DOCSIS clock emulation in distributed access architectures
Systems and methods for implementing a software emulation of a clock calibrated by the software based on sampling a hardware clock.
1. A device comprising:
a first clock operating in hardware and synchronized to a first frequency;
a second clock operating in software and synchronized to second frequency,
the second clock calibrated by the device using samples measured from the first clock,
where the second clock provides a series of time measurements for use by the device after calibration, and over an interval during which the device does not sample the first clock;
where the second clock is calibrated over a calibration interval during which samples are periodically measured; where at least one of a length of the calibration interval and the rate at which samples are taken over the calibration interval are configurable.
2. The device of claim 1 where the first frequency is based on the Precision Riming Protocol (PTP).
3. The device of claim 1 where the second frequency is based on the Data over Cable Service Interface Specification (DOCSIS) standard.
4. The device of claim 1 where the second clock is calibrated using an adjustment factor that samples a delay in reading the first clock.
5. The device of claim 4 where the adjustment factor is averaged over a number of samples.
6. The device of claim 1 where the device recalibrates the second clock after the interval, and subsequently provides a series of time measurements for use by the device after recalibration, and over a second interval during which the device does not sample the first clock.
7. The device of claim 1 wherein the device is implemented in an Remote PHY Device (RPD) of an Remote PHY (R-PHY) Cable Television (CATV) network.
8. The device of claim 7 where the RPD includes at least one other said device, each device being a respective core of the RPD.
9. A method for emulating a first clock in software running on a core of a CPU, and using a second clock in hardware different from the CPU, the first clock having a frequency less than that of the second clock, the method comprising:
sampling the first clock over a first interval to obtain a first sequence of measurement samples;
using the measurement samples to calibrate the second clock; and
operating the second clock over a second interval without sampling the first clock;
including reading and storing a current CPU time and a current Data over Cable Service Interface Specification (DOCSIS) time, calculating a first difference between the current CPU time and a reference CPU time, and calculating a second difference between the current DOCSIS time and a reference DOCSIS time;
including the step of calculating and storing an array of adjustment factors based on a ratio between the first difference and the second difference.
10. The method of claim 9 where the frequency is based on the Precision Riming Protocol (PTP).
11. The method of claim 9 where the second clock has a frequency based on the DOCSIS standard.
12. The method of claim 9 where the second clock is calibrated using an adjustment factor that samples a delay in reading the first clock.
13. The method of claim 12 where the adjustment factor is averaged over a number of samples.
14. The method of claim 9 including averaging the adjustment factors.
15. The method of claim 9 where at least one of the first interval and the rate at which the first clock is sampled over the first interval are configurable.
16. The method of claim 9 executed in an Remote PHY Device (RPD) of an Remote PHY (R-PHY) Cable Television (CATV) network.
17. A device comprising:
a first clock operating in hardware and synchronized to a first frequency;
a second clock operating in software and synchronized to second frequency, the second clock calibrated by the device using samples measured from the first clock,
where the second clock provides a series of time measurements for use by the device after calibration, and
over an interval during which the device does not sample the first clock; wherein said device is implemented in an Remote PHY Device (RPD) of an Remote PHY (R-PHY) Cable Television (CATV) network; where the RPD includes at least one other said device, each device being a respective core of the RPD.
18. The device of claim 17 where the first frequency is based on the Precision Riming Protocol (PTP).
19. The device of claim 17 where the second frequency is based on the Data over Cable Service Interface Specification (DOCSIS) standard.
20. The device of claim 17 where the second clock is calibrated using an adjustment factor that samples a delay in reading the first clock.
21. The device of claim 20 where the adjustment factor is averaged over a number of samples.
22. The device of claim 17 where the second clock is calibrated over a calibration interval during which samples are periodically measured.
23. The device of claim 22 where at least one of a length of the calibration interval and the rate at which samples are taken over the calibration interval are configurable.
24. The device of claim 17 where the device recalibrates the second clock after the interval, and subsequently provides a series of time measurements for use by the device after recalibration, and over a second interval during which the device does not sample the first clock.
25. A method for emulating a first clock in software running on a core of a CPU, and using a second clock in hardware different from the CPU, the first clock having a frequency less than that of the second clock, the method comprising:
sampling the first clock over a first interval to obtain a first sequence of measurement samples;
using the measurement samples to calibrate the second clock; and
operating the second clock over a second interval without sampling the first clock, where at least one of the first interval and the rate at which the first clock is sampled over the first interval are configurable.
26. The method of claim 25 where the frequency is based on the Precision Riming Protocol (PTP).
27. The method of claim 25 where the second clock has a frequency based on the Data over Cable Service Interface Specification (DOCSIS) standard.
28. The method of claim 25 where the second clock is calibrated using an adjustment factor that samples a delay in reading the first clock.
29. The method of claim 28 where the adjustment factor is averaged over a number of samples.
30. The method of claim 25 including reading and storing a current CPU time and a current DOCSIS time, calculating a first difference between the current CPU time and a reference CPU time, and calculating a second difference between the current DOCSIS time and a reference DOCSIS time.
31. The method of claim 30 including the step of calculating and storing an array of adjustment factors based on a ratio between the first difference and the second difference.
32. The method of claim 31 including averaging the adjustment factors.
33. The method of claim 25 executed in an Remote PHY Device (RPD) of an Remote PHY (R-PHY) Cable Television (CATV) network.