MRAM

Abstract

To provide a technique of prolonging the life of an MRAM.SOLUTION: The MRAM has a work region, a boot region, and a reliability determination region. When data is written into the work region, new data different from old data stored in the reliability determination region is written in the reliability determination region and the data stored in the reliability determination region is read. When the read data and the new data are different data, an MRAM in which the work region and another region can be replaced is formed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to MRAM.

Background Art

[0002] Conventionally, a technique is known in which the remaining life of an MRAM is calculated based on statistical information, and writing to the MRAM is prohibited when the life is approaching. (For example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional technology, writing to the MRAM becomes impossible when the life is approaching. The present invention has been made in view of the above problems, and an object thereof is to provide a technique for extending the life of an MRAM.

Means for Solving the Problems

[0005] To achieve the above object, there is provided an MRAM having a work area and a boot area, wherein the work area has a reliability determination area, and when data is written to the work area, the data is written to an area other than the reliability determination area in the work area, and new data different from the old data stored in the reliability determination area is written to the reliability determination area. When the data stored in the reliability determination area is read out and the read data is different from the new data, the work area and another area are swapped to configure the MRAM.

[0006] That is, in the MRAM, when arbitrary data is written to the work area, the data stored in the reliability determination area is rewritten. Therefore, when comparing an arbitrary area in the work area with the reliability determination area, the usage frequency of the reliability determination area becomes the highest, and the reliability determination area reaches the end of its life earliest. Whether it has reached the end of its life can be determined by whether the data stored in the reliability determination area is read out and matches the data that was written. Therefore, if the reliability determination area has reached the end of its life, by swapping the work area with another area, it becomes possible to use the work area for a longer period. As a result, the life of the MRAM can be extended.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0008] Here, embodiments of the present invention will be described in the following order. (1) Configuration of the IC chip: (2) Life management process: (3) Other embodiments, etc.:

[0009] (1) Configuration of the IC chip: FIG. 1 is a block diagram showing the configuration of an IC chip 1 including an MRAM (Magnetoresistive Random Access Memory) 20 according to the present invention. The IC chip 1 is a device provided as a package in which various circuits are formed, and is mounted on a computer included in a general-purpose computer, an in-vehicle device, or the like. The IC chip 1 includes a processor 10 and an MRAM 20, and the processor 10 realizes various functions by executing a program recorded in the MRAM 20. The processor 10 can be realized by various known circuits, and may include a storage device such as an SRAM (Static Random Access Memory), for example.

[0010] In the MRAM 20, areas are distinguished in advance. That is, the MRAM 20 includes a boot area 21 and a work area 22. In the present embodiment, the boot area 21 is a storage area for an operating system. In the present embodiment, when the power supply to the IC chip 1 is started, the processor 10 reads out the operating system stored in the boot area 21, and a startup sequence is executed. When the startup sequence ends, the processor 10 executes various processes under the execution of the operating system. Note that the processing of the operating system includes processing by an application program executed under the execution of the operating system.

[0011] The work area 22 is a storage area for data handled in the processing of the operating system. That is, when storing data in various processes under the execution of the operating system, the data is written into the work area 22.

[0012] Furthermore, in the present embodiment, the work area 22 includes a reliability determination area 22a. In the present embodiment, the reliability determination area 22a is an area having a capacity of 1 bit. When data is written to the work area 22 by the processing of the operating system, new data different from the old data stored in the reliability determination area 22a is written to the reliability determination area.

[0013] Specifically, when any data is written to an area other than the reliability determination area 22a of the work area 22, the reliability determination area 22a is rewritten. That is, when the old data stored in the reliability determination area 22a is 0, new data 1 is written to the reliability determination area 22a. When the old data stored in the reliability determination area 22a is 1, new data 0 is written to the reliability determination area 22a.

[0014] When the above rewriting is performed, each time any data is written to the work area 22, the data in the reliability determination area 22a is rewritten. Therefore, the number of rewrites in the reliability determination area 22a is equal to or greater than the number of rewrites in any area within the work area. Accordingly, the number of rewrites in the reliability determination area 22a becomes the maximum value of the number of rewrites in the work area 22.

[0015] Therefore, the reliability determination area 22a reaches the end of its life earliest within the work area 22. For this reason, if the work area 22 is replaced with another area that has not reached the end of its life when the reliability determination area 22a reaches the end of its life, the life of the work area 22 can be extended.

[0016] Therefore, in the present embodiment, after new data is written to the reliability determination area 22a, a read operation is performed, and if the read data is different from the new data, the work area 22 and another area are swapped.

[0017] In this embodiment, the other area is the boot area 21. That is, writing to the boot area 21 is executed when the operating system is written, but in many cases, writing is not performed thereafter or is rarely performed. Therefore, usually, the number of write operations in the boot area 21 is significantly less than that in the work area 22. Even if the operating system is rewritten or corrected, usually, the number of write operations in the boot area 21 is less than that in the work area 22.

[0018] Therefore, when the data read from the reliability determination area 22a is different from the written data, by swapping the work area 22 and the boot area 21, the effective usable period of the MRAM 20 can be extended.

[0019] (2) Lifetime management process: Next, the lifetime management process performed in the IC chip 1 will be described. When power supply to the IC chip 1 is started, the processor 10 refers to the boot area 21 and reads the operating system (step S100). That is, the data of the operating system stored in the boot area 21 is loaded into the memory in the processor 10, and the execution of the operating system is started. In this state, the processor 10 can execute any process that can be executed under the execution of the operating system.

[0020] The processor 10 executes an arbitrary process under the execution of the operating system at an arbitrary timing (step S105). When an arbitrary process is executed, the processor 10 determines whether data is written to the work area 22 by the process (step S110). In step S110, if it is determined that data is not written to the work area 22, the processor 10 repeats the processes after step S105.

[0021] In step S110, when it is determined that data is to be written to the work area 22, the processor 10 rewrites the reliability determination area 22a (step S115). That is, the old data stored in the reliability determination area 22a is overwritten with new data. Also, the processor 10 writes data to the work area 22 (step S120). That is, the data to be written as a result of the process in step S105 is written to an area other than the reliability determination area 22a within the work area 22.

[0022] Next, the processor 10 reads the data in the reliability determination area 22a (step S125) and determines whether the data is normal (step S130). That is, if the read data matches the data after being rewritten in step S115, it is determined that the data is normal. If the data does not match, it is not determined that the data is normal.

[0023] In step S130, when it is determined that the data is normal, the processor 10 repeats the processes after step S105. In step S130, when it is not determined that the data is normal, the processor 10 exchanges the work area 22 and the boot area 21 (step S135). That is, the processor 10 transfers the data of the operating system stored in the boot area 21 to an area other than the reliability determination area 22a within the work area 22. Note that the exchange may be performed by various methods, and the transfer may be performed while backing up the data to the free area of the MRAM 20 or the backup area in the memory outside the MRAM 20.

[0024] Then, the processor 10 executes the processing after step S100 and restarts from reading the operating system. That is, the IC chip 1 is restarted. However, after the restart, the area that was the boot area 21 before the restart is used as the work area 22, and the area that was the work area 22 before the restart is used as the boot area 21. Note that if the processing in step S105 is interrupted, the data in both the boot area 21 and the work area 22 is saved to another area or the like, and then the data in the boot area 21 and the data in the work area 22 are swapped. If the processing in step S105 can be resumed after the swap is completed, the restart may be omitted.

[0025] FIG. 3 shows the state after the replacement is performed on the MRAM 20 shown in FIG. 1. Since the area that was the boot area 21 before the restart becomes the work area 22, a part of it is used as the reliability determination area 22a. Also, the area that was the work area before the restart becomes the boot area. However, since the area 21a that was used as the reliability determination area before the restart has reached the write cycle life, it is excluded from the boot area 21 and not used.

[0026] According to the above configuration, after using the work area 22 until the life of the reliability determination area 22a, the work area 22 can be further used until the life of another reliability determination area 22a. As a result, the life of the MRAM 20 can be extended by about twice compared to the case where no replacement is performed.

[0027] (3) Other embodiments, etc.: The above embodiments are examples for implementing the present invention, and various other embodiments can be adopted. For example, the usage mode of the MRAM can be various. The circuit for realizing functions other than the MRAM, for example, may not be configured as a chip integrated with a processor, but may be configured as a single MRAM chip. Also, the chip having the MRAM may include circuits other than the processor.

[0028] In addition, the area that can be swapped with the work area is not limited to the boot area. For example, a configuration in which the work area and the unused area of the MRAM are swapped may be used. FIG. 4 is a block diagram showing a configuration in which an unused area 23 is secured in addition to the boot area 21 and the work area 22 after the manufacture of the IC chip 1. In the example shown in FIG. 4, an unused area 23 having the same capacity as the work area 22 is secured in advance.

[0029] Also in this configuration, the lifetime of the MRAM is managed by the process shown in FIG. 2. However, in step S135, the work area 22 and the unused area 23 are swapped. Specifically, in step S135, the processor 10 transfers data other than the reliability determination area 22a stored in the work area 22 to the unused area 23. When the transfer is performed, the area that was the unused area 23 becomes the work area 22 as shown in FIG. 5. In addition, the processor 10 secures a reliability determination area 22a in the new work area 22. Further, the area that was the work area 22 before the transfer is set as an unused area 24. The processor 10 does not use the unused area 24 hereafter.

[0030] According to the above configuration, after using the work area 22 until the lifetime of the reliability determination area 22a, it is possible to further use the work area 22 until the lifetime of another reliability determination area 22a. As a result, the lifetime of the MRAM 20 can be extended approximately two times compared to the case where no swapping is performed. In addition, since the boot area 21 is not swapped, even if the area used as the work area 22 before the swap reaches the end of its life, the data in the boot area 21 is not affected.

[0031] The MRAM is a magnetic random access memory, and any memory that stores information by changing the magnetization state may be used. That is, in the MRAM, compared with other known memories, it has the characteristic that the guaranteed period for data retention is relatively long, but the guaranteed number of data rewrites is relatively small. Even with such a characteristic of the MRAM that the guaranteed number of rewrites is relatively small, it is possible to extend the lifetime by swapping the work area.

[0032] Since the boot area is an area used during booting, for example, it is used when starting up a system using MRAM, etc., but is not frequently accessed after startup. On the other hand, the work area is an area used after startup and is frequently accessed compared to the boot area.

[0033] The reliability determination area may be an area where data is rewritten whenever data is written to the work area. That is, whenever data is written to the work area, new data different from the old data stored in the reliability determination area may be written to the reliability determination area. Note that in the above-described embodiment, the reliability determination area is a part of the area secured within the work area, but the reliability determination area may be secured in an area other than the work area. In this case, when the work area and another area are swapped, a new reliability determination area is secured from the unused area.

[0034] When data is written to the work area, new data different from the old data stored in the reliability determination area is written to the reliability determination area. That is, in the reliability determination area, the stored old data is overwritten with different new data. By performing such rewriting, it is sufficient if the number of rewrites in the reliability determination area can be made equal to or greater than the maximum value of the number of rewrites in the work area.

[0035] The old data and the new data only need to be different. If the reliability determination area is 1 bit as in the above-described embodiment, either the old data or the new data is 1 and the other is 0. The reliability determination area may be multiple bits. In this case, when rewriting the reliability determination area, it is preferable that all bits are rewritten to data with different values.

[0036] Furthermore, the method of the present invention is also applicable as a program or a method. Also, the above-described system, program, and method may be implemented as a single device or as a plurality of devices, and include various aspects. Also, it can be appropriately changed, such as part being software and part being hardware. Furthermore, the invention is also established as a recording medium for a program that controls the system. Of course, the recording medium for the program may be a magnetic recording medium, a semiconductor memory, or any recording medium to be developed in the future, and can be considered in exactly the same way.

Description of Reference Numerals

[0037] 10…Processor, 21…Boot Area, 22…Work Area, 22a…Reliability Judgment Area, 23…Unused Area, 24…Non-Used Area

Claims

1. An MRAM having a work area and a boot area, having a reliability determination area, when data is written to the work area, new data different from the old data stored in the reliability determination area is written to the reliability determination area, when the data stored in the reliability determination area is read out and the read data is different from the new data, the work area and another area are swapped, MRAM.

2. The other area is the boot area, The MRAM according to Claim 1.

3. The other area is an unused area of the MRAM, The MRAM according to Claim 1.

4. The boot area is a storage area of an operating system, The work area is a storage area of data handled in the processing of the operating system, The MRAM according to Claim 1.

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