Reduced latency memory read transactions in storage devices

• US 8,959,307 B1
• Filed: 11/13/2008
• Issued: 02/17/2015
• Est. Priority Date: 11/16/2007
• Status: Active Grant

• Current Assignee: BiTMICRO, LLC (BiTMICRO Networks, Inc.)
• Original Assignee: BiTMICRO Networks, Inc.
• Inventors: Tagayo-Villapana, Elsbeth Lauren, Bruce, Ricardo H., Bruce, Rey H.
• Primary Examiner(s): Parikh, Kalpit
• Application Number:
  US12/270,626
• Time in Patent Office: 2,287 Days
• Field of Search: 711/103, 711/137, 711/170
• US Class Current: 711/170
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 13/28 using burst mode transfer, e.g. direct memory access DMA, cycle steal G06F13/32 takes precedence
• CPC Class Codes: G06F 2212/1024 Latency reduction
• CPC Class Codes: G06F 2212/6022 Using a prefetch buffer or dedicated prefetch cache
• CPC Class Codes: G06F 2212/7203 Temporary buffering, e.g. using volatile buffer or dedicated buffer blocks
• CPC Class Codes: G06F 3/0611 in relation to response time
• CPC Class Codes: G06F 3/0656 Data buffering arrangements
• CPC Class Codes: G06F 3/0688 Non-volatile semiconductor memory arrays

Abstract

A solution for performing reduced latency memory read transactions is disclosed. In one example, a storage apparatus has a memory array that includes: a flash device having a data register, a memory interface coupled to the memory array and a buffer set that includes at least one buffer suitable for use as a prefetch buffer. The memory interface, in response to a memory read transaction request, performs a read operation and, if stored data exists within the memory array that meets a prefetch selection criterion, also performs an internal read operation. The internal read operation includes allocating a prefetch buffer in the buffer set and storing the data as prefetch data in the prefetch buffer. If the memory interface receives a second memory read transaction request for data that is currently available as prefetch data, the memory interface responds by performing a forwarding transaction that includes retrieving the prefetch data from the prefetch buffer and forwarding the prefetch data to a host.

Claims

1. A storage apparatus for performing reduced memory read transactions, said storage apparatus responsive to memory transaction requests from at least one host, the storage apparatus comprising:

a memory array that includes a plurality of flash memory devices including a first flash memory device, said plurality of flash memory devices including a plurality of data registers, each one of said plurality of flash memory devices including a respective one of said plurality of data registers, said first flash memory device including a data register included in said plurality of data registers;

said first flash memory device including a set of non-volatile memory cells and said data register;

a memory interface coupled by a memory bus to said memory array;

said memory interface coupled by a bus to the at least one host during a transmission of memory transaction requests from the at least one host to said memory interface;

said memory interface including a Direct Memory Access (DMA) controller comprising a first buffer and a flash memory controller comprising a second buffer;

a buffer set that includes a plurality of buffers that are suitable for use as prefetch buffers, said buffer set comprising said first buffer in said DMA controller in said memory interface and said second buffer in said flash memory controller in said memory interface;

wherein said memory interface allocates a plurality of prefetch buffers in said buffer set, said plurality of prefetch buffers including said first buffer in said DMA controller and said second buffer in said flash memory controller so that said buffer set includes said plurality of prefetch buffers allocated for storing prefetch data and one or more non-allocated buffers available to said storage apparatus for other memory uses;

wherein, in response to receiving a memory read transaction request, said memory interface performs a read operation, said memory interface configured to identify, within said memory array, stored data that meets a prefetch selection criterion and, if said memory interface identifies stored data existing within said memory array that meets a prefetch selection criterion, said memory interface performs an internal read operation that includes allocating said plurality of prefetch buffers in said buffer set and storing said stored data in at least one of said plurality of prefetch buffers as prefetch data; and

wherein, if said memory interface receives a second memory read transaction request for data and if said data is currently available as said prefetch data in at least one of said plurality of prefetch buffers, said memory interface responds to said second memory read transaction request by performing a forwarding transaction that includes retrieving said prefetch data from at least one of said plurality of prefetch buffers and forwarding said prefetch data to a host, reducing read latency of said second memory read transaction request.

2. The storage apparatus of claim 1, wherein said memory interface further includes a host interface for receiving said memory read transaction request from said host.

3. The storage apparatus of claim 1, wherein said buffer set includes a fixed buffer from said DMA controller.

4. The storage apparatus of claim 1, wherein said buffer set includes a fixed buffer from said flash memory controller.

5. The storage apparatus of claim 1, wherein said flash device contains at least one flash page.

6. The storage apparatus of claim 1, wherein said storage apparatus includes said bus for receiving said memory read transaction request from said host and sending data from the storage apparatus to said host.

7. The storage apparatus of claim 1, wherein said storage apparatus includes a system bus for receiving and sending data between a local processor, said DMA controller, local memory, and a host interface.

8. The storage apparatus of claim 1 wherein said memory interface includes said DMA controller, a local processor, a host interface and local memory coupled together through a system bus;

and said memory interface further includes said flash memory controller coupled to said DMA controller and to said memory array through said memory bus.

9. The storage apparatus of claim 1, wherein said buffer set includes a first data register.

10. A method for reducing latency in memory read transactions by using a low latency memory interface coupled to a memory array that includes a plurality of flash memory devices including a flash memory device, wherein said plurality of flash memory devices includes a plurality of data registers, each one of said plurality of flash memory devices including a respective one of said plurality of data registers, and

wherein said memory interface responds to memory read transaction requests from a host, the method comprising:

receiving a memory read transaction request;

performing a read operation;

identifying prefetch data in said memory array that meets a prefetch selection criterion;

said memory interface coupled by a memory bus to said memory array;

said memory interface coupled by a bus to the host during a transmission of memory transaction requests from the host to said memory interface;

said memory interface including a Direct Memory Access (DMA) controller comprising a first buffer and a flash memory controller comprising a second buffer;

if prefetch data is identified in said memory array, performing an internal read operation that includes transferring prefetch data, allocating said first buffer as a prefetch buffer suitable for storing prefetch data wherein said prefetch buffer is identified from at least one available buffer available in said buffer set that includes said first buffer in said DMA controller in said memory interface and said second buffer in said flash memory controller in said memory interface;

said flash memory device including a set of non-volatile memory cells and said data register;

said memory interface allocates a plurality of prefetch buffers in said buffer set, said plurality of prefetch buffers including said first buffer in said DMA controller and said second buffer in said flash memory controller so that said buffer set includes said plurality of prefetch buffers allocated for storing prefetch data and one or more non-allocated buffers available for other memory uses;

storing said prefetch data in said at least one of said plurality of prefetch buffers; and

performing a forwarding transaction if a second memory read transaction request is received for data stored as prefetch data.

11. The method of claim 10 wherein said prefetching selection criterion is met if said prefetch data is associated with a memory address within the same page as a memory address associated with read data.

12. The method of claim 10 wherein said prefetching selection criterion is met if said prefetch data is associated with a memory address within the same flash device as a memory address associated with data read during said responding to said first memory read transaction request.

13. The method of claim 10 wherein said prefetching selection criterion is met if the memory address of said prefetch data differs within a selected memory address range from the memory address of data read during said responding to said first memory read transaction request.

14. The method of claim 10 wherein said responding to said second memory read transaction request includes transferring said prefetch data from at least one of said plurality of prefetch buffers to local memory.

15. The method of claim 14 wherein said responding to said second memory read transaction request includes forwarding said prefetch data from said local memory to said host.

16. A storage apparatus for performing reduced memory read transactions, the storage apparatus comprising:

a memory array including a plurality of non-volatile memory devices;

said plurality of non-volatile memory devices including a plurality of data registers, each one of said plurality of non-volatile memory devices including a respective one of said plurality of data registers;

each of the non-volatile memory devices including a corresponding set of non-volatile memory cells and a respective data register;

a memory interface coupled by a memory bus to the memory array and responsive to a memory read transaction request;

said memory interface coupled by a bus to the at least one host during a transmission of memory transaction requests from the at least one host to said memory interface;

said memory interface including a Direct Memory Access (DMA) controller comprising a first buffer and a flash memory controller comprising a second buffer; and

wherein said memory interface allocates a plurality of prefetch buffers in said buffer set, said plurality of prefetch buffers including said first buffer in said DMA controller and said second buffer in said flash memory controller so that said buffer set includes said plurality of prefetch buffers allocated for storing prefetch data and one or more non-allocated buffers available to said storage apparatus for other memory uses;

the memory interface configured to perform a read operation on the memory array in response to a memory read transaction request and configured to perform an internal read operation if the memory interface identifies stored data, in the memory array, meeting a prefetch selection criterion;

the internal read operation comprising the memory interface allocating a data store in the buffer set and storing the stored data in the data store as a prefetch data available to a second memory read transaction.

17. The storage apparatus of claim 16, wherein the buffer set is formed in the memory interface.

18. The storage apparatus of claim 16, wherein the memory interface responds to the second memory transaction request by performing a forwarding transaction comprising the memory interface retrieving the prefetch data from the data store and forwarding the prefetch data to said host.

19. The data storage apparatus of claim 16, wherein the data store comprises a data register.

20. The storage apparatus of claim 17, wherein the data store comprises a buffer in the memory interface.

21. The storage apparatus of claim 20, wherein the memory interface includes said flash memory controller and the data store comprises a fixed buffer in the flash memory controller.

22. The storage apparatus of claim 20, wherein the memory interface includes said DMA controller and the data store comprises a fixed buffer in the DMA controller.

23. The storage apparatus of claim 16, wherein the memory array, comprises at least one flash device.

24. A method of performing reduced memory read transactions in a storage apparatus, method comprising:

receiving a memory read transaction request and performing a read operation on a memory array; and

performing an internal read operation if stored data, in the memory array, meets a prefetch selection criterion;

wherein performing the internal read operation comprises;

allocating a data store in a buffer set formed in a memory interface and storing the stored data in the data store as a prefetch data available to a second memory read transaction;

said memory array including a plurality of non-volatile memory devices, said plurality of non-volatile memory devices including a plurality of data registers, each one of said plurality of non-volatile memory devices including a respective one of said plurality of data registers;

each of said non-volatile memory device including a corresponding set of non-volatile memory cells and a respective data register; and

said memory interface coupled by a bus to the at least one host during a transmission of memory transaction requests from the at least one host to said memory interface;

said memory interface including a Direct Memory Access (DMA) controller comprising a first buffer and a flash memory controller comprising a second buffer;

wherein said memory interface, coupled by a memory bus to said memory array, allocates a plurality of prefetch buffers in said buffer set, said plurality of prefetch buffers including said first buffer in said DMA controller said memory interface and said second buffer in said flash memory controller in said memory interface so that said buffer set includes said plurality of prefetch buffers allocated for storing prefetch data and one or more non-allocated buffers available to said storage apparatus for other memory uses.

25. The method of claim 24, wherein the buffer set is formed in the memory interface.

26. The method of claim 24, further comprising:

responding to the second memory transaction request by performing a forwarding transaction comprising retrieving the prefetch data from the data store and forwarding the prefetch data to said host.

27. The method of claim 24, wherein the data store comprises a data register.

28. The method of claim 25, wherein the data store comprises a buffer in the memory interface.

29. The method of claim 28, wherein the memory interface includes said flash memory controller and the data store comprises a fixed buffer in the flash memory controller.

30. The method of claim 28, wherein the memory interface includes said DMA controller and the data store comprises a fixed buffer in the DMA controller.

31. The method of claim 24, wherein the memory array comprises at least one flash device.

32. A method for reducing latency in memory read transactions by using a low latency memory interface coupled to a memory array that includes a flash memory device, and wherein said memory interface responds to memory read transaction requests from a host, the method comprising:

receiving a memory read transaction request;

performing a read operation;

identifying prefetch data in said memory array that meets a prefetch selection criterion;

said memory interface coupled by a memory bus to said memory array;

said memory interface coupled by a bus to the host during a transmission of memory transaction requests from the host to said memory interface;

said memory interface including a Direct Memory Access (DMA) controller comprising a first buffer and a flash memory controller comprising a second buffer;

if prefetch data is identified in said memory array, performing an internal read operation that includes transferring prefetch data, allocating said first buffer as a prefetch buffer suitable for storing prefetch data wherein said prefetch buffer is identified from at least one available buffer available in said buffer set that includes said first buffer in said DMA controller in said memory interface and said second buffer in said flash memory controller in said memory interface;

said flash memory device including a set of non-volatile memory cells and the data register;

storing said prefetch data in said first buffer; and

performing a forwarding transaction if a second memory read transaction request is received for data stored as prefetch data.

33. The method of claim 32 wherein said prefetching selection criterion is met if said prefetch data is associated with a memory address within the same page as a memory address associated with read data.

34. The method of claim 32 wherein said prefetching selection criterion is met if said prefetch data is associated with a memory address within the same flash device as a memory address associated with data read during said responding to said first memory read transaction request.

35. The method of claim 32 wherein said prefetching selection criterion is met if the memory address of said prefetch data differs within a selected memory address range from the memory address of data read during said responding to said first memory read transaction request.

36. The method of claim 32 wherein said responding to said second memory read transaction request includes transferring said prefetch data from at least one of said prefetch buffers to local memory.

37. The method of claim 36 wherein said responding to said second memory read transaction request includes forwarding said prefetch data from said local memory to said host.