System and method for dynamic mirror-bank addressing

• US 7,194,568 B2
• Filed: 03/21/2003
• Issued: 03/20/2007
• Est. Priority Date: 03/21/2003
• Status: Expired due to Fees

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Jeter, Robert E. Jr., Potter, Kenneth H. Jr.
• Primary Examiner(s): PORTKA, GARY J
• Application Number:
  US10/394,984
• Publication Number:
  US 20040186945A1
• Time in Patent Office: 1,460 Days
• Field of Search: None
• US Class Current: 711/5
• CPC Class Codes: G06F 11/1451 by selection of backup contents
• CPC Class Codes: G06F 11/2069 Management of state, configuration or failover
• CPC Class Codes: G06F 11/2087 with a common controller

Abstract

A dynamic addressing technique mirrors data across multiple banks of a memory resource. Information stored in the memory banks is organized into separately addressable blocks, and memory addresses include a mirror flag. To write information mirrored across two memory banks, a processor issues a single write transaction with the mirror flag asserted. A memory controller detects that the mirror flag is asserted and, in response, waits for both memory banks to become available. At that point, the memory controller causes the write to be performed at both banks. To read data that has been mirrored across two memory banks, the processor issues a read with the mirror flag asserted. The memory controller checks the availability of both banks having the desired information. If either bank is available, the read request is accepted and the desired data is retrieved from the available bank and returned to the processor.

Claims

1. In a memory controller having access to a plurality of memory banks, a method for writing data that is mirrored at two memory banks, the method comprising the steps of:

receiving a write request where the write request specifies a first memory bank by inclusion of a bank number in the write request, the write request indicating that it is a mirror write request;

identifying a second memory bank at which the data is mirrored, the second memory bank not specified in the write request;

issuing the write request to the two memory banks at which the data is mirrored; and

executing the write request at the two memory banks without locking either memory bank.

2. The method of claim 1 wherein receipt of a single write request causes both memory banks to be updated.

3. The method of claim 2 wherein:

the memory controller has a plurality of state machines, and each state machine is associated with one of the memory banks, and

the single write request received by the memory controller is sent to the two state machines associated with the two memory banks at which the data is mirrored.

4. The method of claim 1 wherein:

the write request includes a memory address of the first memory bank one of the memory banks, and

the memory address has a flag indicating that the write request is a mirror write request.

5. The method of claim 4 wherein:

the write request is issued to the memory controller by a data processing element that is in communicating relationship with the memory controller, and

the data processing element sets the flag to indicate that the write request is a mirror write request.

6. The method of claim 5 wherein the data processing element is a processor.

7. The method of claim 1 further comprising the step of completing the write request at each memory bank before issuing another request to either of the memory banks.

8. In a memory controller having access to a plurality of memory banks, a method for reading data that is mirrored at first and second memory banks, the method comprising the steps of:

receiving a read request specifying the first memory bank by inclusion of a bank number in the read request, the read request indicating that it is a mirror read request;

identifying the second memory bank at which the data is mirrored, the second memory bank not specified in the read request; and

issuing the read request only to the second memory bank provided that the first memory bank specified by the read request is unavailable.

9. The method of claim 8 wherein:

the read request includes a memory address identifying a location within the first memory bank, and

the memory address has a flag indicating that the read request is a mirror read request.

10. The method of claim 9 wherein the flag is set by a data processing entity in communicating relationship with the memory controller to indicate that the read request is a mirror read request.

11. The method of claim 8 further comprising the steps of:

receiving a read request specifying the first memory bank, the read request indicating that it is a non-mirrored read request; and

waiting for the first memory bank becomes available before issuing the read request to the first memory bank, regardless of the availability of the second memory bank.

12. The method of claim 8 further comprising the steps of:

receiving a write request specifying a selected one of the two memory banks, the write request indicating that it is a mirror write request;

identifying the second memory bank at which the data is mirrored;

issuing the write request to the two memory banks at which the data is mirrored; and

executing the write request at the two memory banks without locking either memory bank.

46. The method of claim 8 wherein the first memory bank is unavailable due to the first memory bank servicing another memory access request when the step of issuing is performed.

13. In a memory controller having access to a plurality of memory banks, a method of performing an atomic read-modify-write transaction to data mirrored at first and second memory banks, the method comprising the steps of:

receiving an atomic read-modify-write transaction specifying the first memory bank of the two memory banks, the read-modify-write transaction indicating that it is a mirror read-modify-write transaction;

identifying the second memory bank at which the data is mirrored;

a selecting one of the first and second memory banks from which to read the data depending on the availability of the first and second memory banks;

in response to selecting the first or second memory bank, modifying the data read from that selected memory bank;

issuing the write request to the two memory banks at which the data is mirrored; and

executing the write request at the two memory banks without locking either memory bank.

14. The method of claim 13 wherein:

the atomic transaction includes a memory address identifying a location within the first memory bank, and

the memory address has a flag indicating that the atomic transaction is a mirror atomic transaction.

15. A memory controller configured to access a plurality of memory banks in which data at a first memory bank is mirrored at a second memory bank, the memory controller comprising:

a plurality of buffers for storing requests received by the memory controller, the requests specifying data stored at the memory banks;

means for identifying at least one request as a mirror read request specifying data stored at the first memory bank by inclusion of a bank number in the request;

means for identifying the second memory bank at which the data specified by the mirror read request is mirrored, the second memory bank not specified in the mirror read request;

means for selecting one of the first and second memory banks from which to read the specified data, depending on the availability of the first and second memory banks; and

means for retrieving the data from the selected one of the first and second memory banks.

16. The memory controller of claim 15 further comprising:

means for identifying at least one request as a mirror write request specifying data stored at the first memory bank;

means for identifying the second memory bank at which the data specified by the mirror write request mirrored;

issuing the write request to the two memory banks at which the data is mirrored; and

means for executing the write request at the two memory banks without locking either memory bank.

17. The memory controller of claim 16 wherein

the data at the memory banks is organized as separately addressable memory blocks, and

data is mirrored between the first and second memory banks on a block level.

18. The memory controller of claim 15 wherein

the requests include a memory address of the specified data,

the memory addresses include a mirror flag,

the means for identifying at least one request as a mirror write request utilizes the mirror flag of the memory address included with the mirror write request.

19. A method for operating a memory controller, comprising:

receiving a memory request at a first memory bank, where the memory request specifies the first memory bank by inclusion of a bank identifier in the memory request, the memory request indicating that it is a mirror memory request;

identifying, in response to the indication that it is a mirror request, a second memory bank, the second memory bank not specified in the memory request;

waiting until the first memory bank and the second memory bank are free; and

executing the memory request at the first memory bank and the second memory bank;

20. The method of claim 19, further comprising:

executing the memory request immediately after both the first memory bank and the second memory bank become free.

21. The method of claim 19, further comprising:

implementing a two-level arbitration scheme for which the memory request is to be executed during any given access cycle.

22. The method of claim 21, further comprising:

determining the availability of resources by a second level of arbitration.

23. The method of claim 19, further comprising:

using microcode to program information about which blocks are mirrored in the first memory bank and the second memory bank.

24. The method of claim 19, further comprising:

determining, by a mirror flag detection circuit, whether a mirror flag of a physical address for a memory bank is associated with the memory request asserted.

25. The method of claim 19, further comprising:

stalling subsequent requests until resources in the memory controller become available and an oldest request can be issued.

26. The method of claim 19, further comprising:

receiving a write request as the memory request.

27. The method of claim 19, further comprising:

receiving a read request as the memory request.

28. A memory controller, comprising:

means for receiving a memory request at a first memory bank, where the memory request specifies the first memory bank by inclusion of a bank identifier in the memory request, the memory request indicating that it is a mirror memory request;

means for identifying, in response to the indication that it is a mirror request, a second memory bank, the second memory bank not specified in the memory request;

means for waiting until the first memory bank and the second memory bank are free; and

means for executing the memory request at the first memory bank and the second memory bank.

29. The apparatus of claim 28, further comprising:

means for executing the memory request immediately after both the first memory bank and the second memory bank become free.

30. The apparatus of claim 28, further comprising:

means for implementing a two-level arbitration scheme for which the memory request is to be executed during any given access cycle.

31. The apparatus of claim 30, further comprising:

means for determining the availability of resources by a second level of arbitration.

32. The apparatus of claim 28, further comprising:

means for using microcode to program information about which blocks are mirrored in the first memory bank and the second memory bank.

33. The apparatus of claim 28, further comprising:

means for determining, by a mirror flag detection circuit, whether a mirror flag of a physical address for a memory bank is associated with the memory request asserted.

34. The apparatus of claim 28, further comprising:

means for stalling subsequent requests until resources in the memory controller become available and an oldest request can be issued.

35. The apparatus of claim 28, further comprising:

means for receiving a write request as the memory request.

36. The apparatus of claim 28, further comprising:

means for receiving a read request as the memory request.

37. A memory controller, comprising:

the memory controller configured to receive a memory request that specifies a first memory bank by inclusion of a bank identifier in the memory request the memory request indicating that it is a mirror memory request;

the memory controller configured to identify a second memory bank, in response to the indication that it is a mirror memory request, the second memory bank not specified in the memory request;

the first memory bank and the second memory bank configured to wait until both the first memory bank and the second memory bank are free; and

the first memory bank and the second memory bank configured to execute the memory request at the same time.

38. The controller of claim 37, further comprising:

the first memory bank and the second memory bank are configured to execute the memory request immediately after both become free.

39. The controller of claim 37, further comprising:

a two-level arbitration scheme for determining which memory request is to be executed during any given access cycle.

40. The controller of claim 39, further comprising:

a second level of arbitration for determining the availability of resources.

41. The controller of claim 37, further comprising:

a microcode to program information about which blocks are mirrored in the first memory bank and the second memory bank.

42. The controller of claim 37, further comprising:

a mirror flag detection circuit to determine whether a mirror flag of a physical address for a memory bank is associated with the memory request asserted.

43. The controller of claim 37, further comprising:

the memory controller configured to stall subsequent requests until resources become available and an oldest request can be issued.

44. The controller of claim 37, further comprising:

the memory request is a write request.

45. The controller of claim 37, further comprising:

the memory request is a read request.

47. A memory controller having access to a plurality of memory banks, the memory controlled adapted to read data that is mirrored at first and second memory banks, the memory controller comprising:

a request queue configured to receive a read request specifying a first memory bank by inclusion of a bank number in the read request, the read request having a flag that indicates the read request is a mirror read request; and

an arbiter configured to identify the second memory bank at which the data is mirrored, the second memory bank not specified in the read request, end to issue the read request only to the second memory bank provided the first memory bank specified by the read request is unavailable.

48. The memory controller of claim 47 wherein:

the read request includes a memory address identifying a location within the first memory bank.

49. The memory controller of claim 47 wherein the arbiter further comprises:

a plurality of state machines, each state machine associated with one of the memory banks and configured to receive any read requests for the memory bank.

50. The memory controller of claim 49 wherein the arbiter further comprises:

a top-level arbiter configured to determine if the request queue holds a request; and

a bottom-level arbiter configured to monitor the availability of the plurality of memory banks.

51. The memory controller of claim 50 wherein the plurality of state machines are a part of the bottom-level arbiter.

52. The memory controller of claim 47 wherein:

the request queue is further configured to receive a second read request specifying the first memory bank, the second read request indicating that it is a non-mirrored read request; and

the arbiter is further configured to wait for the first memory bank to become available before issuing the second read request to the first memory bank, regardless of the availability of the second memory bank.

53. The memory controller of claim 52 wherein the first memory bank is unavailable due to the pendency of another memory access request at the first memory bank.

54. A memory controller having access to a plurality of memory banks, the memory controller adapted to perform an atomic read-modify-write transaction on data mirrored at first and second memory banks, the memory controller comprising:

a request queue configured to receive an atomic read-modify-write transaction that specifies the first memory bank of the two memory banks, the read-modify-write transaction having a flag that indicates the read-modify-write transaction is a mirror read-modify-write transaction; and

an arbiter configured to, in response to the read-modify-write transaction, identify the second memory bank at which the data is mirrored and to select one of the first and second memory banks from which to read the data based on the availability of the first and second memory banks, and to modify the data read from that selected memory bank and, to write to the two memory banks at which the data is mirrored.

55. The memory controller of claim 54 wherein the atomic read-modify-write transaction includes a memory address identifying a location within the first memory bank.

56. The memory controller of claim 54 wherein the arbiter further comprises:

a plurality of state machines, each state machine associated with one of the memory banks and configured to receive any requests for the memory bank.

57. The memory controller of claim 56 wherein the arbiter further comprises:

a top-level arbiter configured to determine if the request queue holds a request; and

a bottom-level arbiter configured to monitor the availability of the plurality of memory banks.

58. The memory controller of claim 57 wherein the plurality of state machines are a part of the bottom-level arbiter.

59. A memory controller having access to a plurality of memory banks, the memory controller adapted to perform an atomic read-modify-write transaction on data mirrored at first and second memory banks, the memory controller comprising:

means for receiving an atomic read-modify-write transaction specifying the first memory bank of the two memory banks, the read-modify-write transaction indicating that the read-modify-write transaction is a mirror read-modify-write transaction;

means for identifying the second memory bank at which the data is mirrored;

means for selecting one of the first and second memory banks from which to read the data depending on the availability of the first and second memory banks;

means for modifying the data read from that selected memory bank; and

means for writing the modified data to the two memory banks at which the data is mirrored.

60. The memory controller of claim 59 wherein the atomic read-modify-write transaction comprises:

a means for identifying a location within the first memory bank.

62. The memory controller of claim 59 further comprising:

means for determining if a request queue holds a request; and

means for monitoring the availability of the plurality of memory banks.

63. The memory controller of claim 62 wherein the means for receiving is a part of the means for monitoring.

61. A computer readable medium containing executable program instructions to perform an atomic read-modify-write transaction on data mirrored at first and second memory banks, the executable program instructions comprising program instructions adapted to:

receive an atomic read-modify-write transaction specifying the first memory bank of the two memory banks, the read-modify-write transaction indicating that it is a mirror read-modify-write transaction;

identify the second memory bank at which the data is mirrored;

select one of the first and second memory banks from which to read the data depending on the availability of the first and second memory banks;

modify the data read from that selected memory bank; and

write the modified data to the two memory banks at which the data is mirrored.