Dynamic information storage or retrieval – Information location or remote operator actuated control – Selective addressing of storage medium
Reexamination Certificate
1999-12-02
2001-06-19
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Information location or remote operator actuated control
Selective addressing of storage medium
C369S047150, C369S053110
Reexamination Certificate
active
06249492
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and an arrangement for controlling the data stream in a vibration-resistant playback device.
2. Related Art
Particularly in the mobile use of playback devices of optical or other information media, vibration-resistant properties are required in order to ensure uninterrupted reproduction of information despite vibrations which lead to interruptions in the reading of data from the information medium.
In order to achieve a vibration-resistant behaviour, the data are written to a buffer memory at a rate which is higher than normal and are read out at the normal rate. If vibrations cause an interruption in the reading of data from the information medium, then this gap in the source data stream can be bridged by reading out the data reserve in the buffer memory which has been stored as a precaution in the meantime.
A method and an apparatur for reproducing data from a disk medium at a variable data rate and for converting the reproduced data to a constant data rate, already have been described in GB 2289158. The apparatus comprises: a reproducing head for reproducing the data from the disk medium at the variable data rate; buffer memory means for storing the reproduced data from the reproducing head and for reading out the stored data at a constant data rate; means for detecting overload of the buffer memory means; and servo means responsive to the overload detecting means for controlling the reproducing head to repeat reproduction of data from the disk medium when overload of the buffer memory means has been detected and the method comprises: storing in a buffer memory data reproduced form the disk medium by a reproducing head at a variable data rate; reading out the stored data from the buffer memory at a constant data rate; detecting overload of the buffer memory; and controlling the reproducing head to repeat reproduction of data from the disk medium when overload of the buffer memory has been detected.
In most of the commercially available devices, the reading of data from the information medium is realized at a doubled rate. However, during operation free from vibrations, this constantly leads to an overflow of the buffer memory, thereby necessitating artificial interruptions in the reading of data from the information medium or returns.
The always doubled rate and the jumps of the scanner cause an increased current consumption. In order to eliminate this disadvantage, it has already been proposed to carry out the reading of data from the information medium with a variable rate. In order not to have to perform the obligatory error checking and possible error correction and/or masking on a source data stream with a variable rate, in accordance with the proposal the requisite processing stages for these measures were connected downstream of the buffer memory. However, this requires an increased storage capacity or, with the existing storage capacity, reduces the useful data that can be stored since, after all, the check data have to be concomitantly stored as well as the useful data.
BRIEF SUMMARY OF THE INVENTION
The invention is based on the object of improving a method and an arrangement for controlling the data stream in a vibration-resistant playback device to the extent that increased storage of useful data in the buffer memory is made possible and the power consumption and wear during read-out of the information medium are reduced.
In the context of a method described below, this object is achieved by means of the features specified in the characterizing part. Developments and advantageous embodiments of the invention emerge from the subclaims.
In the method according to the invention, the rate at which the source data stream is read from the first memory can be switched over between a first and a second data rate. By switching over between the data rates in a variable ratio to one another, it is thus possible to simulate any desired average data rate between the first and the second data rate. The problem of downstream stages having to process a variable data rate is thus considerably reduced in that the processing stages only have to be designed for, and be capable of switching over between, two different data rates.
Furthermore, this measure creates the precondition for matching the read-out of the source data stream from the information medium to the actual average rate, which is composed of periods of time in which data can be read and periods of time in which no data can be read. The rate, resulting from the scanning speed, at which the source data from the information medium are read does not, therefore, have to be kept continually at twice the value of the normal data rate, but rather can be reduced if, for example, no vibrations occur. This results in a considerable saving of power precisely because the drive unit can be operated at a lower speed and the scanner does not have to carry out artificially initiated returns.
Since, according to the invention, the processing stages for error correction and/or masking can be switched over for two different data rates, the useful data contained in the source data stream can be subjected to error checking and possible error correction and/or masking before they are buffer-stored in the second memory. Since the check data are no longer required after error checking, correction and masking, the storage of the data stream can be restricted solely to the useful data. This results in a considerable saving of memory space or, expressed in another way, with the existing memory space, more useful data can be stored and hence a longer time span can be bridged during which no data can be read from the information medium due to vibrations.
The first memory during read-out of the source data stream and the downstream processing stages are preferably switched over between normal data rate and doubled data rate.
This selection of the data rate has the advantage that the switching-over of the processing stages is possible merely by doubling or halving the clock frequency and, therefore, can easily be implemented in existing circuit designs. The selection of the rates also suffices completely to cover the maximum range of the reading rate that is necessary in practice, the range being produced, in the event of vibrations, as a sequence of interruptions and increased reading rates, in order that a resultant average reading rate of the order of the normal data rate is obtained. The switch-over of the first memory is performed in such a way that a switch-over to the doubled data rate is made in the event of a first difference between the addresses of the first memory to which a write and a read pointer point, and a switch-over to the normal data rate is made in the event of a second difference smaller than the first difference. The measure of evaluating the difference between the write and read pointers enables a very fast reaction against overflow, so that the first memory manages with a relatively small storage capacity, which is distinctly smaller than the gain in storage capacity in the second memory by dispensing with the storage of the check data.
The data rate at which the source data stream is read from the information medium can be regulated in a continuously variable manner between normal data rate and increased data rate as a function of the occupancy of the second memory. This has the advantage that given, on average, constant ratios between periods of time in which data can be read and periods of time in which no data can be read, the reading rate can be kept at a constant value, in other words the information medium does not have to be decelerated and accelerated in the way that would be necessary given step-by-step regulation.
In this case, the maximum value of the increased data rate may be less than or equal to the doubled data rate. The maximum value is preferably 1.5 times the normal data rate. This restriction of the regulating range prevents unnecessarily high accelerations and speeds of the information medium, with the result that
Deutsche Thomson-Brandt GmbH
Kiel Paul P.
Neyzari Ali
Tripoli Joseph S.
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