Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2001-02-02
2004-03-02
Dildine, R. Stephen (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S769000
Reexamination Certificate
active
06701481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recording apparatus and a recording system having a disk-shaped recording medium or the like, and an error notification method used in the same, and particularly to a recording apparatus, a recording system and an error notification method that are preferably used in recording audio signals and moving pictures.
2. Description of the Related Art
A disk drive, which is one type of recording apparatus, receives input and output commands such as read command and write command through a disk interface, and records data in a specified recording area (sector) or reads data from a specified recording area (sector).
The disk drive incorporates a recording medium. The recording medium is divided into divisions called tracks having concentric or spiral configuration. The track is further divided into divisions of the same lengths called sectors. Data are recorded in the sectors. While the recording medium is rotating, a head disposed to oppose the surface of the recording medium is moved by an actuator in the radial direction of the recording medium thereby to position the head above a target location of the recording medium, where the data are read or written.
However, signal level recorded on the recording medium may deteriorate. Positioning of the head may also fail due to mechanical vibration or electrical noise generated when reading or writing the data. Thus one often encounters missing error where a part of the data could not be read and is not represented, or mutation error where read data or written data is misrepresented to have a value different from the true value.
In the prior art, as measures to solve the problem of missing error or mutation error, error control code (ECC) is written in the recording medium for detecting and correcting errors, in addition to the contents data.
In this case, when an error is found in the contents data with the error control code that has been read, correction is attempted by means of an error correction circuit. When the error cannot be corrected by this operation, an error detection signal is output.
In a case where the error correction circuit fails to correct the error, error processing means makes an attempt to read the data again, repeating the attempt till correctable data are successfully read. In a case where the error cannot be corrected after a certain number of retrials, the error correcting means determines that a data error has occurred.
A number of disk drives such as that described above have been used in computer systems dedicated to computation or database management. In such systems, requests to the disk drive for input or output of data and processing of the input or output data are all carried out by a general-purpose processor.
Due to the characteristics of the data to be input or output, there is not such a demanding limitation on the time taken in input and output of data as in the case of program and database data. However, in many cases, even a single error may render the rest of the data meaningless even when they are correctly read.
For these reasons, the disk drive of the prior art is designed to make retrials of reading data over a considerable length of time (several seconds to ten seconds per sector), in case an error cannot be corrected. In a case where the data cannot be read after retrials of reading, and the error processing means has determined that a data error occurred, output of the data is interrupted and an interrupt request is placed on the general-purpose processor, that has made the output request, thereby to notify the occurrence of error thereto.
In recent years, increase in the data storage capacity of the disk drive and the advancements in the compression technology for moving picture data have led to the development of many systems such as video servers that store audio and video data on disk drives.
The audio and video data have two features distinct from the data handled in the conventional computer systems. The first feature is that there is a limitation on the time that is allowed for the input/output from/to the disk (recording medium) when recording a broadcast program or reproducing the data on a TV monitor. That is, it is not allowed to make many attempts to read data. Another feature is that the presence of uncorrectable error does not make it meaningless to read the rest of the data, because disturbance due to the data error is restricted within the vicinity of the erroneous data.
Recently, from the point of view described above, such improvements of the disk drive have been studied as (a) to provide a function for specifying from the outside a maximum limit to the time taken for input/output including retrials of reading; (b) to eliminate the function that stops the input/output in the event of data error; and (c) to eliminate the function that omits output of data which include data error.
With the function mentioned in (b), when data that have been read include an error, the data including the error are not output to the outside of the disk drive. But even in this case, reading operation is not stopped and the subsequent data are read with only such data that do not include error being output.
The reason why the function mentioned in (c) is being studied is that a decoder for moving picture or audio data has a function to process data errors, and therefore reproduced data with less deterioration in quality may often be achieved by processing the entire data including errors, than omitting the data that include errors from the processing operation with the function mentioned in (b). In the case of the function mentioned in (c), however, it is difficult to precisely estimate the effect of an error inside of the disk drive, because the extent of the effect varies depending on which part of MPEG (Moving Picture Experts Group) data includes the error and on the length of the data including the error.
Improvements being studied for the storage of audio or moving picture data include, besides those described above, such a constitution as processing of the audio and moving picture data is assigned to a dedicated processor, because a large amount of audio or moving picture data must be processed without interrupt. In this case, a general-purpose processor is required to only make input and output requests to the disk drive. The output data are input to the dedicated processor without being processed in the general-purpose processor.
An example of processor dedicated for the processing of audio or moving picture data is the MPEG2 (Moving Picture Experts Group phase 2) decoder. The MPEG technology compresses video data by eliminating the redundancy in space domain and time domain. To eliminate the redundancy in time domain, in particular, moving picture data are divided into sets of still picture frames, each set consisting of a plurality of still picture frames of which one frame is compressed as a still picture while the other frames are compressed by extracting only the differential information among the frames. The MPEG decoder reproduces the original moving pictures from the MPEG data.
There are a filter and/or a dedicated communication processor installed between the disk drive and the MPEG decoder. As an example of such dedicated processor, a filter processor is disclosed in Japanese Patent Laid-Open Publication No. Hei 03-235589. The filter processor discriminates valid data packets which are necessary for reproduction and invalid data packets which are not necessary for reproduction, among the train of packets of moving picture or audio data that has been received through communication, and removes the invalid packets to reduce the amount of data, thereby increasing the equivalent length of time of the data that can be recorded on the disk.
The filter processor records the number of invalid packets, which have been removed, on the recording apparatus while being appended to the valid packets and, when retrieving the data from the recording apparatus, transmits the data while inserting the recor
Dildine R. Stephen
NEC Corporation
Sughrue & Mion, PLLC
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