JPH11167518A - Using method for memory of moving picture decoding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the using method for the memory of the moving picture decoding device of simple constitution capable of reducing the memory bandwidth of memory access in access units for reading reference image data out of a 2-bank constitution memory. SOLUTION: By the using method for the memory of the moving picture decoding device, the storage areas of the respective banks of the 2-bank constitution memory are divided into specific unit storage areas, reference image data to be stored in the 2-bank constitution memory are divided into specific storage units 13 to be stored in the unit storage areas, and the reference image data are stored so that mutually adjacent storage units 13 are stored in unit storage areas belonging to the different banks; when an access unit for reading reference image data includes more than one unit storage area, the access is gained by the unit storage areas and when access is switched from one unit storage area to another unit storage area, the access is switched to a unit storage area belonging to a different bank as much as possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of using a memory in a moving picture decoding apparatus, and more particularly to a method of using a synchronous DR.
The present invention relates to a method of using a two-bank memory such as an AM.

[0002]

2. Description of the Related Art Hitherto, an MPEG2 video decoder has often been implemented as an LSI alone, or as an LSI together with an MPEG program stream decoder. For example, an MPEG2 video decoder, an AC-3 (MPEG) audio decoder, a sub-picture decoder, and the like, which are necessary for configuring a DVD player, have conventionally been separately implemented as LSIs. However, the number of gates of a circuit that can be formed into an LSI has increased due to an improvement in LSI manufacturing technology, and it has been required to integrate these decoders into one LSI.

By the way, these decoders usually have
A two-bank configuration memory such as a synchronous DRAM is required as an external device. In order to achieve high integration, an external memory access required by each decoder is required.
If only the 16-Mbit synchronous DRAM occupied by the MPEG2 video decoder and the MPEG program stream decoder is used, the following problem occurs. That is, since each decoder accesses one synchronous DRAM, the memory band defined as the ratio of the number of clock cycles consumed for memory access by one decoder to the total number of clock cycles per unit time The width is restricted to be smaller than before, and it becomes difficult to ensure normal memory access by each decoder.

Therefore, it is necessary to reduce the memory bandwidth, but nearly half of the memory bandwidth is occupied by the number of clock cycles for reading reference image data.
Therefore, as an effective means for reducing the memory bandwidth, it is conceivable to reduce the number of clock cycles for reading the reference image data.

Hereinafter, a conventional method of storing and accessing reference image data in a two-bank memory will be described.

FIG. 4 is an explanatory diagram schematically showing a configuration of a page in a storage area of a two-bank configuration memory.

[0007] As shown in FIG.
The storage area of a two-bank memory such as an AM is composed of two banks a and b, and the storage area of each of the banks a and b is divided into pages to which row addresses are sequentially assigned. Each rectangle in each of the banks a and b is a page, and each page or an area obtained by dividing each page into several parts constitutes each page. Of the codes assigned to each page, Arabic numerals represent row addresses, and a and b represent bank numbers.

When the access destination is switched from one page to another page at the time of memory access, the switching is called page switching, and the one page and another page belong to different banks. When, the switching is called bank switching. In the case of a 16-megabit synchronous DRAM having a column address of 8 bits and a data width of 16 bits, the capacity of each storage area corresponding to each row address of each bank is 512 bytes.

FIG. 5 is an explanatory diagram schematically showing allocation of reference image data to unit storage areas in a conventional method of storing reference image data in a two-bank memory.
The reference image is composed of a plurality of lines.

When the reference image data is stored in the two-bank configuration memory, the data of two consecutive lines of the reference frame image or the data of each corresponding line of the reference top field image and the reference bottom field image is paired, The data is stored in the unit storage area in raster scan order. That is, as shown in FIG. 5, the reference image data is stored from left to right for every two lines of the reference image,
When the data at the right end of the two lines is stored, the data of the two lines immediately below the two lines are stored again in the order from left to right, and so on.

The storage order of the reference image data is as described above. The storage method of the reference image data in the two-bank configuration memory is as follows. First, data is stored in the unit storage area 0a of the first row address 0 of one bank a, and when the unit storage area 0a is full, the data is stored in the unit storage area 0b of the same row address 0 of the other bank b. Store. When the unit storage area 0b becomes full, data is stored in the unit storage area 1a of the next row address 1 of one bank a, and the unit storage area 1a is stored.
Is full, data is stored in the unit storage area 1b of the same row address 1 in the other bank b. Similarly, regarding the storage order between the banks, when data is stored in a certain unit storage area belonging to one bank, the data is stored in the unit storage area belonging to the other bank next,
Switching between banks is performed in a certain order. Regarding the storage order between pages, if data is stored in a certain unit storage area and a unit storage area belonging to a different bank with the same row address is vacant, the data is stored in that unit storage area, and If the unit storage area belonging to a different bank at the row address is not vacant, data is stored in the unit storage area belonging to a different bank at a row address incremented by one.

On the other hand, the access unit for reading the reference image data is, for example, 5 words (1 word = 1 word) in the case of a luminance signal.
(4 pixels) × 17 lines or 5 words × 9 lines, and in the case of a color difference signal, 5 words × 9 lines or 5 words × 5 lines. The access order of the data in the access unit is a raster scan order in which access is performed from the upper left to the lower right.

[0013]

However, when the conventional method of storing reference image data in a two-bank configuration memory as described above is adopted, when decoding NTSC image data or PAL image data, the reference image data In memory access in read access units,
Page switching occurs frequently, and the ratio of page switching without bank switching is not small. In the case of the 16-Mbit synchronous DRAM, the number of clock cycles required for bank switching is two, whereas the number of clock cycles required for page switching without bank switching is eight.
Clock. Therefore, if page switching without bank switching is included in memory access in units of access, the memory bandwidth due to reading of reference image data increases.

On the other hand, the image is divided into macro blocks,
There is a method of storing image data included in the same macro block on the same page. Here, the luminance signal contains 16 pixels × 16 pixels × 8 bits of data in the macroblock, and the color difference signal contains 8 pixels × 8 pixels × 8 bits of Cr signal data and 8 bits in the macroblock.
It is assumed that Cb signal data of pixels × 8 pixels × 8 bits is included. However, even if this data storage method is used, it is difficult to reduce the memory bandwidth unless a storage method that takes into account the 2-bank configuration of the synchronous DRAM or an access method that reduces page switching is used.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to reduce a memory bandwidth in a memory access in an access unit for reading reference image data from a two-bank memory such as a synchronous DRAM. It is an object of the present invention to provide a method of using a memory in a moving picture decoding device having a configuration capable of performing the above.

[0016]

According to a method of using a memory in a moving picture decoding apparatus according to the present invention, in a method of using a memory in a moving picture decoding apparatus for performing moving picture decoding using a two-bank memory, Dividing the storage area of each bank of the bank configuration memory into predetermined unit storage areas, dividing reference image data to be stored in the two-bank configuration memory into predetermined storage units to be stored in the unit storage areas,
Further, reference image data is stored such that storage units adjacent to each other are stored in unit storage areas belonging to different banks.

When the access unit for reading the reference image data includes a plurality of unit storage areas, access is performed for each unit storage area, and switching of access from one unit storage area to another unit storage area is performed. As far as possible, switching to a unit storage area belonging to a different bank is performed.

With the above configuration, it is possible to reduce the number of times of page switching and to eliminate page switching without bank switching. Therefore, the memory in the memory access in the access unit for reading the reference image data can be reduced. Bandwidth can be reduced.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for using a memory in a moving picture decoding apparatus according to the present invention is described below.
A page to which a storage area of each bank of the bank configuration memory is divided and row addresses are sequentially assigned, or an area obtained by further dividing the page into several sections by column addresses is used as a unit storage area, and a reference image is used as a unit storage area. It is characterized in that reference image data is stored such that storage units adjacent to each other are stored in unit storage areas belonging to different banks, respectively.

In reading reference image data from a two-bank memory, an access unit extends over a plurality of unit storage areas, and data included in each unit storage area in the access unit is accessed collectively. In the method of using the memory in the moving picture decoding apparatus according to the present invention, since the storage units adjacent to each other are stored in the unit storage areas belonging to different banks, the storage unit in the access unit is The access is performed in the order of alternately accessing the unit storage areas belonging to different banks.

By employing the storage method and the access method described above, it is possible to reduce the number of page switching in the access in an access unit for reading the reference image data, and it is necessary to switch the page. Even in this case, it is only necessary to perform “page switching with bank switching” with a small overhead without performing “page switching without bank switching” with a large overhead in the memory bandwidth, and it is possible to reduce the memory bandwidth. it can.

Hereinafter, embodiments of a method of using a memory in the moving picture decoding apparatus according to the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram schematically showing the allocation of each storage unit of reference image data to a unit storage area according to a method of using a memory in the moving picture decoding apparatus according to the first embodiment of the present invention. It is.

In the first embodiment, when decoding a PAL size image, an external 2-bank configuration memory of the decoder has a capacity of 16 Mbits, a column address of 8 bits, and a data width of 16 bits. It is assumed that a synchronous DRAM is used, and the capacity of each storage area corresponding to each row address of each bank is 512 bytes. In this case, synchronous D
Since the reference image buffer secured in the RAM may be controlled every 0.5 frame, a method of storing and accessing the reference image data in that case will be described. The configuration of the synchronous DRAM is the same as that shown in FIG.

A reference frame image or an image in which a reference top field image and a reference bottom field image are alternately arranged line by line is defined as a unit image, which is divided into macroblocks. For a luminance image, only 16 pixels × 16 pixels × 8 bits are included in a macroblock, and for a chrominance image, a Cr signal is 8 pixels ×
It is assumed that 8 pixels × 8 bits and the Cb signal include only 8 pixels × 8 pixels × 8 bits. Also, a macroblock in each column in an odd-numbered macroblock row and a macroblock in the same column in an adjacent even-numbered macroblock row below the same are respectively collected, and the two macroblocks are used as storage units.

A portion 11 surrounded by one thick line in FIG.
Shows a luminance image of 0.5 frame in PAL size, and a portion 12 surrounded by a bold line on the other side shows a color difference image of 0.5 frame in PAL size. Also,
Each of the rectangles 13 separating each image constitutes a storage unit.

The method of storing each storage unit of the luminance image data in the synchronous DRAM is as follows.

As shown in FIG. 4, the synchronous DRA
The storage area for M is divided into two banks, bank a and bank b, and each bank is further divided into storage areas for each row address. In storing the luminance image data, each storage area identified by a bank number and a row address is defined as a unit storage area. When a synchronous DRAM having a column address of 8 bits and a data width of 16 bits is used, one storage unit of luminance signal data can be stored in a unit storage area.

The storage unit is stored in raster order. That is, starting from the storage unit at the upper left corner of the luminance image and sequentially storing it to the right, and after storing one storage unit row, storage is sequentially performed from the left end of the storage unit row adjacent to the lower side to the right.

The order of the unit storage areas in which the data of the storage units should be stored is as follows. First, it is assumed that data storage is started from a certain unit storage area. Next, the bank number of the unit storage area for storing data is a value obtained by toggling the bank number of the previous unit storage area. Toggle means changing the bank number from a to b or from b to a. The row address of the unit storage area is unchanged if the bank number of the previous unit storage area is a, and is a value incremented by 1 if the bank number is b. A unit storage area is selected according to this order, and the storage units are stored in the selected unit storage area in the storage order described above.

On the other hand, for the color difference image, each storage area distinguished by the bank number and the row address, an upper area having a column address of 00h to 7Fh, and a lower area having a column address of 80h to FFh.
Each of the divided areas is defined as a unit storage area. When a synchronous DRAM having a column address of 8 bits and a data width of 16 bits is used, one storage unit of the color difference signal can be stored in the unit storage area.

The storage order of the storage units is the raster order as in the case of the luminance image.

The order of the unit storage areas in which the data of the storage units should be stored is as follows. First, it is assumed that data storage is started from a certain unit storage area. Next, the bank number of the unit storage area for storing data is a value obtained by toggling the bank number of the previous unit storage area. Also, the row address of the unit storage area is a value incremented by 1 if the bank number of the previous unit storage area is b and the lower area, and does not change otherwise. Further, the selection of the upper area / lower area of the unit storage area is changed if the bank number of the previous unit storage area is b, and
If it is not changed.

FIG. 1 shows the storage destination unit when 0.5 frame of luminance signal data and 0.5 frame of chrominance signal data are stored in the synchronous DRAM in accordance with the above storage method. It shows the address of the storage area. As shown in FIG. 1, each storage unit is stored in a unit storage area belonging to a bank having a bank number different from that of the storage unit adjacent to the upper, lower, left, and right sides.

FIG. 2 is an explanatory diagram schematically showing an access unit for reading reference image data on a reference image. A dashed line 21 is a boundary line of a storage unit, and rectangular frames 22, 23.
Indicates an example of an access unit.

The access unit for reading the reference image data is, for example, 5 words (1 word = 4 pixels) × 17 lines or 5 words × 9 lines in the case of luminance signal data. In the case of the color difference signal data, it is 5 words × 9 lines or 5 words × 5 lines. When the access unit for reading the reference image data is represented on the reference image, the access units are as shown by rectangular frames 22 and 23 in FIG. Access unit 2
In the storage units 2 and 23, there is always one vertical boundary and zero or one horizontal boundary of the storage unit.

The order of access in the access unit for reading reference image data is as follows. In the case of an access unit divided into four unit storage areas, such as the access unit 23, the readout is performed in the order of the upper left, upper right, lower right, and lower left unit storage areas. As a result, it is sufficient for the page switching during access to perform the page switching accompanied by the bank switching only three times. In the case of an access unit divided into two unit storage areas, such as the access unit 22, the access to the right unit storage area is performed after all the left unit storage areas are accessed. As a result, it is sufficient for the page switching during the access to perform the page switching involving the bank switching only once.

When a synchronous DRAM is used, an overhead in the memory bandwidth usually occurs at the time of page switching, and the page switching without bank switching has a larger overhead than the page switching with bank switching. Become.

However, by using the memory in the moving picture decoding apparatus according to the present invention as described above, it is possible to reduce the number of times of page switching and to eliminate page switching without bank switching. Therefore, it is possible to reduce the memory bandwidth in the memory access in the access unit for reading the reference image data.

For example, in the case of the frame structure and the field prediction, the moving picture decoding according to the present invention is different from the conventional technique described above, that is, the method of storing the reference image data in the synchronous DRAM in raster scan order every two lines. When the memory access is performed by the method of using the memory in the digitizing device, the memory bandwidth can be reduced by about 25%.

Similarly, in the case of the frame structure and the field prediction, the storage method of the storage unit of the reference image data is the same as that of the present invention, but the access order of the access unit is compared with the method of the raster scan order. When the memory access is performed as in the method of using the memory in the moving picture decoding apparatus according to the present invention, the memory bandwidth is set to 20.
% Can be reduced.

FIG. 3 is an explanatory view schematically showing the allocation of each storage unit of reference image data to a unit storage area according to a method of using a memory in the moving picture decoding apparatus according to the second embodiment of the present invention. It is.

In the second embodiment, when decoding an image of the NTSC size, a memory having a capacity of 16 Mbits, a column address of 8 bits and a data width of 16 bits is provided as an external 2-bank configuration memory of the decoder. It is assumed that a synchronous DRAM is used, and the capacity of each storage area corresponding to each row address of each bank is 512 bytes. In this case, synchronous D
Since the reference image buffer secured in the RAM may be controlled for each frame, a method of storing and accessing the reference image data in that case will be described. The configuration of the synchronous DRAM is the same as that shown in FIG.

A portion 31 surrounded by one thick line in FIG.
Indicates a luminance image for one frame in the NTSC size, and the other part 32 surrounded by a thick line indicates a color difference image for one frame in the NTSC size. In addition, each of the rectangles 33 separating each image constitutes a storage unit.

The synchronous DR of the reference image data
The storage method in the AM is the same as in the first embodiment.
FIG. 3 shows the storage destination unit for each storage unit when one frame of luminance signal data and one frame of chrominance signal data are stored in a synchronous DRAM according to the same storage method as in the first embodiment. It shows the address of the storage area. As shown in FIG. 3, each storage unit is stored in a unit storage area belonging to a different bank from storage units adjacent to the top, bottom, left and right.

The access method at the time of reading the reference image data is the same as that of the first embodiment, and the same effect can be obtained.

Finally, a method of using a memory in the moving picture decoding apparatus according to the third embodiment of the present invention will be described. The third embodiment uses the NTSC size or PAL
It is intended to decode an image having a size smaller than the size.

In the case of an image having a size smaller than the NTSC size or the PAL size, virtual macroblocks are added to the right and lower edges of the image, and the NTS size is virtually reduced.
After making the size the same as the C size or the PAL size, the same storage method as in the first embodiment is applied. That is, a synchronous DRAM corresponding to a virtual macro block
The upper unit storage area is not stored and is not used.

The access method at the time of reading the reference image data is the same as in the first and second embodiments. As in the first and second embodiments, the number of page switching is reduced, Page switching without switching can be eliminated.

[0050]

According to the method of using the memory in the moving picture decoding apparatus according to the present invention, the storage area of each bank of the two-bank configuration memory is divided into predetermined unit storage areas and is stored in the two-bank configuration memory. The reference image data to be stored is divided into predetermined storage units to be stored in the unit storage area, and the adjacent storage units are stored in the unit storage areas belonging to different banks. When the access unit for reading the reference image data includes a plurality of unit storage areas, access is performed for each unit storage area, and switching of access from one unit storage area to another unit storage area is possible. Switching to unit storage areas belonging to different banks as much as possible reduces the number of page switching and page switching without bank switching It is possible to almost completely eliminated. As a result, it is possible to reduce a memory bandwidth in a memory access in an access unit for reading reference image data.

For example, in the case of the frame structure and the field prediction, the moving picture decoding according to the present invention is different from the conventional technique described above, that is, the method of storing the reference image data in the synchronous DRAM in raster scan order every two lines. When the memory access is performed by the method of using the memory in the digitizing device, the memory bandwidth can be reduced by about 25%. Similarly, in the case of the frame structure and the field prediction, the storage method of the storage unit of the reference image data uses the same method as in the present invention, but the access order of the access unit is smaller than that of the raster scan order. When a memory access is performed as in the method of using the memory in the moving picture decoding apparatus according to the present invention, the memory bandwidth is set to 2
It can be reduced by about 0%.

For example, the extra memory bandwidth is as follows.
It can be used for other memory accesses, such as increasing the amount of access to the video STD buffer and OSD area. Conversely, power consumption can be reduced by reducing the clock frequency.

Further, it is possible to configure a system such as a DVD player using a low-cost synchronous DRAM having a small capacity, so that the price of the entire system using the synchronous DRAM can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram schematically showing allocation of reference image data to a unit storage area of a reference image data according to a method of using a memory in a video decoding device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram schematically showing an access unit for reading reference image data on a reference image.

FIG. 3 is an explanatory diagram schematically showing assignment of reference image data to each unit storage area in a moving image decoding apparatus according to a second embodiment of the present invention, based on a method of using a memory.

FIG. 4 is an explanatory diagram schematically showing a page configuration in a storage area of a two-bank configuration memory.

FIG. 5 is an explanatory diagram schematically showing allocation of reference image data to unit storage areas in a conventional method of storing reference image data in a two-bank configuration memory.

[Explanation of symbols]

11 Luminance image for 0.5 frame in PAL size 12 Color difference image for 0.5 frame in PAL size 13 Storage unit 21 Boundary line of storage unit 22, 23 Access unit 31 Luminance image for 1 frame in NTSC size 32 NTSC Color difference image for one frame in size 33 Storage units a, b Bank numbers 0a to 14a,. . . , 0b-14b,. . . Page address

Claims (2)

[Claims] 1. A method of using a memory in a moving picture decoding apparatus that performs moving picture decoding using a two-bank configuration memory, comprising: dividing a storage area of each bank of the two-bank configuration memory into a predetermined unit storage area; The reference image data to be stored in the two-bank configuration memory is divided into predetermined storage units to be stored in the unit storage area, and the storage units adjacent to each other belong to the different banks. A method of using a memory in a moving image decoding apparatus, wherein the reference image data is stored so as to be stored in an area. 2. The method of using a memory in the moving picture decoding apparatus according to claim 1, wherein when the access unit for reading the reference image data includes a plurality of unit storage areas, access is performed for each of the unit storage areas. A moving image decoding apparatus, wherein switching of access from one unit storage area to another unit storage area is, as much as possible, switching to the unit storage area belonging to a different bank. How to use memory in