Increasing the memory performance of flash memory devices by...

Details Increasing the memory performance of flash memory devices by... Increasing the memory performance of flash memory devices by...

2000-11-02

2002-05-28

Yoo, Do Hyun (Department: 2185)

Electrical computers and digital processing systems: memory

Storage accessing and control

Access timing

C711S103000, C711S005000, C711S202000, C365S189040, C365S230030

Reexamination Certificate

active

06397314

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of digital systems, such as personal computers and digital cameras, employing nonvolatile memory as mass storage, for use in replacing hard disk storage or conventional film. More particularly, this invention relates to an architecture for increasing the performance of such digital systems by increasing the rate at which digital information is read from and written to the nonvolatile memory.
2. Description of the Prior Art
With the advent of higher capacity solid state storage devices (nonvolatile memory), such as flash or EEPROM memory, many digital systems have replaced conventional mass storage devices with flash and/or EEPROM memory devices. For example, personal computers (PCs) use solid state storage devices for mass storage purposes in place of conventional hard disks. Digital cameras employ solid state storage devices in cards to replace conventional films.
FIG. 1
shows a prior art memory system
10
including a controller
12
, which is generally a semiconductor (or integrated circuit) device, coupled to a host
14
which may be a PC or a digital camera. The controller
12
is farther coupled to a nonvolatile memory bank
16
. Host
14
writes and reads information, organized in sectors, to and from memory bank
16
which includes a first nonvolatile memory chip
18
and a second nonvolatile memory chip
20
. Chip
18
includes: an I/O register
22
having a port
24
connected to a port
26
of controller
12
via a first bus
28
which includes 8 bit lines; and a storage area
30
coupled with I/O register
22
. Chip
20
includes: an I/O register
32
having a port
34
connected to a port
36
of controller
12
via a second bus
38
which includes 8 bit lines; and a storage area
40
coupled with I/O register
32
. The first and second buses
28
,
38
are used to transmit data, address, and command signals between the controller and the memory chips
18
and
20
. The least significant
8
bits (LSBs) of 16 bits of information are provided to chip
18
via the first bus
28
, and the most significant 8 bits (MSBs) are provided to the chip
20
via the second bus
38
.
Memory bank
16
includes a plurality of block locations
42
each of which includes a plurality of memory row locations. Each block location of the memory bank is comprised of a first sub-block
44
located in the first non-volatile memory chip, and a corresponding second sub-block
46
located in the second non-volatile memory chip. Each memory row location includes a first row-portion
48
and a corresponding second row-portion
50
. In the depicted embodiment each of the first and second row-portions
48
and
50
includes storage for 256 bytes of data information plus an additional 8 bytes of storage space for overhead information. Where a sector includes 512 bytes of user data and 16 bytes of non-user data (the latter commonly referred to as overhead information), 256 bytes of the user data and 8 bytes of the overhead information of the sector may be maintained in the first row portion
48
of chip
18
and the remaining 256 bytes of user data and remaining 8 bytes of overhead information of the same sector may be maintained in the second row portion
50
of chip
20
. Thus, half of a sector is stored in a memory row location
48
of chip
18
and the other half of the sector is stored in memory row location
50
of chip
20
. Additionally, half of the overhead information of each stored sector is maintained by chip
18
and the other half by chip
20
.
In general, reading and writing data to flash memory chips
18
and
20
is time consuming. Writing data to the flash memory chips is particularly time consuming because data must be latched in I/O registers
22
and
32
, which are loaded 1 byte at a time via the first and second buses, and then transferred from the I/O registers
22
and
32
to the memory cells of the flash memory chips
18
and
20
respectively. The time required to transfer data from the I/O registers to memory, per byte of data, is proportional to the size of the I/O registers and the size of the flash memory chip.
During a write operation, controller
12
writes a single sector of information to memory bank
16
by: (1) transmitting a write command signal to each of chips
18
and
20
via buses
28
and
38
simultaneously; (2) transmitting address data to chips
18
and
20
specifying corresponding sub-blocks
44
and
46
of the chips via buses
28
and
38
simultaneously; and (3) sequentially transmitting a byte of user data to each of chips
18
and
20
via buses
28
and
38
simultaneously for storage in the corresponding sub-blocks
44
and
46
. The problem with such prior art systems is that while two bytes of information are written and read at a time, only one sector. of information is accommodated at a time by the memory bank
16
during a write command initiated by the host
14
.
Another prior art digital system
60
is shown in
FIG. 2
to include a controller
62
coupled to a host
64
, and a nonvolatile memory bank
66
for storing and reading information organized in sectors to and from nonvolatile memory chip
68
, included in the memory bank
66
. While not shown, more chips may be included in the memory bank, although the controller, upon command by the host, stores an entire sector in one chip. A block, such as block
0
, includes
16
sectors S
0
, S
1
, . . . , S
15
. Also included in the chip
68
is an I/O register
70
, which includes 512 bytes plus 16 bytes, a total of 528 bytes, of storage space. The controller transfers information between host
64
and memory
66
a byte at-a-time. A sector of 512 bytes of user data plus 16 bytes of overhead information is temporarily stored in the I/O register during a write operation and then transferred to one of the blocks within the memory device for storage thereof. During a read operation, a sector of information is read from one of the blocks of the memory device and then stored in the I/O register for transfer to the controller. An important problem with the prior art architecture of
FIG. 2
is that while a total of 528 bytes may be stored in the I/O register
36
, only one byte of sector information may be transferred at a time between the controller and the memory bank thereby impeding the overall performance of the system.
Both of the prior art systems of
FIGS. 1 and 2
maintain LBA to PBA mapping information for translating a host-provided logical block address (LBA) identifying a sector of information to a physical block address (PBA) identifying the location of a sector within the memory bank. This mapping information may generally be included in volatile memory, such as a RAM, within the controller, although it may be maintained outside of the controller.
FIG. 3
shows a table diagram illustrating an example of an LBA-PBA map
300
defined by rows and columns, with each row
302
being uniquely identified, addressed, by a value equal to that of the LBA received from the host divided by 16. The row numbers of
FIG. 3
are shown using hexadecimal notation. Thus, for example, row 10H (in Hex.) has an address value equal to 16 in decimal. Each row
302
of map
300
, includes a storage location field
304
for maintaining a virtual PBA value, an ‘old’ flag field
306
, a ‘used’ flag field
308
, and a ‘defect’ flag field
310
. The flag fields provide information relating to the status of a block of information maintained within the memory bank (in FIGS.
1
and
2
). The virtual PBA field
304
stores information regarding the location of the block within the memory bank.
FIG. 4
shows a table diagram illustrating an exemplary format for storage of a sector of data maintained in a memory bank. The virtual PBA field
304
(
FIG. 3
) provides information regarding the location of a block
400
of information with each block having a plurality of sectors
402
. Each sector
402
is comprised of a user data field
404
, an ECC field
406
, an ‘old’ flag field
408
, a ‘used’ flag field
410
and a ‘d

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