A flash memory chip fast testing method based on flash memory weak pages

Abstract

The present invention discloses a flash memory chip fast testing method based on flash memory weak pages, comprising the following steps: 1) reading the information of a specified flash memory block through a flash memory testing device, the information including: the total number of pages of the block; 2) searching for the flash memory weak page of the specified block in the specified block; 3) evaluating the reliability of the flash memory chip according to the found flash memory weak page. The present invention proposes a flash memory testing process and method based on fast search for flash memory weak pages, which only needs to read the status of the flash memory weak page to be tested, and can accurately and efficiently evaluate the quality of the entire flash memory through the number of error bit flips of the flash memory weak page, which can greatly reduce the flash memory testing time in mass production testing and improve the mass production testing efficiency of flash memory screening.

Description

Technical Field

[0001] The invention relates to memory technology, and in particular to a flash memory chip fast testing method based on flash memory weak pages. Background Art

[0002] Being able to quickly discover problems with key core components during the production process of storage products is an important step to ensure product quality and improve production efficiency. An efficient flash memory testing solution can detect and repair flash memory reliability problems in advance, reducing the cost of product recalls and after-sales service. In addition, formulating an efficient flash memory testing program based on clear and effective flash memory characteristic research results is an important step in efficiently testing flash memory chips.

[0003] After the flash memory chip packaging test is completed, the tested flash memory chips are usually shipped to the module factory as finished products. The module factory will surface mount the above flash memory chips, controller chips and other components in the SMT workshop. In order to ensure the reliability of storage products, flash memory particles are generally tested and screened before SMT mounting to eliminate flash memory chips that do not meet quality requirements. However, mass production lines have very high requirements for production efficiency, and how to efficiently screen flash memory within an effective time is particularly important. Therefore, both original manufacturers and module manufacturers in the industry are trying various methods to study the characteristics of flash memory chips in order to quickly evaluate the quality and quality of flash memory. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a flash memory chip fast testing method based on flash memory weak pages in view of the defects in the prior art.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a flash memory chip fast testing method based on flash memory weak pages, comprising the following steps:

[0006] 1) Read the information of the specified block of the flash memory through the flash memory test device, the information includes: the total number of pages of the block;

[0007] 2) Find the flash memory weak page of the specified block in the specified block. The flash memory weak page is a page in a given flash memory chip whose RBER of raw data error bit flips per KB is greater than or equal to twice the average of the RBER of raw data error bit flips per KB of other pages in the same block;

[0008] 3) Evaluate the reliability of the flash memory chip based on the found weak flash memory pages.

[0009] After the weak pages of the flash memory are found, the reliability of the entire flash memory chip can be quickly evaluated by monitoring the weak pages of the flash memory in real time.

[0010] According to the above scheme, in step 2), the weak page of the flash memory of the block is found by using the following steps:

[0011] 2.1) Read the areas corresponding to the page header, page middle and page end in the specified block, and record the number of error bit flips of the page corresponding to each area of ​​the page header, page middle and page end without erasing or writing;

[0012] 2.2) Select the location page corresponding to the maximum value of the error bit flip number in each area as the search result of the flash memory weak page.

[0013] According to the above scheme, the corresponding areas selected at the top, middle and end of the page are: the corresponding area selected at the top of the page is: 0 to 20% of the total number of pages, the corresponding area selected at the middle of the page is: 30% to 60% of the total number of pages, and the corresponding area selected at the end of the page is: 80 to 100% of the total number of pages.

[0014] According to the above scheme, in step 2.1), the corresponding areas selected at the top, middle and end of the page are: select three consecutive Page pages with two intervals each in the top, middle and end of the page.

[0015] According to the above scheme, in step 2.1), the corresponding areas selected for the three positions of page head, page middle and page end are: the corresponding area selected for the page head position is: Page0 to Page 2 and Page6 to Page 8; the corresponding area selected for the page middle position is: Page (N / 2-8) to Page (N / 2-6) and Page (N / 2-2) to Page (N / 2); the corresponding area selected for the page end position is: Page (N-8) to Page (N-6) and Page (N-2) to PageN, where N represents the maximum number of pages configured for the flash memory chip and 0 represents the page head.

[0016] According to the above scheme, in step 2.2), the details are as follows:

[0017] 2.2.1) According to the number of error bit flips of the Page page corresponding to each area of ​​the page head, page middle and page tail, determine the distribution type of the flash memory weak page in the specified block and the location of the flash memory weak page in the corresponding area;

[0018] Among them, the weak page distribution type of the flash memory is determined by analyzing the difference in the number of bit flips;

[0019] The flash memory weak page distribution types include: edge type, intermediate type and mixed type;

[0020] Edge type: Flash memory weak pages are distributed in the page header and / or page footer area of ​​the page range within the Block;

[0021] The intermediate type is: the weak pages of the flash memory are distributed in the middle of the page range within the Block;

[0022] The mixed type is: the weak pages of the flash memory are distributed in at least one of the middle area of ​​the page range within the Block block and the head area or the tail area of ​​the page.

[0023] According to the above scheme, in step 2.2.1), the bit flip number differentiation model is used for analysis to determine the distribution type of the flash memory weak pages, as follows:

[0024] 1) In the areas corresponding to the top, middle and end of the page, two word lines are selected in each of the three areas, and each word line consists of three adjacent pages;

[0025] 2) Record the maximum value of the error bit flip number in the head, middle and tail of the 6 pages and the corresponding position page respectively; record the maximum error bit flip number of the "header group" as Max1; similarly, record the maximum error bit flip number of the "middle group" as Max2; and record the maximum error bit flip number of the "tail group" as Max3;

[0026] Take the minimum value of the three and record it as Min{ Max1, Max2, Max3}, calculate the maximum error bit difference rate corresponding to the "page head group", "page middle group" and "page tail group", and record them as E1, E2, and E3 respectively:

[0027] Error bit difference rate of "header group": E1= Max1 / Min{ Max1, Max2, Max3};

[0028] Error bit difference rate of "group in page": E2= Max2 / Min{ Max1, Max2, Max3};

[0029] Error bit difference rate of "page end group": E3= Max3 / Min{ Max1, Max2, Max3};

[0030] In E1, E2, E3: When E1 = 1:

[0031] If E2≥2 and E3≥2, the flash memory weak page is recorded as the page corresponding to Max2 and Max3, and the flash memory weak page type distribution is determined to be "mixed";

[0032] If E2≥2, the flash memory weak page is recorded as the page corresponding to Max2. At this time, the flash memory weak page type distribution belongs to "intermediate type";

[0033] If E3≥2, the flash memory weak page is recorded as the page corresponding to Max3. At this time, the flash memory weak page type distribution belongs to "marginal type";

[0034] When E2=1:

[0035] If E1≥2 and E3≥2, the flash memory weak page is recorded as the page corresponding to Max1 and Max3, and the flash memory weak page type distribution is determined to be "marginal";

[0036] If E2≥2, the weak page of the flash memory is recorded as the page corresponding to Max2. At this time, the distribution of the weak page type of the flash memory belongs to the "marginal type";

[0037] If E3≥2, the flash memory weak page is recorded as the page corresponding to Max3. At this time, the flash memory weak page type distribution belongs to the "marginal type".

[0038] According to the above scheme, in step 2.2.1), the bit flip number differentiation model is used for analysis to determine the distribution type of the flash memory weak pages, as follows:

[0039] In the areas corresponding to the top, middle and end of the page, two word lines are selected at the beginning and end of each area, and each word line consists of three adjacent pages.

[0040] Record the maximum value of the error bit flip number in the head, middle and tail of the 6 pages and the corresponding position page respectively; record the maximum error bit flip number of the "header group" as Max1; similarly, record the maximum error bit flip number of the "middle group" as Max2; and record the maximum error bit flip number of the "tail group" as Max3;

[0041] Take the minimum value of the three and record it as Min{ Max1, Max2, Max3}, calculate the maximum error bit difference rate corresponding to the "page head group", "page middle group" and "page tail group", and record them as E1, E2, and E3 respectively:

[0042] Error bit difference rate of "header group": E1= Max1 / Min{ Max1, Max2, Max3};

[0043] Error bit difference rate of "group in page": E2= Max2 / Min{ Max1, Max2, Max3};

[0044] Error bit difference rate of "page end group": E3= Max3 / Min{ Max1, Max2, Max3};

[0045] In E1, E2, E3: In E1, E2, E3: When E1 = 1:

[0046] If E2≥2 and E3≥2, the flash memory weak page is recorded as the page corresponding to Max2 and Max3, and the flash memory weak page type distribution is determined to be "mixed";

[0047] If E2≥2 (or E3≥2), the weak page of the flash memory is recorded as the page corresponding to Max2 (Max3). At this time, the distribution of the weak page type of the flash memory belongs to the "intermediate type" ("marginal type");

[0048] When E2=1:

[0049] If E1≥2 and E3≥2, the flash memory weak page is recorded as the page corresponding to Max1 and Max3, and the flash memory weak page type distribution is determined to be "marginal";

[0050] If E2≥2, the weak page of the flash memory is recorded as the page corresponding to Max2. At this time, the distribution of the weak page type of the flash memory belongs to the "marginal type";

[0051] If E3≥2, the flash memory weak page is recorded as the page corresponding to Max3. At this time, the flash memory weak page type distribution belongs to "marginal type";

[0052] When E3=1, it is similar to E1=1.

[0053] According to the above scheme, in step 3), the location of the flash memory weak page monitored by the flash memory test is determined according to the distribution type of the flash memory weak page in the specified block and the location of the flash memory weak page in the corresponding area, and the reliability of the entire flash memory chip is evaluated by real-time monitoring of the flash memory weak page.

[0054] According to the above solution, in step 3), the flash memory weak page position monitored by the flash memory test is determined to be the flash memory weak page position in the area corresponding to the distribution type of the flash memory weak page in the block.

[0055] According to the above scheme, in the step 3), the flash memory weak page position monitored by the flash memory test is determined, specifically as follows: after determining the flash memory weak page type, find three adjacent pages before and after the above flash memory weak page position as flash memory weak page candidate items, and then perform a wear test on the Block block where the Page page is located, and count the maximum error bit flip numbers of the flash memory weak page candidate items corresponding to the seven conditions of erase and write times of 1, 501, 1001, 1501, 2001, 2501, and 3001, respectively, and count the number of times the maximum error bit flip number of the three pages of the "flash memory weak page candidate items" occurs under the above seven conditions, and take the flash memory page with the largest proportion of occurrences as the flash memory weak page of the entire flash memory chip.

[0056] The beneficial effects produced by the present invention are:

[0057] 1. The present invention proposes a flash memory testing process and method based on fast search for flash memory weak pages. This method does not need to perform full disk erase and read tests on the entire chip (or in proportion) to obtain all test results. It only needs to read the status of the flash memory weak pages that need to be tested. The error bit flipping of the flash memory weak pages can accurately and efficiently evaluate the quality of the entire flash memory. In mass production tests, the flash memory testing time can be greatly reduced, and the mass production test efficiency of flash memory screening can be improved.

[0058] 2. After the weak pages of the flash memory are found using the present invention, the reliability of the entire flash memory chip can be quickly evaluated by real-time monitoring of the weak pages of the flash memory, which facilitates the optimization of the entire firmware periodic inspection algorithm;

[0059] 3. The present invention proposes an effective process and method for quickly finding the weak pages of a flash memory and their distribution by region, which can improve the efficiency of finding the location of the weak pages of the flash memory.

[0060] 4. The present invention proposes a bit flip number difference model, which can assist in analyzing and quickly finding the type and specific location of flash memory weak pages. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0062] Figure 1 is a method flow chart of an embodiment of the present invention;

[0063] Figure 2 Schematic diagram of three types of weak page distribution of flash memory according to an embodiment of the present invention. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0065] like Figure 1 As shown, a flash memory chip fast testing method based on flash memory weak pages includes the following steps:

[0066] 1) Reading the configuration information of the flash memory particles through the flash memory test device, wherein the configuration information includes: the flash memory particle type, the total number of blocks, and the total number of pages of each block;

[0067] 2) Search for a weak flash memory page of a specified block in the specified block. The weak flash memory page is a page in a given flash memory chip whose error bit flip number RBER per KB of raw data is greater than or equal to twice or more of the average value of the error bit flip number RBER of other pages in the same block;

[0068] The specified Block can be randomly specified;

[0069] 2.1) Select the corresponding area at the beginning, middle and end of the page in the specified block for reading. Under the condition of no erasure, record the number of error bit flips of the corresponding page in each area at the beginning, middle and end of the page;

[0070] 2.2) Select the location page corresponding to the maximum value of the error bit flip number in each area as the search result of the flash memory weak page.

[0071] The corresponding areas selected at the top, middle and end of the page are: According to the total number of pages in each Block, the corresponding areas selected at the top, middle and end of the page are set to 0-20%, 30%-60%, and 80-100% of the total number of pages.

[0072] In this embodiment, in order to further speed up the search for weak pages of the flash memory, in step 2.1), the corresponding areas selected from the three positions of the page head, page middle and page end are: Page0 to Page 2 and Page6 to Page 8; the corresponding areas selected from the page middle position are: Page (N / 2-8) to Page (N / 2-6) and Page (N / 2-2) to Page (N / 2); the corresponding areas selected from the page end position are: Page (N-8) to Page (N-6) and Page (N-2) to PageN, where N represents the maximum number of pages configured for the flash memory chip and 0 represents the page head.

[0073] In step 2.2), the details are as follows:

[0074] 2.2.1) According to the number of error bit flips of the Page page corresponding to each area of ​​the page head, page middle and page tail, determine the distribution type of the flash memory weak page in the specified block and the location of the flash memory weak page in the corresponding area;

[0075] Analyze the difference in the number of bit flips to determine the distribution type of flash memory weak pages;

[0076] like Figure 2 ,The types of weak page distribution of flash memory include : edge type, intermediate type and mixed type;

[0077] Edge type: Flash memory weak pages are distributed in the page header and / or page footer area of ​​the page range within the Block;

[0078] The intermediate type is: the weak pages of the flash memory are distributed in the middle of the page range within the Block;

[0079] The mixed type is: the weak pages of the flash memory are distributed in at least one of the middle area of ​​the page range within the Block block and the head area or the tail area of ​​the page.

[0080] In step 2.2.1), the bit flip number differentiation model is used to analyze and determine the distribution type of flash memory weak pages, as follows:

[0081] In the regions corresponding to the page head, page middle and page end positions, the first and last two word lines of each region are selected as a group in each of the three regions, and each word line is composed of three adjacent pages to form a page head group, a page middle group and a page end group, which are used to determine the weak page distribution type of the flash memory;

[0082] Record the maximum value of the error bit flip number in the head, middle and tail of the 6 pages and the corresponding position page respectively; record the maximum error bit flip number of the "header group" as Max1; similarly, record the maximum error bit flip number of the "middle group" as Max2; and record the maximum error bit flip number of the "tail group" as Max3;

[0083] Take the minimum value of the three and record it as Min{ Max1, Max2, Max3}, calculate the maximum error bit difference rate corresponding to the "page head group", "page middle group" and "page tail group", and record them as E1, E2, and E3 respectively:

[0084] Error bit difference rate of "header group": E1= Max1 / Min{ Max1, Max2, Max3};

[0085] Error bit difference rate of "group in page": E2= Max2 / Min{ Max1, Max2, Max3};

[0086] Error bit difference rate of "page end group": E3= Max3 / Min{ Max1, Max2, Max3};

[0087] In E1, E2, E3: When E1 = 1:

[0088] If E2≥2 and E3≥2, the flash memory weak page is recorded as the page corresponding to Max2 and Max3, and the flash memory weak page type distribution is determined to be "mixed";

[0089] If E2≥2 (or E3≥2), the weak page of the flash memory is recorded as the page PageN / 2-6 (PageN-8) corresponding to Max2 (Max3). At this time, the weak page type distribution of the flash memory belongs to the "intermediate type" ("marginal type");

[0090] When E2=1:

[0091] If E1≥2 and E3≥2, the flash memory weak page is recorded as the page corresponding to Max1 and Max3, and the flash memory weak page type distribution is determined to be "marginal";

[0092] If E2≥2 (or E3≥2), the weak page of the flash memory is recorded as the page PageN / 2-6 (PageN-8) corresponding to Max2 (Max3). At this time, the weak page type distribution of the flash memory belongs to the "marginal type".

[0093] When E3=1, it is similar to E1=1;

[0094] 3) Evaluate the quality and quality of the flash memory based on the location of the weak flash page in the specified block and give the final test results.

[0095] According to the location of the flash memory weak page in the specified block, the location of the flash memory weak page monitored by the flash memory test is determined, and the reliability of the entire flash memory chip is quickly evaluated by real-time monitoring of the flash memory weak page.

[0096] The location of the flash memory weak page monitored by the flash memory test can also be determined according to the distribution type of the flash memory weak page in the specified block and the location of the flash memory weak page in the corresponding area, and the reliability of the entire flash memory chip can be quickly evaluated by real-time monitoring of the flash memory weak page.

[0097] In practice, we can directly determine that the flash memory weak page position monitored by the flash memory test is the flash memory weak page position in the area corresponding to the distribution type of the flash memory weak page in the block.

[0098] To further improve the accuracy, we optimized the method for determining the flash memory weak page position monitored by the flash memory test, as follows: after determining the flash memory weak page type, find three adjacent pages before and after the flash memory weak page position in the corresponding area as flash memory weak page candidates, and then perform a wear test on the Block where the Page page is located. Count the maximum number of error bit flips of the flash memory weak page candidates under seven conditions with erase times of 1, 501, 1001, 1501, 2001, 2501, and 3001, respectively. Count the number of times the maximum number of error bit flips of the three pages of the "flash memory weak page candidate" occurs under the above seven conditions, and take the flash memory page with the largest proportion of occurrences as the flash memory weak page of the entire flash memory chip.

[0099] When the final test result is given, if the number of flash memory error bit flips corresponding to the monitored flash memory weak page is less than the preset threshold value T1, the quality of the flash memory chip is judged to meet the requirements; if the corresponding number of flash memory error bit flips exceeds the preset threshold value T1, the flash memory quality is judged to not meet the requirements.

[0100] For the above method, we conducted flash memory tests on 18 mainstream TLC particles on the market and found that all of them are applicable.

[0101] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A flash memory chip fast testing method based on flash memory weak pages, characterized in that: The following steps are involved: 1) Obtain information about a specified block of the flash memory, including the total number of pages of the block; 2) Search for a weak flash memory page of a specified block in the specified block; the weak flash memory page is a page in a given flash memory chip, where the number of error bit flips per KB of raw data on a page in a block is greater than or equal to twice or more of the average value of the number of error bit flips per KB of raw data on a page in the same block; In step 2), the weak page of the flash memory of the block is found by using the following steps: 2.1) Read the areas corresponding to the page header, page middle and page end in the specified block, and record the number of error bit flips of the page corresponding to each area of ​​the page header, page middle and page end without erasing or writing; The corresponding areas for the top, middle and end of the page are: the top of the page corresponds to 0 to 20% of the total number of pages; the middle of the page corresponds to 30% to 60% of the total number of pages; the end of the page corresponds to 80% to 100% of the total number of pages; 2.2) Select the page corresponding to the maximum value of the error bit flip number in each area as the search result of the flash memory weak page; 3) Evaluate the reliability of the flash memory chip based on the found weak flash memory pages.

2. A flash memory chip fast testing method based on flash memory weak pages according to claim 1, characterized in that: In step 2.2), the details are as follows: 2.2.1) According to the number of error bit flips of the Page page corresponding to each area of ​​the page head, page middle and page tail, determine the distribution type of the flash memory weak page in the specified block and the location of the flash memory weak page in the corresponding area; Among them, the weak page distribution type of the flash memory is determined by analyzing the difference in the number of bit flips; The flash memory weak page distribution types include: edge type, intermediate type and mixed type; Edge type: Flash memory weak pages are distributed in the page header and / or page footer area of ​​the page range within the Block; The intermediate type is: the weak pages of the flash memory are distributed in the middle of the page range within the Block; The mixed type is: the weak pages of the flash memory are distributed in at least one of the middle area of ​​the page range within the Block block and the head area or the tail area of ​​the page.

3. A flash memory chip fast testing method based on flash memory weak pages according to claim 2, characterized in that: In step 2.2.1), the bit flip number differentiation model is used to analyze and determine the distribution type of the flash memory weak pages, as follows: In the areas corresponding to the top, middle and end of the page, two word lines are selected as a group in each of the three areas, and each word line is composed of three adjacent pages; Record the maximum value of the error bit flip number and the corresponding position page of the head, middle and tail of the page in the 6 pages respectively; The maximum error bit flip number of the page head group is recorded as Max1; the maximum error bit flip number of the page middle group is recorded as Max2; the maximum error bit flip number of the page tail group is recorded as Max3; Take the minimum value of the three and record it as Min{ Max1, Max2, Max3}, calculate the maximum error bit difference rate corresponding to the page head group, page middle group, and page tail group, and record them as E1, E2, and E3 respectively: Error bit difference rate of header group: E1= Max1 / Min{ Max1, Max2, Max3}; Error bit difference rate of groups in a page: E2 = Max2 / Min{ Max1, Max2, Max3}; Error bit difference rate of the page end group: E3 = Max3 / Min{ Max1, Max2, Max3}; In E1, E2, and E3: When E1= 1: If E2≥2 and E3≥2, the flash memory weak page is recorded as the page corresponding to Max2 and Max3, and the flash memory weak page type distribution is determined to be mixed; If E2≥2, the flash memory weak page is recorded as the page corresponding to Max2. At this time, the flash memory weak page type distribution belongs to the intermediate type; If E3≥2, the weak page of the flash memory is recorded as the page corresponding to Max3. At this time, the distribution of the weak page type of the flash memory belongs to the marginal type; When E2=1: If E1≥2 and E3≥2, the weak page of the flash memory is recorded as the page corresponding to Max1 and Max3, and the distribution of the weak page type of the flash memory is determined to be marginal; If E2≥2, the weak page of the flash memory is recorded as the page corresponding to Max2. At this time, the distribution of the weak page type of the flash memory belongs to the marginal type; If E3≥2, the flash memory weak page is recorded as the page corresponding to Max3. At this time, the flash memory weak page type distribution belongs to the marginal type.

4. A flash memory chip fast testing method based on flash memory weak pages according to claim 3, characterized in that: In step 2.2.1), In the regions corresponding to the three positions of the page head, the page middle and the page tail, two separated word lines are selected in each of the three regions as the first and last word lines of the region.

5. The flash memory chip fast testing method based on flash memory weak pages according to claim 1, characterized in that: In the step 3), three adjacent pages are found before and after the flash memory weak page position in the specified Block as flash memory weak page candidates, and then a wear test is performed on the Block where the Page page is located, and the maximum error bit flip numbers of the flash memory weak page candidates corresponding to the seven conditions of erase times of 1, 501, 1001, 1501, 2001, 2501, and 3001 are counted respectively, and the number of times the maximum error bit flip numbers of the three pages of the "flash memory weak page candidates" appear under the above seven conditions is counted, and the flash memory page with the largest number of occurrences is taken as the flash memory weak page of the entire flash memory chip.

6. A flash memory chip fast testing method based on flash memory weak pages according to claim 2, characterized in that: In the step 3), the position of the weak page of the flash memory monitored by the flash memory test is determined, specifically as follows: after determining the type of the weak page of the flash memory, three adjacent pages are found before and after the position of the weak page of the flash memory in the area corresponding to the distribution type as the weak page of the flash memory candidate, and then a wear test is performed on the Block where the Page page is located, and the maximum error bit flip numbers of the weak page of the flash memory candidate corresponding to the seven conditions of erase times of 1, 501, 1001, 1501, 2001, 2501, and 3001 are counted respectively, and the number of times the maximum error bit flip number of the three pages of the "weak page of the flash memory candidate" occurs under the above seven conditions is counted, and the flash memory page with the largest number of occurrences is taken as the weak page of the flash memory of the entire flash memory chip for monitoring.

7. An electronic device, characterized in that: include: one or more processors; as well as a storage device for storing one or more programs, When the one or more programs are executed by the one or more processors, the one or more processors are caused to execute the method according to any one of claims 1 to 6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

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