Method for improving accuracy of a time estimate from a memory device

• US 20080306710A1
• Filed: 06/08/2007
• Published: 12/11/2008
• Est. Priority Date: 06/08/2007
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: Holtzman, Michael, Barzilai, Ron, Sela, Rotem, Jogand-Coulomb, Fabrice E.
• Granted Patent: US 8,688,924 B2
• Time in Patent Office: Days
• US Class Current: 702/178
• CPC Class Codes: G06F 21/10 Protecting distributed programs or content, e.g. vending or licensing of copyrighted material protection in video systems or pay television H04N7/16 ; Digital rights management [DRM]
• CPC Class Codes: G06F 21/725 operating on a secure reference time value
• CPC Class Codes: H04L 2463/121 Timestamp cryptographic mechanisms or cryptographic arrangements involving time stamps H04L9/3297
• CPC Class Codes: H04L 63/123 received data contents, e.g. message integrity

Abstract

A method for improving accuracy of a time estimate from a memory device is disclosed. In one embodiment, a memory device receives a time stamp and measures active time with respect to the received time stamp. The memory device determines accuracy of previously-measured active time and generates a time estimate using the measured active time, the accuracy of previously-measured active time, and the received time stamp. In another embodiment, measured active time is adjusted, with or without generating a time estimate. Other embodiments are disclosed, and each of the embodiments can be used alone or together in combination.

Claims

1. A method for improving accuracy of a time estimate from a memory device, the method comprising:

receiving a time stamp;

measuring active time of a memory device with respect to the received time stamp;

determining accuracy of previously-measured active time; and

generating a time estimate using the measured active time, the accuracy of previously-measured active time, and the received time stamp.

2. The method of claim 1 further comprising:

measuring a number of power cycles with respect to the received time stamp; and

if the number of power cycles exceeds a threshold, requesting a new time stamp instead of generating the time estimate.

3. The method of claim 1 further comprising:

measuring a number of power cycles with respect to the received time stamp; and

if the number of power cycles equals zero, generating a time estimate using the measured active time and the received time stamp but not using the accuracy of previously-measured active time.

4. The method of claim 1 further comprising:

if the measured active time exceeds a threshold, requesting a new time stamp instead of generating the time estimate.

5. The method of claim 1, wherein determining accuracy of previously-measured active time comprises determining a plurality of stretch factors, and wherein the method further comprises:

measuring a standard deviation of the plurality of stretch factors; and

if the standard deviation of the plurality of stretch factors exceeds a threshold, performing one of the following;

requesting a new time stamp instead of generating the time estimate; and

generating a time estimate using the measured active time and the received time stamp but not using the accuracy of previously-measured active time.

6. The method of claim 1, wherein determining accuracy of previously-measured active time comprises determining a plurality of stretch factors and calculating a running average of the plurality of stretch factors.

7. The method of claim 1, wherein determining accuracy of previously-measured active time comprises comparing previously-measured active time with actual time between time stamps.

8. The method of claim 1, wherein determining accuracy of previously-measured active time comprises comparing down time with actual time between time stamps.

9. The method of claim 1, wherein determining accuracy of previously-measured active time comprises comparing previously-measured active time with down time.

10. The method of claim 1, wherein determining accuracy of previously-measured active time comprises determining a stretch factor per power cycle of the memory device, wherein the method further comprises measuring a number of power cycles with respect to the received time stamp, and wherein the time estimate is generated based on the stretch factor per power cycle and the number of power cycles.

11. The method of claim 1, wherein active time is measured by incrementing a value in a counter in response to an interrupt signal, and wherein the time estimate is generated by adding the received time stamp to an adjusted active time value, wherein the adjusted active time value is generated by multiplying the value in the counter by an amount based on the accuracy of previously-measured active time instead of by a frequency at which the interrupt signal is generated.

12. The method of claim 1, wherein active time is measured by incrementing a value in a counter in response to an interrupt signal and multiplying the value in the counter by a frequency at which the interrupt signal is generated, and wherein the time estimate is generated by multiplying the measured active time by an amount based on the accuracy of previously-measured active time and adding that product to the received time stamp.

13. The method of claim 1, wherein the time estimate is generated by adding the received time stamp to the measured active time and multiplying that sum by an amount based on the accuracy of previously-measured active time.

14. The method of claim 1, wherein the time stamp is generated by a time server.

15. The method of claim 14, wherein the time stamp is signed by the time server.

16. The method of claim 1, wherein the time stamp is generated by a host device connected with the memory device.

17. The method of claim 1, wherein the memory device stores digital rights management (DRM) keys and licenses to unlock protected content stored on the memory device.

18. The method of claim 1 further comprising using the time estimate in one or more of the following operations:

an authentication operation, a host revocation operation, and a digital rights management (DRM) operation.

19. A method for improving accuracy of measured active time in a memory device, the method comprising:

measuring active time of a memory device;

determining accuracy of previously-measured active time; and

adjusting the measured active time based on the accuracy of previously-measured active time.

20. The method of claim 19 further comprising:

generating a time estimate using the adjusted measured active time.

21. The method of claim 19 further comprising:

measuring a number of power cycles with respect to the received time stamp; and

if the number of power cycles exceeds a threshold, requesting a new time stamp instead of adjusting the measured active time.

22. The method of claim 19 further comprising:

measuring a number of power cycles with respect to the received time stamp;

wherein the measured active time is not adjusted if the number of power cycles equals zero.

23. The method of claim 19, wherein the measured active time is not adjusted if the measured active time exceeds a threshold.

24. The method of claim 19, wherein determining accuracy of previously-measured active time comprises determining a plurality of stretch factors, and wherein the method further comprises:

measuring a standard deviation of the plurality of stretch factors; and

performing one of the following;

adjusting the measured active time only if the standard deviation of the plurality of stretch factors does not exceed a threshold; and

requesting a new time stamp instead of adjusting the measured active time if the standard deviation of the plurality of stretch factors exceeds a threshold.

25. The method of claim 19, wherein determining accuracy of previously-measured active time comprises determining a plurality of stretch factors and calculating a running average of the plurality of stretch factors.

26. The method of claim 19, wherein determining accuracy of previously-measured active time comprises comparing previously-measured active time with actual time between time stamps.

27. The method of claim 19, wherein determining accuracy of previously-measured active time comprises comparing down time with actual time between time stamps.

28. The method of claim 19, wherein determining accuracy of previously-measured active time comprises comparing previously-measured active time with down time.

29. The method of claim 19, wherein determining accuracy of previously-measured active time comprises determining a stretch factor per power cycle of the memory device, wherein the method further comprises measuring a number of power cycles with respect to the received time stamp, and wherein measured active time is adjusted using the stretch factor per power cycle and the number of power cycles.

30. The method of claim 19, wherein active time is measured by incrementing a value in a counter in response to an interrupt signal, and wherein the measured active time is adjusted by multiplying the value in the counter by an amount based on the accuracy of previously-measured active time instead of by a frequency at which the interrupt signal is generated.

31. The method of claim 19, wherein active time is measured by incrementing a value in a counter in response to an interrupt signal and multiplying the value in the counter by a frequency at which the interrupt signal is generated, and wherein the measured active time is adjusted by multiplying the measured active time by an amount based on the accuracy of previously-measured active time.

32. The method of claim 19, wherein the time stamp is generated by a time server.

33. The method of claim 32, wherein the time stamp is signed by the time server.

34. The method of claim 19, wherein the time stamp is generated by a host device connected with the memory device.

35. The method of claim 19, wherein the memory device stores digital rights management (DRM) keys and licenses to unlock protected content stored on the memory device.

36. The method of claim 19 further comprising using the adjusted measured time in one or more of the following operations:

an authentication operation, a host revocation operation, and a digital rights management (DRM) operation.