JPH0355900B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic tape device such as a cartridge library system (CLS), and particularly to a data reproducing circuit thereof.

[Conventional technology]

CLS uses a wide magnetic tape in the form of a cartridge, and data is recorded on the tape in diagonal strips. Referring to FIG. 2, in FIG. 2c, MP indicates the magnetic tape, and ST indicates a stripe, which is a band-shaped area extending diagonally in the width direction of the tape, and data is written onto the stripe ST. For example, the length of tape MP is
At 20m, tens of thousands of stripes are formed. As shown in Figure 2a, each stripe has a burst pattern BP for synchronizing the playback frequency at the starting end.
is followed by a beginning mark indicating the beginning of the data.
BM is written, and then data D is written with section marks SM in between to divide the data into blocks.

Since it is a magnetic tape device, it is expected that there will be slight fluctuations in the reading speed, but the burst pattern BP deals with this by bursting information that instructs the frequency at which the data written in the stripe will be played back. Expressed in the form of a signal. A magnetic tape device is equipped with a variable frequency oscillator for data reproduction, and the output frequency of the oscillator is set in a burst pattern.
It adjusts (phase adjustment) to the value indicated by BP and holds that value until the next stripe burst pattern is input. For details, see Burst Pattern BP.
Change the gain of the VFO tracking control system that follows the frequency specified by to high when BP is input, and to low after that. In this way, the frequency for data reproduction is adjusted,
Next, when the beginning mark BM is detected, the data reproduction circuit starts operating, reproduces the data D read from the data block, and rearranges it into 8-bit data. Section mark SM helps with data synchronization.

Magnetic tapes may suffer from failures such as parts of the magnetic film falling off, and of course if such failures occur, magnetic recording and reproduction will not be possible, so stripes are avoided from being used. If such a fault or defective stripe is found to be defective by write or read check, a burst pattern BP for frequency synchronization is written on most of it, and a beginning pattern is written on the rest, as shown in Figure 2b. Write mark BM repeatedly. Especially the pattern
The repetition of BM is called a demark pattern (or special pattern). If it is found to be a demarked stripe when reading data, the read data is not sent to the host device. Therefore the stripes
If STi, ST _i+1 , ST _i+2 , ... and ST _i+1 is a demark stripe, then the data Di, D _i+1 , ... are
Since the data is written in STi and ST _i+2 , if the read data of ST _i+1 is not sent, the data received by the host device will be Di, D _i+1 , . . . , which is the same as in the normal state.

[Problem that the invention seeks to solve]

By the way, even normal stripes may be damaged, resulting in data dropout. Since it is equipped with an ECC circuit, a small number of bit errors can be corrected, but a large number of bit errors cannot be corrected, and the error is notified to the host device. If the burst pattern BP section for synchronizing the playback frequency is scratched, the burst pattern may not appear or its level may become low, and in this case, the output frequency of the VFO cannot be adjusted sufficiently. If data is reproduced at such an inappropriate frequency, the reproduced data will be messed up, the ECC circuit will display an error, and the demark pattern detection circuit may also generate a detection output. Since it is necessary to move on to the next stripe if it is a demarked stripe, the demarked pattern detection circuit is treated with priority, and when it produces an output, the stripe in question is treated as a demarked stripe and its data is not sent, and the read data of the next stripe is Waiting for input. However, data was also written in this stripe, and if it is not sent, data will be dropped in the host device. That is, the stripes are STi, ST _i+1 , ST _i+2 , . . . as described above.
Then, when writing, everything is normal, so the data is
Di, D _i+1 , D _i+2 , ... have been written, and if D _i+1 is damaged and becomes as shown above, the data received by the host device will be Di, D _i+2 , ...and data D _i+1
falls off.

The present invention aims to improve this problem by clearly distinguishing between an error occurrence stripe and a demark stripe, and performing error processing in the case of the former, and performing skip processing in the case of the latter.

[Means for solving problems]

The present invention divides a tape into a large number of stripes, writes a burst pattern and data for reproduction frequency synchronization to a normal stripe, and writes a special pattern indicating a defect to a defective stripe from the burst pattern. Using the magnetic tape written next to the elongated burst pattern,
In a magnetic tape device, the reproduction data decoding circuit includes a reproduction data decoding circuit that operates at a reproduction frequency adjusted according to the read burst pattern, and a circuit that detects the special pattern and prohibits the transmission of read data of a defective stripe. The present invention is characterized by comprising an erroneous detection prohibition circuit that disables the special pattern detection circuit within a certain period of time after inputting stripe read data and starting decoding of the data of the stripe.

To explain it with a drawing, as shown in Fig. 2, the length t3 of the burst pattern BP for reproduction frequency synchronization of the Demark stripe is much larger than that of the normal stripe, t1, and if the stripe is normal during t3, the data block is already Some are appearing. To detect a demark pattern, the number of beginning marks BM following the burst pattern BP is counted, and when a predetermined number is reached, a demark pattern detection output is generated.
Therefore, if it is a normal stripe, there will be no detection output, and if it is a demarked stripe, a detection output will occur after time t3, but such an operation does not necessarily occur. In other words, if the defect is at the beginning of the stripe and the reproduction frequency is not fully adjusted, accurate data reproduction will not be possible.
If you misunderstand that there is a predetermined number of BMs, or if you read the Demark Stripe burst pattern BP but find a beginning mark BM in it,
The mark pattern detection circuit may generate a detection output by misunderstanding that there is a predetermined number of patterns. The demark pattern should be detected after t3, and if it is before t3, it can be said to be a false detection. The present invention focuses on this point, and an erroneous detection prohibition circuit is added to the demark pattern detection circuit, and the demark pattern detection circuit is disabled within time t3.

〔Example〕

FIG. 1 shows a circuit according to an embodiment of the present invention, 10 is a frequency synchronization circuit (VFO circuit), 12 is a reproduced data decoding circuit (data reproducing circuit), 14 is a buffer memory for reproduced data, and the reproduced data is passed through the buffer 14. Sent to the higher-level device. 16 is a burst pattern detection circuit, which detects the burst pattern BP.
When detected, the control signal S1 is reproduced by the data decoding circuit 12 and the demark pattern erroneous detection prohibition circuit 2.
Send to 4. Reference numeral 18 denotes a beginning mark BM and section mark SM detection circuit, which, when detected, sends a signal S2 to the reproduction operation control circuit 20 and the demark pattern detection circuit 22.

When tape reading is started, the circuit 16 detects a burst pattern from the read output, recognizes the start of supply of reproduced data, and sends a signal S1 to the decoding circuit 12 to instruct preparations to start decoding, and also sends a signal S1 to the decoding circuit 12 to instruct the false detection prevention circuit 24. A signal S1 is sent to invalidate the demark pattern detection. This invalidation can be achieved by prohibiting the detection operation of the detection circuit 22 during the time t3, or by allowing the detection operation to be performed, but if the demark pattern is detected during the time t3, the control circuit 22
This can be determined as an error, etc.
Here, we assume the former. Next, when the mark detection circuit 18 detects the beginning mark BM, the decoding circuit 12 starts decoding the reproduced data and sequentially writes the decoding results to the buffer memory 14. Writing into the buffer memory 14 is performed by the control circuit 20. The control circuit 20 is equipped with an ECC circuit, and if the decoded data has a 1-bit error, it is corrected.
If the error is 2 bits or more and cannot be corrected, remember that fact. The false detection prohibition circuit 24 includes a timer, and releases the prohibition of the demark pattern detection operation of the circuit 22 when a certain period of time t3 has elapsed since the input of the signal S1. Therefore, the circuit 22 is hereinafter referred to as the detection circuit 18.
When the beginning mark BM detection signal is sent from the beginning mark BM detection signal, it is counted, and when it reaches a predetermined number, it sends the demark pattern detection signal S3 to the control circuit 20.The control circuit 20 receives the demark pattern detection signal S3.
is input, the stripe in question is determined to be a demark stripe, and the data in the buffer memory 14 is not sent to the higher-level device. Even after time t3, the demark pattern detection signal S3 is not input, and the ECC
If the result is normal, the data in the buffer memory 14 is sent to the higher-level device (more specifically, it prompts the higher-level device to take in the data), and if the ECC result is bad, an error notification is sent to the higher-level device.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to almost reliably determine whether a stripe is a mark stripe or an error stripe, and there is an advantage that no defects occur in the data sent to the host device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram of a recording data format of a magnetic tape. In the drawing, ST is a stripe, BP is a burst pattern, D is data, MP is a magnetic tape, BM is a beginning mark and its repetition is a special pattern, 2
2 is a special pattern detection circuit.

Claims (1)

[Scope of Claims] 1. A tape is divided into a large number of stripes, a burst pattern and data for reproduction frequency synchronization are written to a normal stripe, and a special pattern indicating a defect is written to a defective stripe. A reproduced data decoding circuit operates using a magnetic tape written next to a burst pattern that is longer than the burst pattern, and operates at a reproduction frequency adjusted according to the read burst pattern;
In a magnetic tape device equipped with a circuit that detects the special pattern and prohibits the transmission of read data of a defective stripe, the playback data decoding circuit receives the stripe read data and starts decoding the data of the stripe for a certain period of time. A magnetic tape device comprising: an erroneous detection prevention circuit for disabling the special pattern detection circuit.