buffer with a threshold level;
correcting a clock frequency for said sink device when said accumulated data level exceeds said threshold level, said correcting step correcting the clock frequency by an amount equal to a constant K divided by a drift time required for the accumulated data level to drift from a reference level to the threshold level; and
inhibiting a next execution of said comparing step and said correcting step for a predetermined period after said correcting step.
2. The method according to claim 1 , wherein the predetermined period is between three or five times said drift time.
3. The method according to claim 1 , wherein said predetermined period is reduced if said data level traverses said reference level or exceeds twice the threshold level.
4. The method according to claim 1 , wherein the reference level is the data level measured over a first measurement period.
5. The method according to claim 1 , wherein said comparing step is executed periodically.
6. The method according to claim 1 , wherein the threshold level is set to be greater than three times a maximum data level jitter.
7. The method according to claim 1 , wherein a size of the buffer is set to be greater than three times said threshold level.
8. A system for adaptive synchronization of a data sink device to a data source device, comprising:
a source device; and
a sink device coupled to said source device by a USB, and comprising a buffer, and
wherein said sink device stores data in said buffer at an average data rate representative of a data rate of said source device;
determines a data level for said buffer based on input packet size and output packet size;
compares an accumulated data level for said buffer with a threshold level; and
corrects a clock frequency for said sink device when said accumulated data level exceeds said threshold level by correcting the clock frequency by an amount equal to a constant K divided by a drift time required for the accumulated data level to drift from a reference level to the threshold level; and
wherein said sink device inhibits a next execution of said comparing operation and said correcting operation for a predetermined period after said correcting operation.
9. The system according to claim 8 , wherein the predetermined period is between three or five times said drift time.
10. The system according to claim 8 , wherein said predetermined period is reduced if said data level traverses said reference level or exceeds twice the threshold level.
11. The system according to claim 8 , wherein the reference level is the data level measured over a first measurement period.
12. The system according to claim 8 , wherein said comparing operation is executed periodically.
13. The method according to claim 8 , wherein the threshold level is set to be greater than three times a maximum data level jitter.
14. The method according to claim 8 , wherein a size of the buffer is set to be greater than three times said threshold level.
15. A sink device for receiving data from a USB-coupled source device, comprising:
a buffer;
receiving means for receiving data at said buffer of said sink device at an average data rate representative of a data rate of said source device;
determining means for determining a data level for said buffer based on input packet size and output packet size;
comparing means for comparing an accumulated data level for said buffer with a threshold level;
correcting means for correcting a clock frequency for said sink device when said accumulated data level exceeds said threshold level, wherein said correcting means corrects the clock frequency by an amount equal to a constant K divided by a drift time required for the accumulated data level to drift from a reference level to the threshold level; and
inhibiting means for inhibiting next execution of said comprising step and said correcting step for a predetermined period after said correcting step.
16. The sink device according to claim 15 , wherein the predetermined period is between three or five times said drift time.
17. The sink device according to claim 15 , wherein said predetermined period is reduced if said data level traverses said reference level or exceeds twice the threshold level.
18. The sink device according to claim 15 , wherein the reference level is the data level measured over a first measurement period.
19. The sink device according to claim 15 , wherein said comparing means is executed periodically.
20. The sink device according to claim 15 , wherein the threshold level is set to be greater than three times a maximum data level jitter.
21. The sink device according to claim 15 , wherein a size of the buffer is set to be greater than three times said threshold level.