Method for releasing space in flash EEPROM memory array to allow the storage of compressed data

• US 5,337,275 A
• Filed: 11/01/1993
• Issued: 08/09/1994
• Est. Priority Date: 10/30/1992
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Garner, Richard P.
• Primary Examiner(s): Fears, Terrell W.
• Application Number:
  US08/146,439
• Time in Patent Office: 281 Days
• Field of Search: 365/900, 365/189.01, 365/189.02, 365/189.08, 365/230.01, 365/230.03
• US Class Current: 365/189.16
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/401 Compressed data
• CPC Class Codes: G06F 3/0601 Interfaces specially adapted for storage systems
• CPC Class Codes: G06F 3/0664 at device level, e.g. emulation of a storage device or system

Abstract

A process for releasing sectors of a flash EEPROM memory array in which data furnished by a host computer is stored in compressed form so that memory space used for the sectors may be used to store new data. The flash EEPROM memory array includes a plurality of individually erasable blocks and stores sectors of data in such blocks with a header providing a logical sector number, an indication of validity of data stored. The process stores a list of files and sectors which have been deleted by a host computer in a first table in host memory, stores a value indicating an amount of free space remaining in the flash EEPROM memory array, provides a first signal to the host computer when the value indicating the amount of free space falls below a first predetermined value to indicate that sectors listed in the first table should be released, and provides a second signal when the value indicating the amount of free space falls below a second predetermined value to terminate writes to and erasures of the array.

Claims

1. A process for releasing sectors of a flash EEPROM memory array in which data furnished by a host computer is stored in compressed form so that memory space used for the sectors may be used to store new data, the flash EEPROM memory array including a plurality of individually erasable blocks and storing sectors of data in such blocks with a header providing a logical sector number, an indication of validity of data stored, the process comprising the steps of:

storing a list of files and sectors which have been deleted by a host computer in a first table in host memory,

storing a value indicating an amount of free space remaining in the flash EEPROM memory array,

providing a first signal to the host computer when the value indicating the amount of free space falls below a first predetermined value to indicate that sectors listed in the first table should be released, and

providing a second signal when the value indicating the amount of free space falls below a second predetermined value.

2. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 1 further comprising the step of responding to the second signal by disabling write and erase operations in the flash EEPROM memory array.

3. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 1 further comprising the step of providing a third signal to the host computer when the value indicating the amount of free space falls below a third predetermined value which is less than the first predetermined value but greater than the second predetermined value to indicate that it is more urgent that sectors listed in the first table be released than when the first signal was given.

4. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 1 further comprising the step of responding to the first signal by automatically releasing the data allotted to a predetermined number of sectors listed in the first table.

5. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 4 in which the step of responding to the first signal by automatically releasing the data allotted to a predetermined number of sectors listed in the first table comprises the steps of writing any valid data remaining in a selected portion of the flash EEPROM memory array having a predetermined number of headers specified as invalid to free space in the flash EEPROM memory array, and

erasing the entire selected portion of the flash EEPROM memory array.

6. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 4 in which the step of responding to the first signal by automatically releasing the data allotted to a predetermined number of sectors listed in the first table comprises the steps of:

selecting a first sector from the first table,

searching a second table for a physical position of a sector selected,

seeking a sector specified by a physical position of a sector selected,

marking a header of a sector specified by a physical position of a sector selected as invalid,

writing a new header for a sector selected in free space in the flash EEPROM memory array without data,

updating the second table with a new physical position of a new header for a sector specified by the first designation, and

repeating the process from the step of selecting a first designation for a sector from the first table until the predetermined number of sectors listed in the first table have been released.

7. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 4 in which the predetermined number of sectors listed in the first table is all of the sectors listed in the first table.

8. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 4 in which the predetermined number of sectors listed in the first table is selected to leave a number of sectors equal to at least one host computer file in the first table.

9. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 3 further comprising the step of responding to the third signal by automatically releasing the data allotted to a predetermined number of sectors listed in the first table.

10. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 9 in which the step of responding to the third signal by automatically releasing the data allotted to a predetermined number of sectors listed in the first table comprises the steps of writing any valid data remaining in a selected portion of the flash EEPROM memory array having a predetermined number of headers specified as invalid to free space in the flash EEPROM memory array, and

erasing the entire selected portion of the flash EEPROM memory array.

11. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 9 in which the step of responding to the third signal by automatically releasing the data allotted to sectors listed in the first table comprises the steps of:

selecting a first sector from the first table,

searching a second table for a physical position of a sector selected,

seeking a sector specified by a physical position of a sector selected,

marking a header of a sector specified by a physical position of a sector selected as invalid,

writing a new header for a sector selected in free space in the flash EEPROM memory array without data,

updating the second table with a new physical position of a new header for a sector specified by the first designation, and

repeating the process from the step of selecting a first designation for a sector from the first table until a selected number of sectors listed in the first table have been selected.

12. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 9 in which the predetermined number of sectors listed in the first table is all of the sectors listed in the first table.

13. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 9 in which the predetermined number of sectors listed in the first table is selected to leave a number of sectors equal to at least one host computer file in the first table.

14. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 1 in which the step of storing a list of files and sectors which have been deleted by a host computer in a first table in host memory comprises listing all files and sectors of files indicated to be deleted in a host file allocation table.

15. A process for releasing sectors of a flash EEPROM memory array in which data furnished by a host computer is stored in compressed form so that memory space used for the sectors may be used to store new data, the flash EEPROM memory array including a plurality of individually erasable blocks and storing sectors of data in such blocks with a header providing a logical sector number, an indication of validity of data stored, the process comprising the steps of:

storing a list of files and sectors which have been deleted by a host computer in a first table in host memory, storing a value indicating an amount of free space remaining in the flash EEPROM memory array,

providing a first signal to the host computer when the value indicating the amount of free space falls below a first predetermined value to indicate that sectors listed in the first table should be released,

responding to the first signal by automatically releasing the data allotted to a predetermined number of sectors listed in the first table,

providing a second signal to the host computer when the value indicating the amount of free space falls below a second predetermined value to indicate that it is more urgent that sectors listed in the first table be released than when the first signal was given, and

responding to the second signal by automatically releasing the data allotted to a predetermined number of sectors listed in the first table,

providing a third signal when the value indicating the amount of free space falls below a third predetermined value, and

responding to the third signal by disabling write and erase operations in the flash EEPROM memory array.

16. A process for releasing sectors of a flash EEPROM memory array as claimed in claim 15 in which the steps of responding to the first and the second signals by automatically releasing the data allotted to a predetermined number of sectors listed in the first table

comprises the step of writing all sectors containing valid data to new storage areas from a block storing a plurality of invalid indications, and

erasing the block from which the valid data has been written.