JP2011097495A - Recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording apparatus capable of fully utilizing an original write performance under multiple AU continuous write conditions. <P>SOLUTION: A recording apparatus 103 includes a buffer memory 108 for holding data input by an input section 104; a recording medium control section 106 for controlling writing/reading of data to/from a recording medium 102, which guarantees writing at a first guaranteed speed, when writing data for a first size unit; and a control section 110 for writing the data held in the buffer memory 108 onto the recording medium 102 for a second size unit larger than the first size, at a second guaranteed speed which is higher than the first guaranteed speed, while the recording medium control section 106 is used. The second guaranteed speed is determined so that the probability, in writing for the second size unit, of exceeding a second allowable value in an average write time per first size becomes lower than or equal to the probability of exceeding a first allowable value in a write time for the first size unit onto the recording medium 102. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a recording device for recording data transmitted from a host device onto a memory card incorporating a nonvolatile memory.

  2. Description of the Related Art Conventionally, a memory card, which is a card-type recording medium with a built-in flash memory such as an SD (Secure Digital) card, is ultra-small, ultra-thin and easy to handle. Further, since a large capacity memory card can be realized by using a single flash memory with process miniaturization and multi-value recording, the memory card is widely used in digital devices such as digital still cameras and video cameras.

  Generally, the flash memory used in such a memory card cannot overwrite digital data once recorded on the principle of operation of the storage cell. Further, the flash memory has a characteristic that it can be erased only in a relatively large block unit called an erase block, and cannot be handled as it is like a conventional data recording device such as a magnetic disk drive. Therefore, a memory card using flash memory has a built-in controller that controls the flash memory and performs additional processing to realize random access including overwriting in sector units, similar to conventional magnetic disk drives. ing. That is, when recording data on a memory card, in addition to writing the data, securing a new erased block, converting logical and physical addresses, updating management data such as address correspondence, etc. Performs various processes such as moving recorded data.

  Therefore, even when the amount of data written to the memory card is the same, the time required for data writing varies greatly depending on the data recording state of the memory card at that time.

  On the other hand, in a digital video camera, for example, a fixed amount of compressed video data is generated for every 1 / 30th of a video frame. Therefore, it is necessary to write a fixed amount of data to a memory card within a fixed time. In such a case, fluctuations in the data recording time as described above are undesirable.

  Therefore, in the SD card standard, assuming such a case, a method called a speed class is defined to guarantee the minimum value of the data writing speed under a certain condition.

  That is, in the SD card speed class specification, a certain amount of constant data called AU (Allocation Unit) is set, and the condition is limited so that data is written in AU units. If the AU data amount is appropriately set depending on the above-described controller algorithm, the maximum time required for the additional processing performed in the SD memory card can be obtained. The maximum guaranteed value of the time required for 1 AU writing is determined by the sum of the maximum value of the additional processing time and the maximum value of the time required to write / erase actual data. The minimum guaranteed value of the data writing speed is derived from the maximum value of the writing time and the AU data amount.

  When data writing at a higher speed is required for an SD card whose minimum data writing speed is guaranteed according to the speed class specification described above, a single data writing speed can be obtained by writing in parallel to a plurality of SD cards. An example corresponding to the parallel number multiple is shown in Patent Document 1.

JP 2004-343682 A

  In guaranteeing the data write speed as described above, the data write time and block erase time, which occupy the main part of the factors that determine the maximum value of 1 AU write time, are the physical state of the storage cell array of the flash memory. Also, it fluctuates greatly depending on the erase count history. Therefore, in order to guarantee the maximum value of the write time, it is necessary to determine the guaranteed value of the AU write time based on the maximum values within the normal operation range of the page write time and the block erase time.

  The guaranteed value of the AU write time is determined as follows. That is, when the write time is measured while changing the above various fluctuation factors, the 1 AU write time shows a certain probability distribution. An example of the probability distribution of such 1 AU writing time is shown in FIG. In FIG. 8, the horizontal axis represents the write time, the vertical axis represents the occurrence probability, the curve 801 represents the write time distribution during 1 AU write, and 802 represents the guaranteed write time. As shown in FIG. 8, by determining the writing time 802 such that the occurrence probability of 1 AU writing exceeding the writing time 802 is less than a predetermined value γ that is practically negligible depending on the purpose of use of the recording apparatus. The writing speed is guaranteed without any practical problems.

  However, since conventional recording devices are designed according to speed class regulations, even if the recording capacity is sufficient with one SD card, multiple SD cards can be operated in parallel according to the required transfer rate. There is a problem that the configuration is more complicated than necessary, and the cost and power consumption are increased.

  In order to solve this problem, the recording apparatus of the present invention includes an input unit to which data is input, a buffer that holds data input by the input unit, and a first size of data that is written in the first unit. A recording medium control unit that controls writing and reading of data to and from a recording medium that guarantees writing at a guaranteed speed, and a second that is faster than the first guaranteed speed by using the recording medium control unit. A controller that reads data held in the buffer continuously at a guaranteed speed of a second size larger than the first size and writes the data read from the buffer to the recording medium, and The probability that the second allowable value in the average writing time per the first size in the second size writing exceeds the second allowable value is written to the recording medium. So that the probability less that exceeds a first tolerance value in write time, defining the second guaranteed rate.

  With the above-described configuration, the recording apparatus realizes continuous data writing at a second speed higher than the first guaranteed speed of the recording medium at low cost and low power consumption without increasing the number of parallel recording media. can do.

FIG. 2 is a block diagram illustrating a configuration of a recording apparatus according to Embodiment 1. The figure which shows the change of the transfer data amount at the time of 1 AU writing in Embodiment 1 The figure which shows the change of the transfer data amount in case data accumulation in Embodiment 1 becomes the maximum. The figure which shows the change of the transfer data amount in case data consumption in Embodiment 1 becomes the maximum The figure which shows probability distribution of AU write time in Embodiment 1 FIG. 6 is a block diagram illustrating another configuration of the recording apparatus according to the first embodiment. FIG. 3 is a block diagram illustrating another configuration of the recording apparatus according to the first embodiment. The figure which shows the probability distribution of the conventional AU write time

(Embodiment 1)
FIG. 1 shows a configuration of a recording apparatus according to the first embodiment, and a block diagram including a host apparatus and an SD card connected to the recording apparatus.

  In FIG. 1, a host device 101 transfers continuous data such as a video stream to a recording device 103, and the recording device 103 records received data on an SD card 102, which is a recording medium for recording data. The recording device 103 can be connected to and disconnected from the host device 101 and can perform command and data communication processing using the interface signal 105, and the command and data can be inserted and removed from the SD card 102 using the interface signal 107. A card interface 106 for performing communication processing, a buffer memory 108 for temporarily storing data to be recorded on the SD card 102 from the host device 101 through the recording device 103, and a memory for reading and writing commands and data to the buffer memory 108 CPU 110 for controlling interface 109, host interface 104, memory interface 109, and card interface 106 through control bus 111, and a program executed by CPU 110 It comprises a ROM112 for storing, and RAM113 to hold temporary data during the execution of the program in CPU 110, a.

  When recording continuous data such as a video stream, the host apparatus 101 holds data to be recorded in a data buffer built in itself, and sets a write command on the interface signal 105 in the host interface 104.

  The command at this time conforms to, for example, the ATA interface standard, and parameters such as the address of the data buffer in the host apparatus 101 that holds the data to be recorded, the sector address of the data recording destination, and the data size are set. Is done.

  Receiving this, the host interface 104 notifies the CPU 110 that the write command has been set.

  Upon receiving the command notification, the CPU 110 reads the command and parameters from the host interface 104, interprets the contents, and sends the address indicating the data transfer source buffer in the host device 101 to the data transfer DMA function built in the host interface 104. The data transfer destination address and the number of transfer data in the buffer memory 108 are set.

  At this time, the CPU 110 determines a data transfer destination address in the buffer memory 108 so that the buffer memory 108 functions as a data FIFO.

  The host interface 104 reads data of the set number of transfer data from the address of the set data transfer source buffer in the host device 101 by the built-in data transfer DMA function, and the data transfer destination in the designated buffer memory 108 In order to write to the area starting from the address, the address is designated and the data is transferred to the memory interface 109.

  The memory interface 109 performs processing for writing designated data to an address designated by the host interface 104 of the buffer memory 108.

  The host interface 104 that has finished transferring the specified number of data notifies the CPU 110 of the end of the data transfer process.

  Upon receiving the notification, the CPU 110 obtains the sector address of the SD card 102 corresponding to the sector address of the data recording destination, and sets a transfer command in the card interface 106 together with the data transfer destination address in the buffer memory 108 and the number of transfer data.

  Further, the host device 101 is notified of the end of command processing through the host interface 104.

  Receiving the command processing end notification, the host apparatus 101 sets the next successive data write command in the same manner as described above.

  On the other hand, the card interface 106 to which the transfer command is set reads out the set number of data from the set data transfer destination address in the buffer memory 108, and starts from the sector address in the set SD card 102. Data transfer processing to be written to is performed according to a predetermined card interface protocol. The card interface 106 that has finished transferring the specified number of data notifies the CPU 110 of the end of the data transfer process. The CPU 110 notified of the end of the data transfer process from the card interface 106 similarly sets a data transfer command corresponding to the next data write command in the card interface 106.

  As described above, the CPU 110, the control bus 111, the ROM 112, and the RAM 113 constitute a control unit that controls writing of data temporarily stored in the buffer memory 108 to the SD card 102 that is a recording medium.

  Next, a method in which the recording apparatus 103 determines the writing speed based on the probability distribution of the writing time when recording data from the host apparatus 101 on the SD card 102 will be described.

  FIG. 5 shows the probability distribution of the conventional 1 AU write time shown in FIG. 8 and the probability distribution of the write time at the time of multiple AU continuous writing in the first embodiment.

  Consider a case where a plurality of AUs are continuously written to an SD memory card having a writing time probability distribution as indicated by a curve 501 for a writing time of 1 AU. The average writing time per AU obtained by dividing the time taken for continuous AU writing by the number of continuous AUs is measured, and the probability distribution is obtained. At this time, the distribution of the statistical average value obtained by dividing the number of consecutive write AUs for various write times on the original 1 AU write time distribution by the number of continuous AUs results in the distribution of the original 1 AU write time. The probability distribution and the average value are the same, resulting in a narrower and steeper distribution.

  An example of the probability distribution of the average write time per AU at the time of this multiple AU continuous write is shown by a curve 503 in FIG. As described above, since averaging results in a narrower and steeper distribution than the probability distribution 501, the probability that the average write time per AU exceeds the guaranteed write time 502 in the curve 503 is much smaller than in the case of the curve 501. That is, it can be seen that, under the condition that a plurality of AUs are continuously written, it can be expected to operate practically even with a writing time shorter than the guaranteed writing time of 1 AU.

  In the following, in order to describe and describe specific numerical values, the SD card 102 records AU = 4 MB in class 6, that is, the worst value (first guaranteed speed) when writing data with an AU size of 4 MB is 6 MB. It is assumed that it is possible to record more than / s. That is, the distribution of the writing time of one block when 4 MB is one block is represented by the curve 501 in FIG. 5 and the first guaranteed writing speed is 6 MB / s. The allowable writing time 502 can be expressed as T = 4/6 seconds, and it is assumed that the probability γ that the writing time of 1 AU exceeds T is negligibly small.

  At this time, when the distribution of the writing time per AU when 16 AU is continuously written to the same SD card 102 is measured, a distribution curve 503 narrower than the original distribution curve 501 due to the average effect as shown in FIG. become.

  Therefore, in the curve 503, when the maximum allowable average write time 504 per AU is set so that the probability of exceeding it is equal to or less than the predetermined value γ, which is the conventional value, a guaranteed value 504 smaller than the conventional guaranteed value 502 is set. can do. As a result, the second writing speed can be set faster than the first guaranteed writing speed by a magnification β obtained by β = guaranteed value 502 / guaranteed value 504.

  Next, the capacity of the buffer memory 108 necessary for the recording apparatus 103 to prevent overflow and underflow from occurring during data writing will be described.

  In the following description, the second write speed β set as described above is assumed to be 12 MB / s, which is twice the first guaranteed write speed.

  Further, the host device 101 is a device that records a high-definition video stream in real time, and is designed assuming performance equivalent to class 12 (12 MB / s).

  The progress of data writing during this time can be expressed as shown in FIG. 2 by plotting the time on the horizontal axis and the amount of data written on the vertical axis.

  At this time, in general, the progress of data writing can be represented by a curve 203 that goes from the origin 206 to an arbitrary point between the points 201 and 202.

  In particular, when writing is performed at the theoretically latest timing within the guaranteed speed range, it can be represented by a broken line 204, and conversely, when writing is performed at the earliest timing, it can be represented by a straight line 205. These broken line 204 and straight line 205 include the moment when the instantaneous writing rate becomes infinite, and this cannot occur in reality, but these cases are assumed as the limits satisfying the speed guarantee, and the cases of these limits By satisfying even if it contains, the buffering which presupposes the speed guarantee of SD card can be performed.

  Assuming that data writing from the host interface 104 to the buffer memory 108 is performed at 12 MB / s and 1 AU is written to the SD card 102 as indicated by the above-mentioned broken line 204, the buffer is in the meantime. Data in the memory 108 is written in 2 AU, and 1 AU of the data is read from the buffer memory 108 and written in the SD card 102. At this time, since 1 AU of data remains in the buffer memory 108 without being read, the amount of data in the buffer memory 108 increases by 1 AU.

  On the other hand, since it is assumed that 12 MB / s writing is possible as the capability of the SD card 102 in the case of 16 AU continuous writing, if there is AU written at a low speed like the above-mentioned broken line 204, within 16 AU There must be AUs that are written to other AUs at high speed. The data stored in the buffer memory 108 is read and written to the SD card 102 in another high-speed AU in 16 AU.

  In such a case, the amount of data accumulated in the buffer is maximized when AU written as a broken line 204 continues for 8 AU, and then AU written as a straight line 205 continues for 8 AU.

  FIG. 3 shows the progress of 16 AU data transfer at that time.

  In FIG. 3, a broken line 301 represents the progress of data writing while 16 AU is written to the SD card 102, and a straight line 302 represents the progress of data written to the buffer memory 108 at 12 MB / s. The difference represents the amount of data remaining in the buffer memory 108 at that time.

  As can be seen from FIG. 3, the broken line 301 is composed of eight low-speed AUs corresponding to the broken line 204 and eight high-speed AUs corresponding to the following straight line 205, and the amount of data remaining in the buffer memory 108. Is maximized at the end of the 8 AU slow AU. In this case, the maximum value of the data amount remaining in the buffer memory 108 is 9 AU (that is, 36 MB).

  Therefore, it can be seen that the data capacity of the buffer memory 108 needs to have a free space of 9 AU at the start of 16 AU transfer in order to cope with such a variation in write time. If the free space is 9 AU or more, even under the worst condition shown in FIG. 3, the free space of the buffer memory 108 is lost on the way, and the writing of data to the buffer memory 108 is awaited. It won't happen that you can't continue.

  On the other hand, when there is no data held in the buffer memory 108 during data writing to the SD card 102, it is necessary to wait for data writing to the SD card 102. Therefore, continuous data writing is interrupted, and the entire 16 AU is correspondingly lost. The writing time will also increase. In that case, since recording at 12 MB / s cannot be realized, it is necessary to prevent such a situation from occurring.

  Of the combinations in which 16 AU continuous data writing to the SD card 102 is exactly the target time (8T), the fastest AU written as shown by the straight line 205 is 8 AU. This is a case where the low-speed AU written as the broken line 204 continues for 8 AUs after the continuation.

  FIG. 4 shows the progress of 16 AU data transfer at that time.

  In FIG. 4, a broken line 401 indicates the progress of data writing while 16 AU is written to the SD card 102, and a straight line 402 indicates the progress of data written to the buffer memory 108 at 12 MB / s. And a broken line 401 represents the amount of data remaining in the buffer memory 108 at that time.

  As can be seen from FIG. 4, the broken line 401 includes eight high-speed AUs corresponding to the straight line 205 and eight low-speed AUs corresponding to the following straight line 204.

  The amount of data that is read from the buffer memory 108 and written to the SD card 102 becomes maximum when 8 AU high-speed AU is written. Therefore, wait until 8 AU data accumulates in the buffer memory 108 before starting to read data from the buffer memory 108. Starting from. Thereby, even when the writing to the SD card 102 of the high-speed AU of 8 AU is completed, the delay due to the underflow of the buffer memory 108 does not occur, and the SD card 102 of 16 AU in 8T time from the start time 4T to the end time 12T. You can finish writing to.

  From the above, it can be seen that 8 AU of data needs to be held in the buffer memory 108 at the start of 16 AU transfer in order to cope with such a variation in the writing time.

  As described above, if the buffer memory 108 is given a capacity of 17 AU or more and the 8 AU data is stored and then the 16 AU continuous writing is started to the SD card 102, all cases including those shown in FIGS. It can be seen that

  Further, when 8 AU data is stored, continuous writing to the SD card 102 is started, and when a high-speed AU as shown in FIG. 4 is preceded, an underflow occurs in the buffer memory 108 and a delay occurs. However, such a delay is substantially equivalent to the case where the start of continuous writing is delayed by the delay time, and does not affect the write time to be guaranteed. Therefore, it is not always necessary to control so that a certain amount of data is stored in the buffer memory 108 at the start of continuous writing, but recording at the second speed as shown in FIGS. If they are continuous, the delay once generated cannot be recovered. Therefore, it is necessary to secure a capacity of the buffer memory 108 that can hold the 8 AU data at the start of transfer.

  In general, for an SD card 102 in which the statistical ability value (second speed guarantee value) of the writing speed when αAU is continuously written is β times the first speed guaranteed value at the time of writing 1 AU. When writing from the host apparatus 101 at the second speed via the buffer memory 108 built in the recording apparatus 103, the condition for preventing the buffer overflow corresponding to FIG. The condition for having a free space equal to or larger than (α / β) AU + AU and not causing the buffer underflow corresponding to FIG. 4 is to hold data equal to or larger than (α−α / β) AU in the buffer memory 108. That is.

  Therefore, the buffer memory 108 needs to have a capacity of {2 × (α−α / β) +1} AU or more including these.

  3 and 4 illustrate the case where α = 16 and β = 2.

  The present embodiment described above can be used as a memory card by integrating the buffer memory 108, the buffer control units 110 to 113, and the SD card 102, which is a recording medium, as shown in FIG. The recording apparatus 601 can be configured.

  Further, as shown in FIG. 7, by integrating the buffer memory 108, the buffer control units 110 to 113, and the host device 101, it is possible to adopt a configuration of a recording device 701 that can be used as a new host device.

  In any case, as in the present embodiment shown in FIG. 1, continuous data writing at a second speed higher than the first guaranteed speed of the SD card 102 as a recording medium is performed in parallel with the recording medium. It can be realized at low cost and low power consumption without increasing the number.

  In the above description, the SD card is used as the recording medium and the block is described as AU in the speed class specification of the SD card. However, a general flash memory is used as the recording medium, and the block in the present embodiment is the erase block of the flash memory. This is also effective.

  That is, in a general flash memory, data is recorded in units of a fixed amount of data called a page, and data can be erased in units of erase blocks composed of a plurality of pages. Recording includes all control operations necessary for data recording in the flash memory, and the statistical distribution of the recording time of one erase block has a certain statistical distribution similar to the AU recording time of the SD card. It will be. Therefore, if the distribution is measured and a predetermined value γ that is practically negligible is set according to the purpose of use of the apparatus, the above-described embodiment can be applied.

  The recording apparatus according to the present embodiment relates to a recording apparatus such as a memory card, and in particular, the write speed obtained on the average in the recording medium by temporarily holding the write data to the recording medium in the buffer is based on the guaranteed worst value. It can be made to show. Therefore, the present invention is useful as a recording apparatus such as a high quality digital video camera that records a high data rate signal such as a high quality digital video stream on a large capacity recording medium using a flash memory.

  Further, since it is not necessary to make any changes to the host device and the memory card as the recording medium, the recording device of this embodiment can be an independent memory card adapter. Thereby, an inexpensive memory card having a large capacity by multi-value recording can be used as a recording medium in the same host device as the conventional one.

101 Host device 102 SD card 103, 601, 701 Recording device 104 Host interface 106 Card interface 108 Buffer memory 109 Memory interface 110 CPU
111 Control bus 112 ROM
113 RAM

Claims (7)

An input section for inputting data;
A buffer for holding data input at the input unit;
A recording medium control unit that controls data writing and data reading to a recording medium that guarantees writing at a first guaranteed speed when writing data of a first size;
Using the recording medium control unit, at a second guaranteed speed higher than the first guaranteed speed, continuously read data held in the buffer by a second size larger than the first size, A controller that writes data read from the buffer to the recording medium;
With
In the second size writing, the probability that the second allowable value in the average writing time per the first size exceeds the first allowable value in the first size writing time to the recording medium. The recording device that determines the second guaranteed speed so as to be less than or equal to the probability of exceeding. An input section for inputting data;
A buffer for holding data input at the input unit;
A recording medium that guarantees writing at a first guaranteed speed when writing data of a first size;
A recording medium control unit for controlling writing and reading of data to and from the recording medium;
Using the recording medium control unit, at a second guaranteed speed higher than the first guaranteed speed, continuously read data held in the buffer by a second size larger than the first size, A controller that writes data read from the buffer to the recording medium;
With
In the second size writing, the probability that the second allowable value in the average writing time per the first size exceeds the first allowable value in the first size writing time to the recording medium. The recording device that determines the second guaranteed speed so as to be less than or equal to the probability of exceeding. A generator for generating data;
A buffer for holding data output by the generation unit;
A recording medium control unit that controls data writing and data reading to a recording medium that guarantees writing at a first guaranteed speed when writing data of a first size;
Using the recording medium control unit, at a second guaranteed speed higher than the first guaranteed speed, continuously read data held in the buffer by a second size larger than the first size, A controller that writes data read from the buffer to the recording medium;
With
In the second size writing, the probability that the second allowable value in the average writing time per the first size exceeds the first allowable value in the first size writing time to the recording medium. The recording device that determines the second guaranteed speed so as to be less than or equal to the probability of exceeding. The buffer is
The ratio of the second size to the first size is α,
When the ratio of the second guaranteed speed to the first guaranteed speed is β,
The recording apparatus according to claim 1, wherein the recording apparatus has a capacity of {(α−α / β) +1} times or more of the first size. The buffer is
The ratio of the second size to the first size is α,
When the ratio of the second guaranteed speed to the first guaranteed speed is β,
The recording apparatus according to claim 1, wherein the recording apparatus has a capacity that is at least {2 × (α−α / β) +1} times the first size. The recording medium is
An SD (Secure Digital) card,
The recording apparatus according to claim 1, wherein the first size is an AU (Allocation Unit) in the SD card. The recording medium is
The recording apparatus according to claim 1, wherein the first size is an erase size of the flash memory.

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