Data storage device and method for operating nonvolatile memory

• US 10,229,054 B2
• Filed: 03/15/2018
• Issued: 03/12/2019
• Est. Priority Date: 06/19/2017
• Status: Active Grant

• Current Assignee: Silicon Motion, Inc. (Silicon Motion)
• Original Assignee: Silicon Motion, Inc. (Silicon Motion)
• Inventors: Hung, Ying-Chun
• Primary Examiner(s): Byrne, Harry W
• Application Number:
  US15/922,666
• Publication Number:
  US 20180365143A1
• Time in Patent Office: 362 Days
• Field of Search: 36518501-18533
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/7208 Multiple device management, e.g. distributing data over multiple flash devices
• CPC Class Codes: G06F 3/0604 Improving or facilitating administration, e.g. storage management
• CPC Class Codes: G06F 3/0608 Saving storage space on storage systems
• CPC Class Codes: G06F 3/0616 in relation to life time, e.g. increasing Mean Time Between Failures [MTBF]
• CPC Class Codes: G06F 3/064 Management of blocks
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: G06F 9/5016 the resource being the memory

Abstract

An optimized operating method for a nonvolatile memory. A microcontroller allocates the nonvolatile memory to store write data requested by a host. According to a first accumulated amount of data written to the nonvolatile memory in a first writing mode and a second accumulated amount of data written to the nonvolatile memory in a second writing mode, the microcontroller allocates the nonvolatile memory to store write data requested by the host in the first writing mode and in the second writing mode alternately. In comparison with the first writing mode, more bits of data are stored in one storage cell in the second writing mode.

Claims

1. A data storage device, comprising:

a nonvolatile memory; and

a microcontroller, allocating the nonvolatile memory to store write data requested by a host,

wherein;

according to a first accumulated amount of data written to the nonvolatile memory in a first writing mode and a second accumulated amount of data written to the nonvolatile memory in a second writing mode, the microcontroller allocates the nonvolatile memory to store write data requested by the host in the first writing mode and in the second writing mode alternately; and

in comparison with the first writing mode, more bits of data are stored in one storage cell in the second writing mode.

2. The data storage device as claimed in claim 1, wherein:

when the first accumulated amount of data written to the nonvolatile memory in the first writing mode exceeds a dynamic threshold value, the microcontroller escapes from the first writing mode to allocate the nonvolatile memory to store write data requested by the host in the second writing mode; and

the dynamic threshold value depends on the second accumulated amount of data written to the nonvolatile memory in the second writing mode.

3. The data storage device as claimed in claim 2, wherein:

the microcontroller escapes from the first writing mode to allocate the nonvolatile memory to store write data requested by the host in the second writing mode when a judgment is true,

the judgment determines whether a value, (WCnt#2+N)/M, is smaller than a value WCnt#1, wherein

WCnt#1 is the first accumulated amount of data written to the nonvolatile memory in the first writing mode;

WCnt#2 is the second accumulated amount of data written to the nonvolatile memory in the second writing mode; and

N and M are numbers, and (WCnt#2+N)/M is the dynamic threshold value.

4. The data storage device as claimed in claim 3, wherein:

N and M are provided to satisfy warranty requirements of the data storage device.

5. The data storage device as claimed in claim 4, wherein:

the nonvolatile memory is a flash memory; and

N and M further depend on a total amount of blocks of the flash memory, block size, and an upper limit of an erasure count of each block.

6. The data storage device as claimed in claim 2, wherein:

the microcontroller allocates the nonvolatile memory to store write data requested by the host in the first writing mode when a spare space waiting to be allocated for data storage in the nonvolatile memory is larger than a threshold size for switching to the first writing mode.

7. The data storage device as claimed in claim 6, wherein:

the microcontroller allocates the nonvolatile memory to store write data requested by the host in the second writing mode when the spare space waiting to be allocated for data storage in the nonvolatile memory is not larger than the threshold size.

8. The data storage device as claimed in claim 2, wherein:

the nonvolatile memory is a flash memory;

the first writing mode is a single-level cell writing mode, by which each storage cell of an allocated block stores one bit of data; and

according to the second writing mode, each storage cell of an allocated block stores multiple bits of data.

9. The data storage device as claimed in claim 8, wherein:

the second writing mode is a triple-level cell writing mode, by which each storage cell of an allocated block stores data of three bits.

10. The data storage device as claimed in claim 9, wherein:

when the host does not request access to the flash memory, the microcontroller moves data stored in single-level cells to blocks storing data in triple-level cells.

11. A method for operating a nonvolatile memory, comprising:

allocating a nonvolatile memory to store write data requested by a host; and

according to a first accumulated amount of data written to the nonvolatile memory in a first writing mode and a second accumulated amount of data written to the nonvolatile memory in a second writing mode, allocating the nonvolatile memory to store write data requested by the host in the first writing mode and in the second writing mode alternately,

wherein, in comparison with the first writing mode, more bits of data are stored in one storage cell in the second writing mode.

12. The method as claimed in claim 11, further comprising:

when the first accumulated amount of data written to the nonvolatile memory in the first writing mode exceeds a dynamic threshold value, escaping from the first writing mode to allocate the nonvolatile memory to store write data requested by the host in the second writing mode,

wherein the dynamic threshold value depends on the second accumulated amount of data written to the nonvolatile memory in the second writing mode.

13. The method as claimed in claim 12, further comprising:

escaping from the first writing mode to allocate the nonvolatile memory to store write data requested by the host in the second writing mode when a judgment is true,

wherein;

the judgment determines whether a value, (WCnt#2+N)/M, is smaller than a value WCnt#1;

WCnt#1 is the first accumulated amount of data written to the nonvolatile memory in the first writing mode;

WCnt#2 is the second accumulated amount of data written to the nonvolatile memory in the second writing mode; and

N and M are numbers, and (WCnt#2+N)/M is the dynamic threshold value.

14. The method as claimed in claim 13, wherein:

N and M are provided to satisfy the warranty requirements of a data storage device equipped with the nonvolatile memory.

15. The method as claimed in claim 14, wherein:

the nonvolatile memory is a flash memory; and

N and M further depend on the total amount of blocks of the flash memory, block size, and an upper limit of an erasure count of each block.

16. The method as claimed in claim 12, further comprising:

allocating the nonvolatile memory to store write data requested by the host in the first writing mode when a spare space waiting to be allocated for data storage in the nonvolatile memory is larger than a threshold size for switching to the first writing mode.

17. The method as claimed in claim 16, further comprising:

allocating the nonvolatile memory to store write data requested by the host in the second writing mode when the spare space waiting to be allocated for data storage in the nonvolatile memory is not larger than the threshold size.

18. The method as claimed in claim 12, wherein:

the nonvolatile memory is a flash memory;

the first writing mode is a single-level cell writing mode, by which each storage cell of an allocated block stores one bit of data; and

according to the second writing mode, each storage cell of an allocated block stores multiple bits of data.

19. The method as claimed in claim 18, wherein:

the second writing mode is a triple-level cell writing mode, by which each storage cell of an allocated block stores data of three bits.

20. The method as claimed in claim 19, further comprising:

moving data stored in single-level cells to blocks storing data in triple-level cells when the host does not request access to the flash memory.