Dynamic information storage or retrieval – Control of storage or retrieval operation by a control...
Reexamination Certificate
1998-12-11
2001-07-10
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
C369S053200, C369S053410
Reexamination Certificate
active
06259659
ABSTRACT:
FIELD OF INVENTION
This invention relates to information storage equipment and more particularly to optical information storage equipment.
BACKGROUND OF THE INVENTION
Different types of information can be digitally represented and stored on optically read discs. Compact Disc (CD) drives and Digital Versatile Disc (DVD) drives may be used to read the information from the discs. Examples of media that may be read using a CD or DVD drive are Compact Disc-Digital Audio (CD-DA), Compact Disc-Read Only Memory (CD-ROM), Compact Disc-Recordable (CD-R), Compact Disc-ReWritable (CD-R/RW and CD-RW), and Digital Versatile Disc-Read Only Memory (DVD-ROM).
While all CD fonnats define sectors having a length of 2352 bytes, the composition of information contained in the sectors differs depending on the format. The data size may be less than the full 2352 bytes if other information, such as error checking or correction coding, is included within the sector. CD-DA discs contain digitally encoded audio information organized into sectors containing 2352 bytes of data without sector level error checking or correction capabilities. In comparison, CD-ROM discs contain a variety of digital computer data including text, data records, and multimedia information such as graphics, audio, and video. Information on CD-ROM discs may be organized according to a variety of different sector formats, as indicated by a sector's MODE and FORM data fields. For example, a standard (Mode-1) CD-ROM sector contains 2048 bytes of data, but a multimedia (Mode-2, Form-2) CD-ROM/XA sector contains 2324 bytes of data. There are three modes defined for CD-ROM. These are Mode-0, Mode-1, and Mode-2. The currently defined Modes in the CD-ROM specification are shown below in Table 1.
TABLE 1
Mode
Data Size
Characteristics
Mode-0
2336 Bytes
Contains all zeros in the data field
Mode-1
2048 Bytes
Contains real data in addition to
error-detection and correction
capabilities
Mode-2
No Form
2336 Bytes
Contents further depend on the Form
Form-1
2048 Bytes
Field
Form-2
2324 Bytes
A Mode-2 sector format may further be one of several defined forms: “No Form,” Form-1, or Form-2. The currently defined forms for a Mode-2 CD-ROM sector and the available features are shown below in Table 2.
TABLE 2
Subheader
&
MODE
Synchro-
Duplicate
Error
Error
2
nization
Header
Subheader
Data
Detection
Correction
FORM
Field
Field
Field
Field
Field
Field
No
Yes
Yes
No
Yes
No
No
Form
Form-1
Yes
Yes
Yes
Yes
Yes
Yes
Form-2
Yes
Yes
Yes
Yes
No
No
As seen in the tables above, error detection and correction depend on the sector type and format of the CD-ROM. While CD-DA discs typically contain no sector level error detection or correction, a CD-ROM may or may not contain error detection and/or correction information depending on the sector format indicated by the mode and form fields.
Systems capable of reading different formats of optical discs must be able to differentiate between the formats to properly read and access the stored information. Typically, software or firmware has been used to examine the mode and form fields of the sector format to determine the format of a CD-ROM. These software and firmware techniques require a microcontroller or microprocessor to frequently access the stored information to determine its format. Accessing the sector fields to determine the mode and form causes delays that may result in bottlenecks for the drive. This is especially true as the speed of CD-ROM data reads becomes faster. In the early 1990's CD-ROM's were operating at up to the quad-speed (4×) level. In 1998, it is not uncommon to find CD-ROM's operating at 32× and beyond. As speeds have increased, challenges have arisen in the area of error detection and correction, as well as in other areas dependant on control of the CD sectors being serially transferred from the disc to the buffer.
As CD-ROM speeds increase, there is an increased need for fast buffer accesses. In order to effectively stream data from the optical disc to the host computer or device, it becomes desirable to reduce the delays associated with frequent microprocessor or microcontroller accesses. Needed is a device to determine the information storage format that minimizes the impact on system resources.
Economic pressures are making it more desirable to use less expensive, lower performance microprocessors and microcontrollers. When used with existing format detection and selection systems, these lower performance devices make it more difficult to achieve high data access speeds.
Hardware has been used to automate and streamline a limited portion of the format identification process, such as detecting the Q-Channel CD-ROM bit to determine whether the current sector is a CD-ROM sector. However, it would be desirable to use logic circuitry in conjunction with other hardware to automate the entire process, including identification of mode and form, in order to improve access speeds while allowing the use of less expensive, lower performance microprocessors and microcontrollers.
SUMMARY OF THE INVENTION
In accordance with an illustrative embodiment of the present invention, problems associated with identifying the format of a sector from an optical disc, and automatically adjusting the size of the data field in buffer memory are addressed. In an illustrative embodiment, the present invention provides a method and apparatus for efficiently determining the type, mode, and form of information on a sector of an optical disc, and for setting the data field size and organization based on the type, mode, and form. A novel hardware-based solution is presented, resulting in faster operation than the software/firmware-based solutions typically in use today.
The sector must first be determined to be a CD-DA type or CD-ROM type sector. A CD-DA sector consists entirely of audio data with no sector level error checking/correcting capabilities. A CD-ROM sector can be any one of several formats, requiring further differentiation after the first step of determining the type is complete.
To automatically determine whether the sector is CD-DA or CD-ROM data, the sector information on the CD is split into a data portion and a subcode portion. In the preferred embodiment, the decoder logic examines the subcode to determine the type of disc. The subcode may further comprise a plurality of channels. One of the plurality of channels, the Q-channel in the present embodiment, includes control information regarding the type of the disc. Decoder logic determines the type of the sector by automatically decoding the Q-channel as it is received from the disc. The first full byte of data in the Q-Channel contains a data-type indicator bit (bit-
6
), called the CD-ROM bit, which differentiates between CD-ROM data (the bit is set high) and CD-DA data (the bit is set low).
If a CD-ROM sector is detected, the decoder logic determines the mode of the CD-ROM sector. To automatically determine the mode of a CD-ROM sector, the decoder logic detects the header field, extracts the mode byte, and determines the proper mode of the sector. In this present example, CD-ROM sectors generally begin with a 12-byte “Sync” field followed by a 4-byte “Header” field. The fourth byte of the header field is the mode byte. Bits
1
:
0
of this byte are used to determine the mode of the sector.
If a Mode-2 sector format is detected, the decoder logic further determines the form of the sector. This invention uses hardware to detect the existence of a subheader field, extract the submode byte, and determine the proper form of the sector. The subheader field of a Mode-2 sector consists of four bytes of information repeated once (a total of eight bytes). The third and seventh byte is the “submode” byte and contains the form information. The first four-subheader bytes are compared with the second four subheader (duplicate subheader) bytes. If the bytes do not match, then the sector is determined to be “no form.” If the bytes do match, then the fifth bit of the third subheader byte is polled. If it has a low logic level, the sector i
Fechser David A.
Manter Venitha L.
Edun Muhammad
LSI Logic Corporation
LandOfFree
Method and apparatus for configuring a sector map for an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for configuring a sector map for an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for configuring a sector map for an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2489088