Flash controller cache architecture

• US 7,173,863 B2
• Filed: 03/08/2004
• Issued: 02/06/2007
• Est. Priority Date: 03/08/2004
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Conley, Kevin M., Elhamias, Reuven
• Primary Examiner(s): Nguyen; Tuan T.
• Application Number:
  US10/796,575
• Publication Number:
  US 20050195635A1
• Time in Patent Office: 1,065 Days
• Field of Search: 365/189.05, 365/189.04, 365/221
• US Class Current: 365/189.05
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0862 with prefetch
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 2212/1016 Performance improvement
• CPC Class Codes: G06F 2212/2022 Flash memory
• CPC Class Codes: G06F 2212/214 Solid state disk
• CPC Class Codes: G06F 2212/2146 being detachable, e.g.. USB memory
• CPC Class Codes: G06F 2212/282 Partitioned cache
• CPC Class Codes: G06F 2212/502 using adaptive policy

Abstract

A buffer cache interposed between a non-volatile memory and a host may be partitioned into segments that may operate with different policies. Cache policies include write-through, write and read-look-ahead. Write-through and write back policies may improve speed. Read-look-ahead cache allows more efficient use of the bus between the buffer cache and non-volatile memory. A session command allows data to be maintained in volatile memory by guaranteeing against power loss.

Claims

1. A removable memory card for storing data in a non-volatile, non-rotating storage medium, comprising:

a host interface;

a non-volatile memory array; and

a buffer cache in communication with the host interface and the non-volatile memory array, the buffer cache having at least a first portion and a second portion for storing data, the first portion having a first policy, the second portion having a second policy, the first policy and the second policy being separately selected.

2. The removable memory card of claim 1 wherein the first policy is a write-through cache policy.

3. The removable memory card of claim 1 wherein the first policy is a write-back cache policy.

4. The removable memory card of claim 1 wherein the first portion functions as a read cache such that when a first group of data that is stored in the non-volatile memory array is requested, the first group of data and a second group of data that is not requested are read from the non-volatile memory array and the second group of data is stored in the first portion.

5. The removable memory card of claim 1 wherein the first portion is used to store data that is used by a central processing unit that is not part of a data stream.

6. The removable memory card of claim 1 wherein the first portion and the second portion are segments of a segmented cache.

7. The removable memory card of claim 1 further comprising a third portion having a third policy and a fourth portion having a fourth policy.

8. The removable memory card of claim 7, further comprising a central processing unit, wherein the first policy is a write-through policy, the second policy is a write-back policy, the third policy is a read cache policy and the fourth policy is a central processing unit data storage policy.

9. The removable memory card of claim 1 wherein the size of the first portion may be modified.

10. The removable memory card of claim 1 wherein the size of the first portion may be modified during operation of the card in response to host command sequences.

11. The removable memory card of claim 1 further comprising a central processing unit that controls the operation of the buffer cache.

12. A removable memory card for storing data in a non-volatile, non-rotating storage medium, comprising:

a host interface for connecting to a host;

a non-volatile, non-rotating memory array; and

a read-look-ahead cache interposed between the host interface and the non-volatile, non-rotating memory array, the read-look-ahead cache storing a non-requested portion of data that is sequential to a requested portion of data requested by the host.

13. The removable memory card of claim 12 wherein the read-look-ahead cache is a segment of a segmented buffer cache.

14. The removable memory card of claim 12 wherein the non-requested portion of data is the maximum amount of data that may be stored in the read-look-ahead cache.

15. The removable memory card of claim 12 further comprising a central processing unit that controls the read-look-ahead cache and a static random access memory connected to the central processing unit.