System and method for an asynchronous data buffer having buffer write and read pointers

• US 7,594,088 B2
• Filed: 05/04/2006
• Issued: 09/22/2009
• Est. Priority Date: 06/04/2004
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: LaBerge, Paul A.
• Primary Examiner(s): Ellis; Kevin L
• Assistant Examiner(s): Farrokh; Hashem
• Application Number:
  US11/418,897
• Publication Number:
  US 20060200642A1
• Time in Patent Office: 1,237 Days
• Field of Search: 711/5, 711/167, 365/233.1
• US Class Current: 711/167
• CPC Class Codes: G06F 13/1684 using multiple buses
• CPC Class Codes: G06F 13/1689 Synchronisation and timing concerns synchronisation on a memory bus G06F13/4234
• CPC Class Codes: G11C 29/02 Detection or location of defective auxiliary circuits, e.g. defective refresh counters
• CPC Class Codes: G11C 29/022 in I/O circuitry
• CPC Class Codes: G11C 29/023 in clock generator or timing circuitry
• CPC Class Codes: G11C 29/025 in signal lines
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters
• CPC Class Codes: G11C 29/50012 of timing
• CPC Class Codes: G11C 5/04 Supports for storage elements , e.g. memory modules; Mounting or fixing of storage elements on such supports
• CPC Class Codes: G11C 7/1012 Data reordering during input/output, e.g. crossbars, layers of multiplexers, shifting or rotating
• CPC Class Codes: G11C 7/1039 using pipelining techniques, i.e. using latches between functional memory parts, e.g. row/column decoders, I/O buffers, sense amplifiers
• CPC Class Codes: G11C 7/1051 Data output circuits, e.g. read-out amplifiers, data output buffers, data output registers, data output level conversion circuits
• CPC Class Codes: G11C 7/1066 Output synchronization
• CPC Class Codes: G11C 7/1069 I/O lines read out arrangements
• CPC Class Codes: G11C 7/1093 Input synchronization
• CPC Class Codes: G11C 7/22 Read-write [R-W] timing or clocking circuits; Read-write [R-W] control signal generators or management

Abstract

A system and method for facilitating the adjustment of timing parameters between a memory controller operating in a first clock domain and a memory device operating in a second clock domain. A write pointer and a read pointer are monitored to provide a write-read pointer offset representing the timing between when read data is made available by the memory device and when the read data is retrieved by the memory controller. Based on the write-read pointer offset, adjustment to different timing parameters can be made.

Claims

1. A method, comprising:

storing read data in sequentially selected data locations of a buffer responsive to a first clock signal;

retrieving read data from sequentially selected data locations of the buffer responsive to a second clock signal;

identifying a first data location in the buffer where read data is stored responsive to the first clock signal;

identifying a second data location in the buffer where read data is retrieved responsive to the second clock signal;

comparing the first data location and the second data location to determine a number of data locations between the first data location and the second data location, the number of data locations indicative of a timing offset; and

adjusting timing parameters responsive to the timing offset.

2. The method of claim 1 wherein identifying the first data location in the buffer where read data is stored in responsive to the first clock signal comprises providing a write pointer indicative of the first data location in the buffer, the write pointer sequentially incremented responsive to the first clock signal as read data is stored in the buffer, wherein identifying the second data location in the buffer where read data is retrieved from responsive to the second clock signal comprises providing a read pointer indicative of the second data location in the buffer, the read pointer sequentially incremented responsive to the second clock signal as read data is retrieved from the buffer, and wherein comparing the first data location and the second data location to determine a number of data locations between the first data location and the second data location comprises comparing the write pointer and the read pointer to determine a write-read pointer offset indicative of the relative timing between storing read data in the buffer and retrieving read data from the buffer.

3. The method of claim 2 wherein adjusting timing parameters responsive to the timing offset comprises decreasing the time between storing read data in the buffer and retrieving read data from the buffer in response to the write-read pointer offset being greater than a predetermined value.

4. The method of claim 2 wherein adjusting timing parameters responsive to the timing offset comprises increasing the time between storing read data in the buffer and retrieving read data from the buffer in response to the write-read pointer offset being less than a predetermined value.

5. The method of claim 2 wherein adjusting timing parameters responsive to the timing offset comprises adjusting timing between issuance of memory write commands and memory read commands based on the write-read pointer offset.

6. The method of claim 5 wherein adjusting timing between issuance of memory write commands and memory read commands based on the write-read pointer offset comprises adjusting timing of when to issue a memory write command immediately following a memory read command based on the write-read pointer offset.

7. The method of claim 5 wherein adjusting timing between issuance of memory write commands and memory read commands based on the write-read pointer offset comprises adjusting timing of when to issue a memory read command immediately following a memory write command based on the write-read pointer offset.

8. The method of claim 1 wherein adjusting timing parameters responsive to the timing offset comprises adjusting timing of retrieving read data from the buffer relative to storing read data in the buffer when no memory requests are pending.

9. The method of claim 2 wherein comparing the write pointer and the read pointer comprises comparing the write pointer and the read pointer during a burst memory read operation.

10. The method of claim 1 wherein storing read data in sequentially selected data locations of the buffer comprises providing a selection signal for sequentially selecting the data locations by shifting a first flag bit in response to a rising edge of a strobe signal through a first set of series-coupled flip-flops having a last flip-flop coupled to a first flip-flop of the first set, and by shifting a second flag bit in response to a falling edge of the strobe signal through a second set of series-coupled flip-flops having a last flip-flop coupled to a first flip-flop of the second set.

11. The method of claim 1 wherein the first clock signal comprises a memory device clock signal, and wherein the second clock signal comprises a core clock signal.

12. A method, comprising:

identifying a first data location in a buffer where read data is stored in responsive to the first clock signal, the read data stored in sequentially selected data locations of the buffer;

identifying a second data location in the buffer where read data is retrieved from responsive to the second clock signal, the read data retrieved from sequentially selected data locations of the buffer;

comparing the first data location and the second data location to determine a number of data locations between the first data location and the second data location, the number of data locations indicative of a timing offset; and

executing data transfer operations responsive to the timing offset.

13. The method of claim 12 wherein executing data transfer operations responsive to the timing offset comprises decreasing the time between storing read data in the buffer and retrieving read data from the buffer in response to the number of data locations between the first data location and the second data location being greater than a predetermined number.

14. The method of claim 12 wherein executing data transfer operations responsive to the timing offset comprises increasing the time between storing read data in the buffer and retrieving read data from the buffer in response to the number of data locations between the first data location and the second data location being less than a predetermined number.

15. The method of claim 12 wherein executing data transfer operations responsive to the timing offset comprises adjusting timing between issuance of memory write commands and memory read commands based on the timing offset.

16. The method of claim 15 wherein adjusting timing between issuance of memory write commands and memory read commands based on the timing offset comprises adjusting timing of when to issue a memory write command immediately following a memory read command based on the timing offset.

17. The method of claim 15 wherein adjusting timing between issuance of memory write commands and memory read commands based on the timing offset comprises adjusting timing of when to issue a memory read command immediately following a memory write command based on the timing offset.

18. The method of claim 12 wherein executing data transfer operations responsive to the timing offset comprises adjusting timing of retrieving read data from the buffer relative to storing read data in the buffer when no memory requests are pending.

19. The method of claim 12 wherein determining a number of data locations between the first data location and the second data location comprises determining a number of data locations between the first data location and the second data location during a burst memory read operation.

20. The method of claim 12 wherein storing read data in sequentially selected data locations of the buffer comprises providing a selection signal for sequentially selecting the data locations by shifting a first flag bit in response to a rising edge of a strobe signal through a first set of series-coupled flip-flops having a last flip-flop coupled to a first flip-flop of the first set, and by shifting a second flag bit in response to a falling edge of the strobe signal through a second set of series-coupled flip-flops having a last flip-flop coupled to a first flip-flop of the second set.

21. The method of claim 12 wherein the first clock signal comprises a memory device clock signal, and wherein the second clock signal comprises a core clock signal.

22. An apparatus, comprising:

a synchronization module operable to couple data between a first time domain and a second time domain, the synchronization module comprising;

a first pointer circuit, the first pointer circuit operable to generate a first pointer signal indicative of a data location in a buffer where data is to be stored in responsive to a first clock signal;

a buffer coupled to the first pointer circuit, the buffer having a plurality of data locations;

a second pointer circuit, the second pointer circuit operable to generate a second pointer signal indicative of a data location in the buffer where data is to be retrieved from responsive to a second clock signal;

a selection circuit coupled to the buffer and the second pointer circuit, the selection circuit operable to selectively couple data stored in the plurality of data locations of the buffer to an output terminal of the selection circuit responsive to the second clock signal;

data latch coupled to the output terminal of the selection circuit to latch the data selectively coupled thereto responsive to the first clock signal; and

a comparison circuit coupled to the first pointer circuit and the second pointer circuit, the comparison circuit operable to compare the first pointer signal and the second pointer signal to generate a pointer offset signal indicative of a pointer offset.

23. The apparatus of claim 22 wherein the first pointer circuit comprises:

a first set of series-coupled flip-flops having an output of a last flip-flop coupled to an input of a first flip-flop, the first set of series-coupled flip-flops operable to shift a first flag through each flip-flop in response to a rising edge of the first clock signal; and

a second set of series-coupled flip-flops having an output of a last flip-flop coupled to an input of a second flip-flop, the second set of series-coupled flip-flops operable to shift a second flag through each flip-flop in response to a rising edge of the second clock signal,

output signals of the flip-flops of the first and second sets of series-coupled flip-flops representative of the first pointer signal.

24. The apparatus of claim 23 wherein the second pointer circuit comprises a plurality of flip-flops, each of the plurality of flip-flops operable to output a respective bit of a count value responsive to the second clock signal, the count value representative of the second pointer signal.

25. The apparatus of claim 24 wherein the comparison circuit comprises:

a logic circuit having a plurality of input nodes and a plurality of output nodes, the plurality of input nodes coupled to outputs of the first and second sets of series-coupled flip-flops, the logic circuit operable to generate flag signals at each of the plurality of output nodes indicative of location of the first and second flags in the first and second sets of series-coupled flip-flops;

a first multiplexer having a plurality of input terminals coupled to the plurality of output nodes of the logic circuit, a selection terminal coupled to the second pointer circuit, and further having an output terminal, the first multiplexer operable to selectively couple one of the plurality of input terminals to the output terminal responsive to the second pointer signal provided by the second pointer circuit; and

a second multiplexer having a plurality of input terminals coupled to the plurality of output nodes of the logic circuit, a selection terminal coupled to the second pointer circuit, and further having an output terminal, the second multiplexer operable to selectively couple one of the plurality of input terminals to the output terminal responsive to the second pointer signal provided by the second pointer circuit,

outputs of the first and second multiplexers representative of the pointer offset signal.

26. The apparatus of claim 25 wherein the logic circuit comprises a plurality of three-input logic OR gates, each of the plurality of three-input logic OR gates having a first and a second inputs coupled to outputs of two flip-flops of the first set of series-coupled flip-flops and further having a third input coupled to an output of a respective flip-flop of the second set of series-coupled flip-flops.

27. The apparatus of claim 25, further comprising:

a first pair of series-coupled flip-flops coupled to the output terminal of the first multiplexer, the first pair of series-coupled flip-flops operable to shift the output of the first multiplexer through the first pair of series-coupled flip-flops responsive to the second clock signal; and

a second pair of series-coupled flip-flops coupled to the output terminal of the second multiplexer, the second pair of series-coupled flip-flops operable to shift the output of the second multiplexer through the second pair of series-coupled flip-flops responsive to the second clock signal.

28. The apparatus of claim 22 wherein the first clock signal comprises a memory device clock signal, and wherein the second clock signal comprises a core clock signal.

29. A memory hub, comprising:

a link interface adapted to receive memory requests for access to memory locations in at least one memory device of a plurality of memory devices;

a memory device interface adapted to receive read data in response to memory requests;

a memory controller coupled to the link interface and the memory device interface, the memory controller operable to couple memory requests to the memory device interface responsive to memory requests received from the link interface and further operable to adjust timing parameters responsive to a pointer offset signal indicative of a pointer offset; and

a synchronization module coupled to a memory device, the memory device interface and the memory controller, the memory device operating according to a first clock signal, the synchronization module operable to couple read data from the memory device to the memory controller, the memory controller operable to receive memory requests from the link interface responsive to a second clock signal, the synchronization module comprising;

a first pointer circuit, the first pointer circuit operable to generate a first pointer signal indicative of a data location in a buffer where data is to be stored in responsive to the first clock signal;

a second pointer circuit, the second pointer circuit operable to generate a second pointer signal indicative of a data location in the buffer where data is to be retrieved from responsive to the second clock signal; and

a comparison circuit coupled to the first pointer circuit and the second pointer circuit, the comparison circuit operable to compare the first pointer signal and the second pointer signal to generate the pointer offset signal.

30. The memory hub of claim 29, further comprising:

a buffer coupled to the first pointer circuit, the buffer having a plurality of data locations; and

a selection circuit coupled to the buffer and the second pointer circuit, the selection circuit operable to selectively couple data stored in the plurality of data locations of the buffer to an output terminal of the selection circuit responsive to the second clock signal.

31. The memory hub of claim 30, further comprising a data latch coupled to the output terminal of the selection circuit to latch the data selectively coupled thereto responsive to the first clock signal.

32. The memory hub of claim 29 wherein the first pointer circuit comprises:

a first set of series-coupled flip-flops having an output of a last flip-flop coupled to an input of a first flip-flop, the first set of series-coupled flip-flops operable to shift a first flag through each flip-flop in response to a rising edge of the first clock signal; and

a second set of series-coupled flip-flops having an output of a last flip-flop coupled to an input of a second flip-flop, the second set of series-coupled flip-flops operable to shift a second flag through each flip-flop in response to a rising edge of the second clock signal,

output signals of the flip-flops of the first and second sets of series-coupled flip-flops representative of the first pointer signal.

33. The memory hub of claim 32 wherein the second pointer circuit comprises a plurality of flip-flops, each of the plurality of flip-flops operable to output a respective bit of a count value responsive to the second clock signal, the count value representative of the second pointer signal.

34. The memory hub of claim 33 wherein the comparison circuit comprises:

a logic circuit having a plurality of input nodes and a plurality of output nodes, the plurality of input nodes coupled to outputs of the first and second sets of series-coupled flip-flops, the logic circuit operable to generate flag signals at each of the plurality of output nodes indicative of location of the first and second flags in the first and second sets of series-coupled flip-flops;

a first multiplexer having a plurality of input terminals coupled to the plurality of output nodes of the logic circuit, a selection terminal coupled to the second pointer circuit, and further having an output terminal, the first multiplexer operable to selectively couple one of the plurality of input terminals to the output terminal responsive to the second pointer signal provided by the second pointer circuit; and

a second multiplexer having a plurality of input terminals coupled to the plurality of output nodes of the logic circuit, a selection terminal coupled to the second pointer circuit, and further having an output terminal, the second multiplexer operable to selectively couple one of the plurality of input terminals to the output terminal responsive to the second pointer signal provided by the second pointer circuit,

outputs of the first and second multiplexers representative of the pointer offset signal.

35. The memory hub of claim 34 wherein the logic circuit comprises a plurality of three-input logic OR gates, each of the plurality of three-input logic OR gates having a first and a second inputs coupled to outputs of two flip-flops of the first set of series-coupled flip-flops and further having a third input coupled to an output of a respective flip-flop of the second set of series-coupled flip-flops.

36. The memory hub of claim 34, further comprising:

a first pair of series-coupled flip-flops coupled to the output terminal of the first multiplexer, the first pair of series-coupled flip-flops operable to shift the output of the first multiplexer through the first pair of series-coupled flip-flops responsive to the second clock signal; and

a second pair of series-coupled flip-flops coupled to the output terminal of the second multiplexer, the second pair of series-coupled flip-flops operable to shift the output of the second multiplexer through the second pair of series-coupled flip-flops responsive to the second clock signal.

37. The memory hub of claim 29 wherein the first clock signal comprises a memory device clock signal, and wherein the second clock signal comprises a core clock signal.

38. The memory hub of claim 29 wherein the memory controller operable to decrease the time between storing read data in the buffer and retrieving read data from the buffer in response to the pointer offset being greater than a predetermined value.

39. The memory hub of claim 29 wherein the memory controller operable to increase the time between storing read data in the buffer and retrieving read data from the buffer in response to the pointer offset being less than a predetermined value.

40. The memory hub of claim 29 wherein the memory controller operable to adjust timing between issuance of memory write commands and memory read commands based on the pointer offset.

41. The memory hub of claim 40 wherein the memory controller operable to adjust timing of when to issue a memory write command immediately following a memory read command based on the pointer offset.

42. The memory hub of claim 40 wherein the memory controller operable to adjust timing of when to issue a memory read command immediately following a memory write command based on the pointer offset.

43. The memory hub of claim 29 wherein the memory controller operable to adjust timing of retrieving read data from the buffer relative to storing read data in the buffer when no memory requests are pending.

44. The memory hub of claim 29 wherein the memory controller operable to compare the first pointer signal and the second pointer signal during a burst memory read operation.

45. A memory module, comprising:

a plurality of memory devices;

a memory bus coupled to the plurality of memory devices; and

a memory hub coupled to the plurality of memory devices through the memory bus, the memory hub comprising;

a link interface adapted to receive memory requests for access to memory locations in at least one memory device of the plurality of memory devices;

a memory device interface adapted to receive read data in response to memory requests;

a memory controller coupled to the link interface and the memory device interface, the memory controller operable to couple memory requests to the memory device interface responsive to memory requests received from the link interface and further operable to adjust timing parameters responsive to a pointer offset signal indicative of a pointer offset; and

a synchronization module coupled to a memory device, the memory device interface and the memory controller, the memory device operating according to a first clock signal, the synchronization module operable to couple read data from the memory device to the memory controller, the memory controller operable to receive memory requests from the link interface responsive to a second clock signal, the synchronization module comprising;

a first pointer circuit, the first pointer circuit operable to generate a first pointer signal indicative of a data location in a buffer where data is to be stored in responsive to the first clock signal;

a second pointer circuit, the second pointer circuit operable to generate a second pointer signal indicative of a data location in the buffer where data is to be retrieved from responsive to the second clock signal; and

a comparison circuit coupled to the first pointer circuit and the second pointer circuit, the comparison circuit operable to compare the first pointer signal and the second pointer signal to generate the pointer offset signal.

46. The memory module of claim 45, further comprising:

a buffer coupled to the first pointer circuit, the buffer having a plurality of data locations; and

a selection circuit coupled to the buffer and the second pointer circuit, the selection circuit operable to selectively couple data stored in the plurality of data locations of the buffer to an output terminal of the selection circuit responsive to the second clock signal.

47. The memory module of claim 46, further comprising a data latch coupled to the output terminal of the selection circuit to latch the data selectively coupled thereto responsive to the first clock signal.

48. The memory module of claim 45 wherein the first pointer circuit comprises:

a first set of series-coupled flip-flops having an output of a last flip-flop coupled to an input of a first flip-flop, the first set of series-coupled flip-flops operable to shift a first flag through each flip-flop in response to a rising edge of the first clock signal; and

a second set of series-coupled flip-flops having an output of a last flip-flop coupled to an input of a second flip-flop, the second set of series-coupled flip-flops operable to shift a second flag through each flip-flop in response to a rising edge of the second clock signal,

output signals of the flip-flops of the first and second sets of series-coupled flip-flops representative of the first pointer signal.

49. The memory module of claim 48 wherein the second pointer circuit comprises a plurality of flip-flops, each of the plurality of flip-flops operable to output a respective bit of a count value responsive to the second clock signal, the count value representative of the second pointer signal.

50. The memory module of claim 49 wherein the comparison circuit comprises:

a logic circuit having a plurality of input nodes and a plurality of output nodes, the plurality of input nodes coupled to outputs of the first and second sets of series-coupled flip-flops, the logic circuit operable to generate flag signals at each of the plurality of output nodes indicative of location of the first and second flags in the first and second sets of series-coupled flip-flops;

a first multiplexer having a plurality of input terminals coupled to the plurality of output nodes of the logic circuit, a selection terminal coupled to the second pointer circuit, and further having an output terminal, the first multiplexer operable to selectively couple one of the plurality of input terminals to the output terminal responsive to the second pointer signal provided by the second pointer circuit; and

a second multiplexer having a plurality of input terminals coupled to the plurality of output nodes of the logic circuit, a selection terminal coupled to the second pointer circuit, and further having an output terminal, the second multiplexer operable to selectively couple one of the plurality of input terminals to the output terminal responsive to the second pointer signal provided by the second pointer circuit,

outputs of the first and second multiplexers representative of the pointer offset signal.

51. The memory module of claim 50 wherein the logic circuit comprises a plurality of three-input logic OR gates, each of the plurality of three-input logic OR gates having a first and a second inputs coupled to outputs of two flip-flops of the first set of series-coupled flip-flops and further having a third input coupled to an output of a respective flip-flop of the second set of series-coupled flip-flops.

52. The memory module of claim 50, further comprising:

a first pair of series-coupled flip-flops coupled to the output terminal of the first multiplexer, the first pair of series-coupled flip-flops operable to shift the output of the first multiplexer through the first pair of series-coupled flip-flops responsive to the second clock signal; and

a second pair of series-coupled flip-flops coupled to the output terminal of the second multiplexer, the second pair of series-coupled flip-flops operable to shift the output of the second multiplexer through the second pair of series-coupled flip-flops responsive to the second clock signal.

53. The memory module of claim 45 wherein the first clock signal comprises a memory device clock signal, and wherein the second clock signal comprises a core clock signal.

54. The memory module of claim 45 wherein the memory controller operable to decrease the time between storing read data in the buffer and retrieving read data from the buffer in response to the pointer offset being greater than a predetermined value.

55. The memory module of claim 45 wherein the memory controller operable to increase the time between storing read data in the buffer and retrieving read data from the buffer in response to the pointer offset being less than a predetermined value.

56. The memory module of claim 45 wherein the memory controller operable to adjust timing between issuance of memory write commands and memory read commands based on the pointer offset.

57. The memory module of claim 56 wherein the memory controller operable to adjust timing of when to issue a memory write command immediately following a memory read command based on the pointer offset.

58. The memory module of claim 56 wherein the memory controller operable to adjust timing of when to issue a memory read command immediately following a memory write command based on the pointer offset.

59. The memory module of claim 45 wherein the memory controller operable to adjust timing of retrieving read data from the buffer relative to storing read data in the buffer when no memory requests are pending.

60. The memory module of claim 45 wherein the memory controller operable to compare the first pointer signal and the second pointer signal during a burst memory read operation.

61. A processor-based system, comprising:

a processor;

a system controller coupled to the processor;

a memory bus coupled to the system controller, the memory bus adapted to transmit memory requests and responses; and

a plurality of memory modules, each of the plurality of memory modules comprising;

a plurality of memory devices;

a memory bus coupled to the plurality of memory devices; and

a memory hub coupled to the plurality of memory devices through the memory bus, the memory hub comprising;

a link interface adapted to receive memory requests for access to memory locations in at least one memory device of a plurality of memory devices;

a memory device interface adapted to receive read data in response to memory requests;

a memory controller coupled to the link interface and the memory device interface, the memory controller operable to couple memory requests to the memory device interface responsive to memory requests received from the link interface and further operable to adjust timing parameters responsive to a pointer offset signal indicative of a pointer offset; and

a synchronization module coupled to a memory device, the memory device interface and the memory controller, the memory device operating according to a first clock signal, the synchronization module operable to couple read data from the memory device to the memory controller, the memory controller operable to receive memory requests from the link interface responsive to a second clock signal, the synchronization module comprising;

a first pointer circuit, the first pointer circuit operable to generate a first pointer signal indicative of a data location in a buffer where data is to be stored in responsive to the first clock signal;

a second pointer circuit, the second pointer circuit operable to generate a second pointer signal indicative of a data location in the buffer where data is to be retrieved from responsive to the second clock signal; and

a comparison circuit coupled to the first pointer circuit and the second pointer circuit, the comparison circuit operable to compare the first pointer signal and the second pointer signal to generate the pointer offset signal.

62. The processor-based system of claim 61, further comprising:

an input device coupled to the system controller;

an output device coupled to the system controller; and

a data storage device coupled to the system controller.

63. The processor-based system of claim 62, further comprising:

a buffer coupled to the first pointer circuit, the buffer having a plurality of data locations; and

a selection circuit coupled to the buffer and the second pointer circuit, the selection circuit operable to selectively couple data stored in the plurality of data locations of the buffer to an output terminal of the selection circuit responsive to the second clock signal.

64. The processor-based system of claim 63, further comprising a data latch coupled to the output terminal of the selection circuit to latch the data selectively coupled thereto responsive to the first clock signal.

65. The processor-based system of claim 61 wherein the first pointer circuit comprises:

a first set of series-coupled flip-flops having an output of a last flip-flop coupled to an input of a first flip-flop, the first set of series-coupled flip-flops operable to shift a first flag through each flip-flop in response to a rising edge of the first clock signal; and

a second set of series-coupled flip-flops having an output of a last flip-flop coupled to an input of a second flip-flop, the second set of series-coupled flip-flops operable to shift a second flag through each flip-flop in response to a rising edge of the second clock signal,

output signals of the flip-flops of the first and second sets of series-coupled flip-flops representative of the first pointer signal.

66. The processor-based system of claim 65 wherein the second pointer circuit comprises a plurality of flip-flops, each of the plurality of flip-flops operable to output a respective bit of a count value responsive to the second clock signal, the count value representative of the second pointer signal.

67. The processor-based system of claim 66 wherein the comparison circuit comprises:

a logic circuit having a plurality of input nodes and a plurality of output nodes, the plurality of input nodes coupled to outputs of the first and second sets of series-coupled flip-flops, the logic circuit operable to generate flag signals at each of the plurality of output nodes indicative of location of the first and second flags in the first and second sets of series-coupled flip-flops;

a first multiplexer having a plurality of input terminals coupled to the plurality of output nodes of the logic circuit, a selection terminal coupled to the second pointer circuit, and further having an output terminal, the first multiplexer operable to selectively couple one of the plurality of input terminals to the output terminal responsive to the second pointer signal provided by the second pointer circuit; and

a second multiplexer having a plurality of input terminals coupled to the plurality of output nodes of the logic circuit, a selection terminal coupled to the second pointer circuit, and further having an output terminal, the second multiplexer operable to selectively couple one of the plurality of input terminals to the output terminal responsive to the second pointer signal provided by the second pointer circuit,

outputs of the first and second multiplexers representative of the pointer offset signal.

68. The processor-based system of claim 67 wherein the logic circuit comprises a plurality of three-input logic OR gates, each of the plurality of three-input logic OR gates having a first and a second inputs coupled to outputs of two flip-flops of the first set of series-coupled flip-flops and further having a third input coupled to an output of a respective flip-flop of the second set of series-coupled flip-flops.

69. The processor-based system of claim 67, further comprising:

a first pair of series-coupled flip-flops coupled to the output terminal of the first multiplexer, the first pair of series-coupled flip-flops operable to shift the output of the first multiplexer through the first pair of series-coupled flip-flops responsive to the second clock signal; and

a second pair of series-coupled flip-flops coupled to the output terminal of the second multiplexer, the second pair of series-coupled flip-flops operable to shift the output of the second multiplexer through the second pair of series-coupled flip-flops responsive to the second clock signal.

70. The processor-based system of claim 61 wherein the first clock signal comprises a memory device clock signal, and wherein the second clock signal comprises a core clock signal.

71. The processor-based system of claim 61 wherein the memory controller operable to decrease the time between storing read data in the buffer and retrieving read data from the buffer in response to the pointer offset being greater than a predetermined value.

72. The processor-based system of claim 61 wherein the memory controller operable to increase the time between storing read data in the buffer and retrieving read data from the buffer in response to the pointer offset being less than a predetermined value.

73. The processor-based system of claim 61 wherein the memory controller operable to adjust timing between issuance of memory write commands and memory read commands based on the pointer offset.

74. The processor-based system of claim 73 wherein the memory controller operable to adjust timing of when to issue a memory write command immediately following a memory read command based on the pointer offset.

75. The processor-based system of claim 73 wherein the memory controller operable to adjust timing of when to issue a memory read command immediately following a memory write command based on the pointer offset.

76. The processor-based system of claim 61 wherein the memory controller operable to adjust timing of retrieving read data from the buffer relative to storing read data in the buffer when no memory requests are pending.

77. The processor-based system of claim 61 wherein the memory controller operable to compare the first pointer signal and the second pointer signal during a burst memory read operation.