Method for redundant suspend to RAM

• US 20020073358A1
• Filed: 12/07/2000
• Published: 06/13/2002
• Est. Priority Date: 12/07/2000
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Atkinson, Lee. W.
• Granted Patent: US 6,694,451 B2
• Time in Patent Office: Days
• US Class Current: 714/21
• CPC Class Codes: G06F 11/1004 to protect a block of data words, e.g. CRC or checksum G06F11/1076 takes precedence; security arrangements for protecting computers or computer systems against unauthorized activity G06F21/00
• CPC Class Codes: G06F 11/1441 Resetting or repowering
• CPC Class Codes: G06F 9/4418 Suspend and resume; Hibernate and awake
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

A computer system supports suspend operations to save power. The suspend operation maintains power to the system memory to enable a quick recovery from the suspend mode. To insure the accuracy of the data in system memory, a copy of the data is backed up to non-volatile memory, such as a hard disk drive, prior to entering the suspend mode. In addition, a signature value representing blocks or pages of memory also is saved with the data. When normal operation resumes, data in system memory is validated by calculating a new signature for each data block or page, and comparing it with the save signature values. If the signatures match, the data is assumed to be valid. If the values do not match, a restore operation proceeds to load the back up copy to that block of system memory. The algorithm may be run immediately upon resuming operation, or may run in the background when the CPU is idle. In the event a transaction occurs prior to validation of a particular memory location, the access is interrupted and the data is validated or restored. In addition, the error checking and restoration operations may be used during normal system operations to insure the integrity of data in the system memory or other volatile memory components.

Claims

1. A method of validating the contents of system memory, comprising:

storing a substantial image of the contents of system memory to non-volatile memory;

reading the contents of system memory;

checking the contents of system memory for errors; and

restoring the image stored in non-volatile memory to system memory if a non-correctable error is found in the contents of system memory.

2. The method as in claim 1, wherein said system memory comprises error checking and correction random access memory.

3. The method as in claim 1, wherein said system memory comprises parity memory.

4. The method as in claim 1, wherein the non-volatile memory comprises a hard disk.

5. The method as in claim 2, wherein the act of checking the contents of system memory comprises having error checking logic examine the contents of system memory for non-correctable errors.

6. The method as in claim 1, wherein the system memory is partitioned into pages prior to storing the substantial image of system memory to the non-volatile memory.

7. The method as in claim 6, wherein the act of checking the contents of system memory for errors occurs page-by-page.

8. The method as in claim 7, wherein the act of restoring occurs on a page-by-page basis for pages where an error is found.

9. The method as in claim 8, further comprising the act of calculating a signature value for each page of memory prior to storing a substantial image to non-volatile memory.

10. The method as in claim 9, further comprising the act of storing the signature value for each page.

11. The method as in claim 10, wherein the act of checking the contents of system memory includes:

calculating a second signature value for each page of memory; and

comparing the second signature value for each page with the saved signature value for that page.

12. The method as in claim 1, wherein the act of storing includes:

identifying each page directory that has valid data;

identifying each page table that has valid data;

storing a copy of a page frame addressed by each page table that has valid data, together with a value identifying the associated page table.

13. The method as in claim 12, further comprising the act of calculating a cumulative signature value for each stored page frame associated with a particular page directory.

14. The method as in claim 13, further comprising the act of calculating a size value representing the cumulative number of page frames stored for a page directory.

15. The method as in claim 14, further comprising the act of storing the cumulative signature value and the cumulative number of page frames for each page directory.

16. The method as in claim 15, wherein the cumulative signature value and cumulative size value are stored as an entry in a page entry backup register.

17. The method as in claim 16, wherein the copy of the page frame from all valid pages of system memory together with the value identifying the associated page table are stored in a hibernation data file.

18. The method of claim 17, wherein the page entry backup register is stored in non-volatile memory.

19. The method of claim 18, wherein the page directory has an associated page directory register entry, and the page directory register entry includes a designated bit that is cleared until its associated page frames are validated after checking the contents of system memory.

20. The method of claim 19, wherein the act of reading the contents of system memory occurs after a suspend mode is exited.

21. The method of claim 20, wherein the act of reading occurs on a page directory basis in response to a memory access to an address within the page directory.

22. The method of claim 21, wherein the act of reading only occurs if the page directory register present bit is set.

23. The method of claim 22, wherein the act of reading only occurs if the designated bit is cleared.

24. The method of claim 23, wherein the act of checking includes calculating a signature value for each page directory and comparing the calculated signature value with the signature value stored in the page entry backup register.

25. The method as in claim 24, wherein the act of checking is performed on a page directory basis.

26. The method as in claim 24, wherein the act of restoring occurs on a page directory basis if the page directory signature values do not match.

27. The method as in claim 1, wherein the act of storing the substantial image occurs prior to a system suspend operation, and the error checking and restoration occurs after a system resume operation.

29. The method of claim 28, wherein each page of memory is read and a signature is calculated for each page of system memory that contains valid data, and each page and associated signature is stored in non-volatile memory.

30. The method of claim 29, wherein each page of memory is read and a signature is calculated and compared to the saved signature to determine if each page of system memory is valid after resuming operation.

31. The method of claim 28, wherein the non-volatile memory comprises a hard disk drive.

32. The method of claim 28, wherein the signature comprises a checksum value.

33. The method of claim 28, wherein the signature comprises a cycle redundancy check value.

34. The method of claim 28, wherein the page of memory is assumed to be valid if the signatures match.

35. The method of claim 28, wherein the suspend state is a Suspend to RAM state where the RAM remains powered.

36. The method of claim 28, wherein the suspend state includes turning off system clocks and removing power from peripheral devices, and the act of resuming normal operation includes turning on system clocks and returning power to the peripheral devices.

37. The method of claim 28, wherein the acts of reading the page of system memory and calculating a signature, comparing the signature with the saved signature, and restoring the substantial image of the page of system memory, all occur in response to an access to that page of memory.

38. The method of claim 28, wherein the acts of reading the page of system memory and calculating a signature, comparing the signature with the saved signature, and restoring the substantial image of the page of system memory, all occur prior to restoring operation to the user.

40. The method of claim 39, wherein the data that is not validated is restored from non-volatile memory.

41. The method of claim 39, wherein the act of storing data includes:

determining if a Page Directory includes valid data;

identifying each Page Table within a Page Directory that includes valid data in system memory, and

saving a copy of the valid data from each table in non-volatile memory, together with a value representing the Page Table number associated with the data from each page of memory.

42. The method of claim 41, wherein the act of calculating a signature value includes concatenating all data from each Page Table within a Page Directory to determine the signature value.

43. The method of claim 41, wherein the signature value is a cumulative checksum of all Page Tables within a Page Directory.

44. The method of claim 43, further comprising the act of saving a value indicating the number of page tables with valid data for each Page Directory.

45. The method of claim 44, wherein the method is repeated for each Page Directory.

46. The method of claim 45, further comprising storing a page entry backup register that includes a signature value and a size value for each Page Directory.

47. The method of claim 41, wherein the method is repeated for each page of memory.

49. A system as in claim 48, wherein the system memory is partitioned into pages by the CPU, and the CPU calculates a signature value for each page.

50. A system as in claim 49, wherein, after the system exits from the low power mode, the CPU calculates a second signature value and compares that value with the stored signature value.

51. A system as in claim 50, wherein the stored signature value is also stored in non-volatile memory.

52. A system as in claim 50, wherein the non-volatile memory comprises a hard disk.

53. A system as in claim 50, wherein the non-volatile memory comprises static RAM.

54. A system as in claim 51, wherein the CPU restores the copy of the memory page stored in non-volatile RAM to system memory for any memory page for which the second signature value does not match the stored signature value.

55. A system as in claim 48, wherein the system memory comprises error checking and correction memory.

56. A system as in claim 48, wherein the system memory comprises parity memory.

57. A system as in claim 49, wherein the CPU includes page translation hardware that partitions memory into pages.

59. The method of claim 58, wherein the low power state comprises a hibernation state.

60. The method of claim 59, wherein the low power state comprises a suspend to RAM state.

61. The method of claim 60, wherein the act of restoring the accessed memory page includes determining if the accessed memory page is valid, and copying the stored memory page to system memory if the accessed memory page is invalid.

62. The method of claim 61, wherein the stored memory page is not restored if the accessed memory page is valid.

28. A method of placing a computer system into a suspend mode, and resuming normal operation, comprising the acts of:

reading a page of system memory;

calculating a signature for the page;

saving a substantial image of the page of system memory to non-volatile memory;

saving the signature;

entering a suspend state;

resuming normal operation;

reading the page of system memory and calculating a signature of the page of memory;

comparing the signature calculated after resuming normal operation with the signature saved prior to entering the suspended state;

restoring the substantial image of the page of system memory from non-volatile memory and writing to system memory if the signatures do not match.

39. A method of placing a computer system into a low power state, comprising the acts of:

determining if a page of system memory includes valid data;

storing a copy of any valid data into non-volatile memory;

calculating a signature value associated with the stored data, and saving that signature value in memory;

placing the computer into a suspend mode where the system memory remains powered;

resuming operation of the computer system; and

validating the contents of system memory by calculating a new signature value and comparing the new signature value with the saved signature value.

48. A computer system capable of entering a low power mode of operation, comprising:

a CPU;

a system memory that remains powered during the low power mode of operation;

a non-volatile memory device;

wherein the CPU calculates a signature value for data stored in said system memory prior to entering the low power mode, and stores the signature value; and

wherein the CPU copies the data stored in said system memory to non-volatile memory prior to entering the low power mode.

58. A method of restoring a computer system from a low power state, comprising the acts of:

configuring system memory as a plurality of memory pages;

storing said memory pages to non-volatile memory;

initiating entry into a low power state;

resuming normal operation from the low power state;

intercepting an access to a memory page that has not been restored from non-volatile memory; and

restoring the accessed memory page from non-volatile memory.