JP2009003843A - Flash rom data management device and flash rom data management method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flash ROM data management device capable of managing data by more accurately predicting a marginal time at which data retained in a flash ROM possibly disappears. <P>SOLUTION: A control circuit 2 predicts a retainable time TId of data retained in the flash ROM 14 on the basis of the device characteristic and state of use of the flash ROM 14 being a device for retaining data of a navigation system 1 for vehicle, and rewrites the data retained in the flash ROM 14 before the retainable time TId elapses. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus and a method for managing data stored in a flash ROM used as a data holding device of an in-vehicle electronic device.

  A flash ROM, which is a nonvolatile memory, is often used in a NOR type for a relatively small capacity and a NAND type for a large capacity. The NAND flash ROM has a relatively high rate of so-called data corruption, in which retained data is lost when electrons (hot electrons) injected into the floating gate are removed, and such data corruption is prevented. There is a case where a controller for performing management is used.

By the way, a navigation device, which is a kind of in-vehicle electronic device, is also equipped with a flash ROM for holding data, but a NOR type flash ROM is used because its capacity is relatively small, about several megabytes to several tens of megabytes. It is common. However, even in the case of navigation devices, the capacity of data to be retained has increased recently with the increase in functionality and functionality, and along with this, the capacity of the flash ROM will be on the order of several tens to several hundreds of megabytes. It is said. As a result, even if it is a NOR type flash ROM, it is assumed that data corruption will be a problem.
As a technique for coping with data corruption as described above, Patent Document 1 counts the number of times data is written to the flash ROM, and rewrites the data when the number exceeds a predetermined value. Technology is disclosed.
JP 2000-251483 A

  Certainly, the number of times data is written is a parameter that affects the data retention characteristics of the flash ROM, but in an environment where the flash ROM is actually used, various other factors affect the data retention characteristics. It should be. Therefore, it is inaccurate to predict garbled data based on only the number of writes as in Patent Document 1, and the result of shortening the device life of the flash ROM by repeating rewriting unnecessarily is also possible. There is a problem that could be.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a data management device for a flash ROM capable of more accurately predicting a limit time at which data stored in the flash ROM is likely to disappear and managing the data. It is to provide a method.

  According to the data management device of the flash ROM of claim 1, the time predicting means is stored in the ROM based on the device characteristics and / or usage status of the flash ROM used for the data holding device of the in-vehicle electronic device. The rewrite means rewrites the data stored in the flash ROM before the holdable time elapses. That is, since the data retention time is predicted based on the device characteristics and usage status, it is possible to more accurately predict the limit time at which data corruption is likely to occur. And since data is rewritten based on the prediction result, it can suppress repeating rewriting unnecessarily and can prolong a device lifetime.

  According to the data management device for the flash ROM of the second aspect, the rewrite means rewrites data to an unused area reserved in the flash ROM. That is, when the flash ROM has a sufficient capacity, the data can be held more reliably by rewriting the data in the unused area.

  According to the flash ROM data management device of the third aspect, the time predicting means predicts the holdable time for each area set in the flash ROM corresponding to the type of stored data. That is, what actually becomes a problem in data writing is a memory cell in a state where electrons are injected into the floating gate, but it is very complicated to manage the writing state for each cell. Therefore, by managing each type and area of data stored in the flash ROM, it is possible to reduce the complexity of management and appropriately monitor each state.

  According to the flash ROM data management device of the fourth aspect, the time predicting means predicts the holdable time based on the data holding characteristics of the flash ROM. That is, since the data retention characteristics are presented as device specifications for each flash ROM product, the retention time can be accurately predicted by referring to the data retention characteristics.

  According to the flash ROM data management device of the fifth aspect, the time predicting means counts the number of times data is written to the flash ROM, and predicts the holdable time based on the number of times of writing. That is, the number of times data is written is a parameter that greatly affects the data holding state, and therefore the prediction accuracy can be improved by predicting the holdable time based on the number of writing times.

  According to the data management device for the flash ROM according to claim 6, the time predicting unit measures an interval at which data is written to the flash ROM, counts the occurrence frequency of each write interval, and distributes the occurrence frequency. Predict the holdable time based on the state. That is, it is considered that the length of the interval at which data is written to the flash ROM also affects the data retention characteristics. Therefore, it is possible to classify the lengths of intervals at which writing is performed a plurality of times for each predetermined range and predict the holdable time based on the number of times belonging to each range.

  According to the flash ROM data management device of claim 7, the time predicting means measures the temperature in the vicinity of the flash ROM when data is written, and counts the frequency of writing at each temperature. The holdable time is predicted based on the distribution state of the writing frequency. In other words, the temperature when data is written to the flash ROM is also considered to affect the data retention characteristics. Therefore, the temperature when data is written a plurality of times is classified into predetermined ranges. The holdable time can be predicted based on the number of times belonging to each range.

  According to the flash ROM data management device of the eighth aspect, the time predicting means measures the retention time of the data written to the flash ROM, and predicts the retention time based on the continuation time. That is, it is considered that the retention time of data written to the flash ROM also affects the data retention characteristics. Therefore, it is possible to classify the time during which written data is held for each predetermined range, and predict the holdable time based on the number of times belonging to each range.

  According to the flash ROM data management device according to claim 9, the time predicting means measures a temperature change in the vicinity of the flash ROM during a period in which the written data is held, and the data is held for a plurality of temperature zones. Is accumulated, and the holdable time is predicted based on the distribution state of the accumulated period. That is, it is considered that the temperature change state during the period in which the data written in the flash ROM is retained also affects the data retention characteristics. Therefore, it is possible to classify the temperature zones in the data retention period for each predetermined range and predict the retention time based on the number of times belonging to each range.

  According to the data management device of the flash ROM of claim 10, the rewrite means compares the holdable time with a threshold value determined based on the product lifetime of the in-vehicle device, and the data when the former is less than the latter Rewrite the file. In other words, when the holdable time of the flash ROM is less than the product life of the in-vehicle device, it is possible to avoid erasing the data during the period when the in-vehicle device is assumed to be operating by rewriting the data. .

  According to the data management device of the flash ROM of the eleventh aspect, the rewriting means determines the threshold by multiplying the product lifetime by a coefficient less than 1.0. In other words, the loss of data can be more reliably avoided by multiplying the lifetime defined as the product specification by the above coefficient and taking a margin.

(First embodiment)
Hereinafter, a case where the first embodiment of the present invention is applied to a vehicle navigation device which is one of in-vehicle electronic devices will be described with reference to FIGS. FIG. 1 is a block diagram showing an electrical configuration of the vehicle navigation apparatus 1. As shown in the figure, the vehicle navigation apparatus 1 includes a control circuit (time prediction means, rewrite means, data management device) 2 as control means, a position detection device 3 as position detection means, and data storage means. A data storage device 4, an operation switch group 5, a touch panel 6, a display device 7 as a display means, a sound generator 8, a remote control sensor 9, a remote control 10 that makes a pair with the remote control sensor 9, and the like are provided.

  The control circuit 2 has a function of controlling the overall operation of the vehicle navigation apparatus 1 and is configured mainly with a microcomputer. That is, the control circuit 2 includes a CPU, a ROM, a RAM, an I / O, a bus that connects these, and the like (all not shown). Of these, an execution program for operating the vehicle navigation device 1 is stored in the ROM, and temporary data at the time of program execution, map data acquired from the data storage device 4 and the like are temporarily stored in the RAM. It has become.

  The position detection device 3 includes a gyroscope 11, a distance sensor 12, a GPS receiver 13, and the like. Since these sensors 11 to 13 have detection errors having different properties, combining these sensors 11 to 13 enables highly accurate position detection while correcting the detection errors. It should be noted that depending on the required detection accuracy level, it is not necessary to provide all the sensors 11 to 13, and a configuration in which they are appropriately selected and provided. Further, the position detection device 3 may be configured by combining a steering rotation sensor, a wheel sensor that detects the rotation of each tire, and the like.

  The data storage device 4 includes an information recording medium such as a DVD-ROM or a hard disk and a reading device that reads data from the information recording medium. The control circuit 2 reads data from the information recording medium by the reading device. To enter. Here, as the data provided in the data storage device 4, the map data, the map matching data, the data for guiding the route by voice, the location (coordinates) on the map from the address, the facility name, etc. are searched. Position data, keyword search data for searching for a place by keyword, genre data for enabling a destination to be searched by genre, and the like. The above location data is for searching the location when the departure point, waypoint, or destination is entered as an address, building name, facility name, intersection name, telephone number, etc. It is configured as map index data in which building names, facility names, intersection names, telephone numbers, etc. are associated with the corresponding coordinates on the map.

  The display device 7 includes a liquid crystal display as a display screen for displaying map data, characters or symbols, and the transparent touch panel 6 is pasted on the surface of the liquid crystal display. The operation switch group 5, the touch panel 6, and the remote controller 10 are used as input means for inputting data, inputting setting items, and performing various inputs for destination setting. Is composed of, for example, a push button switch provided around the liquid crystal display.

  The control circuit 2 has a function as display control means, calculates the current position of the vehicle based on information input from the position detection device 3, and displays a road map around the current position based on map data. 7 is displayed on the liquid crystal display, and a pointer indicating the current position and traveling direction of the vehicle is displayed over the displayed road map. The scale of the road map displayed on this display screen can be changed by operating the operation switch group 5.

  The control circuit 2 has a function of setting a route to the destination, and a travel guidance function for instructing the direction in which the vehicle should travel according to the route by voice output from the voice generator 8. That is, when a destination or waypoint is set by operating the operation switch group 5, the touch panel 6 or the remote controller 10, an optimum route from the current position to the destination is automatically searched as a guidance route, and the guidance route is displayed on the display device. 7 is displayed in a color different from the normal road color on the road map displayed on the liquid crystal display 7. And the control circuit 2 guides the advancing direction of a vehicle with an audio | voice etc. according to a guidance route. The Dijkstra method or the like is used as a method for setting the optimum route.

  Further, the control circuit 2 stores, for example, a part of map data, setting data, user data, program data, inspection data, multimedia (related to control of car audio, television, etc.) data in a flash ROM 14 of about several tens of megabytes. Etc. are written and stored in a corresponding storage area (see FIG. 2). In order to measure the temperature in the vicinity of the flash ROM 14, a temperature sensor 15 is arranged, and the control circuit 2 reads the sensor signal output from the temperature sensor (temperature detection means) 15 by A / D conversion. It has become. The flash ROM 14 may be built in the control circuit 2.

  Next, the operation of the present embodiment will be described with reference to FIGS. First, an outline of garbled data in a general flash ROM will be described. As shown in FIG. 3A, data garble in the flash ROM is caused by the fact that the data that has been written by injecting charges into the floating gate decreases with the passage of time. appear. As shown in FIG. 3 (b), the temperature when data is written, the number of times the data is written, and the data are written as those that affect the likelihood of data corruption. As shown in FIG. 3C, there are intervals, a time during which the written data is held, and a temperature state during the holding time.

In other words, the lower the temperature at the time of writing, the more the number of writing times, the shorter the writing interval, the more the data (charge) retention characteristics deteriorate, and the longer the data retention time, the higher the temperature during the retention time, the data retention The characteristics deteriorate. In addition, the area | region shown by hatching in a figure is an area | region assumed that possibility that data corruption will generate | occur | produce is very high.
Therefore, in this embodiment, the data retention time of the flash ROM 14 is predicted based on these data retention characteristics (see FIG. 3D), and data is rewritten (refreshed) at an appropriate timing according to the prediction result. ).

  FIG. 4A is a flowchart showing data acquisition processing related to “write” performed when the control circuit 2 writes data to the flash ROM 14. When the control circuit 2 obtains the temperature TE at the time of writing data from the temperature sensor 15 for each region shown in FIG. 2 (step S1), the control circuit 2 increments a counter for counting the number of times of writing TI (step S1). S2). Then, when the interval IT from the previous writing to the same area until the current writing is measured (step S3), the processing is terminated (these data are also stored in a predetermined area of the flash ROM 14). .

  FIG. 4B is a flowchart showing a process for monitoring the data holding state in the area where the control circuit 2 has already written data, and is executed at regular intervals (for example, several hours). When the data holding state is continued for each region, the control circuit 2 updates the duration time to measure the holding time Tk (step S4), and further uses the temperature data Te at that time as the temperature sensor. 15 (step S5), the process is terminated (these data are also stored in a predetermined area of the flash ROM 14). Also, as shown in FIG. 4A, when new data is written and updated, the data acquired in the process of FIG. 4B is cleared.

  FIG. 5A is a flowchart showing a data retention determination process of the flash ROM 14 performed by the control circuit 2. First, in steps S11a to S11e, the data of the device holding characteristic Fs, the number of times of rewriting TIx, the rewriting interval ITx, the rewriting temperature TEx, the holding time Tk, and the holding temperature Te are read for any data area x of the flash ROM 14. Note that the device holding characteristic Fs in step S11a is a product-specific holding characteristic of the flash ROM 14, and the data S related to the corresponding device (A) is obtained, for example, in the control circuit 2 from the characteristic data acquired in advance for each memory device. Is read from the ROM and the data is converted into a function as the retention characteristic Fs (therefore, it is common to each region).

Next, based on each data acquired in step S11, a data holdable time TId is calculated for the region x (step S12). In this case, a predetermined function f using the data Fs, TIx, ITx, TEx, Tk, Te as parameters is used. That is,
TId = f (Fs, TIx, ITx, TEx, Tk, Te)
And As the function f, for example, a function of multiplying each data by a weighting factor of a predetermined ratio and adding / subtracting is selected. Further, the initial value of the data retention possible time TId is determined according to at least the device retention characteristic Fs, and the numerical value is gradually decreased by performing an operation based on other parameters.

  In addition, for the rewrite interval ITx, the rewrite temperature TEx, the holding time Tk, and the holding temperature Te, the data acquired every time a rewrite event occurs is statistically processed by classifying the range to which each data value belongs. The influence on the data holdable time TId is considered in accordance with what value range the values are distributed. For example, in the case of the rewrite interval ITx, the occurrence frequency of each interval is counted and based on the distribution state of the occurrence frequency, the influence of the length of the interval at which data is written on the data retention characteristics of the flash ROM 14 is taken into consideration. For the rewrite temperature TEx, the frequency of writing at each temperature is counted, the temperature TEx is classified into predetermined ranges based on the distribution state of each writing frequency, and predicted based on the number of times belonging to each range. To do. If the holding time Tk, the time Tk is classified for each predetermined range and predicted based on the number of times belonging to each range. If the holding temperature Te, the temperature Te is classified for each predetermined range. Prediction based on the number of times belonging to.

  It is to be noted that the determination processing is performed for each area of the flash ROM 14 is actually a memory cell in a state where electrons are injected into the floating gate, but the writing state is in each cell. This is because it becomes extremely complicated.

  Subsequently, the control circuit 2 compares the calculated holdable time TId with the product lifetime TIp of the vehicle navigation device 1 multiplied by a coefficient α less than “1” (step S13), and TId <α · If it is TIp (YES), a data holding process is executed (step S14). That is, the data in the area x is read and transferred to a RAM or the like, and the same data is overwritten in the area x. At this time, a DMA (Direct Memory Access) controller may be used. Then, when the holdable time TId is reset and returned to the initial value (step S16), the data holding determination process is terminated.

  If it is determined (YES) in step S13, the data retention possible time of the flash ROM 14 is less than the time obtained by multiplying the product lifetime of the vehicle navigation device 1 by the margin coefficient α, and therefore the data retention of the region x may not be guaranteed. There is. Therefore, the data holding process is executed. FIG. 5B is an image showing the execution timing of the data holding process. That is, it is necessary to finish the refresh process before the holdable time TId elapses at the latest. On the other hand, when it is determined as (YES) in step S13, it is determined that the data holding process is unnecessary because the data holding time is longer than the product lifetime equivalent time of the vehicle navigation device 1. Therefore, the determination process is finished as it is.

  As described above, according to the present embodiment, the control circuit 2 can hold the data stored in the flash ROM 14 based on the device characteristics and usage status of the flash ROM 14 that is a data holding device of the vehicle navigation apparatus 1. The time TId is predicted, and the data stored in the flash ROM 14 is rewritten before the holdable time TId elapses. Therefore, it is possible to more accurately predict the limit time at which garbled data is likely to occur, and to rewrite data based on the prediction result, thereby suppressing unnecessary rewriting and extending the device life. .

  Since the control circuit 2 performs the prediction of the holdable time TId for each area set in the flash ROM 14 corresponding to the type of stored data, the management complexity is reduced, and each Status monitoring can be performed reasonably. Further, since the control circuit 2 predicts the holdable time based on the data holding characteristics of the flash ROM 14, the holdable time TId can be accurately predicted with reference to the data holding characteristics presented as specifications for each product. .

Furthermore, since the control circuit 2 counts the number of times data has been written to the flash ROM 14 and predicts the holdable time based on the number of times of writing, the control circuit 2 is based on the number of times of writing that greatly affects the data holding state. The prediction accuracy of the holdable time TId can be improved.
Further, the control circuit 2 measures the interval at which data is written to the flash ROM 14 and counts the occurrence frequency of each write interval, and predicts the holdable time TId based on the distribution state of the occurrence frequency. The prediction can be performed in consideration of the influence of the length of the writing interval on the data retention characteristics of the flash ROM 14.

Further, the control circuit 2 measures the temperature in the vicinity of the flash ROM 14 when data is written, and counts the frequency at which data is written at each temperature. Since the TId is predicted, the temperature when a plurality of times of writing is performed can be classified for each predetermined range and predicted based on the number of times belonging to each range.
Further, the control circuit 2 measures the retention time of the data written to the flash ROM 14 and predicts the retention time TId based on the continuation time, so that the time during which the written data is retained is set to a predetermined value. Classification can be performed for each range, and prediction can be made based on the number of times belonging to each range.

  Further, the control circuit 2 measures a temperature change in the vicinity of the flash ROM 14 during the period in which the written data is held, accumulates the length of the period in which the data is held for a plurality of temperature zones, and the accumulation period Since the holdable time is predicted based on the distribution state, it is possible to classify the temperature zone in the data holding period for each predetermined range and predict the holdable time based on the number of times belonging to each range.

  In addition, the control circuit 2 compares the holdable time TId with a threshold value determined on the basis of the product lifetime of the vehicle navigation device 1, and rewrites data when the former falls below the latter. It is possible to avoid data loss during a period in which the apparatus 1 is assumed to be operating. In that case, the threshold value is determined by multiplying the product lifetime by a coefficient α of less than 1.0. In other words, the loss of data can be more reliably avoided by multiplying the lifetime defined as the product specification by the above coefficient and taking a margin.

(Second embodiment)
6 and 7 show a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted. Hereinafter, different parts will be described. In the first embodiment, the data to be rewritten is overwritten in the same area in the refresh process in step S14. However, in the second embodiment, as shown in FIG. 7, a margin is given in advance to the capacity of the flash ROM 14A. deep. If a free area exists at the time when data is rewritten, data is written to the free area.

  FIG. 6 is a flowchart showing a data holding process performed in place of step S14. In step S21, when the capacity SA in which data is written in the area x at that time and the free capacity Se of the flash ROM 14A are obtained, the magnitudes of both are compared (step S22). If SA <Se (YES), the data in the area x is written and saved in the empty area (step S23).

On the other hand, if SA ≧ Se in step S22 (NO), the data in the area x cannot be transferred to the empty area. Therefore, it is confirmed whether or not the flash ROM 14 is being accessed at that time (step S24), and if it is not being accessed (NO), the same data is overwritten in the same area x as in the first embodiment (step S24). S25).
As described above, according to the second embodiment, the control circuit 2 rewrites data to an unused area reserved in the flash ROM 14A. Therefore, when the capacity of the flash ROM 14A has a margin, By rewriting data in the unused area, the data can be held more reliably.

(Third embodiment)
FIG. 8 shows a third embodiment of the present invention. In the third embodiment, assuming that the function corresponding to the control circuit 2 that performs processing on the flash ROM 14 as in the first and second embodiments is the control unit 21, which part between the CPU 21 and the flash ROM 14, for example, Or shows variations. FIG. 8A is an image similar to the configuration of the first embodiment assuming that the CPU 22 constitutes the control circuit 2, and is a case where the control unit 21 is included in the CPU 22.

  FIG. 8B shows a case where the control unit 21 is outside the CPU 22 (between the flash ROM 14) and is configured as an independent memory controller that controls writing in the flash ROM 14. FIG. 8C shows a case where the control unit 21 is configured inside the flash ROM 14. In any case, the control unit 21 may be a software function unit realized by a control program, or may be configured by hardware logic.

The present invention is not limited to the embodiments described above and shown in the drawings, and the following modifications or expansions are possible.
The present invention may be applied to either NAND type or NOR type flash ROM.
The holdable time TId in step S12 may be calculated based on at least one of the data Fs, TIx, ITx, TEx, Tk, and Te, and may be calculated by combining some of them. good.
In step S13, the coefficient α may be multiplied as necessary, and may be directly compared with the product life TI. Further, the threshold value is not necessarily compared with the threshold value set based on the product life, and a threshold value set regardless of the product life time may be used.
The calculation and determination of the holdable time TId is not necessarily performed for each data area.
The in-vehicle electronic device is not limited to the vehicle navigation device 1 and may be applied to other car audio devices.

The block diagram which is 1st Example of this invention and shows the electrical structure of the navigation apparatus for vehicles. The figure which shows an example of the data storage area of flash ROM (A) is an image diagram showing garbled data in the flash ROM, and (b) and (c) are diagrams showing charge retention characteristics of the flash ROM. (A) is a flowchart showing data acquisition processing related to “writing” performed when data is written to the flash ROM, and (b) is a flowchart showing holding state monitoring processing for an area where data is written. (A) is a flowchart showing the data retention determination process of the flash ROM, (b) is an image diagram showing the execution timing of the data retention process FIG. 5A shows a second embodiment of the present invention, corresponding to step S14 in FIG. 2 equivalent diagram FIG. 4 is a third embodiment of the present invention, and (a) to (c) are diagrams showing variations of where the control unit is arranged between the CPU and the flash ROM.

Explanation of symbols

  In the drawings, 1 is a vehicle navigation device (on-vehicle electronic device), 2 is a control circuit (time prediction means, rewriting means, data management device), 14 is a flash ROM, and 21 is a control unit.

Claims (22)

An apparatus for managing data stored in a flash ROM used as a data holding device for in-vehicle electronic equipment,
Time predicting means for predicting the retention time of the data stored in the ROM based on the device characteristics and / or usage of the flash ROM;
A data management apparatus for a flash ROM, comprising: a rewriting unit that rewrites data stored in the flash ROM before the holdable time elapses.   2. The flash ROM data management apparatus according to claim 1, wherein the rewrite means rewrites the data to an unused area reserved in the flash ROM.   3. The flash according to claim 1, wherein the time predicting unit predicts the holdable time for each area set in the flash ROM corresponding to the type of stored data. ROM data management device.   4. The flash ROM data management device according to claim 1, wherein the time predicting unit predicts the holdable time based on data holding characteristics of the flash ROM.   5. The time predicting unit counts the number of times data is written to the flash ROM, and predicts the holdable time based on the number of times of writing. A data management device for the flash ROM as described.   The time predicting means measures the interval at which data is written to the flash ROM, counts the frequency of occurrence of each write interval, and predicts the holdable time based on the distribution state of the frequency of occurrence. 6. The flash ROM data management device according to claim 1, wherein the data management device is a flash ROM data management device.   The time prediction means measures the temperature in the vicinity of the ROM when data is written to the flash ROM, counts the frequency of writing for each temperature, and based on the distribution state of the writing frequency 7. The flash ROM data management device according to claim 1, wherein the holdable time is predicted.   8. The time predicting unit according to claim 1, wherein the time predicting unit measures a holding time of data written to the flash ROM, and predicts a holding time based on the duration time. Flash ROM data management device.   The time predicting unit measures a temperature change in the vicinity of the ROM during a period in which data written to the flash ROM is held, and accumulates the length of the period in which data is held for a plurality of temperature zones. 9. The flash ROM data management apparatus according to claim 1, wherein the holdable time is predicted based on a distribution state of the cumulative period.   The rewriting means compares the holdable time with a threshold value determined based on a product life time of the in-vehicle device, and rewrites data when the holdable time is less than the threshold value. A data management device for a flash ROM according to any one of claims 1 to 9.   11. The flash ROM data management device according to claim 10, wherein the rewriting means determines the threshold by multiplying the product lifetime by a coefficient less than 1.0. A method for managing data stored in a flash ROM used as a data holding device of an in-vehicle electronic device,
Based on the device characteristics and / or usage status of the flash ROM, predict the retention time of data stored in the ROM,
A data management method for a flash ROM, wherein the data stored in the flash ROM is rewritten before the holdable time elapses.   13. The flash ROM data management method according to claim 12, wherein the data is rewritten to an unused area reserved in the flash ROM.   14. The flash ROM data management method according to claim 12, wherein the prediction of the holdable time is performed for each area set in the flash ROM corresponding to the type of stored data.   15. The flash ROM data management method according to claim 12, wherein the holdable time is predicted based on data holding characteristics of the flash ROM.   16. The data of the flash ROM according to claim 12, wherein the number of times data is written to the flash ROM is counted, and the holdable time is predicted based on the number of times of writing. Management method.   13. The interval at which data is written to the flash ROM is measured, the occurrence frequency of each write interval is counted, and the holdable time is predicted based on the distribution state of the occurrence frequency. The flash ROM data management method according to any one of items 1 to 16.   The temperature in the vicinity of the ROM when data is written to the flash ROM is measured, the frequency at which writing is performed for each temperature is counted, and the holdable time is predicted based on the distribution state of the writing frequency 18. The flash ROM data management method according to claim 12, further comprising:   19. The data management of the flash ROM according to claim 12, wherein a retention time of data written to the flash ROM is measured, and a retention time is predicted based on the continuation time. Method.   The temperature change in the vicinity of the ROM during a period in which data written to the flash ROM is retained is measured, and the length of the period in which data is retained for a plurality of temperature zones is accumulated. 20. The flash ROM data management method according to claim 12, wherein the holdable time is predicted based on the distribution state.   13. The holdable time is compared with a threshold value determined based on a product lifetime of the in-vehicle device, and data is rewritten when the holdable time is less than the threshold value. The flash ROM data management method according to claim 20.   The flash ROM data management method according to claim 21, wherein the threshold value is determined by multiplying the product life time by a coefficient less than 1.0.

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