FR2935501A1 - Reinscribable non-volatile memory e.g. FLASH memory, access operation management method for e.g. subscriber identity module card, involves storing usage table in RAM or quick access storage - Google Patents

Abstract

The method involves determining a hot spot (121) of a non-volatile memory (100) from a usage table (410). Operation to access the determined hot spot of the non-volatile memory is detected. The access operation in aging zone of the non-volatile memory is realized, where the aging zone of the non-volatile memory is determined using a usage distribution mechanism. The usage table is stored in a RAM (400) or quick access storage. A part of the usage table is recopied in a safeguard table (410'). Independent claims are also included for the following: (1) a computer program comprising a set of instructions for implementing a method for management of access operation of a reinscribable non-volatile memory of a device (2) a recording medium comprising program for a non-volatile memory of a device (3) a device comprising a determination unit for determining hot spot of a non-volatile memory.

Description

BACKGROUND OF THE INVENTION The invention lies in the optimization of read / write operations in a rewritable non-volatile memory. First of all, a non-volatile memory is a memory adapted to keep its data in the absence of power supply. In a known manner, the non-volatile rewritable memories are partitioned into a plurality of zones, each of these zones being able to be erased / written individually a limited number of times, typically of the order of one million for the most efficient memories. In order to extend the life of such a memory as much as possible, it is known to seek to distribute the writing operations over all of its areas (so-called wear leveling technique, usage distribution). The document US 2006/0155917 describes such a method in which a counter of the number of erasures effected on this block is recorded in a table of a FLASH memory, for each block of this memory, and one selects, for a writing , the available block associated with the smallest counter. For a FLASH memory of 4096 blocks, the size of this table is of the order of 8 KB. This method also requires regularly copying the table in the RAM, which, because of the size of this table is a major disadvantage.

OBJECT AND SUMMARY OF THE INVENTION The present invention proposes a method for managing access operations to a rewritable non-volatile memory of a device that does not have the drawbacks of those of the prior art.

This method comprises: a step of determining, from a usage table, at least one hot point of said non-volatile memory; a step of detecting at least one operation aimed at accessing this hot spot thus determined; and a step of performing the aforementioned operation in a zone of a non-volatile rewritable so-called aging memory determined by a usage distribution mechanism. According to the invention, the usage table is stored in a random access memory or in a fast access memory, for example a RAM (Random Access Memory) type memory. In general, the invention proposes, unlike the aforementioned prior art, detecting the hot spots of the non-volatile memory rewritable, namely the areas of this memory most solicited reading, writing, erasure, and put in place a distribution mechanism of use only for these hot spots. This policy very advantageously allows the use of a very small usage table, typically of the order of a few tens of bytes for a rewritable non-volatile memory of 4096 blocks, in comparison with the 8 KB of the table used. in the aforementioned prior art. And it is thanks to this advantageous feature that the use table according to the invention can be stored in RAM, or in a fast access memory, by nature expensive, something unthinkable in the prior art. It follows that the access management method according to the invention is much faster execution than that of the prior art. Correlatively, the invention relates to a device comprising: a rewritable non-volatile memory; means for determining, from a usage table stored in a random access memory or in a fast access memory, at least one hot point of the non-volatile memory; means for detecting at least one operation aimed at accessing the hot spot thus determined; and means for carrying out the aforesaid operation in a zone of a non-volatile rewritable so-called aging memory determined by means for implementing a usage distribution mechanism. The device according to the invention may in particular be constituted by a microcircuit card, such as a SIM card or by a USB key.

In a preferred embodiment of the invention, at least part of the usage table is saved in a backup table stored in a rewritable non-volatile memory of the device. This feature is important when the invention is implemented in a device that can be turned off frequently because it can save information on hot spots. In a particular embodiment of the invention, the backup table is smaller than the usage table and during the backup step, the records of the table are saved in the backup table. corresponding use at the hottest points. This feature makes it very advantageous to continue searching and detecting new hot spots when the backup table is full. In a particular embodiment, the device according to the invention comprises means for transmitting at least a portion of said backup table upon receipt of a request. This characteristic advantageously makes it possible to obtain information remotely on the position and the degree of wear of its hot spots. Due to the use of a distribution mechanism of use, the information collected on these hot spots alone makes it possible to deduce, with an excellent probability, the degree of wear of the memory as a whole. In one embodiment of the management method of the invention, the backups may be performed at randomly selected times. In a preferred variant, the backup is performed when a number of accesses to one of the determined hot spots exceeds a dynamically adjusted threshold according to a frequency of powering up the device. This characteristic advantageously makes it possible to optimize the timing of the backups as a function of the frequency of power-up of the device. In particular, it increases the rate of backups when the frequency of power up increases. In a particular mode of the management method according to the invention, the zone of the aging memory in which the access operation is actually performed is cyclically selected in a buffer reserved for this purpose. This characteristic greatly simplifies the data reading operations that were intended for a given hot spot, since it is sufficient, in order to find the last writing intended for this hot spot, to locate, in the aging memory, the last zone comprising the address of this hot spot. In a particular embodiment, the various steps of the management method are determined by instructions of 10 computer programs. Consequently, the invention also relates to a computer program on an information carrier, this program being capable of being implemented in a device as mentioned above or more generally in a computer, this program comprising instructions adapted to the implementation of the steps of a management method as described above. This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any another desirable form. The invention also relates to a computer-readable information medium, comprising instructions of a computer program as mentioned above. The information carrier may be any entity or device capable of storing the program. For example, the medium may comprise storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording means, for example a floppy disk or a floppy disc. Hard disk. On the other hand, the information medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can in particular be downloaded to an Internet type network.

Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character. In the figures: - Figure 1 shows a device according to the invention, in a preferred embodiment; and - Figures 2 and 3 show, in flowchart form, the main steps of a management method according to a particular embodiment of the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT FIG. 1 represents a device 1000 according to the invention. This device can in particular be constituted by a microcircuit card, such as a SIM card or by a USB key. This device 1000 comprises a processor 200, a non-volatile rewritable memory 100 (hereinafter referred to as nonvolatile memory 100), a ROM-type ROM 300 and a random-access memory of the RAM type 400. The read-only memory 300 constitutes a storage medium. recording according to the invention, readable by the processor 200, on which is recorded a computer program according to the invention, this program comprising instructions for executing the steps of a management method according to the invention , the main steps of this method being represented in flow chart form in FIGS. 2 and 3. In a known manner, the processor 200 comprises an input / output bus 500 on which it can receive read or write commands in the non-volatile memory 100. The non-volatile memory 100 can in particular be a FLASH memory or an EEPROM memory.

The ROM 300 includes an operating system 310 comprising a program 311 for managing the non-volatile memory 100 and the random access memory 400, hereinafter referred to as the memory manager 311.

In the embodiment described here, the non-volatile memory 100 is divided in two and comprises a first portion 120 constituted by a standard working memory and a second part 110, called the aging buffer, for the implementation of the invention. By way of example, reference 121 is made to an area of the working memory 120, starting at the X address. In the embodiment described here, the boundary 113 between the two parts of the non-volatile memory 100 is configurable. during the personalization of the device 1000. In accordance with the invention, the device 1000 comprises in a fast access memory, a usage table 410 for storing information representative of the areas of the working memory 120 frequently accessed for reading or in writing, such areas being called hot spots. In the embodiment described here, the usage table 410 is stored in the random access memory 400. In the embodiment described here, the table 410 is organized in lines, each line having a record associated with a hot point with the following fields: • address field 411: start address of the hotspot; • field length 412: size of the hot spot in bytes; • counter field 415: counter representative of hot spot activity.

In the embodiment described here, at least a portion of the usage table 410 is copied regularly to a backup table 410 'of the nonvolatile memory 100, so that the information on the activity of the hot spots is not lost when the device 1000 is turned off. In the exemplary embodiment described here, the backup table 410 'is stored in a sub-part 111 of the aging buffer 110 reserved for system information.

In the embodiment described here, the backup table 410 'is smaller than the usage table 410. Y is the number of records that can be stored in the backup table 410', this number Y being , in the embodiment described here, stored in a register 330 of the read-only memory 300. In another embodiment, the number Y could be stored in the reserved sub-part 111 of the aging buffer 110 for example. According to the invention, the aging buffer 110 aims at preserving the hot spots of the working memory 120. For this purpose, the accesses to these hot spots are diverted to zones of the aging buffer, these zones being determined by a distribution mechanism of use. In the embodiment described here, the aging buffer is constituted, except for subpart 111 reserved for the system information, by a rotating buffer in which the zones are chosen cyclically. Any other usage division mechanism may be used, and in particular that described in document US2006 / 0155917 introduced in the preamble of the present application. FIG. 1 shows 3 successive records 112a, 112b, 112c, including data M1, M2, M3 that would have been written, without the implementation of the invention, in the area 121 of the working memory 120 Starting at the X address. In the embodiment described here, each record 112a, 112b, 112c includes: a field TLi having the size of the record in bytes; An address field, comprising the address X in the working memory 120 from which the data M should have been recorded; and a field containing these data Mi themselves. In the embodiment described here, the processor 200 is adapted to transmit at least a portion of the backup table 140 'on receipt of a request for this purpose, for example on the bus 500.

Referring to Figure 2, we will now describe a management method according to the invention in a preferred embodiment. We will assume that this method is implemented by the device 1000 of FIG. 1. It is assumed that one is at the end of the customization (step [10) of this device, the customization having in particular fixed: configurable 113 between the working memory 120 and the aging buffer 110 of the non-volatile memory 100; and the size of the use tables 410 and 410 '. In the example described here, the backup table 410 'of the system information area 111 of the aging buffer 110 is initialized empty during the personalization (that is to say with the value 0 in each of its registers) .

We will assume that device 1000 is then powered on during a step [15. During a step [20, the memory manager 311 copies the contents of the backup table 410 'into the usage table 410 of the random access memory 400. This operation does not generate an overflow, the table 410 being larger than table 410 '. We will assume that the device 1000 receives in step E25 a command leading this device 1000 to perform read / write operations in the nonvolatile memory 100. This command can for example be received on the bus 500 input / output of processor 200.

The read / write operation can also be performed on the initiative of the device 1000. In the embodiment described here, the management program according to the invention comprises a loop consisting of the steps E35 to [105 which will now be described, for processing each of the read or write operations in the nonvolatile memory 100, following the command received in step [25. In the embodiment described here, this loop is implemented jointly by the memory manager 311 and the processor 200.

We will assume that this read or write operation is for an area 121 of the working memory 120, starting at the X address. During a test [40, the processor 200 checks whether the usage table 410 comprises at least one record starting at this address X, namely a record including the address X in its field 411. When the result of the test E40 is negative, this test is followed by a step E42 in which a user initializes a counter C with the value 0, to represent the fact that the table 410 does not yet include a record covering the address X. Then, during a step [45, the memory manager 311 performs the read operation or write to the X address of the working memory 120.

Step E45 is then followed by an E50 test in which the memory manager 311 determines whether the operation being processed is a read operation or a write operation. If it is a read operation, the test E50 is followed by a response step E55 during which the memory manager 311 returns the read data and informs the entity at the origin of the command received in step E25 that the read operation has been performed. If it is a write operation, the test E50 is followed by a test E58 during which the processor 200 checks whether the counter C equals 0, which means that a record must be created in the table X. If this is the case, the test E58 is followed by an E60 test during which the processor 200 determines whether there is at least one free line in the table 410 of the RAM 400. If this is the case, the E60 test result is positive, otherwise it is negative.

When the result of the test E60 is positive, this test is followed by a step E65 during which the processor 200 creates a record in the table 410, with the following information: • address field 411: address X of the beginning of the area 121; • field length 412: size of the area 121; • counter field 415: 1 The step E65 creation of recording, or the test E58 when its result is negative, or the test E60 when its result is negative, is followed by the step E55 of answer already described during the which the memory manager 311 informs the entity causing the command received in step E25 that the write operation has been performed. When the result of the test E40 is positive, this test is followed by a step E67 during which the processor 200 increments by one unit the counter field 415 of the recording starting at the address X. We will assume that the recording concerned is that of the L1th line of the usage table 410, in other words that it bears the number L. The step E67 is followed by a test E70 during which the memory manager 311 checks whether the number L of this recording is less than the number Y of records that can be stored in the backup table 410 '.

If this is the case, the result of the E70 test is positive, otherwise it is negative. When the result of the test E70 is negative, it is followed by all the steps E45 to E65 already described. When the result of the test E70 is positive, it is considered that a read / write operation is being processed on a hot point of the working memory 120 and a mechanism for protecting this hot point is implemented. saving the area 121 of the working memory 120 and going to write / read in the aging buffer 110. If the operation concerned is a write operation, the test E70 is followed, when its result is positive, by a test [85, in which the memory manager 311 determines whether the aging buffer 110 is full. If this is the case, the result of the E85 test is positive, otherwise it is negative. If the result of the test E85 is negative, the memory manager 311 performs, during a step E90, the write operation that was intended for the zone 121 of address X of the working memory 120, in the aging buffer 110, with a wear management mechanism. In the embodiment described here, it creates for this a record 112i at the beginning of the free zone of the aging buffer 110 with: a field TL including the length of the record; An address field comprising the address X of the zone 121; and • a field containing these data themselves. Step E90 is followed by the already described step E55 of the response during which the memory manager 311 informs the entity causing the command received in step E25 that the write operation has been successful. been carried out. In the embodiment described here, when the aging buffer 110 is full (result of the positive test E85), this buffer 110 is empty, after having taken care of copying into the working memory 120 (or in RAM), the last one. contents M1, M2, M3 associated with each of the records of the table 410. For this purpose, during a step [100, the memory manager 311 traverses the table 410, and copies, for each record of this table, the last content associated with this record in the working memory 120. Thus, in the example of FIG. 1, when browsing the table 410, the memory manager 311 identifies the record {X, 2, C}, it looks in the aging buffer 110 for the last content corresponding to the address X, gets M3, and copies this content M3, of a length of TL3 bytes, to the address X of the working memory 120, that is ie in the area 121 to which this content was intended. The memory manager then erases the contents of the aging buffer during a step [105, with the exception of the area 111 reserved for the system information.

This step [105 is followed by the step E90 already described in which the memory manager creates a record 112 at the beginning of the free zone of the aging buffer for the write operation X associated with the command received at the step [25, then reports this operation (step E55) to the entity at the origin of this command.

If during the test E70 the memory manager determines that the operation concerned is a read operation, this test E70 is followed, when its result is positive, by a step [75, during which the memory manager 311 reads in the aging buffer 110, the last content Mi associated with this address X.

In the example of FIG. 1, the last content corresponding to the address X, is the content M3.

This content is returned to the entity at the origin of the command received in step [25, during the step E55 already described. In any case, the response step E55 is followed by the waiting step E25 of a new command to be processed.

In the embodiment described here, the management method according to the invention regularly saves hot spots, namely the first Y records of the usage table 410, in the backup table 410 '. In the embodiment described, this backup is performed during a PS backup process, implemented each time a write command is received in step E25 and will now be described with reference In this exemplary embodiment, the area 111 of the system information comprises four registers, CPT_PWON, CPT_MAJ, CPT_W, 15 SEUIL_W, which store respectively: • the number of power-ups of the device 1000; • the number of backups already performed '; • the number of writes since the last backup; And the number of write operations to be performed between two consecutive backups. During the personalization, the first three counters CPT_PWON, CPT_MAJ, and CPT_W are initialized to 0 and the register SEUIL_W is initialized with a constant, for example chosen between 1000 and 100,000. The power-up counter CPT_PWON is incremented each time power is turned on (step [15]). The PS backup process includes a first step E300 in which the processor 200 increments the write counter CPT W. In the embodiment described here, the backup process comprises a step E305 in which, the processor 200 optionally adjusts the number SEUIL_W of write operations to be performed between two consecutive backups, depending on the frequency of writes to the non-volatile memory 100 and the power-on frequency of the device 1000.

Those skilled in the art will understand that these frequencies can be obtained from the power-up counter CPT_PWON, the total number of writes (cumulative counters CPT_W since customization) and the time elapsed since the end of this personalization. For example, if the device 1000 is very frequently turned on, it may be preferable to reduce the number SEUIL_W. Then, during an E310 test, the processor 200 checks whether the number of writes CPT_W since the last backup is greater than this threshold SEUIL_W. If this is the case the result of the test E310 is positive and this test is followed by a step E315, during which the processor 200 sorts the usage table 410 in descending order of the counters. This step makes it possible to update the hottest points 15 in the first Y records of the usage table 410. Then, during a step E320, these first Y records are saved in the backup table 410 '. The counter CPT_W is then reset during a step E325.

Claims (14)

REVENDICATIONS1. A method for managing access operations to a rewritable non-volatile memory (100) of a device (1000), this method comprising: a step ([40) of determining, from a usage table, ( 410), at least one hot spot (121) of said non-volatile memory; a step (E35) of detecting at least one operation for accessing said hot spot (121) thus determined; a step of performing said operation (E75, E90) in a zone (112i) of a so-called aging non-volatile rewritable memory (111), said zone being determined ([90] by a usage distribution mechanism; said method being characterized in that said usage table (410) is stored in a random access memory or in a fast access memory (400). 2. Management method according to claim 1, characterized in that it comprises a step (E320) for saving at least a portion of said usage table (410) in a backup table (410 ') stored in a rewritable non-volatile memory (111) of said device (1000). 3. Management method according to claim 2, characterized in that said step (E320) of backup is performed when a number of accesses (CPT_W) to at least one of said hot point (121) exceeds a predetermined threshold (NB_W) dynamically adjusted (E305) according to a power-on frequency of said device (1000). 4. Management method according to any one of claims 1 to 3, characterized in that said zone (112i) of the aging memory (111) is selected cyclically in a buffer reserved for this purpose. 5. Management method according to any one of claims 2 to 4, characterized in that said backup table (410 ') is smaller than said usage table (410) and in that, during said step of saving (E320), saving in said backup table (410 '), the records of said usage table (410) corresponding to the hottest points. Computer program comprising instructions for executing the steps of the management method according to any one of claims 1 to 5 when said program is executed by a computer. A computer readable recording medium on which a computer program is recorded including instructions for performing the steps of the management method according to any one of claims 1 to 5. 8. Device (1000) comprising: - a rewritable non-volatile memory (100); means (311) for determining, from a usage table (410), at least one hot point (121) of said non-volatile memory; means (311) for detecting at least one operation for accessing said hot spot (121) thus determined; means (311) for carrying out said operation (E75, E90) in a zone (112i) of a non-volatile rewritable memory (111) called aging memory, said zone being determined ([90] by means (200) implementation of a user allocation mechanism; said device being characterized in that said table (410) is stored in a random access memory (400) or in a fast access memory (400). 30 9. Device according to claim 8, characterized in that it comprises means (200) for saving at least a portion of said usage table (410) in a backup table (410 ') stored in a memory non-volatile rewritable (111) of said device (1000). 35 10. Device according to claim 9, characterized in that it comprises means (200) for counting accesses to said at least one hot spot and in that said means (200) for saving perform said backup when a number of access (CPT_W) to at least one of said hot spot (121) exceeds a predetermined threshold (NB_W) adjusted (E305) dynamically according to a power-on frequency of said device (1000). 11. Device according to any one of claims 8 to 10, characterized in that it comprises means (311) for selecting said zone (112i) of the aging memory (111) cyclically in a buffer reserved for this effect. 12. Device according to any one of claims 9 to 11, characterized in that said backup table (410 ') is smaller than said usage table (410) and in that said backup means (200) save ([320], in said backup table (410, the records of said usage table (410) corresponding to the hottest points. 13. Device according to any one of claims 9 to 12, characterized in that it comprises means (200) for transmitting at least a portion of said backup table (140 ') on receipt of a request. 14. Device according to any one of claims 8 to 13, characterized in that it consists of a microcircuit card, such as a SIM card or by a USB key.