JPS6155134B2 - - Google Patents

Description

[Detailed Description of the Invention] Information and control are transmitted between devices constituting an electronic computer system (for example, between a channel device and various control devices, or between a control device and a drive device) using so-called commands. However, the present invention relates to the method of executing this command.

Commands are generally divided into the following two types. One is that the execution of the command involves the transfer of data. For example, this corresponds to a command for writing data to or reading data from a magnetic tape of a magnetic tape device. For convenience, this type of command is referred to as a burst command. The other is to give specific control instructions through the command. For example, a rewind command or an unload command in a magnetic tape device corresponds to this command. These commands are generally referred to as control commands because they do not involve any information transfer and are simply commands for triggering control operations.

The present invention relates to a method for executing the above-mentioned control commands.

The prior art will be explained below using a specific example. As an example, the execution method of a rewind command, which is a type of control command and is used in a magnetic tape device, will be explained with reference to a time chart shown in FIG. As is well known, the rewind command is a command for rewinding the magnetic tape to the BOT (Beginning of Tape) mark. In Figure 1, 1 is a rewind command signal issued from a channel device and recognized within the magnetic tape device, 2 is a rewind signal that rewinds the magnetic tape, and 3 is detection of a BOT marker affixed to the magnetic tape during rewinding. The BOT detection signal 4 issued by is a rewind completion report signal for notifying the above-mentioned that the rewind has ended. As can be seen from FIG. 1, in the rewind command, by obtaining a BOT detection signal, it is determined that the tape has been rewound to the beginning of the tape, and the end of the command is notified to the higher level. In other words, conventionally it was assumed that BOT detection was always performed normally;
If a false detection occurs, a completion report will be issued even if the command execution does not complete normally.

Normally, BOT detects BOT reflective markers pasted on tape using photoelectric conversion, etc.
BOT if there is dust etc. on the tape.
It may be mistakenly detected as a marker, and a BOT detection signal may also be erroneously output due to noise in the detection circuit.

Figure 2 is incorrect due to the reasons mentioned above.
This is a time chart when a BOT detection signal is issued. As shown in the figure, if the BOT erroneous detection signal 3' is output before the regular BOT detection signal, rewinding is interrupted and a rewind completion report is made.
If such an error occurs, the next time a write command arrives, there will be an unnecessary record on the tape between the legitimate BOT and the erroneously detected position, and the read command will In some cases, there may be problems such as data not being read from the BOT to the erroneous detection point.

The purpose of this invention is to provide a new command execution method that prevents the above-mentioned inconveniences and reliably executes issued commands.

However, the gist of the present invention is that in a device that receives a command issued from a host device and executes an operation specified by the control command, after issuing a certain control command, the device itself issues the same control command. The command execution method is characterized in that the command is issued more than once, and the process required for completing the operation specified by the command is executed in the device twice or more.

The present invention will be specifically described below in connection with a rewind command in a magnetic tape device.

FIG. 3 is a block diagram showing the main parts of a magnetic tape device embodying the present invention, in which 11 is a command detection circuit, 12 is a rewind instruction circuit, 13 is a BOT detection circuit, 14 is a stop position adjustment circuit, and 15 is a command rewind instruction circuit. An issue check circuit 16 is a termination interrupt issuing circuit.

When a rewind command is issued, the command detection circuit 11 detects it and outputs a rewind instruction signal. In response to this, a rewind signal is issued from the rewind instruction circuit 12, and the tape drive circuit (not shown) starts rewinding the tape. After that, the BOT detector (not shown)
When a BOT marker (or dust etc. attached to the tape) is detected, the BOT detection circuit 13 sends a BOT
A detection signal is issued (an erroneous signal may be caused by noise in the BOT detection circuit). When the BOT detection signal is generated, a signal is sent from the stop position adjustment circuit 14 to the tape drive circuit, whereby the tape is sent in the opposite direction and returned by a predetermined distance.

On the other hand, the command reissue check circuit 15
The number of occurrences of the BOT detection signal is counted, and if it is the first time, a rewind instruction signal is generated to the rewind instruction circuit 12, and if it is the second time, the rewind instruction signal is not issued and is sent to the end interrupt issuing circuit 16. Issues end interrupt instruction signal.

Since this is the first BOT detection signal, the command reissue check circuit 15 provides the rewind instruction signal to the rewind instruction circuit 12. Therefore, the rewind signal is given again to the tape drive circuit, and tape rewinding is restarted without requesting the host device to reissue the rewind command. Then BOT
When the second BOT detection signal is output from the detection circuit 13, in response to this, the command reissue check circuit 15 outputs a termination interrupt instruction signal to the termination interrupt issuing circuit 16. A rewind completion report signal is issued to the device, and the rewind command ends.

In order to facilitate the explanation of the above operation, a time chart is shown in FIG. In Fig. 4, signals 1 to
4 is the same signal as the signal with the same symbol in FIGS. 1 and 2, and 5 is a rewind instruction signal output from the command detection circuit 11 or the command reissue check circuit 15.

Therefore, if the first BOT detection signal is an erroneous detection signal caused by dust attached to the tape, circuit noise, etc., the causes of these erroneous detections are often eliminated by the subsequent rewind operation. Therefore, the second BOT detection signal is generated by the detection of the regular BOT marker. In this way, the tape can be reliably positioned at the BOT position.

Although the above embodiment relates to a rewind command for a magnetic tape device, the present invention can be similarly applied to other control commands such as an unload command and a data security erase command. Furthermore, the present invention is of course applicable not only to magnetic tape devices but also to other devices that will not be affected even if a control command is reissued. Note that in the above example, the control command is reissued only once, but it goes without saying that it may be reissued two or more times.

As is clear from the above description, according to the present invention, control commands can be reliably executed and reliability of electronic computer systems and control systems can be improved. Also, the control command from the second time is
Since the command is issued by the device itself that executes it,
There is no need to request the higher-level device to reissue the command, which speeds up processing, and simplifies functionality because the higher-level device does not need to be configured to handle command reissue requests. is brought about.

[Brief explanation of the drawing]

Figure 1 is a time chart for explaining the normal execution operation of the rewind command according to the conventional method, Figure 2 is a time chart for explaining the execution operation that caused an error in the rewind command according to the conventional method, and Figure 3 is FIG. 4 is a block diagram showing one embodiment of the present invention, and is a time chart for explaining the operation of the same embodiment. 11...Command detection circuit, 12...Rewind instruction circuit, 13...BOT detection circuit, 14...
Stop position adjustment circuit, 15...command reissue check circuit, 16...end interrupt issuing circuit.

Claims (1)

[Claims] 1. In a device that receives a command (hereinafter referred to as a control command) issued from a higher-level device to instruct a specific operation other than data transfer, and executes the operation specified by the control command, the higher-level device issues a command. When the action specified by the control command is executed, the device itself issues the same control command again, and the device performs the necessary processing to complete the action specified by the control command. A command execution method that is characterized in that it is essentially executed more than once.