U.S. patent application number 13/270224 was filed with the patent office on 2012-07-12 for memory system.
This patent application is currently assigned to SOLID STATE STORAGE SOLUTIONS LLC. Invention is credited to Hiroyuki Goto, Fumio Hara, Yasuhiro Nakamura, Hirofumi Shibuya, SHIGEMASA SHIOTA.
Application Number | 20120176842 13/270224 |
Document ID | / |
Family ID | 27654730 |
Filed Date | 2012-07-12 |
United States Patent
Application |
20120176842 |
Kind Code |
A1 |
SHIOTA; SHIGEMASA ; et
al. |
July 12, 2012 |
Memory System
Abstract
The present invention provides a memory system which contributes
to improvement in efficiency of a data process accompanying a
memory access. A memory system has a rewritable nonvolatile memory,
a buffer memory, and a controller. The controller controls, in
response to an access request from an external apparatus, first
data transfer between the controller and the external apparatus,
second data transfer between the controller and the nonvolatile
memory, and third data transfer between the controller and the
buffer memory, controls transfer from the controller to the buffer
memory in the third data transfer and transfer from the buffer
memory to the controller in a time sharing manner, and enables the
first data transfer or the second data transfer to be performed in
parallel with the transfer carried out in the time sharing
manner.
Inventors: |
SHIOTA; SHIGEMASA;
(Tachikawa, JP) ; Goto; Hiroyuki;
(Higashimurayama, JP) ; Shibuya; Hirofumi;
(Matsuda, JP) ; Hara; Fumio; (Higashikurume,
JP) ; Nakamura; Yasuhiro; (Tachikawa, JP) |
Assignee: |
SOLID STATE STORAGE SOLUTIONS
LLC
|
Family ID: |
27654730 |
Appl. No.: |
13/270224 |
Filed: |
October 10, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12251444 |
Oct 14, 2008 |
8036040 |
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13270224 |
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11785177 |
Apr 16, 2007 |
7450457 |
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12251444 |
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11082859 |
Mar 18, 2005 |
7206233 |
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11785177 |
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10404547 |
Apr 2, 2003 |
6882568 |
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11082859 |
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10341367 |
Jan 14, 2003 |
6744692 |
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10404547 |
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Current U.S.
Class: |
365/185.18 |
Current CPC
Class: |
G06F 2212/7206 20130101;
G06F 13/161 20130101; G06F 12/0246 20130101; G11C 7/1006 20130101;
G06F 13/1673 20130101 |
Class at
Publication: |
365/185.18 |
International
Class: |
G11C 16/04 20060101
G11C016/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 7, 2002 |
JP |
2002-030191 |
Claims
1. A memory system comprising: a rewritable nonvolatile memory; a
buffer memory; and a controller, wherein said controller controls,
in response to an access request from an external apparatus, first
data transfer between said controller and said external apparatus,
second data transfer between said controller and said nonvolatile
memory, and third data transfer between said controller and said
buffer memory, controls transfer from said controller to said
buffer memory and transfer from said buffer memory to said
controller in said third data transfer in a time sharing manner,
and enables said first data transfer or said second data transfer
to be performed in parallel with the transfer carried out in the
time sharing manner.
2-22. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a technique of buffering
access data in a memory system for performing access control
between an external interface and a nonvolatile memory in response
to an access request from the outside and, for example, to a
technique effectively applied to a flash memory card.
[0002] A flash memory card has a flash memory and a controller.
Since the operation speed, particularly, writing or rewriting
operation speed of the flash memory is lower than operation speed
of a host connected to the flash memory card, the controller has a
buffer memory in order to absorb the difference between the
operation speeds. In response to a write request from the outside,
the controller controls to input write data from the outside to the
buffer memory and write the input data into the flash memory. In
response to a read request from the outside, the controller
temporarily stores data read out from the flash memory into the
buffer memory and outputs the stored data to the outside. As a
conventional buffer memory, an SRAM (Static Random Access Memory)
of a relatively small capacity, a static latch, or the like is
often employed.
SUMMARY OF THE INVENTION
[0003] In the case of employing an SRAM of a small capacity,
however, until writing of data input from the outside to the buffer
memory into the flash memory is completed, data transfer from the
host to the memory card has to be waited. Until read data stored in
the buffer memory from the flash memory is output to the outside, a
new reading operation of the flash memory has to be waited.
Particularly, in the case where writing of data into the flash
memory fails, for example, when the data has to be written again to
a replacing sector due to a failure in a sector to which the
writing operation is performed first, the next write data from the
host cannot be received by the buffer memory. Consequently, due to
a problem between the flash memory and the controller, data
transfer between the host and the controller has to be waited. It
increases burden on the host and processing time, and a problem
such that the data processing efficiency deteriorates occurs.
[0004] In a process of examining the problems, the inventor herein
has recognized the existence of patent applications, although not
well known, filed by the applicant herein. The patent application
Nos. are 2001-174978, 2001-177924, 2001-213639, and 2001-213640.
The applications provide a technique using a flash memory as a
nonvolatile memory for backing up information stored in an SDRAM as
a volatile memory. The SDRAM is not evaluated as a buffer
memory.
[0005] An object of the present invention is to provide a memory
system contributing improvement in efficiency of a data process
accompanying a memory access.
[0006] Another object of the invention is to provide a memory
system for performing an access control between an external
interface and a nonvolatile memory in response to an access request
from the outside, which can contribute to reduction in waiting time
of a host in data transfer to/from the host, reduction in process
load, and reduction in process time.
[0007] The above and other objects and novel features of the
invention will become apparent from the description of the
specification and the accompanying drawings.
[0008] Representative ones of inventions disclosed in the
specification will be briefly described as follows. [0009] [1] A
memory system has a rewritable nonvolatile memory, a buffer memory,
and a controller. The controller controls, in response to an access
request from an external apparatus, first data transfer between the
controller and the external apparatus, second data transfer between
the controller and the nonvolatile memory, and third data transfer
between the controller and the buffer memory, controls transfer
from the controller to the buffer memory and transfer from the
buffer memory to the controller in the third data transfer in a
time sharing manner, and enables the first data transfer or the
second data transfer to be performed in parallel with the transfer
carried out in the time sharing manner.
[0010] With the above configuration, in response to a write access
request from the outside, the controller stores write data to the
buffer memory and outputs the write data stored in the buffer
memory in a time sharing manner, in parallel with the write data
storing process, can transfer write data to the nonvolatile memory
by the second data transfer and, in parallel with the write data
outputting process, input the following write data from the
external apparatus by the first data transfer. In response to a
read access request from the outside, the controller stores read
data to the buffer memory and outputs the read data stored in the
buffer memory in a time sharing manner, in parallel with the read
data storing process, can transfer the read data to the external
apparatus by the first data transfer and, in parallel with the read
data outputting process, input the following read data from the
nonvolatile memory by the second data transfer.
[0011] By the buffering function of the buffer memory, long waiting
time is unnecessary for the timing of supplying a plurality of
write data pieces by an external apparatus such as a host, and long
waiting time is unnecessary for the timing of obtaining a plurality
of read data pieces by the host. Therefore, the invention can
contribute to reduction in waiting time of the host in the data
transfer between the host and a controller, reduction in a process
load, and reduction in processing time. Thus, the invention can
contribute to improvement in the efficiency of a data process
accompanying a memory access.
[0012] As a desired mode of the invention, in order to maximally
display the buffering function, operation speed of the third data
transfer is about twice as high as data transfer speed of the first
data transfer. In theory, the waiting time of the host becomes
zero.
[0013] As a desired mode of the invention, the buffer memory is a
single-port clock-synchronous volatile memory and operates in an
FIFO manner. Higher speed of the buffer memory and easy access
control can be realized. The nonvolatile memory is, for example, a
flash memory.
[0014] As a mode of realizing buffering between the first transfer
and the third transfer and buffering between the second transfer
and the third transfer, preferably, the controller has a dual-port
data buffer disposed between the external apparatus and the buffer
memory and a dual-port data buffer disposed between the buffer
memory and the nonvolatile memory. Control for paralleling the
first data transfer and the third data transfer and paralleling the
second data transfer and the third data transfer is further
facilitated. [0015] [2] A memory system according to another aspect
of the invention has a rewritable nonvolatile memory, a buffer
memory, and a controller. The controller has: a first data transfer
control unit connected to an external apparatus; a second data
transfer control unit connected to the nonvolatile memory; and a
transfer arbitrator which is connected to the buffer memory and
controls data transfer to/from the buffer memory in response to a
transfer request from the first data transfer control unit and a
transfer request from the second data transfer control unit. The
first data transfer control unit is connected to the external
apparatus and the transfer arbitrator via a dual-port data buffer
and outputs a transfer request to the transfer arbitrator. The
second data transfer control unit is connected to the nonvolatile
memory and the transfer arbitrator via a dual-port data buffer and
outputs a transfer request to the transfer arbitrator. The transfer
arbitrator controls transfer of write data to the buffer memory and
transfer of read data from the buffer memory in a time sharing
manner in response to a transfer request from the first data
transfer control unit and a transfer request from the second data
transfer control unit.
[0016] With the above configuration, the data transfer between the
external apparatus and the controller is buffered by the data
buffer in the first data transfer control unit, the data transfer
between the nonvolatile memory and the controller is buffered by
the data buffer in the second data transfer control unit, and the
data transfer between both of the data buffers and the buffer
memory can be performed in a time sharing manner. Therefore, in
response to a write access request from the outside, the controller
stores write data into the buffer memory and outputs the write data
stored in the buffer memory in a time sharing manner. In parallel
with the write data storing process, transfer of write data from
the data buffer in the second transfer control unit to the
nonvolatile memory can be performed. In parallel with the write
data outputting process, the following write data from the external
apparatus can be transferred to the data buffer in the first
transfer control unit. In response to a read access request from
the external apparatus, the controller stores read data into the
buffer memory and outputs the read data stored in the buffer memory
in a time sharing manner. In parallel with the read data storing
process, transfer of read data from the data buffer in the first
transfer control unit to the external apparatus can be performed.
In parallel with the read data outputting process, the following
read data from the nonvolatile memory can be transferred to the
data buffer in the second transfer control unit.
[0017] By the buffering function, long waiting time is unnecessary
for the timing of supplying a plurality of write data pieces by an
external apparatus such as a host, and long waiting time is
unnecessary for the timing of obtaining a plurality of read data
pieces by the host. Therefore, the invention can contribute to
reduction in waiting time of the host in the data transfer between
the host and a controller, reduction in a process load, and
reduction in processing time. Thus, the invention can contribute to
improvement in the efficiency of a data process accompanying a
memory access.
[0018] As a concrete mode of the invention, in response to a write
access request from the outside, the first data transfer control
unit outputs a transfer request for writing data to the buffer
memory to the transfer arbitrator when a predetermined amount of
data is stored in the data buffer from the external apparatus, and
the second data transfer control unit outputs a transfer request
for reading data from the buffer memory to the data buffer to the
transfer arbitrator when data in the data buffer is less than the
predetermined amount. In response to a read access request from the
outside, the second data transfer control unit outputs a transfer
request for writing data to the buffer memory to the transfer
arbitrator when a predetermined amount of data is stored in the
data buffer from the buffer memory, and the first data transfer
control unit outputs a transfer request for reading data from the
buffer memory to the transfer arbitrator when data in the data
buffer is less than the predetermined amount.
[0019] As a desired mode of the invention, in order to maximally
display the buffering function, preferably, operation speed of the
data transfer to/from the buffer memory by the transfer arbitrator
is about twice as high as operation speed of data transfer to/from
the outside by the first transfer control unit. In theory, the
waiting time of the host becomes zero.
[0020] As a desired mode of the invention, the buffer memory is a
single-port clock-synchronous volatile memory and operates in an
FIFO manner. Higher speed of the buffer memory and easier access
control can be realized. The nonvolatile memory is, for example, a
flash memory.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a block diagram of a flash memory card as an
example of a memory system according to the invention.
[0022] FIG. 2 is a diagram showing local memory address mapping of
a flash memory functioning as a file memory.
[0023] FIG. 3 is an explanatory diagram generally showing address
mapping of a host interface part of a controller.
[0024] FIG. 4 is an explanatory diagram showing an FIFO form of an
SDRAM.
[0025] FIG. 5 is a flowchart illustrating a control operation
performed by a transfer arbitrator.
[0026] FIG. 6 is a flowchart showing a control operation of a CPU
at the time of a write transfer request.
[0027] FIG. 7 is a flowchart showing a control operation of a CPU
at the time of a read access request.
[0028] FIG. 8 is a timing chart showing a correlation of data
transfer operations among a host, an SDRAM, and a flash memory when
a write access request is received.
[0029] FIG. 9 is a timing chart showing a correlation of data
transfer operations among the host, SDRAM, and flash memory when a
read access request is received.
[0030] FIG. 10 is a timing chart showing an example of a write
cycle Tdw of the SDRAM.
[0031] FIG. 11 is a timing chart showing an example of a read cycle
Tdr of the SDRAM.
[0032] FIG. 12 is a timing chart showing an example of a write
cycle Tfw of a flash memory.
[0033] FIG. 13 is a timing chart showing an example of a read cycle
Tfr of the flash memory.
[0034] FIG. 14 is a flowchart showing a case where there is no
write error in the flash memory in the flow of a data transferring
process performed in response to a write access request.
[0035] FIG. 15 is a flowchart showing a case where there is a write
error in the flash memory in the flow of another data transfer
process performed in response to the write access request.
[0036] FIG. 16 is a flowchart of the flow of a data transferring
process performed in response to a read access request.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] FIG. 1 shows a memory flash card as an example of a memory
system according to the invention. A flash memory card 1 has a
flash memory (nonvolatile memory) 2 having a data storage area and
an area for managing the data storage area for each predetermined
sector address (physical address), a controller 4 for controlling
an access to the flash memory 2 in response to a request from an
external information processor, for example, a host 3, connected on
the outside of the memory system, and a buffer memory 5 connected
to the controller 4.
[0038] The flash memory 2 has, although not particularly shown, a
memory cell array in which electrically erasable and writable flash
memory cells are arranged in a matrix. The flash memory cell has,
although not limited, a floating gate and a control gate isolated
from each other via an insulating film on a channel region. For
example, by injecting hot electrons into the floating gate, the
threshold voltage of the memory cell is increased (this operation
is called, for example, writing). By discharging electrons injected
in the floating gate by a tunneling current via a gate insulating
film, the threshold voltage of the memory cell is lowered (this
operation is called erasing). The drain of the flash memory cell is
connected to a bit line, the source is connected to a source line,
and the control gate is connected to a word line. For example, an
address assigned to the word line is the sector address. Selection
of a word line by a sector address signal is performed by a word
line selecting circuit. A part of a plurality of flash memory cells
designated by a sector address is selected on the basis of a column
address signal generated by a column address counter by using a
column address as a starting point. The flash memory can employ,
for example, the configuration disclosed in Japanese Unexamined
Patent Application No. 2001-23383.
[0039] The flash memory 2 functions as, for example, a file memory.
In local memory address mapping, as shown in FIG. 2, a management
area and a user data storing area are assigned to each of sector
addresses 1 to n and information such as whether each sector is
good (valid) or not and further the presence/absence of a spare is
stored in the management area.
[0040] The buffer memory 5 takes the form of, for example, a
single-port SDRAM (Synchronous Dynamic Random Access Memory) as a
clock synchronous volatile memory. The buffer memory 5 will be also
simply described as SDRAM 5. The SDRAM 5 has, for example, a memory
cell array in which dynamic memory cells are arranged in a matrix,
receives a command, an address, and the like synchronously with
clocks, and can perform a write access, a read access, or the like
designated by a command synchronously with clock signals at high
speed. For example, when it is assumed that the speed of a data
transfer (first data transfer) via a bus between the host 3 and the
controller 4 is 100 MB (megabytes)/sec, the speed of a data
transfer (third data transfer) via a bus between the SDRAM 5 and
the controller 4 is 266 MB/sec which is more than twice as high as
that of the first data transfer. The speed of a data transfer
(second data transfer) via a bus between the flash memory 2 and the
controller 4 is about 20 MB/sec so as to be matched with access
speed of the flash memory 2 itself which is low.
[0041] The controller 4 is constructed by a host data transfer
control unit (first data transfer control unit) 11, a flash data
transfer control unit (second data transfer control unit) 12, a
transfer arbitrator 13, a CPU 14, and a control register 15.
[0042] The control register 15 has a command register (15C), an
address register (15A), and a status register (15S). At the time of
accessing the flash memory card 1, the host 3 sets a read or write
command in the command register 15C and sets an access address in
the address register 15A. States of the host 3 and the flash memory
card 1 are mutually recognized via the status register 15S.
[0043] The CPU 14 generally controls the flash memory card 1. When
a command is set in the command register 15C, the CPU 14 interprets
the command, and performs a control on a memory interface with the
flash memory 2, a control on a data interface with the host 3, a
buffer control on data subjected to the interface control, and the
like, thereby completing an access to a sector in the flash memory
2 corresponding to the address set in the address register 15A.
[0044] The host data transfer control unit 11 connects the host 3
and the transfer arbitrator 13 via a dual-port data buffer 20. When
a transfer request circuit 21 sends a transfer request to the
transfer arbitrator 13 by a signal HDRQ, and receives
acknowledgment by a signal HDACK, the data buffer 20 inputs/outputs
data from/to the transfer arbitrator 13. The inputting or
outputting operation is instructed to the transfer arbitrator 13 by
the host data transfer control unit 11 by using a signal HDIR. The
signal HDIR is set in the host data transfer control unit 11 before
the CPU 14 starts a transferring operation. When an amount of the
input or output operation to/from the transfer arbitrator 13 of the
data buffer 20 started in response to the acknowledge by the signal
HDACK reaches a specific amount, the host data transfer control
unit 11 asserts a signal HEND_IRQ to the CPU and finishes the
transfer operation. The CPU 14 allows the transfer arbitrator 13 to
accept a new transfer request. The host data transfer control unit
11 can instruct the host 3 to stop the operation by outputting a
wait signal HWAIT to the host 3 and asserting the signal.
[0045] Although not shown, whether the transfer operation between
the data buffer 20 and the host 3 can be performed or not is
determined by exchanging the status via the status register 15S.
When seen from the host 3, the data buffer 20 is mapped in its
address space. FIG. 3 shows general address mapping of the host
interface part of the controller 4.
[0046] The flash data transfer control unit 12 connects the flash
memory 2 and the transfer arbitrator 13 via a dual-port data buffer
22. The data buffer 22 takes the form of a dual-port FIFO buffer.
When a transfer request circuit 23 sends a transfer request to the
transfer arbitrator 13 by a signal FDRQ and receives acknowledgment
by a signal FDACK, the data buffer 22 inputs/outputs data from/to
the transfer arbitrator 13. The inputting/outputting operation is
instructed by the flash data transfer control unit 13 to the
transfer arbitrator 13 by using a signal FDIR. The signal FDIR is
set in the flash data transfer control unit 12 before the CPU 14
starts transferring operation. When an amount of the
inputting/outputting operation to the transfer arbitrator 13 of the
data buffer 22 started in response to the acknowledgment by the
signal FDACK reaches a specific amount, the flash data transfer
control unit 12 asserts a signal FEND_IRQ to the CPU and finishes
the transfer operation. In response to this, the CPU 14 allows the
transfer arbitrator 13 to accept a new transfer request. Although
not shown, the flash data transfer control unit 12 determines
whether the transfer operation between the data buffer 22 and the
flash memory 2 can be performed or not by exchanging the status via
the status register of the flash memory 2.
[0047] The transfer arbitrator 13 is constructed by a transfer
permission circuit 30, an address counter 31 for host data
transfer, and an address counter 32 for flash data transfer. The
address counter 31 for host data transfer generates an access
address of the SDRAM 5 in data transfer between the data buffer 20
and the buffer memory 5. The address counter 32 for flash data
transfer generates an access address of the SDRAM 5 in data
transfer between the data buffer 22 and the flash memory 2. An
address is preset in the address counters 31 and 32 by the CPU 14
in response to an access request from the host 3. The access to the
SDRAM 5 is controlled in an FIFO manner as illustrated in FIG. 4.
The address counter 31 for host data transfer functions as a write
address pointer at the time of writing data from the data buffer 20
to the SDRAM 5 and functions as a read address pointer at the time
of reading data from the SDRAM 5 to the data buffer 20. The address
counter 32 for flash data transfer functions as a write address
pointer at the time of writing data from the data buffer 22 to the
SDRAM 5 and functions as a read address pointer at the time of
reading data from the SDRAM 5 to the data buffer 22. The transfer
permission circuit 30 arbitrates competition between the transfer
request signals HDRQ and FDRQ and returns a result of the
arbitration to the transfer request circuits 21 and 23 by the
signals HDACK and FDACK.
[0048] FIG. 5 illustrates the control operation by the transfer
arbitrator 13. The transfer arbitrator 13 sequentially cyclically
determines whether there is a host data transfer request by the
signal HDRQ (S1), whether there is a flash data transfer request by
the signal FDRQ or not (S2), and whether it is necessary to refresh
or not (S3). In the case where there is the host data transfer
request by the signal HDRQ, in a process responding to a write
access request from the host 3, data is written to an address in
the SDRAM 5 indicated by the address counter 31 and, in a process
responding to a read access request from the host 3, data is read
from an address in the SDRAM 5 indicated by the address counter 31
(S1A). After that, the address counter 31 is incremented (S1B). In
the case where there is a flash data transfer request by the signal
FDRQ, in a process responding to the write access request from the
host 3, data is read from an address in the SDRAM 5 indicated by
the address counter 32 and, in a process responding to a read
access request from the host 3, data is written into an address in
the SDRAM 5 indicated by the address counter 32, and the address
counter 32 is incremented. When it is determined that refreshing is
necessary, information stored in the SDRAM 5 is refreshed. A
refresh address is generated by a not-shown refresh address counter
of the transfer arbitrator 13.
[0049] As obviously understood from FIG. 5, in the process
performed in response to the write access request from the host 3,
writing to the address in the SDRAM 5 indicated by the address
counter 31 and reading of data from the address in the SDRAM 5
indicated by the address counter 32 can be performed in a time
sharing manner, that is, alternately on an 8-byte unit basis or the
like. In the process responding to the read access request from the
host 3, reading of data from the address in the SDRAM 5 indicated
by the address counter 31 and writing of data to the address in the
SDRAM 5 indicated by the address counter 32 can be performed in a
time sharing manner, that is, alternately on the 8-byte unit basis
or the like.
[0050] FIG. 6 illustrates a control operation of the CPU when the
write transfer request is received. When a write access request
from the host 3 is detected (S10), the CPU 14 sets the address
counter 31 for host data transfer, that is, initializes or presets
an initial value (S11). Further, the CPU 14 instructs the host data
transfer control unit 11 to transfer data to be input from the host
3 to the data buffer 20 to the transfer arbitrator 13 (S12). After
that, the CPU 14 sets a transfer enable status in the status
register 15S and notifies the host 3 of start of transfer of write
data to the data buffer 20 (S13). The transfer arbitrator 13
consequently performs the process which is carried out in response
to the host transfer request (S1) described by referring to FIG. 5,
thereby enabling the data to be stored into the SDRAM 5 designated
by the address counter 31 each time 8-byte data is input from the
host 3 to the data buffer 20. Further, the CPU 14 calculates a
physical address, that is, a sector address in the flash memory 2
from the access address input to the address register 15A (S14) and
sets a command to write data into the calculated sector address
into the flash memory 2 via the flash data transfer control unit 4
(S15). After that, the CPU 14 sets the address counter 32 for flash
data transfer, that is, initializes or presets an initial value
(S16). Each time 8-byte data is input from the SDRAM 5 to the data
buffer 22, the CPU 14 instructs the flash data transfer control
unit 12 to enable the data to be transferred to the flash memory 2
(S17). During this period, the transfer arbitrator 13 performs the
process which is carried out in response to the flash data transfer
request (S2) described by referring to FIG. 5, thereby transferring
the data stored in the SDRAM 5 to the data buffer 22 in accordance
with the value of the address counter 32 so that the data held in
the data buffer 22 becomes eight bytes.
[0051] When the process responding to the host data transfer
request in FIG. 5 and the process responding to the flash data
transfer request are repeated in a time sharing manner, the CPU 14
detects a state where both the signals HEND_IRQ and FEND_ IRQ are
active (S18) and enters a write access request waiting mode (S10).
Specifically, when data according to the number of write data
pieces to be written in response to the write access request made
by the host 3 is stored in the SDRAM 5, the signal HEND_IRQ is made
active. When data according to the number of write data to be
written is read from the SDRAM 5, the signal FEND_IRQ is made
active.
[0052] FIG. 7 illustrates the control operation of the CPU
performed in response to the read access request. When a read
access request from the host 3 is detected (S20), the CPU 14
calculates a physical address, that is, a sector address in the
flash memory 2 from the access address input to the address
register 15A (S21), and sets a read command to the calculated
sector address into the flash memory 2 via the flash data transfer
control unit 4 (S22). The CPU 14 sets the address counter 32 for
flash data transfer, that is, initializes or presets the initial
value (S23). Further, the CPU 14 instructs the flash data transfer
control unit 12 to transfer data which is input from the flash
memory 2 to the data buffer 22 to the transfer arbitrator 13 (S24).
By performing a process which is carried out in response to the
flash data transfer request (S2) described by referring to FIG. 5,
for example, each time 8-byte data is input from the flash memory 2
to the data buffer 22, the transfer arbitrator 13 enables the data
to be stored into the SDRAM 5 designated by the address counter 32.
After that, the CPU 14 sets the address counter 31 for host data
transfer, that is, initializes or presets an initial value (S25).
The CPU 14 instructs the host data transfer control unit 11 to read
out data from the SDRAM 5 and supply the data to the data buffer 20
(S26). The CPU 14 sets a transfer enable status in the status
register 15S and notifies the host 3 of the fact that the read data
can be fetched (S13). The transfer arbitrator 13 performs the
process which is carried out in response to the host transfer
request (S1) that has been described by referring to FIG. 5 to
transfer the data stored in the SDRAM 5 into the data buffer 20 in
accordance with the value of the address counter 31 so that the
data held by the data buffer 20 becomes eight bytes.
[0053] When the process performed in response to the host transfer
request in FIG. 5 and the process performed in response to the
flash data transfer request are repeated in a time sharing manner,
the CPU 14 detects a state in which both of the signals HEND_IRQ
and FEND_IRQ are active (S28), and enters a read access request
waiting mode (S20) Specifically, when data according to the number
of data to be read in response to the read access request
instructed by the host 3 is stored in the SDRAM 5, the signal
FEND_IRQ is made active. When data according to the number of data
to be read is read from the SDRAM 5, the signal HEND_IRQ is made
active.
[0054] FIG. 8 shows the correlation of data transfer operations of
the host 3, SDRAM 5, and flash memory 2 when a write access request
is received. (A) shows the operation state of the host 3, (B) shows
the operation state of the SDRAM 5, and (C) shows the operation
state of the flash memory 2. Shown are an address bus H_ADR
connected from the host 3 to the controller 4, a data bus H_DAT for
connecting the host 3 and the controller 4, a write enable signal
H_WE output from the host 3, an output enable signal H_OE output
from the host 3, a sync clock signal D_CLK supplied to the SDRAM 5,
a write enable signal D_WE supplied from the controller 4 to the
SDRAM 5, a data bus D_DAT for connecting the controller 4 and the
SDRAM 5, an output enable signal F_OE which is output from the
controller 4 to the flash memory 2, a write enable signal F_WE
supplied from the controller 4 to the flash memory 2, a serial
clock signal F_CS output from the controller 4 to the flash memory
2, and a data bus F_DAT connecting the controller 4 and the flash
memory 2.
[0055] The host 3 outputs an address value to the address register
15A in the controller 4 and a write transfer command to the command
register 15C in the controller 4 and reads the status set in the
status register 15S of the controller 4. After reading a transfer
enable status, the host 3 transfers data to the data register in
the data buffer 20. The data transfer is performed on a block unit
basis and each block consists of, for example, eight bytes. The
controller 4 gives the flash memory 2 a sector address value for
writing and a write transfer command. When data of a data block 1
is received, the controller 4 writes the data into the SDRAM 5. A
write cycle at this time is indicated by Tdw. The data of the data
block 1 written is read from the SDRAM 5 to the controller 4. A
read cycle at this time is indicated by Tdr. The data of the data
block 1 read to the controller 4 is transferred to the flash memory
2. While the SDRAM 5 performs the write cycle Tdw and the read
cycle Tdr on the data of the data block 1, the host 3 outputs data
of the following data block 2 toward the buffer 20 in the
controller 4. When the data of the data block 1 is transferred to
the flash memory 2, the write cycle and the read cycles on the data
of the data block 2 are performed by the SDRAM 5 in a time sharing
manner. A process similar to the above is performed on data up to a
data block 4.
[0056] According to the example, when the controller 4 reads the
data of the data block 3 from the port on the transfer arbitrator
13 side of the data buffer 20, stores it into the SDRAM 5 (Ti to
Tj) and, subsequently, stores the data stored in the SDRAM 5 into
the data buffer 22 from the port on the transfer arbitrator 13 side
(Tj to Tk), the data of the following data block 4 is input to the
data buffer 20 from the port on the host 3 side of the data buffer
20 and the data of the data block 2 preceding to the data block 3
is transferred to the flash memory 2 from the port on the flash
memory 2 side of the data buffer 22. In short, in response to a
write access request from the host 3, the controller 4 stores write
data to the SDRAM 5 and outputs the write data stored in the SDRAM
5 in a time sharing manner. In parallel with the process of storing
write data into the SDRAM 5, the write data can be transferred to
the flash memory 2. In parallel with the process of outputting the
write data from the SDRAM 5, the next write data can be input from
the host 3.
[0057] In the example of FIG. 8, a write command sequence to the
flash memory 2 includes the address value (sector address value),
write transfer command, write data (data blocks 1 to 4), and write
start command. On condition that the write start command is input,
the flash memory 2 interprets information which has been input just
moments before that as a command sequence and, in accordance with
the result, starts the writing operation in the flash memory 2. In
FIG. 8, a command sequence supply cycle from the input of the
address value to the input of the write start command is indicated
as Tfw.
[0058] FIG. 9 shows the correlation of data transferring operations
of the host, SDRAM, and flash memory when the read access request
is received. (A) shows the operation state of the host 3, (B) shows
the operation state of the SDRAM 5, and (C) shows the operation
state of the flash memory 2.
[0059] The host 3 outputs an address value to the address register
15A and a read transfer command to the command register 15 in the
controller 4. The controller 4 supplies the address value and the
flash read transfer command to the flash memory 2. In response to
the command, the flash memory 2 sequentially reads out the data in
the data blocks 1 to 4 synchronously with the clock signal F_CS. In
FIG. 9, the read cycle is indicated as Tfr. The data of the data
block 1 which is read first is written into the SDRAM 5 via the
data buffer 22. The write cycle is indicated as Tdw. Further, the
written data of the data block 1 is read out from the SDRAM 5 and
supplied to the data buffer 20. The read cycle is indicated as Tdr.
After all of the data of the data block 1 is stored in the data
buffer 20, a transfer enable status is set in the status register
15S. The host 3 recognizes the status and fetches the data of the
data block 1. With respect to the data blocks 2 to 4 as well, a
process similar to the above is performed.
[0060] According to the example, during the controller 4 reads out
the data of the data block 3 from, for example, the port on the
transfer arbitrator 13 side of the data buffer 22, stores the read
data into the SDRAM 5 (Tp to Tq) and, subsequently, stores the data
stored in the SDRAM 5 into the data buffer 20 (Tq to Tr), the data
of the next data block 4 is input from the port of the flash memory
2 side of the data buffer 22 to the data buffer 22 and the
preceding data of the data block 2 is supplied from the port on the
side of the host 3 of the data buffer 20 to the host 3. In short,
in response to the read access request from the host 3, the
controller 4 stores the read data into the SDRAM 5 and outputs the
read data stored in the SDRAM 5 in a time sharing manner. In
parallel with the process of storing the read data into the SDRAM
5, the host 3 can fetch the read data from the buffer memory 20. In
parallel with the process of outputting the read data from the
SDRAM 5, a process of inputting the next read data from the flash
memory 2 to the buffer memory 22 can be performed.
[0061] FIG. 10 shows an example of the write cycle Tdw of the
SDRAM. Shown are a clock CLK corresponding to the clock D_CLK, a
clock enable signal CKE, a chip select signal CS_N, a row address
strobe signal RAS_N, a column address strobe signal CAS_N, a write
enable signal WE_N corresponding to the signal D_WE, address
signals A14 to A0, and data D15 to D0.
[0062] FIG. 11 shows an example of the read cycle Tdr of the
SDRAM.
[0063] FIG. 12 shows an example of the write cycle Tfw to the flash
memory 2. 1FH denotes a write transfer command, SA(1) and SA(2)
denote address values, and 40H indicates a write start command.
Write data (Din) is input synchronously with a serial clock SC.
[0064] FIG. 13 shows an example of the read cycle Tfr to the flash
memory 2. 00H/F0H denotes a read transfer command and SA(1) and
SA(2) denote address values. Read data (Dout) is output
synchronously with the serial clock SC.
[0065] FIG. 14 illustrates the flow of a data transfer process
performed in response to a write access request. The process flow
of FIG. 14 assumes a case where there is no write error in the
flash memory 2. When a write access request is issued from the host
3, the controller 4 notifies the host 3 of a write transfer
prepared status and sends a write transfer request to the flash
memory 2. On receipt of the notification, the host 3 transfers
write data to the controller 4 and the controller 4 transfers the
write data to the flash memory 2. The flash memory 2 performs the
writing operation and returns a normal end signal to the controller
4. In the case such that there is no allowance to store write data
of a new block in the data buffer 20, the controller 4 asserts the
signal HWAIT and sends a write transfer temporary interruption
request to the host 3. When the write data of a new block becomes
storable, the controller 4 negates the signal HWAIT and supplies a
write transfer restart signal to the host 3. The host 3 restarts
transferring write data to the controller 4 and the controller 4
restarts transferring the write data to the flash memory 2. After
all of processes responding to the write access request are
finished, the controller 4 sends a write transfer end notification
to the host 3.
[0066] FIG. 15 shows an example of the flow of another data
transfer process performed in response to the write access request.
The process flow in the diagram assumes that there is a write error
in the flash memory 2. When a write access request is issued from
the host 3, the controller 4 notifies the host 3 of a write
transfer prepared status and sends a write transfer request to the
flash memory 2. The host 3 receives the notification and transfers
write data to the controller 4, and the controller 4 transfers the
write data to the flash memory 2. The flash memory 2 performs a
writing operation, in this example, a write error occurs, and the
flash memory 2 notifies the controller 4 of a write failure end.
The controller 4 receives the notification, asserts the signal
HWAIT, and sends a write data transfer temporary interruption
request to the host 3. After that, the controller 4 negates the
signal HWAIT, notifies the host 3 of write data transfer restart,
and sends a spare block write data transfer request to the flash
memory 2. The host 3 transfers write data to the controller 4 and
the controller 4 transfers the write data to the flash memory 2. In
this example, the writing to the flash memory 2 fails again and a
write error end is notified to the controller 4. After that, the
controller 4 requests the flash memory 2 to perform the writing
process which has failed. During the period, the host 3 can
transfer the following write data to the controller 4 in advance.
Finally, after all of processes responding to the write access
request are finished, the controller 4 sends a write transfer end
notification to the host 3.
[0067] FIG. 16 shows the flow of a data transfer process responding
to a read access request. When a read access request is issued by
the host 3, the controller 4 notifies the host 3 of a read transfer
prepared status and sends a read data transfer request to the flash
memory 2. The flash memory 2 receives the request and transfers
read data to the controller 4. The controller 4 transfers the read
data to the host 3. In this example, the flash memory 2 returns a
normal end to the controller 4. In the case where there is no
allowance of storing read data of a new block in the data buffer
20, the controller 4 asserts the signal HWAIT and sends a read
transfer temporary interruption request to the host 3. When read
data of a new block becomes storable, the controller 4 negates the
signal HWAIT, requests the host 3 to restart transferring read
data, and sends a read data transfer request to the flash memory 2.
In a manner similar to the above, the flash memory 2 transfers read
data to the controller 4 and the controller 4 transfers the read
data to the host 3. After finishing all of processes responding to
the read access request, the controller 4 notifies the host 3 of a
read data transfer end.
[0068] By the buffering function using the SDRAM 5 of the
controller 4, long waiting time is not required for the timing of
supplying a plurality of write data pieces by the host 3, and long
waiting time is not required for the timing of obtaining a
plurality of read data pieces by the host 3. Therefore, the
invention can contribute to reduction in waiting time of the host 3
regarding data transfer between the host 3 and the controller 4,
reduction in a processing load, and reduction in process time. It
can improve efficiency of the data process accompanying an access
to the flash memory card 1.
[0069] Although the invention achieved by the inventor herein has
been described concretely on the basis of the embodiments,
obviously, the invention is not limited to the embodiments but can
be variously changed without departing from the gist.
[0070] For example, the nonvolatile memory is not limited to a
flash memory but may be a rewritable nonvolatile memory employing
other storing methods such as a high-dielectric-constant memory.
The number of information memory bits per memory cell is not
limited to one bit but may be two or more bits. The memory system
is not limited to a flash memory card such as a PC card but can be
constructed on a processor board on which a data processor is
mounted. The data buffer in the host interface part in the
controller and the data buffer in the nonvolatile memory interface
part are not limited to a dual-port type but may be a memory of a
single port, a register, or a latch circuit. In short, any device
may be used as long as data can be input/output in the host
interface part or flash interface part in parallel with data
transfer to a buffer memory in a time sharing manner.
[0071] Effects produced by representative ones of the inventions
disclosed in the specification will be briefly described as
follows.
[0072] In response to a write access request from the outside, the
controller can store write data to the buffer memory and output the
write data stored in the buffer memory in a time sharing manner. By
using a data buffer of a dual port type, write data can be
transferred to the nonvolatile memory (second data transfer) in
parallel with the write data storing process, and the following
write data from an external apparatus can be input (first data
transfer) in parallel with the write data outputting process.
[0073] In response to a read access request from the outside, the
controller can store read data to the buffer memory and output the
read data stored in the buffer memory in a time sharing manner. By
using a data buffer of a dual port type, read data can be
transferred to an external apparatus (first data transfer) in
parallel with the read data storing process, and the following read
data from the nonvolatile memory can be input (second data
transfer) in parallel with the read data outputting process.
[0074] In such a manner, long waiting time is unnecessary for the
timing of supplying a plurality of write data pieces by an external
apparatus such as a host, and long waiting time is unnecessary for
the timing of obtaining a plurality of read data pieces by the
host. Therefore, the invention can contribute to reduction in
waiting time of the host in the data transfer between the host and
a controller, reduction in a process load, and reduction in
processing time. Thus, the efficiency of a data process
accompanying a memory access can be improved.
* * * * *