U.S. patent application number 17/103441 was filed with the patent office on 2022-05-26 for temperature-based block family combinations in a memory device.
The applicant listed for this patent is Micron Technology, Inc.. Invention is credited to Steven Michael Kientz, Larry J. Koudele, Bruce A. Liikanen, Shane Nowell, Michael Sheperek.
Application Number | 20220164112 17/103441 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-26 |
United States Patent
Application |
20220164112 |
Kind Code |
A1 |
Kientz; Steven Michael ; et
al. |
May 26, 2022 |
TEMPERATURE-BASED BLOCK FAMILY COMBINATIONS IN A MEMORY DEVICE
Abstract
An example memory sub-system includes a memory device and a
processing device, operatively coupled to the memory device. The
processing device is configured to identify a first temperature
level of a first block family associated with a memory device;
identify a second temperature level of a second block family
associated with the memory device; determine if a condition is
satisfied based on the first temperature level and the second
temperature level; and in response to the condition being
satisfied, combine the first block family and the second block
family to generate a combined block family.
Inventors: |
Kientz; Steven Michael;
(Westminster, CO) ; Koudele; Larry J.; (Erie,
CO) ; Nowell; Shane; (Boise, ID) ; Sheperek;
Michael; (Longmont, CO) ; Liikanen; Bruce A.;
(Berthoud, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Micron Technology, Inc. |
Boise |
ID |
US |
|
|
Appl. No.: |
17/103441 |
Filed: |
November 24, 2020 |
International
Class: |
G06F 3/06 20060101
G06F003/06; G06F 11/30 20060101 G06F011/30 |
Claims
1. A system comprising: a memory device; and a processing device,
operatively coupled to the memory device, the processing device to:
identify a first temperature level of a first block family
associated with a memory device; identify a second temperature
level of a second block family associated with the memory device;
determine if a condition is satisfied based on the first
temperature level and the second temperature level; and in response
to the condition being satisfied, combine the first block family
and the second block family to generate a combined block
family.
2. The system of claim 1, wherein the first temperature level
comprises one of a program temperature associated with an opening
of the first block family, the program temperature associated with
a closing of the first block family, a lowest program temperature
recorded during an open block tenure of the first block family, or
a highest program temperature recorded during the open block tenure
of the first block family.
3. The system of claim 1, wherein the condition is satisfied upon
determining a difference between the first temperature level and
the second temperature level is less than a threshold level.
4. The system of claim 1, wherein the condition is satisfied upon
determining the first temperature level and the second temperature
level are within a same preset temperature range of a plurality of
preset temperature ranges.
5. The system of claim 1, wherein the processing device is further
to record a third temperature level of the combined block family,
and wherein the third temperature level comprises an average of the
first temperature level and the second temperature level.
6. The system of claim 1, wherein the first temperature level
comprises a first low program temperature and a first high program
temperature associated with the first block family, and wherein the
second temperature level comprises a second low program temperature
and a second high program temperature associated with the second
block family.
7. The system of claim 6, wherein the processing device is further
to record a third temperature level of the combined block family,
wherein the third temperature level comprises a range spanning a
lower of the first low program temperature and the second low
program temperature and a higher of the first high program
temperature and the second high program temperature.
8. A method comprising: comparing, by a processing device, an
operating parameter to a first threshold to determine if a first
condition is satisfied; in response to the first condition being
satisfied, adjusting a threshold temperature level to establish an
adjusted threshold temperature level; comparing a difference
between a first temperature level of a first block family and a
second temperature level of a second block family to the threshold
temperature level to determine if a second condition is satisfied;
and in response to the second condition being satisfied, combining
the first block family and the second block family to generate a
combined block family.
9. The method of claim 8, wherein the second condition is satisfied
upon determining the difference between the first temperature level
and the second temperature level is less than the adjusted
threshold temperature level.
10. The method of claim 8, wherein the operating parameter
comprises a first data state metric associated with the first block
family and a second data state metric associated with the second
block family.
11. The method of claim 10, wherein the first condition is
satisfied upon determining a difference between the first data
state metric and the second data state metric is greater than the
first threshold, and wherein adjusting the threshold temperature
level comprises decreasing the threshold temperature level.
12. The method of claim 10, wherein the first condition is
satisfied upon determining a difference between the first data
state metric and the second data state metric is less than the
first threshold, and wherein adjusting the threshold temperature
level comprises increasing the threshold temperature level.
13. The method of claim 8, wherein the operating parameter is an
amount of available memory to store data associated with a set of
block families.
14. The method of claim 13, wherein the first condition is
satisfied upon determining the amount of available memory is below
the first threshold.
15. The method of claim 13, wherein adjusting the threshold
temperature level comprises increasing the adjusted threshold
temperature level.
16. A non-transitory computer readable medium comprising
instructions, which when executed by a processing device, cause the
processing device to perform operations comprising: identifying a
first temperature level of a first block family associated with a
memory device; identifying a second temperature level of a second
block family associated with the memory device; determining if a
condition is satisfied based on the first temperature level and the
second temperature level; and in response to the condition being
satisfied, combining the first block family and the second block
family to generate a combined block family.
17. The non-transitory computer readable medium of claim 16,
wherein the first temperature level comprises one of a program
temperature associated with an opening of the first block family,
the program temperature associated with a closing of the first
block family, a lowest program temperature recorded during an open
block tenure of the first block family, or a highest program
temperature recorded during the open block tenure of the first
block family.
18. The non-transitory computer readable medium of claim 16,
wherein the condition is satisfied upon determining a difference
between the first temperature level and the second temperature
level is less than a threshold level.
19. The non-transitory computer readable medium of claim 16,
wherein the condition is satisfied upon determining the first
temperature level and the second temperature level are within a
same preset temperature range of a plurality of preset temperature
ranges.
20. The non-transitory computer readable medium of claim 16,
wherein the processing device is further to record a third
temperature level of the combined block family, and wherein the
third temperature level comprises an average of the first
temperature level and the second temperature level.
Description
TECHNICAL FIELD
[0001] Embodiments of the disclosure are generally related to
memory sub-systems, and more specifically, are related to
temperature-based block family combinations in a memory device.
BACKGROUND
[0002] A memory sub-system can be a storage system, a memory
module, or a hybrid of a storage device and memory module. The
memory sub-system can include one or more memory devices that store
data. The memory devices can be, for example, non-volatile memory
devices and volatile memory devices. In general, a host system can
utilize a memory sub-system to store data at the memory devices and
to retrieve data from the memory devices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] The present disclosure will be understood more fully from
the detailed description given below and from the accompanying
drawings of some embodiments of the disclosure.
[0004] FIG. 1 illustrates an example computing system that includes
a memory sub-system in accordance with some embodiments of the
present disclosure.
[0005] FIG. 2 schematically illustrates the temporal voltage shift
caused by the slow charge loss exhibited by triple-level memory
cells, in accordance with embodiments of the present
disclosure.
[0006] FIG. 3 depicts an example graph illustrating the dependency
of the threshold voltage offset on a program temperature associated
with a block family, in accordance with embodiments of the present
disclosure.
[0007] FIG. 4 illustrates an example block family combination
component and block family metadata memory, in accordance with
embodiments of the present disclosure.
[0008] FIG. 5 is a flow diagram of an example method 500 of block
family combination management implemented by a memory sub-system
controller operating in accordance with embodiments of the present
disclosure.
[0009] FIG. 6 is a flow diagram of an example method 600 of block
family combination management implemented by a memory sub-system
controller operating in accordance with embodiments of the present
disclosure.
[0010] FIG. 7 is a block diagram of an example computer system in
which embodiments of the present disclosure can operate.
DETAILED DESCRIPTION
[0011] Aspects of the present disclosure are directed to
temperature-based block family combinations in a memory device of a
memory sub-system. A memory sub-system can be a storage device, a
memory module, or a hybrid of a storage device and memory module.
Examples of storage devices and memory modules are described below
in conjunction with FIG. 1. In general, a host system can utilize a
memory sub-system that includes one or more memory devices. The
host system can provide data to be stored at the memory sub-system
and can request data to be retrieved from the memory
sub-system.
[0012] A memory sub-system can utilize one or more memory devices,
including any combination of the different types of non-volatile
memory devices and/or volatile memory devices, to store the data
provided by the host system. In some embodiments, non-volatile
memory devices can be provided by negative-and (NAND) type flash
memory devices. Other examples of non-volatile memory devices are
described below in conjunction with FIG. 1. A non-volatile memory
device is a package of one or more dice. Each die can consist of
one or more planes. Planes can be groups into logic units (LUN).
For some types of non-volatile memory devices (e.g., NAND devices),
each plane consists of a set of physical blocks. Each block
consists of a set of pages. Each page consists of a set of memory
cells ("cells"). A cell is an electronic circuit that stores
information.
[0013] Data operations can be performed by the memory sub-system.
The data operations can be host-initiated operations. For example,
the host system can initiate a data operation (e.g., write, read,
erase, etc.) on a memory sub-system. The host system can send
access requests (e.g., write command, read command) to the memory
sub-system, such as to store data on a memory device at the memory
sub-system and to read data from the memory device on the memory
sub-system. The data to be read or written, as specified by a host
request, is hereinafter referred to as "host data". A host request
can include logical address information (e.g., logical block
address (LBA), namespace) for the host data, which is the location
the host system associates with the host data. The logical address
information (e.g., LBA, namespace) can be part of metadata for the
host data. Metadata can also include error handling data (e.g., ECC
codeword, parity code), data version (e.g. used to distinguish age
of data written), valid bitmap (which LBAs or logical transfer
units contain valid data), etc.
[0014] A memory device includes multiple memory cells, each of
which can store, depending on the memory cell type, one or more
bits of information. A memory cell can be programmed (written to)
by applying a certain voltage to the memory cell, which results in
an electric charge being held by the memory cell, thus allowing
modulation of the voltage distributions produced by the memory
cell. Moreover, precisely controlling the amount of the electric
charge stored by the memory cell allows to establish multiple
threshold voltage levels corresponding to different logical levels,
thus effectively allowing a single memory cell to store multiple
bits of information: a memory cell operated with 2.sup.n different
threshold voltage levels is capable of storing n bits of
information. "Threshold voltage" herein shall refer to the voltage
level that defines a boundary between two neighboring voltage
distributions corresponding to two logical levels. Thus, the read
operation can be performed by comparing the measured voltage
exhibited by the memory cell to one or more reference voltage
levels in order to distinguish between two logical levels for
single-level cells and between multiple logical levels for
multi-level cells.
[0015] Due to the phenomenon known as slow charge loss, the
threshold voltage of a memory cell changes in time as the electric
charge of the cell is degrading, which is referred to as "temporal
voltage shift" (since the degrading electric charge causes the
voltage distributions to shift along the voltage axis towards lower
voltage levels). The threshold voltage is changing rapidly at first
(immediately after the memory cell was programmed), and then slows
down in an approximately logarithmic linear fashion with respect to
the time elapsed since the cell programming event. Accordingly,
failure to mitigate the temporal voltage shift caused by the slow
charge loss can result in the increased bit error rate in read
operations.
[0016] To more efficiently manage the memory device, a block family
creation process can be executed to generate multiple block
families that each include a set of a memory cells containing data
that are expected to exhibit similar or related calibration changes
with respect to time or temperature for at least a portion of the
life of the written data. Block families can be created
asynchronously with respect to block programming events. In an
illustrative example, a new block family can be created whenever a
specified period of time (e.g., a predetermined number of minutes)
has elapsed since creation of the last block family or the
reference temperature of memory cells has changed by more than a
specified threshold value. The memory sub-system controller can
maintain an identifier of the active block family, which is
associated with one or more blocks as they are being
programmed.
[0017] The memory sub-system controller can periodically perform a
calibration process in order to associate each die of every block
family with one of the predefined threshold voltage offset bins,
which is in turn associated with the voltage offset to be applied
for read operations. The associations of blocks with block families
and block families and dies with threshold voltage offset bins can
be stored in respective metadata tables maintained by the memory
sub-system controller.
[0018] A memory sub-system has a limited amount of memory for
storing the multiple block families, and as such, a limited number
of block families can be maintained at a time. Therefore,
conventional systems may combine block families that show similar
voltage characteristics to reduce the number of block families in
the memory device and reduce the effort required to manage,
calibrate, and select bins (e.g., a set of read level offsets that
are applied to asset of data) for each of the block families.
However, combining block families based on voltage characteristics
fails to take into account that data programmed at different
temperatures exhibit voltage variation, even when read at a single
temperature. As such, the block families are combined without
considering the program temperature of the data being combined and
the resulting block family combinations include program temperature
related voltage differences within the same block family, resulting
in worse calibration (e.g., altering a read level value (possibly
by adjusting a read level offset or read level base) to better
match the ideal read levels for a read or set of reads), higher
error rates, and higher read retry trigger rates.
[0019] Aspects of the present disclosure address the
above-identified and other deficiencies by implementing a memory
sub-system that combines block families based on combination
criteria that include the block family temperature levels. In an
embodiment, the memory sub-system records or measures a temperature
level of each block family and uses the identified temperature
levels of multiple block families in determining whether to combine
the multiple block families. In an embodiment, a program
temperature level (e.g., an opening temperature recorded at a time
a block family is opened, a closing temperature recorded at a time
a block family is closed, a low temperature level during an open
block tenure, a high temperature level during an open block tenure,
an average of one or more of the aforementioned temperature levels,
etc.) is identified for each block family. Advantageously,
comparing temperature levels of the multiple block families to
identify block family combinations enables the memory sub-system to
overcome issues associated with temperature compensation
miscalibrations and associated voltage variations within a block
family. In addition, combining multiple block families addresses
the constraints on the available memory space allocated for storing
block families and associated metadata. In this regard, combining
multiple block families frees up memory for storing new block
families.
[0020] Therefore, advantages of the systems and methods implemented
in accordance with some aspects of the present disclosure include,
but are not limited to, improving the bit error rate in read
operations by maintaining metadata tracking groups of blocks (block
families) that are presumed to exhibit similar voltage
distributions and selectively performing calibration operations for
limited subsets of blocks based on their block family association,
as described in more detail herein below.
[0021] FIG. 1 illustrates an example computing system 100 that
includes a memory sub-system 110 in accordance with some
embodiments of the present disclosure. The memory sub-system 110
can include media, such as one or more volatile memory devices
(e.g., memory device 140), one or more non-volatile memory devices
(e.g., memory device 130), or a combination of such.
[0022] A memory sub-system 110 can be a storage device, a memory
module, or a hybrid of a storage device and memory module. Examples
of a storage device include a solid-state drive (SSD), a flash
drive, a universal serial bus (USB) flash drive, an embedded
Multi-Media Controller (eMMC) drive, a Universal Flash Storage
(UFS) drive, a secure digital (SD) card, and a hard disk drive
(HDD). Examples of memory modules include a dual in-line memory
module (DIMM), a small outline DIMM (SO-DIMM), and various types of
non-volatile dual in-line memory module (NVDIMM).
[0023] The computing system 100 can be a computing device such as a
desktop computer, laptop computer, network server, mobile device, a
vehicle (e.g., airplane, drone, train, automobile, or other
conveyance), Internet of Things (IoT) enabled device, embedded
computer (e.g., one included in a vehicle, industrial equipment, or
a networked commercial device), or such computing device that
includes memory and a processing device.
[0024] The computing system 100 can include a host system 120 that
is coupled to one or more memory sub-systems 110. In some
embodiments, the host system 120 is coupled to different types of
memory sub-system 110. FIG. 1 illustrates one example of a host
system 120 coupled to one memory sub-system 110. As used herein,
"coupled to" or "coupled with" generally refers to a connection
between components, which can be an indirect communicative
connection or direct communicative connection (e.g., without
intervening components), whether wired or wireless, including
connections such as electrical, optical, magnetic, etc.
[0025] The host system 120 can include a processor chipset and a
software stack executed by the processor chipset. The processor
chipset can include one or more cores, one or more caches, a memory
controller (e.g., NVDIMM controller), and a storage protocol
controller (e.g., PCIe controller, SATA controller). The host
system 120 uses the memory sub-system 110, for example, to write
data to the memory sub-system 110 and read data from the memory
sub-system 110.
[0026] The host system 120 can be coupled to the memory sub-system
110 via a physical host interface. Examples of a physical host
interface include, but are not limited to, a serial advanced
technology attachment (SATA) interface, a peripheral component
interconnect express (PCIe) interface, universal serial bus (USB)
interface, Fibre Channel, Serial Attached SCSI (SAS), a double data
rate (DDR) memory bus, Small Computer System Interface (SCSI), a
dual in-line memory module (DIMM) interface (e.g., DIMM socket
interface that supports Double Data Rate (DDR)), etc. The physical
host interface can be used to transmit data between the host system
120 and the memory sub-system 110. The host system 120 can further
utilize an NVM Express (NVMe) interface to access components (e.g.,
memory devices 130) when the memory sub-system 110 is coupled with
the host system 120 by the PCIe interface. The physical host
interface can provide an interface for passing control, address,
data, and other signals between the memory sub-system 110 and the
host system 120. FIG. 1 illustrates a memory sub-system 110 as an
example. In general, the host system 120 can access multiple memory
sub-systems via a same communication connection, multiple separate
communication connections, and/or a combination of communication
connections.
[0027] The memory devices 130,140 can include any combination of
the different types of non-volatile memory devices and/or volatile
memory devices. The volatile memory devices (e.g., memory device
140) can be, but are not limited to, random access memory (RAM),
such as dynamic random access memory (DRAM) and synchronous dynamic
random access memory (SDRAM).
[0028] Some examples of non-volatile memory devices (e.g., memory
device 130) include a negative-and (NAND) type flash memory and
write-in-place memory, such as a three-dimensional cross-point ("3D
cross-point") memory device, which is a cross-point array of
non-volatile memory cells. A cross-point array of non-volatile
memory can perform bit storage based on a change of bulk
resistance, in conjunction with a stackable cross-gridded data
access array. Additionally, in contrast to many flash-based
memories, cross-point non-volatile memory can perform a write
in-place operation, where a non-volatile memory cell can be
programmed without the non-volatile memory cell being previously
erased. NAND type flash memory includes, for example,
two-dimensional NAND (2D NAND) and three-dimensional NAND (3D
NAND).
[0029] Each of the memory devices 130 can include one or more
arrays of memory cells. One type of memory cell, for example,
single level cells (SLC) can store one bit per cell. Other types of
memory cells, such as multi-level cells (MLCs), triple level cells
(TLCs), and quad-level cells (QLCs), can store multiple bits per
cell. In some embodiments, each of the memory devices 130 can
include one or more arrays of memory cells such as SLCs, MLCs,
TLCs, QLCs, or any combination of such. In some embodiments, a
particular memory device can include an SLC portion, and an MLC
portion, a TLC portion, or a QLC portion of memory cells. The
memory cells of the memory devices 130 can be grouped as pages that
can refer to a logical unit of the memory device used to store
data. With some types of memory (e.g., NAND), pages can be grouped
to form blocks.
[0030] Although non-volatile memory components such as 3D
cross-point array of non-volatile memory cells and NAND type flash
memory (e.g., 2D NAND, 3D NAND) are described, the memory device
130 can be based on any other type of non-volatile memory, such as
read-only memory (ROM), phase change memory (PCM), self-selecting
memory, other chalcogenide based memories, ferroelectric transistor
random-access memory (FeTRAM), ferroelectric random access memory
(FeRAM), magneto random access memory (MRAM), Spin Transfer Torque
(STT)-MRAM, conductive bridging RAM (CBRAM), resistive random
access memory (RRAM), oxide based RRAM (OxRAM), negative-or (NOR)
flash memory, and electrically erasable programmable read-only
memory (EEPROM).
[0031] A memory sub-system controller 115 (or controller 115 for
simplicity) can communicate with the memory devices 130 to perform
operations such as reading data, writing data, or erasing data at
the memory devices 130 and other such operations. The memory
sub-system controller 115 can include hardware such as one or more
integrated circuits and/or discrete components, a buffer memory, or
a combination thereof. The hardware can include a digital circuitry
with dedicated (i.e., hard-coded) logic to perform the operations
described herein. The memory sub-system controller 115 can be a
microcontroller, special purpose logic circuitry (e.g., a field
programmable gate array (FPGA), an application specific integrated
circuit (ASIC), etc.), or other suitable processor.
[0032] The memory sub-system controller 115 can include a processor
117 (e.g., processing device) configured to execute instructions
stored in a local memory 119. In the illustrated example, the local
memory 119 of the memory sub-system controller 115 includes an
embedded memory configured to store instructions for performing
various processes, operations, logic flows, and routines that
control operation of the memory sub-system 110, including handling
communications between the memory sub-system 110 and the host
system 120.
[0033] In some embodiments, the local memory 119 can include memory
registers storing memory pointers, fetched data, etc. The local
memory 119 can also include read-only memory (ROM) for storing
micro-code. While the example memory sub-system 110 in FIG. 1 has
been illustrated as including the memory sub-system controller 115,
in another embodiment of the present disclosure, a memory
sub-system 110 does not include a memory sub-system controller 115,
and can instead rely upon external control (e.g., provided by an
external host, or by a processor or controller separate from the
memory sub-system).
[0034] In general, the memory sub-system controller 115 can receive
commands or operations from the host system 120 and can convert the
commands or operations into instructions or appropriate commands to
achieve the desired access to the memory devices 130. The memory
sub-system controller 115 can be responsible for other operations
such as wear leveling operations, garbage collection operations,
error detection and error-correcting code (ECC) operations,
encryption operations, caching operations, and address translations
between a logical block address (e.g., logical block address (LBA),
namespace) and a physical block address (e.g., physical block
address) that are associated with the memory devices 130. The
memory sub-system controller 115 can further include host interface
circuitry to communicate with the host system 120 via the physical
host interface. The host interface circuitry can convert the
commands received from the host system into command instructions to
access the memory devices 130 as well as convert responses
associated with the memory devices 130 into information for the
host system 120.
[0035] The memory sub-system 110 can also include additional
circuitry or components that are not illustrated. In some
embodiments, the memory sub-system 110 can include a cache or
buffer (e.g., DRAM) and address circuitry (e.g., a row decoder and
a column decoder) that can receive an address from the memory
sub-system controller 115 and decode the address to access the
memory devices 130.
[0036] In some embodiments, the memory devices 130 include local
media controllers 135 that operate in conjunction with memory
sub-system controller 115 to execute operations on one or more
memory cells of the memory devices 130. An external controller
(e.g., memory sub-system controller 115) can externally manage the
memory device 130 (e.g., perform media management operations on the
memory device 130). In some embodiments, a memory device 130 is a
managed memory device, which is a raw memory device combined with a
local controller (e.g., local controller 135) for media management
within the same memory device package. An example of a managed
memory device is a managed NAND (MNAND) device.
[0037] The memory sub-system 110 includes a block family
combination component 113 that can be used to implement block
family combination criteria in accordance with embodiments of the
present disclosure. In some embodiments, the controller 115
includes at least a portion of the block family combination
component 113. For example, the controller 115 can include a
processor 117 (processing device) configured to execute
instructions stored in local memory 119 for performing the
operations described herein. In some embodiments, the block family
combination component 113 is part of the host system 120, an
application, or an operating system. The block family combination
component 113 can manage block families associated with the memory
devices 130, as described in more detail herein below.
[0038] FIG. 2 schematically illustrates the temporal voltage shift
caused by the slow charge loss exhibited by triple-level memory
cells. While the illustrative example of FIG. 2 utilizes
triple-level cells, the same observations can be made and,
accordingly, the same remedial measures are applicable to single
level cells and multi-level cells in order to compensate for the
slow charge loss.
[0039] As noted herein above, a memory cell can be programmed
(written to) by applying a certain voltage to the memory cell,
which results in an electric charge being held by the memory cell,
thus allowing modulation of the voltage distributions produced by
the memory cell. Precisely controlling the amount of the electric
charge stored by the memory cell allows to establish multiple
threshold voltage levels corresponding to different logical levels,
thus effectively allowing a single memory cell to store multiple
bits of information: a memory cell operated with 2n different
threshold voltage levels is capable of storing n bits of
information.
[0040] Each of chart 210 and 230 illustrate program voltage
distributions 220A-220N (also referred to as "program
distributions" or "voltage distributions" or "distributions"
herein) of memory cells programmed by a respective write level
(which can be assumed to be at the midpoint of the program
distribution) to encode a corresponding logical level ("000"
through "111" in case of a TLC). The program distributions 220A
through 220N can illustrate the range of threshold voltages (e.g.,
normal distribution of threshold voltages) for memory cells
programmed at respective write levels (e.g., program voltages). In
order to distinguish between adjacent program distributions
(corresponding to two different logical levels), the read threshold
voltage levels (shown by dashed vertical lines) are defined, such
that any measured voltage that falls below a read threshold level
is associated with one program distribution of the pair of adjacent
program distributions, while any measured voltage that is greater
than or equal to the read threshold level is associated with
another program distribution of the pair of neighboring
distributions.
[0041] In chart 210, eight states of the memory cell are shown
below corresponding program distributions (except for the state
labeled ER, which is an erased state, for which a distribution is
not shown). Each state corresponds to a logical value. The
threshold voltage levels are labeled Va-Vh. As shown, the ER state
has a corresponding level of 111, and any measured voltage below Va
is associated with the ER state. The states labeled P1, P2, P3, P4,
P5, P6, and P7 correspond to distributions 220A-220N.
[0042] Time After Program (TAP) herein shall refer to the time
since a cell has been written and is the primary driver of TVS
(temporal voltage shift). TAP can be estimated (e.g., inference
from a data state metric), or directly measured (e.g., from a
controller clock). A cell, block, page, block family, etc. is young
(or, comparatively, younger) if it has a (relatively) small TAP and
is old (or, comparatively, older) if it has a (relatively) large
TAP. A time slice is a duration between two TAP points during which
a measurement can be made (e.g., perform reference calibration from
8 to 12 minutes after program). A time slice can be referenced by
its center point (e.g., 10 minutes).
[0043] As seen from comparing example charts 210 and 230, which
reflect the time after programming (TAP) of 0 (immediately after
programming) and the TAP of T hours, respectively, the program
distributions change over time due primarily to slow charge loss.
In order to reduce the read bit error rate, the corresponding read
threshold voltages are adjusted to compensate for the shift in
program distributions, which are shown by dashed vertical lines. In
various embodiments of the disclosure, the temporal voltage shift
is selectively tracked for die groups based on measurements
performed at one or more representative dice of the die group.
Based on the measurements made on representative dice of a die
group that characterize the temporal voltage shift and operational
temperature of the dice of the die group, the read threshold
voltage offsets used to read the memory cells for the dice of the
die group are updated and are applied to the base read threshold
levels to perform read operations.
[0044] FIG. 3 depicts an example graph 300 illustrating a
relationship between the variation in threshold voltage offset 310
over time after program 320 (i.e., the period of time elapsed since
the block had been programmed) and a temperature level associated
with the memory device. As illustrated in FIG. 3, blocks of the
memory device are grouped into block families, such that each block
family includes one or more blocks that have been programmed within
a specified temperature window. For example, as shown in FIG. 3,
the memory device can include a first block family having blocks
programmed at a first temperature level 301, a second block family
having blocks programmed at a second temperature level 302, and a
third block family having blocks programmed at a third temperature
level 303. As shown, the different temperature levels associated
with the programmed data of the block family is a factor affecting
the temporal voltage shift, such that all blocks and/or partitions
within a single block family programmed at a same temperature level
301, 302, 303 are presumed to exhibit similar distributions of
threshold voltages in memory cells, and thus would require the same
voltage offsets for read operations.
[0045] Block families can be created asynchronously with respect to
block programming events. In an illustrative example, the memory
sub-system controller 115 of FIG. 1 can create a new block family
whenever a specified period of time (e.g., a predetermined number
of minutes) has elapsed since creation of the last block family or
whenever the reference temperature of memory cells, which is
updated at specified time intervals, has changed by more than a
specified threshold value since creation of the current block
family.
[0046] A newly created block family can be associated with bin 0.
Then, the memory sub-system controller can periodically perform a
calibration process in order to associate each die of every block
family with one of the predefined threshold voltage offset bins,
which is in turn associated with the voltage offset to be applied
for read operations. The associations of blocks with block families
and block families and dies with threshold voltage offset bins can
be stored in respective metadata tables maintained by the memory
sub-system controller. In an embodiment, the block family
combination component can record a temperature level associated
with each block family. The temperature level can be a program
temperature associated with the block family. For example, the
temperature level can be an average program temperature difference
across all memory dies of the block family. In another example, the
temperature level can be an average program temperature across one
memory die per memory package. In another example, the temperature
level can be an average program temperature difference across a
maximum temperature difference of a block family. In another
example, the temperature level can be an average program
temperature difference based on N number of die in the memory
device. In this example, if a memory sub-system includes 32 memory
dies, rather than using the average program temperature difference
of all 32 memory dies, the N number of memory dies (e.g., 6 memory
dies) with the largest temperature difference are averaged
together.
[0047] FIG. 4 schematically illustrates block family combination
operations implemented by the block family combination component
(e.g., block family combination component 113 of FIG. 1) of the
memory-sub-system controller operating in accordance with
embodiments of the present disclosure. As schematically illustrated
in FIG. 4, the block family combination component 413 can manage a
memory or data store (e.g., block family metadata memory 410 of
FIG. 4) configured to store metadata associated with multiple block
families (e.g., block family 1, block family 2, block family 3 . .
. block family N) and one or more combined block families (e.g.,
combine block family A). In an embodiment, the block family
metadata memory 410 has a limited or fixed storage capacity and is
able to store information for a maximum number of block families
(e.g., 64 block families). In an embodiment, the block family
combination component 413 manages the available storage of the
block family metadata memory 410 by generating one or more combined
block families based on one or more block family combination rules
or criteria. In an embodiment, the block family combination rules
can include a comparison of temperature levels of multiple block
families (e.g., a first block family and a second block family) to
determine whether to generate a combined block family.
[0048] In an embodiment, the block family combination component 413
record metadata associated with each of the block families. In an
embodiment, the metadata can include a temperature level associated
with a block family. The temperature level can be a program
temperature associated with the block family. In an embodiment, the
program temperature can be an opening temperature (e.g., a program
temperature at a time the block family is opened), a closing
temperature (e.g., a program temperature at a time the block family
is closed), a low (or minimum) program temperature during an open
block tenure of the block family, a high (or maximum) program
temperature during an open block tenure of the block family, or a
combination of the aforementioned program temperatures (e.g., an
average or integrated value corresponding to program temperatures
of the block family).
[0049] In an embodiment, the metadata can further include data
state metrics associated with the block family. In an embodiment, a
data state metric is a quantity that is measured or inferred from
the behavior of data within the drive that generally provides
insight into the voltage state of that data. In an embodiment, the
data state metrics may indicate the state of the temporal voltage
shift, a state of temperature compensation miscalibration, a degree
of read disturb, or other operating parameter. The act of making
the measurement is a data state measurement. A data state metric
may indicate the bin to which data is to be assigned, the location
of that bin, the state of the temporal voltage shift. In an
embodiment, the metadata can include a composite data state metric,
which is a data state metric which is some function of a set of
component state metrics. For example, one possible composite state
metric is the read level 7 offset+1/2 the read level 6
offset-2*read level 2 offset.
[0050] In an embodiment, the block family combination rule can
include determining a difference between a first temperature level
of a first block family and a second temperature level of a second
block family (also referred to as a "program temperature
difference"). The program temperature difference can be compared to
a threshold level (also referred to as a "program temperature
difference threshold level") to determine if a condition is
satisfied. In an embodiment, the condition is satisfied if the
program temperature difference is less than the threshold level. In
an embodiment, the threshold level is a predetermined or preset
temperature value (e.g., 10.degree. C., 20.degree. C., etc.) for
use in identifying multiple block families that have a same or
similar program temperature and using that criteria in the block
family combination process. In an embodiment, the combined block
family A metadata can indicate that the program temperature of the
resultant combined block family A is an average of the first
temperature level (e.g., a program temperature of block family 1)
and the second temperature level (e.g., a program temperature of
block family 2).
[0051] In an embodiment, the block family combination rule can be
based on a program temperature threshold level that can be adjusted
in view of an operating parameter of the memory sub-system. In an
embodiment, the operating parameter can be an amount of available
storage in the block family metadata memory 410. In an embodiment,
the block family combination component 413 can determine whether
the memory device is running out of available storage space in the
block family metadata memory 410 for storing new block families and
adjust the threshold value used for comparing the program
temperature difference between two block families. In an
embodiment, the block family combination component 413 can compare
the operating parameter (e.g., a level of available memory for
storing block families) to a corresponding threshold level (e.g., a
minimum level of available memory) to determine if a condition is
satisfied. In this embodiment, the condition is satisfied if the
level of available memory is less than or below the minimum level
of available memory (e.g., this condition is also referred to as a
"desperation" state since the memory sub-system is running low on
available memory for storing block families). In this embodiment,
if the condition is satisfied, the block family combination
component 413 can adjust the program temperature difference
threshold level (e.g., the program temperature difference threshold
level can be increased from 10.degree. C. to 20.degree. C.) to
enable block families with a larger program temperature difference
to be combined when the memory sub-system is in a desperation
state.
[0052] For example, the block family combination component 413 can
apply a block family combination rule that enables block families
to be combined when the identified program temperature difference
is 20.degree. C. or less when in a desperation state (e.g., the
available memory in the block family metadata memory 410 is less
than a threshold level), and enables block families to be combined
when the identified program temperature difference is 10.degree. C.
or less when the available memory in the block family metadata
memory 410 is less than the threshold level.
[0053] In an embodiment, the operating parameter can be a cycle
count (e.g., a program/erase cycle (PEC) count) of the memory
sub-system. In this embodiment, the block family combination
component 413 can adjust the program temperature threshold level
based on an identified cycle count. For example, if the PEC count
is above a threshold cycle count level, the block family
combination component 413 can lower the program temperature
threshold level (i.e., requiring the program temperature difference
to be smaller when the PEC count is higher in order to enable a
combination).
[0054] In an embodiment, the block family combination rule can
include determining a first temperature level of a first block
family and a second temperature level of a second block family. In
this embodiment, the block family combination rule can refer to a
data structure (e.g., a table) including multiple temperature
ranges (e.g., each range having a minimum temperature value and a
maximum temperature value). For example, ranges can include a first
range of 0.degree. C. to 30.degree. C., a second range of
31.degree. C. to 60.degree. C., and a third range of 61.degree. C.
to 90.degree. C. In this embodiment, block family combination rule
can enable the combination of the first block family and the second
block family if the first temperature level and the second
temperature level fall within the same range. In this embodiment,
if the identified temperature levels associated with the block
families fall within different ranges, then the block family
combination component 413 can determine that the block families are
not to be combined.
[0055] In an embodiment, the temperature level associated with a
block family can include a low program temperature and a high
program temperature for each block family (identified and stored at
any granularity including by die, by package, by memory device). In
this embodiment, the block family combination rule can be based on
a total range of the temperature levels for the two block families,
by a mean temperature difference, or any other statistic based on
the two temperatures. In an example, the combined block family
(e.g., combined block family A representing a combination of block
family 1 and block family 2, as shown in FIG. 4) can adopt the
combined range of the two component block families. For example, if
block family 1 had a low-to-high program temperature range of
20.degree. C. to 30.degree. C. and block family 2 had a low-to-high
program temperature range of 25.degree. C. to 40.degree. C. block
family would result in the combined block family A having a
20.degree. C. to 40.degree. C. temperature range.
[0056] In an embodiment, the block family combination rule can
determine whether to combine block families based on a
consideration of the program temperature difference and one or more
data state metrics. In this embodiment, the metadata for each block
family includes the temperature level and the data state metrics,
as shown in FIG. 4. In this embodiment, the block family
combination rule can incorporate the program temperature criteria
with other block family combination criteria based on the data
state metrics. For example, the block family combination rule can
enable block family combinations when the program temperature
difference is above a threshold level and the data state metric
varies by a small amount (e.g., a difference between the respective
data state metrics is less than a corresponding threshold level
(e.g., a data state metrics threshold level). In this example, the
block family combination rule can enable block family combinations
when the program temperature difference is below a threshold level
and the data state metric varies by a large amount (e.g., the
difference between the respective data state metrics is greater
than the data state metrics threshold level.
[0057] FIG. 5 is a flow diagram of an example method 500 of block
family combination management implemented by a memory sub-system
controller operating in accordance with some embodiments of the
present disclosure. The method 500 can be performed by processing
logic that can include hardware (e.g., processing device,
circuitry, dedicated logic, programmable logic, microcode, hardware
of a device, integrated circuit, etc.), software (e.g.,
instructions run or executed on a processing device), or a
combination thereof. In some embodiments, the method 500 is
performed by the block family combination component 113 of FIG. 1.
Although shown in a particular sequence or order, unless otherwise
specified, the order of the operations can be modified. Thus, the
illustrated embodiments should be understood only as examples, and
the illustrated operations can be performed in a different order,
while some operations can be performed in parallel. Additionally,
one or more operations can be omitted in some embodiments. Thus,
not all illustrated operations are required in every embodiment,
and other process flows are possible.
[0058] In operation 510, the processing logic (e.g., a processing
device of the block family combination component 113 of FIG. 1)
identifies a first temperature level of a first block family
associated with a memory device. As described in detail above, the
first temperature level can be a program temperature associated
with the first block family. For example, the first temperature
level can be an opening temperature recorded at a time a block
family is opened, a closing temperature recorded at a time a block
family is closed, a low temperature level during an open block
tenure, a high temperature level during an open block tenure, an
average of one or more of the aforementioned temperature levels,
etc.)
[0059] In operation 520, the processing logic identifies a second
temperature level of a second block family associated with the
memory device. As described above in connection with operation 520,
the second temperature level can be a program temperature
associated with the second block family. For example, the second
temperature level can be an opening temperature recorded at a time
a block family is opened, a closing temperature recorded at a time
a block family is closed, a low temperature level during an open
block tenure, a high temperature level during an open block tenure,
an average of one or more of the aforementioned temperature levels,
etc.)
[0060] In operation 530, the processing logic determines if a
condition is satisfied based on the first temperature level and the
second temperature level. In an embodiment, the condition is
satisfied if a difference between the first temperature level and
the second temperature level is less than a threshold level.
[0061] In another embodiment, the condition is satisfied if the
first temperature level and the second temperature level both fall
within a same temperature range. In this embodiment, the processing
logic can maintain multiple temperature ranges (e.g., a first range
of 0.degree. C. to 30.degree. C., a second range of 31.degree. C.
to 60.degree. C., and a third range of 61.degree. C. to 90.degree.
C.). In operation 530, the processing logic can determine which
range of the multiple ranges each of the first temperature level
and the second temperature levels falls within. In response to
determining the first temperature level and the second temperature
level are within the same range, the processing logic determines
the condition is satisfied.
[0062] In operation 540, in response to satisfying the condition,
the processing logic combines the first block family and the second
block family to generate a combined block family. In an embodiment,
metadata associated with the combined block family can be stored in
a data store configured to store the block family metadata (e.g.,
the block family metadata memory 410 of FIG. 4). In an embodiment,
the metadata associated with the combined block family can reflect
a low-to-high temperature range representative of the low-to-high
temperature range of the respective block families. For example, if
the first block family had a low-to-high program temperature range
of 32.degree. C. to 57.degree. C. and the second block family had a
low-to-high program temperature range of 34.degree. C. to
51.degree. C., the combined block family can be identified as
having a 32.degree. C. to 57.degree. C. temperature range.
[0063] FIG. 6 is a flow diagram of an example method of generating
a combined block family based on program temperature levels and one
or more operating parameters of a memory sub-system in accordance
with some embodiments of the present disclosure. The method 600 can
be performed by processing logic that can include hardware (e.g.,
processing device, circuitry, dedicated logic, programmable logic,
microcode, hardware of a device, integrated circuit, etc.),
software (e.g., instructions run or executed on a processing
device), or a combination thereof. In some embodiments, the method
600 is performed by the block family combination component 113 of
FIG. 1 or the block family combination component 413 of FIG. 4.
Although shown in a particular sequence or order, unless otherwise
specified, the order of the operations can be modified. Thus, the
illustrated embodiments should be understood only as examples, and
the illustrated operations can be performed in a different order,
while some operations can be performed in parallel. Additionally,
one or more operations can be omitted in some embodiments. Thus,
not all illustrated operations are required in every embodiment,
and other process flows are possible.
[0064] In operation 610, the processing logic compares an operating
parameter to a first threshold to determine if a first condition is
satisfied. In an embodiment, the operating parameter can be a
difference between a first data state metric of a first block
family and a second data state metric of a second block family. In
this embodiment, the first condition is satisfied if the difference
between the data state metrics is greater than a threshold data
state metric level (i.e., the first threshold level). For example,
the data state metrics (e.g., an amount of charge) of the
respective block families may vary by a large amount (e.g., more
than the threshold data state metric level), and therefore, satisfy
the first condition.
[0065] In an embodiment, the operating parameter can be a level of
available memory for storing block families. In this embodiment,
the first condition is satisfied if the level of available memory
is below a threshold available memory level (i.e., the first
threshold level). In an embodiment, the threshold available memory
level is a predetermined or selected amount of available memory
used to define when the memory device is operating in a desperation
state. In this embodiment, the first condition is satisfied when
the memory device is operating in the desperation state (i.e., the
amount of available memory is below the threshold available memory
level).
[0066] In an embodiment, the operating parameter can be a cycle
count of the memory device. In this embodiment, the first condition
is satisfied if the cycle count is above a threshold cycle count
level (e.g., a predetermined or selected number of cycles).
[0067] In operation 620, in response to satisfying the first
condition, the processing logic adjusts a threshold temperature
level to establish an adjusted threshold temperature level. In
embodiments, the adjustment to the threshold temperature level can
be an increase or a decrease of an initial or current threshold
temperature level, depending on the first condition that is
satisfied. In an embodiment, the processing logic lowers or
decreases the threshold temperature level in response to the
satisfaction of a first condition indicating the difference between
the data state metrics of the first block family and the second
block family is greater than a threshold data state metric level.
In an embodiment, the processing logic lowers or decreases the
threshold temperature level in response to the satisfaction of a
first condition indicating a current cycle count is above the
threshold cycle count level. By decreasing the threshold
temperature level, the processing logic can enable fewer
combinations of block families by lowering the acceptable program
temperature difference between candidate block families, as
described below.
[0068] In an embodiment, the processing logic raises or increases
the threshold temperature level in response to the satisfaction of
a first condition indicating the amount of available memory for
storing block families is below the threshold available memory
level. By increasing the threshold temperature level, the
processing logic can enable the combination of block families
having a larger program temperature difference, as described
below.
[0069] In operation 630, the processing logic compares a difference
between a first temperature level of a first block family and a
second temperature level of a second block family to the adjusted
threshold temperature level to determine if a second condition is
satisfied. In an embodiment, the processing logic uses the
threshold temperature level as adjusted in operation 620 for
comparison purposes to determine if the second condition is
satisfied. In an embodiment, the second condition is satisfied if
the difference between the first temperature level of the first
block family and the second temperature level of the second block
family is less than the threshold temperature level.
[0070] In operation 640, in response to satisfying the second
condition, the processing logic combines the first block family and
the second block family to generate a combined block family. In an
embodiment, the determination whether to combine the first block
family and the second block family is a function of the first
condition (e.g., the condition associated with the operating
parameter (e.g., the available memory, the data state metrics
difference, the cycle count, etc.) and the second condition (e.g.,
the condition associated with the program temperature difference
between the two block families).
[0071] FIG. 7 illustrates an example machine of a computer system
700 within which a set of instructions, for causing the machine to
perform any one or more of the methodologies discussed herein, can
be executed. In some embodiments, the computer system 700 can
correspond to a host system (e.g., the host system 120 of FIG. 1)
that includes, is coupled to, or utilizes a memory sub-system
(e.g., the memory sub-system 110 of FIG. 1) or can be used to
perform the operations of a controller (e.g., to execute an
operating system to perform operations corresponding to the block
family combination component 113 of FIG. 1). In alternative
embodiments, the machine can be connected (e.g., networked) to
other machines in a LAN, an intranet, an extranet, and/or the
Internet. The machine can operate in the capacity of a server or a
client machine in client-server network environment, as a peer
machine in a peer-to-peer (or distributed) network environment, or
as a server or a client machine in a cloud computing infrastructure
or environment.
[0072] The machine can be a personal computer (PC), a tablet PC, a
set-top box (STB), a Personal Digital Assistant (PDA), a cellular
telephone, a web appliance, a server, a network router, a switch or
bridge, or any machine capable of executing a set of instructions
(sequential or otherwise) that specify actions to be taken by that
machine. Further, while a single machine is illustrated, the term
"machine" shall also be taken to include any collection of machines
that individually or jointly execute a set (or multiple sets) of
instructions to perform any one or more of the methodologies
discussed herein.
[0073] The example computer system 700 includes a processing device
702, a main memory 704 (e.g., read-only memory (ROM), flash memory,
dynamic random access memory (DRAM) such as synchronous DRAM
(SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory 710 (e.g.,
flash memory, static random access memory (SRAM), etc.), and a data
storage system 718, which communicate with each other via a bus
730.
[0074] Processing device 702 represents one or more general-purpose
processing devices such as a microprocessor, a central processing
unit, or the like. More particularly, the processing device can be
a complex instruction set computing (CISC) microprocessor, reduced
instruction set computing (RISC) microprocessor, very long
instruction word (VLIW) microprocessor, or a processor implementing
other instruction sets, or processors implementing a combination of
instruction sets. Processing device 702 can also be one or more
special-purpose processing devices such as an application specific
integrated circuit (ASIC), a field programmable gate array (FPGA),
a digital signal processor (DSP), network processor, or the like.
The processing device 702 is configured to execute instructions 728
for performing the operations and steps discussed herein. The
computer system 700 can further include a network interface device
712 to communicate over the network 720.
[0075] The data storage system 718 can include a machine-readable
storage medium 724 (also known as a computer-readable medium) on
which is stored one or more sets of instructions 728 or software
embodying any one or more of the methodologies or functions
described herein. The instructions 728 can also reside, completely
or at least partially, within the main memory 704 and/or within the
processing device 702 during execution thereof by the computer
system 700, the main memory 704 and the processing device 702 also
constituting machine-readable storage media. The machine-readable
storage medium 724, data storage system 718, and/or main memory 704
can correspond to the memory sub-system 110 of FIG. 1.
[0076] In one embodiment, the instructions 728 include instructions
to implement functionality corresponding to the block family
combination component 113 of FIG. 1. While the machine-readable
storage medium 724 is shown in an example embodiment to be a single
medium, the term "machine-readable storage medium" should be taken
to include a single medium or multiple media that store the one or
more sets of instructions. The term "machine-readable storage
medium" shall also be taken to include any medium that is capable
of storing or encoding a set of instructions for execution by the
machine and that cause the machine to perform any one or more of
the methodologies of the present disclosure. The term
"machine-readable storage medium" shall accordingly be taken to
include, but not be limited to, solid-state memories, optical
media, and magnetic media.
[0077] Some portions of the preceding detailed descriptions have
been presented in terms of algorithms and symbolic representations
of operations on data bits within a computer memory. These
algorithmic descriptions and representations are the ways used by
those skilled in the data processing arts to most effectively
convey the substance of their work to others skilled in the art. An
algorithm is here, and generally, conceived to be a self-consistent
sequence of operations leading to a desired result. The operations
are those requiring physical manipulations of physical quantities.
Usually, though not necessarily, these quantities take the form of
electrical or magnetic signals capable of being stored, combined,
compared, and otherwise manipulated. It has proven convenient at
times, principally for reasons of common usage, to refer to these
signals as bits, values, elements, symbols, characters, terms,
numbers, or the like.
[0078] It should be borne in mind, however, that all of these and
similar terms are to be associated with the appropriate physical
quantities and are merely convenient labels applied to these
quantities. The present disclosure can refer to the action and
processes of a computer system, or similar electronic computing
device, that manipulates and transforms data represented as
physical (electronic) quantities within the computer system's
registers and memories into other data similarly represented as
physical quantities within the computer system memories or
registers or other such information storage systems.
[0079] The present disclosure also relates to an apparatus for
performing the operations herein. This apparatus can be specially
constructed for the intended purposes, or it can include a general
purpose computer selectively activated or reconfigured by a
computer program stored in the computer. Such a computer program
can be stored in a computer readable storage medium, such as, but
not limited to, any type of disk including floppy disks, optical
disks, CD-ROMs, and magnetic-optical disks, read-only memories
(ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or
optical cards, or any type of media suitable for storing electronic
instructions, each coupled to a computer system bus.
[0080] The algorithms and displays presented herein are not
inherently related to any particular computer or other apparatus.
Various general purpose systems can be used with programs in
accordance with the teachings herein, or it can prove convenient to
construct a more specialized apparatus to perform the method. The
structure for a variety of these systems will appear as set forth
in the description below. In addition, the present disclosure is
not described with reference to any particular programming
language. It will be appreciated that a variety of programming
languages can be used to implement the teachings of the disclosure
as described herein.
[0081] The present disclosure can be provided as a computer program
product, or software, that can include a machine-readable medium
having stored thereon instructions, which can be used to program a
computer system (or other electronic devices) to perform a process
according to the present disclosure. A machine-readable medium
includes any mechanism for storing information in a form readable
by a machine (e.g., a computer). In some embodiments, a
machine-readable (e.g., computer-readable) medium includes a
machine (e.g., a computer) readable storage medium such as a read
only memory ("ROM"), random access memory ("RAM"), magnetic disk
storage media, optical storage media, flash memory devices,
etc.
[0082] In the foregoing specification, embodiments of the
disclosure have been described with reference to specific example
embodiments thereof. It will be evident that various modifications
can be made thereto without departing from the broader spirit and
scope of embodiments of the disclosure as set forth in the
following claims. The specification and drawings are, accordingly,
to be regarded in an illustrative sense rather than a restrictive
sense.
* * * * *