TWI381383B - Method for storing data in a flash memory medium - Google Patents

Description

Flash memory data storage method

The invention relates to the field of semiconductor data storage, and in particular to a data storage method in a flash memory.

Existing flash memory devices have long been known, and as people's requirements for cost performance continue to increase. However, manufacturers of flash memory chips have made the life of flash memory chips shorter and shorter in order to reduce costs. Typically, each physical block (ie, Block) of the current Nand flash memory has 10,000 read and write times, or even 5,000 fewer. On the other hand, due to the randomness of the write operation to the flash memory device, some physical blocks of the flash memory chip operate more, and some physical blocks operate less, in the same flash memory. The number of erasing between the block and the block is very large, which accelerates the aging of the flash memory chip in advance, greatly shortening the service life of the flash memory chip. To this end, developers have used a variety of wear leveling algorithms to balance the number of uses of each block in a flash memory chip. However, as the capacity of flash memory chips continues to increase, the number of blocks in a single-chip flash memory chip is also increasing, which adds difficulty to the original wear-balance algorithm and is difficult to A true balance is achieved in flash memory chips.

Most of the existing wear leveling algorithms are based on the entire flash memory chip. When there are more blocks in the flash memory chip, for example, there are 8192 blocks in the flash memory chip. If you find one from the back, you can find one. The logic block of relocation (lifetime less than the average life threshold) may be found in the front part of the flash memory chip, but the latter block may not be found at all; if you want to find the youngest block, you have to compare The lifetime of each block in a flash memory chip is not only inefficient, but also inconvenient to record the life table of the entire flash memory chip.

It is an object of the present invention to provide a data storage method for flash memory to extend the life of a flash memory.

The present invention provides a data storage method for a flash memory, the flash memory comprising a plurality of storage blocks, and an empty block pool composed of partial storage blocks, the plurality of storage blocks being divided into two or more The partitioning process of the flash memory includes: a step of reclaiming an invalid block; a step of obtaining an empty block with a small number of erasing times from the empty block pool; and determining that the number of times of erasing and erasing is small Whether the empty block is an aging block.

Preferably, the step of performing a static replacement on the aged block is also included.

The step of recovering the invalid block includes: searching for a partition occupying more extra blocks in the flash memory; finding a suitable logical block from the partition occupying more extra blocks; and taking out the empty block pool; An empty block with a small number of erasures; the physical block in the logical block that is properly recovered is recovered by the empty block having a small number of erasures.

The step of performing static replacement includes: in the flash The step of finding a partition with a small number of erasing times in the memory; the step of finding a logical block with a small number of erasing times from a partition having a small number of erasing times; and taking out an empty block having a large number of erasing and erasing from the empty block pool The step of recovering the physical block in the logical block with a small number of erasures by using the empty block with a large number of erasures.

Preferably, the step of performing static replacement further comprises the step of determining whether the logical block having a small number of erasures is a block in which a file configuration table (FAT) is located.

Preferably, the step of performing static replacement further comprises: determining whether the logical block with the number of times of erasing is the last write operation block.

The data storage method of the flash memory provided by the invention makes it possible to use each physical block in the flash memory more evenly, so that the usage times of all the physical blocks in the flash memory are synchronized and homogenized. Prevents some physical blocks from aging prematurely due to frequent use, thereby extending the life of the entire flash memory.

The implementation, functional features, and advantages of the present invention will be further described in conjunction with the embodiments.

As is known to those skilled in the art, a flash memory, i.e., a flash memory chip, includes a plurality of memory blocks, each of which is comprised of a plurality of pages, each page including data storage bits and redundant bits. The address assigned to the storage block in order in the flash memory is called a physical block, and the fictitious address of the divided block which is used in use is called a logical address. The logical address and the physical address are mapped and converted by a mapping method, and the mapping information is used to form an address map. The address mapping table created by the mapping relationship between the logical block address and the physical block address is called a block address mapping table.

In order to manage the flash memory more effectively, a flash memory storage space can be logically divided into a plurality of partitions, each partition containing a plurality of logical blocks; by scanning the flash memory each The logical block in the partition corresponds to the physical address of the storage block, and the area address mapping table is generated. For a flash memory with 8192 logical blocks, if each partition contains 256 blocks, it can be divided into 32 partitions. However, due to the characteristics of the flash memory block, some blocks are invalid blocks, which will lose some space. Therefore, when partitioning partitions, the remaining blocks are allocated to the next partition only when the current partition is allocated full blocks. For example, if only 8100 valid blocks in the 8192 blocks are used for logical partitions, they can still be divided into 32 partitions. Only the first 31 partitions contain 256 logical blocks, while the 32nd partition contains only 164 logical blocks. The specific structure and allocation method are shown in the first figure.

The area address mapping table is stored in a corresponding spare block in each area of the flash memory; the area address mapping table of the spare block is read out into the RAM to perform conversion between the logical address and the physical address, thereby realizing Data read and write operations in flash memory. The flash memory data storage method by partitioning has the advantages of improving the data access speed. For example, when the flash memory writes the data recorded in the storage block, a new area address mapping table needs to be generated, only The new zone address mapping table needs to be stored in the spare block of the zone for updating the old zone address mapping table. Similarly, in the next data operation and need to switch to the area address mapping table of the area, it is not necessary to scan for each block in the area, and then according to the physical address dynamics of each block. The corresponding area address mapping table is generated, and only the updated area address mapping table is read out from the corresponding spare block.

In addition, since all valid physical blocks of the flash memory are empty before use, when a logical physical address and a physical address are mapped to a valid physical block, a certain number of empty blocks are reserved, and no mapping relationship is established. Thus forming a set, called an empty block pool; the empty block pool is used to record the use of blocks in the flash memory, including the physical address and erasure times corresponding to the empty block, in fact, the empty block The pool can be viewed as a cache here.

When the flash memory is initialized, the logical address and the physical address in the partition address mapping table are one-to-one mapping relationships; however, in the process of reading and writing data in the flash memory, some blocks of the original stored data are stored. When it becomes an empty block, some logical blocks may occupy two or more physical blocks at the same time. These multiple occupied physical blocks are called extra blocks, and the sum of all the logical blocks occupying the extra blocks in the partition is occupied by the partition. An extra block in which the extra block corresponding to the logical block is taken from the empty block pool.

At the same time, in order to understand the use of flash memory, a recording mechanism, referred to herein as a life table, is included, which includes a block life table and a partition life table, wherein the block life table records each flash memory. The number of erasures of logical blocks, the partition life table records the number of times of partition erasing, the number of times of erasing and erasing is the sum of the number of erasing of all logical blocks of the partition; each logical block has another structure to record its correlation. Parameters such as the physical block number and the corresponding number of erases. The structure records the address of all the physical blocks included in the logic block and the corresponding number of erasures; the number of erasures of the logical block is the erasure of the physical block with the least number of erasures in the physical block it contains. number.

The block life table and the partition life table are stored in a dedicated section of the flash memory, which is controlled and operated by firmware. When the data of a physical block of the flash memory is erased, the structure corresponding to the corresponding logical block adds 1 to the lifetime of the physical block. If the physical block is the youngest one of the logical blocks after adding 1 The number of erasures of the logic block in the block life table is also increased by 1. Similarly, the number of partition erases of the partition in which the block is located is also increased by one. The erased physical block becomes an empty block, and the empty block is stored in the empty block pool.

The life table is first read into the RAM from the flash memory by the firmware during use, and the life table is not frequently accessed, only when the life table changes, and the read and write operations cross regions or cross logic blocks. Only need to save. When the block life table of a logic block changes, if the next read and write operation needs to read the information of another logic block into the RAM, the block life table needs to be written to the flash memory for saving. Similarly, when the partition life table of a partition changes, if the next read and write operation needs to read the information of another partition into the RAM, the partition life table needs to be written to the flash memory for saving. Before saving the partition life table, you need to save the partition life table in RAM first. In addition, if the flash memory is in an idle state for a while and the life table changes again, the life table can be saved first.

The focus of the present invention is to explain the data storage method of the flash memory, and thus the related technologies related to the structure of the flash memory, the read/write mechanism, and the like are not described in detail.

The second figure shows the operation of writing data into the flash memory in this embodiment. Process.

Step S200, receiving a write operation command.

In step S201, it is determined whether it is necessary to obtain an empty block from the empty block pool; if the remaining space of the current block is insufficient to write the data of the write operation command, the virtual block needs to be fetched from the empty block pool to perform a write operation, and step S202 is performed; otherwise, The write operation command is directly executed, and the data is written to the physical address corresponding to the logical address in the write operation command, and step S207 is performed.

In step S202, if the empty block of the empty block is insufficient, the invalid block needs to be recovered, and step S203 is performed; otherwise, step S204 is performed.

The so-called empty block is a relative concept. When the flash memory is initialized, each logical block corresponds to one physical block. At the same time, in order to improve the read/write speed, some empty blocks are reserved for the entire flash memory. In the process of writing data to the flash memory, the empty block may be continuously taken away, and the number of empty blocks is less and less. When the number of empty blocks is less than the number of empty blocks preset by the designer, the empty block is insufficient. For example, the empty block pool has a total of 100 empty blocks, and 5 empty blocks are set as the reserved empty block lower limit. When there are less than 5 empty block empty blocks, it is judged that the empty block is insufficient.

In step S203, the invalid block in the flash memory is recovered, and the recovered block is placed in the empty block pool, and the invalid block is recovered, and then step S204 is performed.

Step S204, the youngest block is taken out from the empty pool as an empty block for writing a command to write the above data. The youngest block is the firmware to compare the number of erasures of each empty block in the empty block pool, and the number of erasing is the least. The block is the youngest block.

The youngest block or the block with the least number of erasures is a relative It is relative to the block with a large number of erases. For example, the number of erasing of physical block A in the empty block pool is N, the number of erasing of physical block A+1 is N+1, the number of erasing of physical block A+2 is N+2, and the physical block A+3 If the number of erasures is N+3, the physical block A is the block with the least number of erasures relative to the other blocks of the empty block, and the physical block A+1 is relative to the physical block A+2 and the physical block A+3. The block with the least number of erases. Therefore, the block with the least number of erasures is not limited to the physical block A, and may be a physical block A+1 or A+2 with a small number of erasures. Here, for the convenience of explanation, the terms of the youngest block or the block with the least number of erasures are still used. Therefore, the block with the least number of erasures or the youngest block may be a block with a small number of erasures or a younger block.

Step S205, if the obtained empty block with the least number of erasures is an aging block, all the empty blocks in the empty block pool will be aging blocks, and at this time, the youngest block obtained is not continuously written. Instead, the static replacement operation is performed, and step S206 is performed; if the youngest empty block obtained is a non-aged block, the writing operation is continued, and step S207 is performed; the so-called aging block is a relative concept in the write operation. In the process, the block life table records the number of erasures of each logical block, and there is also a special structure to record the total number of erasures and the average number of erasures of all physical blocks of the entire block of flash memory. When the number of erasures of a physical block exceeds a certain threshold of the average number of erasures, the physical block is considered to be an aged physical block. The average number of erasures refers to the physical block. The number of physical blocks in some flash memory is not necessarily the nth power of 2, and the average value cannot be obtained by shifting. very troublesome. Embodiment of the present invention The average number of erasures is achieved by adding and subtracting. For example, if there are 10000 physical blocks in a flash memory, the total number of erasures of the flash memory when performing a erase operation on a physical block. It will increase by 1. When the total number of erasing times increases to 10,000 of the total number of physical blocks, the average number of erasing times is increased by one, and the total number of erasing times is restarted. The average erasure erasure threshold is set to 5. When the number of block erasures of a physical block exceeds 5, the physical block belongs to the aging block.

In step S206, a static replacement operation is performed to replace a relatively younger block from the data area with the oldest or oldest empty block in the empty block pool.

In step S207, a write operation is performed to write data into the physical block of the flash memory.

In step S208, it is determined whether the write operation is completed, and if so, the write operation is ended; if not, the process proceeds to step S201.

The specific process of recycling the invalid block is as shown in the third figure.

In step S300, the partition occupying the most extra block in the entire flash memory is found, so as to ensure that there are enough logic blocks for selection for recycling. As mentioned before, the partition occupying the most extra blocks may also be a partition occupying more extra blocks.

When the flash memory is initialized, each logical block corresponds to one physical block. At this time, each logical block occupies an additional block of 0, and the extra block occupied by each partition is also 0. However, during the write operation, some logic blocks obtain empty blocks from the empty block pool, that is, one logical block corresponding to a physical block as described above, and the extra block occupied by it increases, and the extra block occupied by the corresponding partition also It will also increase. In this implementation, each partition is recorded in an array. The number of extra blocks.

Step S301, finding a suitable recycled logical block from the partition occupying the most extra block, the suitable recycled logical block includes two factors, one is the number of additional physical blocks in the logical block, and the more physical blocks are added, The higher the recycling efficiency, the more logical blocks with extra blocks are preferred when recycling; the second is the number of erasures of the youngest physical block in the logical block. If the number of erasures of the youngest physical block in the logical block is too many, This logic block cannot be used either.

Therefore, for the purpose of recovery and balance, for a logical block that can be recycled (at least two physical blocks are occupied), a calculation model is established, and the calculation block of the calculation model is used to obtain the most suitable logic block for recovery. The calculation formula of this calculation model is as follows: c=10000+μa-b......(1)

The larger the value of c in equation (1), the more suitable the logic block is. In the above model, a represents the number of extra physical blocks; b represents the minimum number of erasures of the physical blocks contained in the logic block; μ is a coefficient. The coefficient directly determines the proportion of a, and the value of μ is related to the threshold T. The logical block with the largest c value is obtained by the firmware, which is the logical block that is suitable for recycling.

Wherein, the calculation formula of the threshold T is as follows: T=μ(E-A)......(2)

In the calculation formula (2), E is the number of times that each physical block in the flash memory can withstand the erasing, which is related to the type of the flash memory, and is marked by the manufacturer at the time of shipment; A is the average number of erasing times. It will gradually increase during use; from the above calculation formula, T is proportional to E and inversely proportional to A. For different flash memories, the larger the E is, the larger the corresponding threshold is. In the early stage of the flash memory, the condition for judging the aging block is looser, so that the extra loss due to the relocation can be reduced. For a specific flash memory device that uses flash memory as a storage medium, since the flash memory used is fixed, E is also fixed, and the value of T is only inversely proportional to A. During use, as A continues to increase, T slowly shrinks. As the entire flash memory ages, and A approaches E, T slowly shrinks to zero. The number of erases of all physical blocks in the flash memory is slowly approaching A.

At the beginning of the use of the flash memory device, the frequency of erasing and writing of the physical block will be relatively large, which can effectively reduce the extra loss caused by the relocation. As the A increases, the T gradually shrinks, the fluctuation range of the physical block's erasing times is gradually narrowed, and the number of erasing and writing of all physical blocks becomes more and more average, so that it does not exceed E quickly. The entire block of flash memory can't be used, so you can make the most of all the blocks.

In step S302, the youngest empty block is taken out from the empty block pool, that is, the empty block with the least number of erasures. As mentioned earlier, the empty block or the youngest empty block with the least number of erasures may also be an empty block with a small number of erasures or a younger empty block.

Step S303, using the youngest empty block to recover the suitable logical block found, mapping the youngest empty block to the appropriate logical block, and moving the valid data in the appropriate logical block into the youngest space. In the block, the valid data in the physical block corresponding to or contained in the original logical block is erased, and the physical block is put into the empty block pool.

It can be seen that the recycling invalid block will occupy more than two physical blocks. The valid data in the logical block is moved to an empty block, and the empty block is associated with the previous logical block, and several physical blocks of the data are erased and put into the empty block pool, making it empty. The number of hollow blocks in the block pool increases. After being recycled, the hollow block that is placed in the empty block is added to the process of identifying the empty block with the least number of erasures.

The specific process of performing the static replacement operation is as shown in the fourth figure.

In step S400, when the relocation is performed, the partition with the least number of erasures in the entire flash memory is first found; the partition with the least number of erasures refers to the partition with the least number of erasures in the partition life table. As mentioned before, the partition with the least number of erasures may be a partition with fewer erases.

The average lifetime of a partition is the average of the lifetimes of all logical blocks within the partition. The lifetime of the logical block refers to the life of the youngest block in the physical block included in the logical block, that is, the number of times of erasing is at least one block.

When the number of logical blocks included in the partition is not 2 nth power, the 32nd partition as described above contains only 164 blocks, and the average value cannot be calculated by shifting, which is very troublesome if the division is performed. And when there are fewer valid blocks in the partition, the probability of finding logical blocks in the partition for static relocation should be reduced accordingly. In this embodiment, an approximate value is used to obtain an average value of the lifetime of the logic block. When the number of logical blocks is greater than or equal to 2, the (n-1) power is less than 2 nth power, and the (n-1) power of the approximation 2 is taken. For example, the 164 blocks mentioned above are taken as 128 (2 to the power of 7) calculation, so that the average value obtained is larger than the actual value, that is, the average life of the logic block is too large, correspondingly reducing the found The probability of a partition being statically relocated is also convenient for calculation.

Step S401, after finding the partition with the least number of erasures in the flash memory, and finding the logical block with the least number of erasures according to the recorded block life table in the partition with the least number of erasures. As mentioned before, the logic with the least number of erasures may be a logical block with a small number of erasures.

Step S402, in order to avoid relocation of the data of the frequently operated area, the logical block having the least number of erasing and erasing needs to be limited; first, it is determined whether the logical block with the least number of erasing times is the partition of the file configuration table (FAT). If so, it is not operated; otherwise, step S403 is performed.

Step S403, it is determined whether the logical block with the least number of erasures is the last write operation block, and if so, it is not operated; otherwise, step S404 is performed.

In step S404, the empty block with the most erasure is found from the empty block pool, and the physical block in the logical block with the least number of erasures is recovered by the empty block with the most erasure.

If the physical block in the logical block with the least number of erasures has data, the valid data stored in the physical block in the logical block with the least number of times of erasing is relocated to the empty block with the most erasure And erasing the physical block in the logical block and putting it into the empty block pool; after completing the data relocation, returning the physical block of the logical block with the least number of erasures with the empty block with the most erasure.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the invention, and the equivalent structure or equivalent flow transformation made by the specification and the drawings of the present invention may be directly or indirectly applied to other phases. The technical fields of the related art are all included in the scope of patent protection of the present invention.

S200~S209‧‧‧Steps

S300~S304‧‧‧Steps

S400~S406‧‧‧Steps

The first figure is a schematic diagram of a partition structure according to an embodiment of the present invention; the second figure is a flow chart of the operation of writing data according to an embodiment of the present invention; the third figure is a flowchart of the operation of recovering invalid blocks according to an embodiment of the present invention; A flowchart of an embodiment performing a static replacement operation.

S200~S209

Claims (10)

A flash memory data storage method, the flash memory includes a plurality of storage blocks, the plurality of storage blocks are divided into two or more partitions, and the flash memory is provided with an empty block In the process of storing data, the flash memory includes: a step of recovering an invalid block; a step of obtaining an empty block with a small number of erasing times from the empty block; determining the number of times of erasing and erasing The step of whether the empty block is an aged block; wherein the step of recovering the invalid block further comprises: searching for a partition occupying more extra blocks in the flash memory; and having more extra blocks from the occupying Finding a logical block suitable for recycling in the partition; taking out an empty block with a small number of erasures from the empty block pool; and recovering the physical block in the logical block that is properly recovered by using the empty block with a small number of erasures. The flash memory data storage method of claim 1, further comprising the step of performing static replacement on the aged block. The flash memory data storage method of claim 1, further comprising: moving valid data of the physical block in the appropriately recovered logical block into the empty block having a small number of erasures, and erasing the The step of validating the physical block in the logic block. The flash memory data storage method according to claim 2, wherein The step of performing static replacement includes: a step of finding a partition with a small number of erasures in the flash memory; and a step of finding a logical block having a small number of erasures from a partition having a small number of erasures; The step of extracting an empty block with a large number of erasures from the empty block pool; and recovering the physical block in the logical block with a small number of erasing times by using the empty block with a large number of erasures. The flash memory data storage method of claim 4, further comprising the step of determining whether the logical block having a small number of erasures is a block in which a file configuration table (FAT) is located. The flash memory data storage method of claim 4 or 5, further comprising: determining whether the logical block having a small number of erasures is the last write operation block. The flash memory data storage method according to any one of claims 1 to 4, wherein the aged block means that the number of erasures of a certain physical block exceeds the average erase of the flash memory. The physical block of the number of times. The flash memory data storage method according to claim 1 or 3, wherein the logical block that is appropriately recovered refers to the logical block that contains the most physical blocks in the partition occupying more extra blocks. The flash memory data storage method of any one of claims 1 to 4, wherein the flash memory includes a block life table and a partition life table, the block life table recording the flash memory Number of erases per logical block The number, the partition life table records the number of times the partition is erased, and the number of times the partition is erased is the sum of the number of erases of all logical blocks of the partition. The flash memory data storage method of claim 9, wherein the number of erasures of the logical block is the number of erasures of the physical block having the least number of erasures in the physical block included in the logical block.