Method and device for reproducing data

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a disc data playback method and a disc data playback device suitable for playing back data such as video or audio recorded on an optical disc, a magneto-optical disc, or the like, and in particular, special playback such as reverse playback. It relates to a data reproduction method and a data reproduction device that can be quickly performed.

【0002】

[Conventional technology]

The MPEG (Motion Picture coding Experts Group) method has been proposed as a method for compressing and coding a digital image signal recorded on a conventional digital video disc (hereinafter referred to as DVD), and is used for an MPEG encoder. An example will be described with reference to FIG. The MPEG encoder is an encoder that compresses by predictive coding, and the digitized image input signal is blocked in the motion detection circuit 101 for each block (MB), which is the smallest unit of motion compensation prediction. The motion vector for motion compensation prediction is detected for each block.

【0003】

This block is predictively coded in the subsequent predictive coding section, but (1) an intra block that directly DCTs the image input signal (Discrete Cosine Transform), and (2) a forward block that predicts only from the forward direction. It is classified into four types: (3) backward block that predicts only from the backward direction, and (4) bipredictive block that predicts from both directions.

【0004】

That is, DCT, which is a kind of Fourier transform, is applied to DCT 103, and the resulting DCT coefficient is quantized in the quantization circuit 104. Further, after the quantization is performed, the variable-length coding means 109 is assigned a code having a different length according to the probability of occurrence, so that the variable-length coding is performed. Further, the quantized signal is dequantized in the dequantization circuit 105, further dequantized in the inverse DCT 106, and the output from the frame memory predictor 108 is added to obtain the original image signal. Will be played. The reproduced image signal is supplied to the subtractor 102 as a prediction signal.

【0005】

The predictive coded signal output from the variable length coding means 109 is multiplexed with the predictive mode information and the motion vector information in the multiplexing means 110, but these multiplexed data are generated at an irregular rate. Therefore, it is temporarily stored in the buffer 111 and output so that the coding rate becomes constant. In addition, in order to make the average of the coding rates constant, the coding amount may be controlled by changing the quantization scale factor q of the quantization means 104 according to the coding amount stored in the buffer 111. ..

【0006】

The structure of the inter-frame prediction compressed and coded by the MPEG method in this way is shown in FIG. 10 (a). In this figure, 1GOP (Group Of Picture) is composed of, for example, 9 frames, I picture is 1 frame, P picture is 2 frames, and the remaining 6 frames are B pictures, and 1GOP is composed. GOP is a coding unit that divides one sequence of moving images. This I-picture is a predictively coded image within the frame, and the P-picture is an inter-frame predictive coding that predicts by referring to the already coded time-previous frame (I-picture or P-picture). It is a coded image, and the B picture is a frame-to-frame predictive coded image that is predicted by referring to two frames before and after in time.

【0007】

That is, as illustrated by the arrow, I picture I₀ Is predictively coded only within that frame, P picture P₀ Is I picture I₀ It is predictively coded between frames with reference to P-picture P.₁ Is P picture P₀ It is predictively coded between frames with reference to. In addition, B picture B₀ , B₁ Is I picture I₀ And P picture P₀ It is predictively coded between frames with reference to the two, B picture B₂, B₃ Is P picture P₀ And P picture P₁ It is predictively coded between frames with reference to the two. Hereinafter, the subsequent pictures are created by predictive coding in the same manner.

【0008】

By the way, in order to decode such a predictively coded picture, since the I picture is predictively coded in the frame, it can be decoded only by the I picture, but the P picture is temporal. Since it is predictively coded with reference to the previous I-picture or P-picture, the previous I-picture or P-picture in time is required for decoding, and the B-picture is the I-picture or P-picture before and after in time. Since it is predictively coded with reference to, I-pictures or P-pictures before and after the time are required at the time of decoding. Therefore, the pictures are replaced as shown in FIG. 10 (b) so that the pictures required for decoding can be decoded first.

【0009】

This replacement is B picture B as shown in the figure._-1, B_-2Is I picture I when decoding₀ B picture B because it requires_-1, B_-2More I picture I₀ B picture B so that₀ , B₁ Is I picture I when decoding₀ And P picture P₀B picture B because it requires₀ , B₁ More P picture P₀ Similarly, B picture B so that₂ , B₃ Is P picture P when decoding₀ And P picture P₁ B picture B because it requires₂ , B₃ More P picture P₁ B picture B so that₄ , B₅ Is P picture P when decoding₁ And I picture I₁ B picture B because it requires₄ , B₅ More I picture I₁ Has been replaced so that it precedes.

【0010】

Then, the I picture, the P picture, and the B picture are recorded on the DVD in the order shown in FIG. 10 (b), but since these pictures are predictively coded as described above, the amount of the code is each. The amount of code is not constant in the picture and varies depending on the complexity and flatness of the image. Therefore, in order to facilitate the handling of data, when recording these pictures on a DVD, the data is recorded using a sector defined by a fixed code amount. The mode of recording by this sector is shown in FIG. 11, for example, I picture I.₀ Is recorded in a part of sector m, sector (m + 1) and sector (m + 2), B picture B_-2Is recorded in the remaining area of sector (m + 2) and sector (m + 3). Hereinafter, each picture is sequentially recorded in a sector, and in this example, 1 GOP is recorded in a sector of sector m to sector (m + 13). However, GOP is not always recorded with such a number of sectors, and the amount of code differs depending on the complexity and flatness of the image. Therefore, the number of sectors for recording 1 GOP is generally different.

【0011】

The data read from the DVD in units of sectors is temporarily stored in a storage means (ring buffer) that is virtually represented as a ring shape called a ring buffer, and the read pointer and write pointer in the ring buffer are temporarily stored. The operation will be described with reference to FIG. In FIG. 12A, the read pointer RP is located at the address position of a1 in the ring buffer, and the write pointer WP is located at the address position of b1 slightly before a1. The ring buffer reads data in sector units and supplies the data to the decoder while moving the read pointer in the clockwise direction shown in the figure.

【0012】

In addition, by controlling the write pointer WP to be positioned slightly before a1 in terms of time, the unread area (URD) is set as large as possible so that there is no shortage of data to be reproduced. Therefore, the read area (ARD) is a small area between a1 and b1, but this area may be controlled to be zero. Then, the state in which the read pointer RP is advanced and the data is read from the ring buffer is the state shown in FIG. 6B, and the address position of the read pointer RP advances from a1 to a2. Therefore, the URD area is reduced by the amount of advancement of the address position, while the ARD area is increased by that amount.

【0013】

Therefore, as shown in Fig. (C), the data is written to the ring buffer while advancing the write pointer WP clockwise so as to increase the unread area URD. In this case, the data is the data newly read from the disk. As a result, the address position of the write pointer advances from b1 to b2, the ARD area becomes smaller by that amount, and the URD area becomes larger by that amount. By performing such control, a large URD area is always secured in the ring buffer.

【0014】

[Problems to be Solved by the Invention]

However, when the data in units of sectors recorded on the DVD is read from the ring buffer and the video signal is being played back, if special playback such as reverse playback is attempted, for example, at the moment when switching to reverse playback is performed. Since there is almost no data in the reverse direction (that is, ARD data) to be played back in the ring buffer, it is necessary to wait for the data to be read by accessing the DVD, and smooth forward / reverse playback cannot be switched. There was a problem. That is, in order to decode the video signal displayed on the display unit during reverse playback, it is necessary to access and read the DVD by picking up the data of the previous GOP in time following the current GOP. This is because this reading is mechanical and takes time, and it takes time to decode the picture constituting the read GOP and obtain a video signal.

【0015】

Here, the reason why decoding takes time will be described. The GOP immediately before the current GOP is the I picture I shown in FIG. 10 (a) above.₀ Or B picture B₅ Assuming that it is composed of I picture I of the current GOP to perform reverse playback₁ After the decoded video, B picture B₅ Display the decoded video, then B picture B₄ , P picture P₁ , B picture B₃ , B picture B₂ , P picture P₀ , B picture B₁ , B picture B₀ , I picture I₀ It is necessary to perform reverse playback by displaying the decoded video.

【0016】

However, B picture B₅ , B picture B₄ Is I picture I₁ And P picture P₁ Since it was predicted by referring to and, I picture I at the time of decoding₁ And P picture P₁ Despite the need for data with P picture P₁ Is P picture P₀ It was predicted with reference to P picture P₀ Is I picture I₀ After all, I picture I₀ P picture P by decoding and referencing₀ Decode and then P picture P₀See P Picture P₁ Must be decoded. And I picture I decoded in this way₁ And P picture P₁ See and B Picture B₅ , B picture B₄ It takes time to decode because it has to decode.

【0017】

Therefore, an object of the present invention is to provide a data reproduction method and a data reproduction apparatus capable of promptly performing special reproduction even at the time of special reproduction such as reverse reproduction.

【0018】

[Means for solving problems]

In order to achieve the above object, in the data reproduction method of the present invention, the data read by the pickup from the disk is demodulated and written to the storage means, and the original video is obtained by decoding the data read from the storage means. In the data reproduction method for reproducing a signal, the storage means is controlled so that the unread data area and the read data area in the storage means are about half of the total storage capacity. ..

【0019】

Further, in the data reproduction method, the data is controlled so as to be written to the storage means in units of sectors having a fixed amount of data.

【0020】

Further, the data reproduction device of the present invention that achieves the above object includes a demodulation means for demodulating data read by a pickup from a digital video disk, a storage means for temporarily writing the demodulated data, and the storage means. In a data reproduction device including a decoder that decodes the data read from the original video signal, the unread data area and the read data area in the storage means are about half of the total storage capacity. , The control circuit for controlling the storage means is provided.

【0021】

Further, the control circuit in the data reproduction device writes the data to the storage means in units of sectors having a fixed amount of data.

【0022】

[Action]

According to the present invention, since the storage means is controlled so that the unread data area and the read data area in the storage means are about half of the total storage capacity, the data required for reverse reproduction or the like is controlled. Remains in the storage means, so special playback can be performed quickly. Furthermore, for the same reason, switching from special playback to normal playback can be performed quickly. As described above, according to the present invention, by always storing the past data in the buffer, the number of disk accesses can be reduced, and special reproduction can be performed only by controlling the buffer even during normal reproduction.

【0023】

[Example]

FIG. 1 shows a conceptual diagram of a data playback device (DVD player) according to an embodiment of the present invention. In this figure, 1 is a disk (DVD) as a storage medium in which digital video data, digital audio data, etc. are compressed and encoded by the MPEG method and recorded in sector units, and 2 is recorded by accessing disk 1. Pickup as a reproduction means to read out the digital data, 3 is a sector detection circuit that detects sector sync and sector address from the digital data read from disk 1, and 4 is a sector unit under the control of control circuit 8. The data read from the disk 1 is written, and the ring buffer (storage means) that supplies the read data to the decoder 5 as needed, and 5 displays the data in units of the supplied sectors. It is a decoder that decodes the video signal displayed on the device.

【0024】

Furthermore, 6 is a frame memory that stores three frames decoded by the decoder 5, 7 is a display that displays the video signal supplied from the frame memory 6, and 8 is various controls such as a tracking servo circuit 9 as an access means. A control circuit (control means) that sends a signal to perform tracking control, thread control, focus control, etc., and controls writing / reading of the ring buffer 4, and 9 accesses disk 1 under the control of control circuit 8. This is a tracking servo circuit that controls the tracking of pickup 2 in order to do so.

【0025】

The operation of the data reproduction device configured in this way will be described below. The disk 1 is rotation-controlled by a spindle motor (not shown) so as to rotate at a predetermined rotation speed, and when the track of the disk 1 is irradiated with a laser beam from the pickup 2, it is compressed and encoded recorded on the track. Digital data is read out. This digital data is recorded in units of the fixed-length sectors shown in FIG. 11 described above, and a sector sink and a sector header are added to the head of each sector.

【0026】

The digital data read from the pickup 2 is input to the sector detection circuit 3, and the sector sync is detected to detect the sector delimiter, and the sector address and the like are detected from the sector header to detect the control circuit 8. Is supplied to. The focus control and tracking control of the pickup 2 are performed by the tracking servo circuit 9 or the like under the control of a system control (not shown) by the focus error signal and the tracking error signal obtained from the information read from the pickup 2. There is.

【0027】

Then, the control circuit 8 controls the writing of data in units of the sector to the ring buffer 4 based on the detected sector address. The write address in this case is indicated by the write pointer (WP) 8-1 in the control circuit 8. The buffer 5 has a storage capacity capable of storing at least 2 GOP of digital data. Further, for example, a GOP composed of pictures in the order shown in FIG. 10B is read from the ring buffer 4 in units of sectors and supplied to the decoder 5 to form the GOP. The I picture, P picture, and B picture are decoded and written to the frame memory 6 in sequence.

【0028】

The picture is output from the decoder 5 to the frame memory 6 in the order of the pictures shown in FIG. 10B, and is written to the frame memories M1, M2, and M3 constituting the frame memory 6. Here, FIG. 2 shows an example of the decoded frame written in the frame memories M1, M2, and M3 during normal playback. When FIG. 2 is explained with reference to FIG. 10, the state 1 is I picture I.₀ I obtained by decoding₀ The frame is written to frame memory M1 and I picture I₀ A P frame that decodes a P picture that precedes it, and a decoded I in the frame memory M1.₀ B picture B decoded with reference to the frame_-2, B_-1Are written to the frame memories M2 and M3, respectively. In this state 1, from the frame memories M1, M2, M3, B shown in FIG. 10 (a)_-2, B_-1, I₀ It is rearranged in the original image order of the frame and sent to display 7, where the image is displayed.

【0029】

Next, in state 2, ring buffer 4 to P picture P₀ Sector is read and I in frame memory M1₀ It is decoded by referring to the frame and written to the frame memory M2. Then proceed to state 3, B picture B₀ Sector is read from ring buffer 4 and I in frame memory M1₀ Frame and P in frame memory M2₀ It is decoded by referring to the frame and written to the frame memory M3. And B₀ The frame is read from the frame memory M3 and sent to the display 7, and the image is displayed and the state 4 is set.

【0030】

In this state, B picture B₁ Sector is read from ring buffer 4 and I in frame memory M1₀ Frame and P in frame memory M2₀B picture B by referencing the frame₁ Is decoded and written to the frame memory M3. And B₁ , I₀ The images are sent from the frame memories M3 and M1 to the display 7 in the order of frames, and the images are displayed.

【0031】

In the following state 5, ring buffer 4 to P picture P₁ Sector is read and P in frame memory M1₀ It is decoded by referring to the frame and written to the frame memory M1. Then proceed to state 6, B picture B₂ Sector is read from ring buffer 4 and P in frame memory M1₁ Frame and P in frame memory M2₀ Decoded by referencing the frame, decoded B picture B₂ Is written to the frame memory M3. And B decoded from the frame memory M3₂ The frame is read out and sent to the display 7, and the image is displayed. Decoded in the same way below, B₃ , P₁ , B₄ , B₅ The images are sent to the display 7 in the frame order of ..., and the images are displayed in sequence.

【0032】

The video is displayed in this way during normal playback, and the movements of the write pointer WP and read pointer RP on the ring buffer 4 during normal playback will be described with reference to FIG. FIG. 4A shows a case where the read pointer RP8-2 is at the address position R1 and the write pointer WP8-1 is at the address position W1. Writing / reading is done in this direction. Since the address position R1 and the address position W1 are located so as to face each other on the ring buffer 4, the unread data area URD and the read data area ARD are considered to be substantially the same size.

【0033】

Then, the state in which the read pointer RP8-2 advances to the address position R2 and the data is read from the ring buffer 4 is the state shown in FIG. It has increased. This is detected by the control circuit 8, and the pickup 2 is controlled to access the disk 1 to read new data, and the write pointer WP8-1 is advanced to the address position W2 shown in the figure (c). It is controlled so that the read one sector data is written to the ring buffer 4. As a result, the unread data area URD and the read data area ARD are again set to have substantially the same size. The control circuit 8 performs such control at any time, and the unread data area URD and the read data area ARD are controlled so as to always have substantially the same size. In this case, when new data is not read from the disk 1, the pickup 2 is controlled to jump one track and read the data on the same track.

【0034】

By the way, when the operation button is operated from the normal playback mode, for example, in the reverse playback mode, the past video already played during the normal playback is decoded in the order in which the time is reversed, and the decoded video is decoded in the frame memory 6 In the case of the present invention, when the reverse playback mode is set, the data already read in the ring buffer 4 is stored in the read data area ARD as shown in FIG. Since it is stored, the read / write of the ring buffer 4 is simply controlled by the control circuit 8 so that the reverse playback is performed, and the pickup 2 is controlled backtracking to quickly display the reverse playback video without reading new data. It can be displayed on the display 7.

【0035】

Here, the relationship between the picture decoded by the decoder 5 in the reverse playback mode and the frame stored in the frame memories M1, M2, and M3 will be described with reference to FIG. State 0 in Figure 3 is frame B₃ After decoding up to I picture I₁ Is decoded and stored in the frame memory M1. In the reverse playback mode, in the array shown in FIG. 10A, the decoded frames must be sent to the display 7 in the order from the right to the left for display.₁ , B₃ Frame is P₁ , B₃ The frames are sent from the frame memories M2 and M3 to the display 7 in the order of, and the image is displayed on the display 7. Then B₂ First, I picture I because I need to send a frame₀ Is read from the ring buffer 4, decoded, and stored in the frame memory M1 (state 1). Then, P picture P₀ Is read from the ring buffer₀ The frame is referenced, decoded, and stored in frame memory M3 (state 2). And B picture B₂ Is read from ring buffer 4 and P₁ Frame and P₀ The frame is referenced and decoded, stored in frame memory M1 and sent to display 7 B₂ The image of the frame is displayed (state 3).

【0036】

Then I picture I₀ Is read from the ring buffer 4 again, decoded, and stored in the frame memory M2 (state 4). Then B picture B₁ Is read from ring buffer 4 and P₁ Frame and P₀ The frame is referenced and decoded, stored in frame memory M1 and sent to display 7 to B₁ The frame image is displayed (state 5). Then, B picture B₀ Is read from ring buffer 4, and P is similarly₁ Frame and P₀ The frame is referenced and decoded, stored in frame memory M1 and sent to display 7 to B₀ The frame image is displayed (state 6).

【0037】

Next, the movement of the write pointer WP and the read pointer RP during such reverse playback will be described with reference to FIG. In FIG. 6A, the GOP stored in the area from the address position R3 to the address position R4 of the ring buffer 4 is being decoded, and the read pointer RP is in this area. The unread data area URD is the area from the address position R3 to the address position W3 including the area being decoded, and the remaining area is the read data area ARD. The write pointer WP is located at a position substantially opposite to the address position R3. However, since it is in reverse playback, the counterclockwise direction is set as the playback direction in the ring buffer 4.

【0038】

Then, the state in which decoding has progressed to the next GOP is the state shown in FIG. 3B, and the GOP stored in the area from the address position R4 to the address position R5 is read from the ring buffer 4 and decoded. ing. In such a state, the area of the unread area URD becomes small, so that the control circuit 8 controls the pickup 2 back and forth to read new past data from the disk 1. At the same time, the write pointer WP is jumped from the address position W3 to the address position W4, and the data read from the disk 1 is written to the ring buffer 4 while moving the write pointer WP clockwise. In this case, the write pointer WP8-1 for the area where the number of sectors sum of the number of sectors written last time and the number of sectors written this time can be written is controlled to jump.

【0039】

By the way, in the compression by MPEG, as described above, the I picture must be read first before the code can be coded because it is another picture in the GOP. Therefore, even if the GOP is read in order from the subsequent picture during reverse playback, it cannot be decoded. Therefore, write down which sector each GOP is composed of in the TOC recorded at the beginning of disk 1. The control circuit 8 remembers this, jumps the read pointer RP to the beginning of the GOP at the time of reverse playback, is controlled to return while decoding in order from the I picture, and decodes the picture to be output next. There is.

【0040】

The detailed movement of the read pointer RP during such reverse playback is shown in Fig. 7, and the detailed movement of the write pointer WP is shown in Fig. 8. As shown in these figures, the read pointer RP and the write pointer WP move. As a result, as shown in FIG. 3, each decoded frame can be stored in the frame memories M1, M2, and M3. FIG. 7 (a) is the same figure as FIG. 6 (a), but the portion surrounded by the broken line in this figure is enlarged and shown in FIG. 6 (b). As shown in this figure, when decoding the GOP, the read pointer RP first jumps from the address position R3 to the address position R4 in the playback direction and reads out the I picture at the beginning of the GOP.

【0041】

Next, the read pointer RP is jumped by one in the direction opposite to the playback direction to read the P picture, then jumps by one in the same direction to read the next P picture, and then moved toward the address position R3. Read the adjacent B picture. Then, the read pictures are sequentially decoded by the decoder 5, so that the decoded frames are stored in the frame memories M1, M2, and M3 as shown in FIG. In this way, in the reverse playback mode, the GOP unit is decoded toward the past, but in the GOP, it is necessary to first decode each picture referenced at the time of encoding as described above. The picture is read out and decoded in the direction opposite to the playback direction.

【0042】

Further, FIG. 8 (a) is a diagram in the same state as FIG. 6 (c), and the portion shown by the broken line is enlarged and shown in FIG. 6 (b). In this figure, the read pointer WP located at the address position W3 jumps to the address position W4 at the time of data writing, but this jump position is previously moved from the address position W3 to the area of the address position W4 as described above. The data of the number of sectors obtained by adding the number of sectors written and the number of sectors written this time is defined as the writable address position. Then, while returning from the address position W4, the sectors S0, S1, S2, S3, S4, S5 ... Are written.

【0043】

In this way, the data in the GOP is arranged and written in the same direction as during normal playback, but when the reverse playback mode is set, write from before the next sector that was scheduled to be overwritten during normal playback. In addition, the control circuit 8 controls the light pointer WP. That is, as shown in FIG. 5A, when the sector 25 is scheduled to be overwritten during normal playback, the write pointer WP is jumped to the position of the sector 106 when writing the three sectors from the sector 22 to the sector 24. Sector 22 is overwritten on it, and then sectors 23 and 24 are overwritten on sectors 107 and 108.

【0044】

It is natural that the unread data area URD (or read data area ARD) at the time of normal reproduction is reversed from the read data area ARD (or unread data area URD) at the time of reverse reproduction. As described above, the control circuit 8 controls the writing / reading of the ring buffer 4 so that the storage area of the ring buffer 4 is roughly divided into the unread data area URD and the read data area ARD. This makes it possible to quickly respond not only to frame advance in reverse playback mode but also to slow playback, double speed and other variable speed playback.

【0045】

Further, it becomes possible to support variable speed reproduction not only during reverse reproduction but also during normal reproduction. In addition, when the speed change reproduction mode is set, for example, only the I picture or only the I picture and the P picture may be reproduced to correspond to the speed change reproduction such as double speed. The disk 1 can be an optical disk or a magneto-optical disk.

【0046】

[Effect of the invention]

As described above, the present invention controls the writing / reading of the storage means so that the unread data area and the read data area in the storage means are about half of the total storage capacity. You will be able to quickly display special playback. Furthermore, for the same reason, it becomes possible to quickly display when switching from special playback to normal playback. As described above, according to the present invention, by always storing the past data in the buffer, the number of times of disk access is reduced, and even during normal reproduction, special reproduction can be performed only by controlling the storage means.

[Simple explanation of drawings]

[Figure 1]

It is a conceptual diagram which shows the structure of the Example of the data reproduction apparatus of this invention.

[Figure 2]

It is a figure which shows the frame after decoding which is stored in the frame memory at the time of normal reproduction in the data reproduction apparatus of this invention.

[Fig. 3]

It is a figure which shows the frame after decoding stored in the frame memory at the time of reverse reproduction in the data reproduction apparatus of this invention.

[Fig. 4]

It is a figure explaining the movement of the write pointer and the read pointer at the time of normal reproduction in the data reproduction apparatus of this invention.

[Fig. 5]

It is a figure explaining the movement of the light pointer at the time of reverse reproduction in the data reproduction apparatus of this invention.

[Fig. 6]

It is a figure explaining the movement of the write pointer and the read pointer at the time of reverse reproduction in the data reproduction apparatus of this invention.

[Fig. 7]

It is a figure explaining in detail the movement of the read pointer at the time of reverse reproduction in the data reproduction apparatus of this invention.

[Fig. 8]

It is a figure explaining in detail the movement of the light pointer at the time of reverse reproduction in the data reproduction apparatus of this invention.

[Fig. 9]

It is a figure which shows the structural example of the encoder which encodes a digital moving image signal in MPEG.

[Fig. 10]

It is a figure which shows the structure of the inter-frame prediction in GOP, and the structure of a recording frame.

[Fig. 11]

It is a figure which shows the relationship between the sector recorded on an optical disk, and the picture which constitutes GOP.

[Fig. 12]

It is a figure explaining the movement of a read pointer and a write pointer in a ring buffer.

[Explanation of symbols]

1 disk 2 pickup 3-sector detection circuit 4 Ring buffer 5 decoder 6 frame memory 7 display 8 control circuit 9 Tracking servo circuit