Flash controller cache architecture
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.
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.