JP2011081694A - Electronic apparatus and method of controlling memory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To calculate a period during which a flash memory can retain data, thereby preventing the data retained in the flash memory from being lost inadvertently even if the flash memory is highly integrated. <P>SOLUTION: An electronic apparatus 200 includes: an obtaining part 220 which initially retains reference information indicating the relationship between the number of rewrites to the flash memory and the retainable period of the data stored in the flash memory and which obtains the number of rewrites to the flash memory at a certain point of time and the necessary retention period at a certain point of time of the data stored in the flash memory; a deriving part 224 which refers to the reference information to derive the retainable period from the number of rewrites obtained by the obtaining part; a comparison part 226 which compares the necessary retention period obtained by the obtaining part and the retainable period derived by the deriving part; and a warning part 228 that warns if the necessary retention period exceeds the retainable period. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electronic device and a memory control method for preventing data loss in a flash memory.

  Flash memory is a type of EEPROM that can electrically rewrite stored data. There are roughly two types of flash memory, NOR type and NAND type. Among them, the NAND flash memory is configured to include cells for storing 1-bit data for a storage capacity, and data can be written (written) in units of pages composed of a plurality of cells. However, erasure (erase) can be executed only in units of blocks each composed of a plurality of pages. Therefore, the flash memory requires time for random access or the like as compared with the RAM, but is suitable for high integration and has been remarkably spread in recent years.

  A cell of a flash memory is configured by installing a floating gate between a control gate and a silicon substrate. A controller (hereinafter simply referred to as a controller) that includes a circuit that performs read / write control of a cell in a flash memory and a control circuit that performs optimization such as read control and write control supplies a voltage to the cell. When applied, the cell's floating gate holds the electrons. Then, the controller determines a data value based on whether or not the voltage value of each floating gate of the flash memory is equal to or greater than a predetermined value (SLC: Single Level Cell). There is also a flash memory (MLC: Multi Level Cell) for the purpose of judging not only two states but also four states (2 bits) from voltage values.

  When data “1” is written in such a flash memory cell, the controller applies a predetermined voltage to the control gate. When a voltage is applied to the control gate, electrons emitted from the silicon substrate are injected into the floating gate through an oxide film having an insulating function. In addition, when erasing written data, the controller applies a voltage to the source and drain of the silicon substrate to emit electrons from the floating gate.

  The floating gate is covered with an oxide film having an insulating function in order to hold data, that is, hold electrons injected into itself. However, as described above, every time erasing or writing is performed (hereinafter, erasing and writing are simply referred to as rewriting), electrons pass through the oxide film, so that the oxide film is deteriorated. Therefore, in the flash memory, a region where normal rewriting cannot be performed occurs, or a period in which data can be held is limited due to leakage of electrons from the floating gate.

  Therefore, a technique is disclosed in which the memory write command limit number is calculated and held in the storage unit, and that is displayed when the counted number of write commands to the memory exceeds the memory write command limit number (for example, Patent Document 1).

JP 2006-023815 A

  Incidentally, in recent years, with the increase in capacity and integration of flash memories, the size of cells has been reduced to 30 nm or less per cell. In this way, by reducing the size of the cell per cell, the ratio of the outflow to the amount of accumulated electrons from the floating gate due to the deterioration of the oxide film can be reduced to the conventional cell, for example, 130 nm per cell. It will increase in comparison.

  In the flash memory using the MLC described above, four states are determined from the voltage value of the floating gate, and therefore the voltage range for determining each state is smaller than that of the flash memory using the SLC. Therefore, if the outflow of electrons from the floating gate increases with the miniaturization of the cell in the future, the rate of decrease in the voltage value will also increase, and it will be necessary to consider whether it is possible to secure a sufficient data retention period as necessary. You won't get. In particular, in-vehicle flash memories are assumed to be used in a high-temperature environment, and the outflow of electrons from the floating gate cannot be ignored.

  However, in the technique of Patent Document 1 described above, the sector write frequency is a calculation parameter, but there is no concept of a retention period in which data can be retained, and the temperature of the flash memory that affects the retention period is touched. Absent. Therefore, in the technology of Patent Document 1, it is not possible to accurately manage the period in which a flash memory with a recent downsized cell size can hold data, and there is a risk that data will be lost unintentionally. It was.

  In view of such problems, the present invention calculates the period in which the flash memory can hold data even if the integration of the flash memory is advanced, so that the data held in the flash memory is inadvertently lost. It is an object of the present invention to provide an electronic device and a memory control method that can avoid such a situation.

  In order to solve the above-described problem, the electronic device according to the present invention has a relationship between the number of rewrites to the flash memory and the holdable period, which is a period during which the data stored in the flash memory can be held. Subtracting the period in which the flash memory was used at a given time from the holding unit that holds the reference information shown in advance, the number of rewrites to the flash memory at a given time, and the period during which the flash memory must function normally An acquisition unit that acquires a required retention period that is a period, a derivation unit that derives a holdable period from the number of rewrites acquired by the acquisition unit with reference to reference information, a required retention period that is acquired by the acquisition unit, and a derivation A comparison unit that compares the retention period derived by the unit, and a warning unit that warns when the required retention period exceeds the retention period Characterized in that it obtain.

  The reference information is information indicating the relationship between the number of rewrites at a predetermined temperature and the holdable period, and the required hold period acquired by the acquisition unit at the flash memory temperature is held at the predetermined temperature in the previous stage compared with the comparison unit. A conversion unit that converts to a period may further be provided, and the comparison unit may compare the required holding period at a predetermined temperature with the holdable period derived by the deriving unit.

  The reference information is information indicating the relationship between the number of rewrites for each of a plurality of temperatures and the holdable period, and the deriving unit derives the holdable period by referring to the reference information corresponding to the temperature close to the temperature of the flash memory. Also good.

  In order to solve the above-described problem, another electronic device according to the present invention includes a required holding period, which is a period obtained by subtracting a period in which the flash memory is used from a period in which the flash memory must function normally, and the flash memory. A holding unit that holds in advance reference information indicating a relationship with a rewrite limit number indicating the limit of the number of rewrites to the memory, a necessary holding period of data stored in the flash memory at a predetermined time point, and a flash memory at a predetermined time point An acquisition unit that acquires the number of rewrites to the reference, a derivation unit that derives the number of rewrite limits from the necessary holding period acquired by the acquisition unit with reference to the reference information, a number of rewrites acquired by the acquisition unit, and a derivation unit A comparison unit that compares the derived rewrite limit number and a warning unit that warns when the rewrite number exceeds the rewrite limit number , Characterized in that it comprises a.

  The reference information is information indicating the relationship between the required holding period at the predetermined temperature and the number of times of rewriting, and the required holding period acquired by the acquiring unit at the temperature of the flash memory is predetermined before the deriving unit derives the number of times of rewriting. The converter may further include a conversion unit that converts the required holding period at the temperature, and the deriving unit may derive the rewrite limit number from the required holding period at the predetermined temperature.

  The reference information is information indicating the relationship between the required holding period for each of a plurality of temperatures and the rewrite limit number, and the deriving unit derives the rewrite limit number with reference to the reference information corresponding to the temperature close to the temperature of the flash memory. May be.

  The temperature of the flash memory may be calculated using a history of the temperature of the flash memory during a period in which the flash memory is used up to a predetermined time.

  The flash memory may be formed of a plurality of blocks serving as erase units, and the acquisition unit may acquire the maximum number of rewrites in each of the plurality of blocks as the number of rewrites in the entire flash memory.

  The electronic device may further include a rewrite control unit that receives a warning from the warning unit and limits a rewrite frequency or data amount to the flash memory.

  In order to solve the above-described problem, the memory control method according to the present invention relates to the relationship between the number of rewrites to the flash memory and the holdable period, which is a period during which data stored in the flash memory can be held. Is stored in advance, and the number of times the flash memory is rewritten at a predetermined time and the period during which the flash memory must function normally are subtracted from the period when the flash memory is used at the predetermined time Obtain a certain required retention period, refer to the reference information, derive the retention period from the acquired number of rewrites, compare the acquired necessary retention period with the derived retention period, and retain the necessary retention period A warning is given when the possible period is exceeded.

  In order to solve the above problems, another memory control method according to the present invention includes a required holding period, which is a period obtained by subtracting a period during which the flash memory is used from a period during which the flash memory must function normally, Reference information indicating the relationship with the rewrite limit number indicating the limit of the number of rewrites to the flash memory is held in advance, and the necessary retention period of the data stored in the flash memory at a predetermined time point, and the flash memory at the predetermined time point The number of rewrites is obtained, the reference number is referred to, the number of rewrite limits is derived from the acquired required retention period, the obtained number of rewrites is compared with the number of rewrite limits obtained, and the number of rewrites It is characterized by warning when it exceeds.

  The above-described components based on the technical idea of the electronic device and the description thereof can be applied to the memory control method.

  As described above, according to the present invention, even if the flash memory is highly integrated, the flash memory data is inadvertently lost by calculating the period during which the flash memory can hold the data. It becomes possible to avoid the situation.

It is explanatory drawing for demonstrating the rough connection relation of a memory control system. 1 is a functional block diagram illustrating a schematic configuration of an electronic device according to a first embodiment. It is explanatory drawing for demonstrating the reference information concerning 1st Embodiment. It is explanatory drawing for demonstrating the temperature dependence of the frequency | count of rewriting and a holdable period. It is explanatory drawing for demonstrating the calculation of the temperature of the flash memory from the utilization start in the 1st Embodiment to the predetermined | prescribed time. It is a figure which shows the table of the temperature conversion coefficient ATF. It is explanatory drawing for demonstrating the process of the derivation | leading-out part concerning 1st Embodiment. It is explanatory drawing for demonstrating the other example of reference information. It is a flowchart for demonstrating the flow of a process of the memory control method concerning 1st Embodiment. It is the functional block diagram which showed the schematic structure of the electronic device concerning 2nd Embodiment. It is explanatory drawing for demonstrating the reference information concerning 2nd Embodiment. It is a flowchart for demonstrating the flow of a process of the memory control method concerning 2nd Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

(Memory control system 100)
FIG. 1 is an explanatory diagram for explaining a schematic connection relationship of the memory control system 100. As shown in FIG. 1, the memory control system 100 includes a flash memory 110 and an electronic device 200 that uses the flash memory 110 as a storage medium. Here, as the flash memory 110, for example, a NAND flash memory will be described as an example.

  When the controller of the electronic device 200 reads data from the flash memory 110, the value of the voltage held in the floating gate configuring the cell of the flash memory 110 is measured. The controller of the electronic device 200 determines the data value from the voltage value of the floating gate of each cell. The floating gate of the flash memory 110 is covered with an oxide film having an insulating function in order to retain data, that is, retain electrons injected into itself.

  However, when the controller of the electronic device 200 repeats data rewriting (E (Erase) / W (Write)) with respect to the flash memory 110, the passage of electrons through the oxide film is repeated, and the oxide film In the flash memory 110, a region where normal rewriting cannot be performed occurs, or a period during which data can be held is limited due to electron leakage from the floating gate.

  Therefore, in the present embodiment, not only the number of times the flash memory 110 is rewritten, but also the period in which the data can be retained is calculated, so that even if the integration of the flash memory 110 is advanced, the data retained in the flash memory 110 is not stored. Provided are electronic devices 200 and 400 that can avoid a situation where they are easily lost. Hereinafter, specific configurations of the electronic devices 200 and 400 will be described.

(First embodiment: electronic device 200)
FIG. 2 is a functional block diagram showing a schematic configuration of the electronic device 200 according to the first embodiment. The electronic device 200 includes a central control unit 210, a holding unit 212, and a controller 214, and can connect the flash memory 110 as a storage destination of data generated by itself.

  The central control unit 210 controls the entire electronic device 200 by a semiconductor integrated circuit including a central processing unit (CPU), a ROM storing programs, a RAM as a work area, and the like.

  The holding unit 212 holds in advance reference information indicating the relationship between the number of rewrites to the flash memory and the holdable period, which is a period during which data stored in the flash memory can be held. The reference information is information derived in advance using an arbitrary flash memory having substantially the same performance as the flash memory 110.

  The controller 214 includes a circuit that performs read / write control of cells of the flash memory 110 and a control circuit that performs optimization such as read control and write control.

  FIG. 3 is an explanatory diagram for explaining the reference information 310 according to the first embodiment. As shown in FIG. 3, in the present embodiment, the reference information 310 is information indicating the relationship between the number of times data can be rewritten to the flash memory at a predetermined temperature and the retention period. In the present embodiment, the predetermined temperature in the reference information 310 is 60 ° C., for example. The reference information 310 indicates that as the number of rewrites to the flash memory increases, the holdable period, which is a period during which the rewritten data can be held, is shortened. Therefore, it is determined whether the data stored in the connected flash memory 110 can be held for a sufficient period by comparing with the reference information 310 as a reference. However, here, a predetermined margin is given to the limit value of the holdable period of the reference information 310.

  The flash memory is responsible for holding its own data, so that the remaining period from the predetermined point in time until the expected use period (predetermined use period of the flash memory) is completed, regardless of the number of rewrites. Need to hold the data. Here, the required holding period is a period obtained by subtracting the period in which the flash memory is used at the predetermined time from the period from the predetermined time to the end of the assumed usage period, that is, the period in which the flash memory must function normally. And Therefore, during the expected use period, the required holding period must be shorter than the holdable period during which data can be held. Therefore, the data cannot be held, so the required holding for any number of flash memory rewrites The period must always be shorter than the holdable period, and is located in the region on the left side of the reference line 312 in FIG. For example, the flash memory is effective during the expected usage period by following a trajectory as indicated by a broken line 314 in the area on the left side of the reference line 312 in FIG. Note that the expected usage period of the flash memory is, for example, a guaranteed period of operation of the electronic device 200 or a period during which the electronic device 200 can be used (design period) determined when the electronic device 200 is designed. Assuming that the period of using the electronic device 200 (using the flash memory) is 3 years, the required retention period is 27 years.

  In the present embodiment, the central control unit 210 also functions as the acquisition unit 220, the conversion unit 222, the derivation unit 224, the comparison unit 226, the warning unit 228, and the rewrite control unit 230.

  The acquisition unit 220 acquires the number of rewrites to the flash memory 110 from the start of use to a predetermined time at a predetermined time.

  However, the NAND flash memory 110 is formed of a plurality of blocks as erase units, and the number of rewrites is different for each block. Accordingly, the acquisition unit 220 acquires the maximum number of rewrites in each of the plurality of blocks of the flash memory 110 as the number of rewrites in the entire flash memory 110. With such a configuration, it is possible to reliably secure a holdable period even for a block having a large number of rewrites.

  In recent flash memories 110, a wear leveling technique for averaging rewriting to each block is used. In the flash memory 110 using the wear leveling technology, the memory on the flash memory 110 side holds the number of rewrites to each block and / or the maximum value of the number of rewrites. The acquisition unit 220 acquires the maximum number of rewrites in each block by referring to the memory on the flash memory 110 side, or acquires the maximum number of rewrites in each block and extracts the maximum value.

  The acquisition unit 220 also acquires a necessary retention period at a predetermined point in time for data stored in the flash memory 110. In the present embodiment, the acquisition unit 220 acquires the required holding period using the accumulated operation time of the electronic device 200 (the time obtained by integrating the time when the electronic device 200 is operated = the time when the flash memory 110 is used). Since the electronic device 200 derives the accumulated operation time by storing the hour meter and real time clock data in a memory (not shown) and integrating the data, first, the acquisition unit 220 acquires the accumulated operation time.

  For example, the flash memory 110 designed with an assumed use temperature and a usable period (design period) of 30 years will be described as an example. The total operation time for which the electronic device 200 operates in the design period of 30 years is set to 3000 hours. At this time, the operating rate of the electronic device 200 is substantially constant, and the frequency of rewriting the flash memory 110 during the operation of the electronic device 200 is substantially constant.

  Then, at a predetermined point in time, when the electronic device 200 has been operating for 2000 hours, that is, when the accumulated operating time is 2000 hours, the electronic device 200 is operating 2/3 of the total operating time of 3000 hours. Become. Therefore, at a predetermined time point, the electronic device 200 has been 2/3 of the design period of 30 years, that is, 20 years since the start of operation. That is, the acquisition unit 220 acquires 10 years as a necessary data retention period by subtracting 20 years, which is a period from a design period of 30 years to a predetermined time point.

  The relationship between the number of rewrites to the flash memory 110 and the retention period of data stored in the flash memory 110 varies greatly depending on the temperature of the flash memory 110. Therefore, when the temperature of the flash memory 110 and the predetermined temperature in the reference information 310 are different, it is necessary to convert the necessary holding period again.

  FIG. 4 is an explanatory diagram for explaining the temperature dependence of the number of rewrites and the holdable period. As shown in FIG. 4, it can be seen that the holdable period at a predetermined number of rewrites becomes smaller as the temperature of the flash memory 110 rises. Therefore, if the temperature of the flash memory 110 is equal to the predetermined temperature in the reference information 310, it is not necessary to convert the required holding period. However, the predetermined temperature in the reference information 310 and the use temperature of the flash memory 110 assumed in the design stage (hereinafter referred to as the reference information 310). If the predetermined temperature differs from the actual temperature of the flash memory 110 from the start of use to a predetermined time, the required holding period needs to be converted to the predetermined temperature. .

  The conversion unit 222 needs to convert the required holding period at the temperature from the start of use of the flash memory 110 to a predetermined time acquired by the acquiring unit 220 into the required holding period at the predetermined temperature (60 ° C.) of the reference information 310. Calculate the retention period.

  Since the flash memory 110 is assumed to be used in a designed state, the temperature from the start of use of the flash memory 110 to a predetermined time can be a predetermined temperature, for example, the design temperature of the flash memory 110. . Also, in an environment where the temperature history of the flash memory 110 can be acquired, the conversion unit 222 calculates the temperature of the flash memory 110 during the period of use of the flash memory 110 up to a predetermined time in order to derive a more realistic value. It is also possible to calculate the temperature of the flash memory 110 using the history.

  FIG. 5 is an explanatory diagram for explaining the calculation of the temperature of the flash memory 110 from the start of use to a predetermined time in the first embodiment. As shown in FIG. 5A, the temperature of the flash memory 110 varies depending on the season, weather, installation location (outdoor, indoor, in-car, etc.) and the like. Therefore, first, as shown in FIG. 5B, the conversion unit 222 totals the period from the start of use to a predetermined time for each predetermined temperature range. And the conversion part 222 converts and totals the period of each temperature range into the period of predetermined temperature (60 degreeC) using the Arrhenius formula shown to Formula (1) of FIG.5 (c).

In the Arrhenius equation shown in equation (1), ATF represents a temperature conversion coefficient, Ea represents activation energy (eV), and K represents Boltzmann constant 8.62 × 10 ⁻⁵ (eV / K). The absolute temperature to be converted in Equation (1) is a value 313K obtained by adding 273 to a temperature range (for example, 40 ° C.), and the absolute temperature after conversion is 333K obtained by adding 273 to 60 ° C. of the predetermined temperature. Here, when the activation energy is 1.1 eV, the temperature conversion coefficient ATF at 40 ° C. is 0.08641 according to the equation (1).

  And when the 40 degreeC period was 2.01 years as shown in FIG.5 (b), in order to convert this period into 60 degreeC, the conversion part 222 will be temperature conversion coefficient ATF in 2.01 years. Is multiplied by 0.08641 to obtain a conversion value of about 0.174 years. Similarly, the conversion unit 222 converts the period of each temperature range to 60 ° C., sums the converted values of each temperature range, and calculates the total value at 60 ° C. from the start of use to a predetermined time point. 110 usage periods. Here, for example, it is assumed that the usage period converted to 60 ° C. is two years.

  The conversion unit 222 calculates the converted design period by using the actual usage period of 20 years and the converted usage period of 2 years. Here, the converted usage period can be calculated by multiplying the actual usage period by 0.1. Accordingly, assuming that the temperature change of the flash memory 110 from the predetermined time point to the end of the design period is the same as the temperature change of the flash memory 110 from the start of use to the predetermined time point, 0.1 is set to 0.1 in the design period 30 years. The multiplied 3 years is the converted design period. Then, the conversion unit 222 subtracts the converted usage period of 2 years from the converted design period of 3 years to calculate the conversion required holding period of 1 year.

  In the present embodiment, the conversion unit 222 calculates the necessary conversion retention period using a function, but is not limited to this. For example, the temperature conversion coefficient ATF generated using the Arrhenius equation shown in FIG. These tables may be held in the holding unit 212 in advance, and the conversion required holding period may be calculated with reference to the table.

  As described above, although the temperature of the flash memory 110 is predicted to some extent at the design stage, it may differ from the predicted temperature depending on the latitude, altitude, sunshine duration, etc. of the place where the flash memory 110 is used. is there. As described above, the conversion unit 222 accurately calculates the temperature of the flash memory 110 using the history of the temperature of the flash memory 110 during the period of use of the flash memory 110 from the start of use to a predetermined time point. A deviation from the design value of the temperature of the memory 110 can be supplemented, and the temperature of the flash memory 110 can be derived with high accuracy.

  The deriving unit 224 refers to the reference information 310 held in the holding unit 212 and derives a holdable period from the number of rewrites acquired by the acquisition unit 220.

  FIG. 7 is an explanatory diagram for explaining the processing of the derivation unit 224 according to the first embodiment. As shown in FIG. 7, the reference information 310 is information indicating the relationship between the number of rewrites at 60 ° C. and the holdable period. For example, when the number of rewrites acquired by the acquisition unit 220 is 3000 (3K) times, the deriving unit 224 refers to the reference information 310 and derives 0.5 years as the retention period. This suggests that if rewriting has already been performed 3000 times, the rewritten data may be lost after 0.5 years at the earliest.

  The comparison unit 226 compares the required holding period (converted required holding period) at the predetermined temperature (60 ° C.) converted by the conversion unit 222 with the holdable period derived by the derivation unit 224.

  The warning unit 228 warns when the necessary holding period exceeds the holdable period. As shown in FIG. 7, in this embodiment, the conversion required holding period converted by the conversion unit 222 is 1 year, and the holdable period derived by the derivation unit 224 is 0.5 year. Warn. This indicates that, using the graph shown in FIG. 7, the intersection A between the number of rewrites acquired by the acquisition unit 220 and the necessary holding period is on the right side of the reference line 312. Therefore, the warning unit 228 may issue a warning if the intersection A is on the right side of the reference line 312 and may not issue a warning if it is on the left side.

  The warning unit 228 issues a warning by displaying a warning display on a display unit (not shown), outputting a sound indicating a warning to a speaker, or lighting an LED. Further, the warning executed by the warning unit 228 includes transmission of an electrical signal (warning signal) to the rewrite control unit 230 as described later.

  As described above, the data retention period is determined by the temperature of the flash memory 110 and the number of rewrites. Therefore, the temperature and the number of rewrites of the flash memory 110 are acquired, the data retention period is calculated, and a warning is issued when the required retention period of data written to the flash memory 110 exceeds the retention period This makes it possible to avoid a situation in which the data in the flash memory 110 is inadvertently lost.

  When the rewrite control unit 230 receives the warning signal transmitted from the warning unit 228, the rewrite control unit 230 recognizes that the design period (expected usage period) cannot be completed if the rewriting frequency or the rewritten data amount is maintained as it is, and controls the controller 214. Then, the frequency of rewriting to the flash memory 110 (for example, the frequency of logging such as recording of error factors at the time of failure) or the data amount is limited. For example, the rewrite control unit 230 sets the frequency of rewriting to the flash memory 110 or the data amount limit to a plurality of levels in advance, and determines, for example, the difference based on the degree of difference between the holdable period and the necessary hold period. Proportionally, the level corresponding to the frequency of rewriting to the flash memory 110 or the limitation of the data amount may be converted and the corresponding level may be selected.

  With this configuration, the flash memory 110 can be used without data loss until the design period of the flash memory 110.

  FIG. 8 is an explanatory diagram for explaining another example of the reference information. As shown in FIG. 8, the reference information 330 indicates the relationship between the number of rewrites and the holdable period for each of a plurality of assumed temperatures (for example, + 40 ° C., + 50 ° C., + 60 ° C., + 70 ° C., and + 80 ° C.). Information. Here, similarly to the reference information 310 described above, a predetermined margin is given to the limit value of the holdable period.

  When the holding unit 212 holds the reference information 330, the conversion unit 222 uses the reference information 330 corresponding to a temperature close to the temperature of the flash memory 110 (for example, the design temperature or the average value of the temperatures from the start of use to a predetermined time). For example, when the average value of the temperature from the start of use to a predetermined time is 48 ° C., the reference information 330 of + 50 ° C. is selected, and the selection result is transmitted to the derivation unit 224. Then, the deriving unit 224 can derive the holdable period by referring to the reference information 330 corresponding to the temperature close to the temperature of the flash memory 110 based on the selection result transmitted from the conversion unit 222.

  As described above, the electronic device 200 issues a warning in consideration of not only the number of times the flash memory 110 is rewritten but also the data retention period and the necessary retention period. It becomes possible. Further, as described above, the holdable period of the flash memory 110 is greatly affected by the temperature of the flash memory 110. Therefore, by calculating the holdable period using the temperature of the flash memory 110 by the electronic device 200, it is possible to calculate the holdable period in accordance with the actual situation.

(Memory control method)
Next, a memory control method for controlling the flash memory 110 using the electronic device 200 described above will be described. FIG. 9 is a flowchart for explaining a processing flow of the memory control method according to the first embodiment.

  As shown in FIG. 9, first, the holding unit 212 of the electronic device 200 holds in advance reference information indicating the relationship between the number of rewrites to the flash memory 110 and the retention period of the data stored in the flash memory 110. In addition, the acquisition unit 220 acquires the number of rewrites to the flash memory 110 at a predetermined point in time and a necessary holding period, which is a period during which the flash memory 110 must continue to hold data from the predetermined point ( S350).

  The conversion unit 222 calculates the conversion required holding period obtained by converting the required holding period at the temperature of the flash memory 110 acquired in the acquisition step S350 into the required holding period at the predetermined temperature of the reference information 310 (S352).

  Then, the deriving unit 224 refers to the reference information held by the holding unit 212 and derives the holdable period from the number of rewrites acquired in the acquisition step S350 (S354). After that, the comparison unit 226 compares the necessary conversion holding period calculated in the conversion step S352 with the holdable period derived in the derivation step S354, and determines whether the conversion required holding period exceeds the holdable period. (S356).

  In the determination step S356, when the conversion required holding period exceeds the holdable period (YES in S356), the warning unit 228 warns and transmits a warning signal to the rewrite control unit 230 (S358). When the rewrite control unit 230 receives the warning signal, the rewrite control unit 230 controls the controller 214 to limit the frequency of rewriting to the flash memory 110 (for example, the frequency of recording a log of error factors at the time of failure) or the amount of data. (S360).

  As described above, even in the memory control method according to the present embodiment, not only the number of rewrites of the flash memory 110 but also the time period during which data can be retained is calculated, so that even if the integration of the flash memory 110 has advanced. It is possible to avoid a situation where the data held in the flash memory 110 is inadvertently lost.

(Second embodiment: electronic device 400)
The electronic device 200 according to the first embodiment described above issues a warning by comparing the required retention period and the retention period of the flash memory 110, but can also issue a warning by comparing the number of rewrites. In the second embodiment, an electronic device 400 that issues a warning by comparing the number of rewrites will be described. In addition, about the component substantially equivalent to the electronic device 200 of 1st Embodiment mentioned above, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  FIG. 10 is a functional block diagram showing a schematic configuration of the electronic apparatus 400 according to the second embodiment. The electronic device 400 is connected to the flash memory 110 and includes a central control unit 410, a holding unit 412, and a controller 214.

  Similar to the central control unit 210 of the first embodiment, the central control unit 410 includes a central processing unit (CPU), a ROM that stores programs, a semiconductor integrated circuit including a RAM as a work area, and the like, and the entire electronic device 400. To control.

  The holding unit 412 holds reference information indicating the relationship between the required holding period of data stored in the flash memory and the rewrite limit number indicating the limit of the number of rewrites to the flash memory.

  FIG. 11 is an explanatory diagram for explaining the reference information 510 according to the second embodiment. As shown in FIG. 11, in the present embodiment, the reference information 510 is information indicating the relationship between the required holding period at a predetermined temperature and the number of rewrite limits. In the present embodiment, the predetermined temperature in the reference information 510 is 60 ° C., for example. The reference information 510 indicates that the number of rewrite limits increases as the required retention period in the target flash memory 110 becomes shorter. However, here, a predetermined margin is given to the limit value of the rewrite limit number.

  In the present embodiment, the central control unit 410 also functions as the acquisition unit 220, the conversion unit 422, the derivation unit 424, the comparison unit 426, the warning unit 428, and the rewrite control unit 230.

  The conversion unit 422 calculates a conversion required holding period in which the required holding period acquired by the acquisition unit 220 at the temperature of the flash memory 110 is converted into a required holding period at a predetermined temperature.

  The derivation unit 424 refers to the reference information 510 and derives the rewrite limit number from the conversion required holding period calculated by the conversion unit 422. As shown in FIG. 11, for example, when the conversion necessary retention period calculated by the conversion unit 422 is one year, the deriving unit 424 derives the rewrite limit number of 1000 times (1K).

  The comparison unit 426 compares the number of rewrites acquired by the acquisition unit 220 with the number of rewrite limits derived by the derivation unit 424.

  The warning unit 428 gives a warning when the number of rewrites exceeds the rewrite limit number. Also in the present embodiment, the warning unit 428 transmits a warning signal to the rewrite control unit 230 when the number of rewrites exceeds the rewrite limit number. For example, when the rewrite limit number derived by the deriving unit 424 is 1000 (1K) and the rewrite number acquired by the acquiring unit 220 is 3000 (3K), the warning unit 428 warns. This indicates that, when the graph shown in FIG. 11 is used, the intersection B between the number of rewrites acquired by the acquisition unit 220 and the number of rewrite limits is on the right side of the reference line 512. Therefore, the warning unit 428 may issue a warning if the intersection B is on the right side of the reference line 512, and may not issue a warning if it is on the left side.

  Note that the number of rewrites and the retention period of the reference information 310 in the first embodiment described above correspond to the number of rewrite limits and the required retention period of the reference 510 in the second embodiment.

  As described above, even in the electronic device 400 according to the present embodiment, not only the number of rewrites of the flash memory 110 but also the time period in which the data can be retained is calculated, so that even if the integration of the flash memory 110 is advanced. It is possible to avoid a situation where the data held in the flash memory 110 is inadvertently lost.

(Memory control method)
Next, a memory control method for controlling the flash memory 110 using the electronic device 400 described above will be described. FIG. 12 is a flowchart for explaining the processing flow of the memory control method according to the second embodiment. Note that processes substantially equivalent to the memory control method of the first embodiment described above are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 12, first, the holding unit 412 of the electronic device 400 previously stores reference information 510 indicating the relationship between the number of rewrites to the flash memory 110 and the required holding period of the data stored in the flash memory 110. The acquisition unit 220 acquires the number of rewrites to the flash memory 110 at a predetermined time and the necessary retention period of the data stored in the flash memory 110 at a predetermined time (S350).

  The conversion unit 422 calculates a conversion required holding period obtained by converting the required holding period acquired in the acquisition step S350 at the temperature of the flash memory 110 into the required holding period at the predetermined temperature of the reference information 310 (S352).

  Then, the deriving unit 424 refers to the reference information 510 held by the holding unit 412 and derives the rewrite limit number from the conversion required holding period calculated in the conversion step 352 (S552). Thereafter, the comparison unit 426 compares the number of rewrites acquired in the acquisition step S350 with the number of rewrite limits derived in the derivation step S552, and determines whether or not the number of rewrites exceeds the limit number of rewrites (S554).

  In determination step S554, if the number of rewrites exceeds the rewrite limit number (YES in S554), warning unit 428 warns and transmits a warning signal to rewrite control unit 230 (S358). When the rewrite control unit 230 receives the warning signal, the rewrite control unit 230 controls the controller 214 to limit the rewrite frequency or data amount to the flash memory 110 (S360).

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Is done.

  For example, in the first embodiment described above, the holdable period is derived from the number of rewrites and the holdable period is compared with the necessary hold period, and in the second embodiment, the rewrite limit number is derived from the necessary hold period. The number of rewrites is compared with the number of rewrites, and a warning is issued.However, the present invention is not limited to this, and the allowable temperature of the flash memory is derived based on the number of rewrites and the required retention period, and the actual temperature of the flash memory. You can also issue a warning compared to.

  Note that each step in the memory control method of the present specification does not necessarily have to be processed in time series in the order described in the flowchart, and may include processing in parallel or by a subroutine.

  The present invention can be used for an electronic device and a memory control method for preventing data loss in a flash memory.

DESCRIPTION OF SYMBOLS 100 ... Memory control system 110 ... Flash memory 200, 400 ... Electronic device 210, 410 ... Central control part 212, 412 ... Holding part 214 ... Controller 220 ... Acquisition part 222, 422 ... Conversion part 224, 424 ... Derivation part 226, 426 ... Comparison units 228, 428 ... Warning unit 230 ... Rewrite control unit

Claims (11)

A holding unit that holds in advance reference information indicating a relationship between the number of rewrites to the flash memory and a holdable period that is a period during which data stored in the flash memory can be held;
The number of rewrites to the flash memory at a predetermined point in time and a necessary holding period that is a period obtained by subtracting the period of use of the flash memory at the predetermined point from the period during which the flash memory must function normally are acquired. An acquisition unit;
A deriving unit for deriving the holdable period from the number of rewrites acquired by the acquiring unit with reference to the reference information;
A comparison unit that compares the required retention period acquired by the acquisition unit with the holdable period derived by the derivation unit;
A warning section that warns when the required retention period exceeds the retention period;
An electronic device comprising: The reference information is information indicating a relationship between the number of rewrites at a predetermined temperature and the holdable period,
A conversion unit that converts the required holding period acquired by the acquiring unit into the required holding period at the predetermined temperature at the temperature of the flash memory in the previous stage compared by the comparing unit;
The electronic device according to claim 1, wherein the comparison unit compares the required holding period at the predetermined temperature with the holdable period derived by the deriving unit. The reference information is information indicating a relationship between the number of rewrites for each of a plurality of temperatures and the holdable period,
The electronic device according to claim 1, wherein the deriving unit derives the holdable period with reference to reference information corresponding to a temperature close to a temperature of the flash memory. Reference showing the relationship between the required retention period, which is the period when the flash memory must function normally, minus the period when the flash memory is used, and the rewrite limit count indicating the limit of the number of rewrites to the flash memory A holding unit for holding information in advance;
An acquisition unit for acquiring a necessary holding period of data stored in the flash memory at a predetermined time point and the number of rewrites to the flash memory at the predetermined time point;
A deriving unit for deriving the rewrite limit number from the necessary holding period acquired by the acquiring unit with reference to the reference information;
A comparison unit that compares the number of rewrites acquired by the acquisition unit and the number of rewrite limits derived by the derivation unit;
A warning section that warns when the number of times of rewriting exceeds the number of times of rewriting,
An electronic device comprising: The reference information is information indicating a relationship between the necessary holding period and the rewrite limit number at a predetermined temperature,
Before the deriving unit derives the number of rewrite limits, the conversion unit further converts the necessary holding period acquired by the acquiring unit at the temperature of the flash memory into the necessary holding period at the predetermined temperature,
The electronic device according to claim 4, wherein the deriving unit derives the rewrite limit number from a necessary holding period at the predetermined temperature. The reference information is information indicating a relationship between the required holding period and the rewrite limit number for each of a plurality of temperatures,
The electronic device according to claim 4, wherein the deriving unit derives the number of rewrite limits by referring to reference information corresponding to a temperature close to a temperature of the flash memory.   The temperature of the flash memory is calculated using a history of the temperature of the flash memory during a period in which the flash memory has been used up to the predetermined time point. The electronic device as described in. The flash memory is formed of a plurality of blocks as erase units,
The electronic apparatus according to claim 1, wherein the acquisition unit acquires a maximum value of the number of rewrites in each of the plurality of blocks as the number of rewrites in the entire flash memory.   The electronic device according to claim 1, further comprising a rewrite control unit that receives a warning from the warning unit and limits a rewrite frequency or a data amount of the flash memory. Reference information indicating the relationship between the number of rewrites to the flash memory and the holdable period, which is a period during which the data stored in the flash memory can be kept, is held in advance.
The number of rewrites to the flash memory at a predetermined time point and a necessary holding period, which is a period obtained by subtracting the period during which the flash memory is used at the predetermined time point from the period during which the flash memory must function normally, are acquired. ,
Referencing the reference information, deriving the holdable period from the acquired number of rewrites,
Comparing the acquired required retention period with the derived retention period,
A memory control method, wherein a warning is issued when the necessary retention period exceeds the retention period. A reference that shows the relationship between the required retention period, which is the period when the flash memory must function normally, minus the period when the flash memory is used, and the rewrite limit count that indicates the limit on the number of rewrites to the flash memory. Keep information in advance,
Obtaining the required retention period of the data stored in the flash memory at a predetermined time and the number of rewrites to the flash memory at the predetermined time;
With reference to the reference information, the rewrite limit number is derived from the acquired necessary retention period,
Compare the obtained number of rewrites with the derived number of rewrite limits,
A memory control method, wherein a warning is given when the number of rewrites exceeds the limit number of rewrites.

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