JP2000267951A - Data transfer control system and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To guarantee the reliability of data transfer without being provided an exclusive circuit in a data transfer system into/from which an active line can be inserted/detached. SOLUTION: In the data transfer control system, a device connection processing means 43 reads out a serial number at the time of connecting a device 2 and stores the serial number in an ID buffer 52. Even when the device 2 is disconnected from a host computer 1, a command execution processing means 41 continues the execution of command status from an application 3 to the device 2 when the serial number is stored in the buffer 52 so as not to be conscious of the disconnection of the device 2 for fixed time. The time is counted by starting a disconnection timer processing means 42 by a device disconnection processing means 44. When the device 2 is reconnected within the fixed time, a device connection processing means 43 checks whether the serial number is the one stored in the buffer 52 or not, and when the device is the device of the serial number connected at the preceding time, restarts the interrupted data transfer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a data transfer control,
In particular, the present invention relates to hot-swappable data transfer control.

[0002]

2. Description of the Related Art An example of this prior art is disclosed in Japanese Patent Application Laid-Open No. 8-54.
No. 970 describes this as a "hot wire insertion / extraction mechanism".

In the configuration of this prior art, as shown in FIG. 8, three agents 1-1, 1-2 and 1-3 are connected to a data transfer bus 100 to perform data transfer.
Contact / separation notice circuit 2 for each of agents 1-1 to 1-3
-1 to 2-3 output a contact / separation notice signal to another agent when each of the agents 1-1 to 1-3 is connected to / separated from the data transfer bus 100. The contact / separation notice signal is latched by the contact / separation latch circuits 3-1 to 3-3 and 4-1 to 4-3. Latch reset circuits 5-1 to 5-3 are respectively connected / separated latch circuits 3-1 to 3-3 and 4-1 to 4-4 which are set at the end of data transfer by the own agent.
3 is reset. Then, the retransfer circuits 6-1 to 6-
3 is an on / off latch circuit 3-1 to 3-
If 3, 4-1 to 4-3 are set, the data stored in the local memory and retransmitted based on the data which has been transmitted until immediately before, its data length, and the address of the transfer destination are performed. .

The hot-line insertion / extraction mechanism configured as described above
The signal from the notice means of the other agent that gives notice of the connection / separation with the data transfer bus is held, and if the signal from the notice means is held when the data transfer with the other agent is completed, By executing the executed data transfer again, there is an effect that the reliability of the data can be reliably guaranteed.

[0005]

However, in the above-mentioned prior art, there is a first problem that it is not possible to avoid an error if software has provided a time-out judgment for data transfer. The timeout determination is one of error determinations in software having the initiative in data processing, and if data transfer is not completed within a predetermined time, a timeout error is determined.

[0006] Even if signal transfer is guaranteed at the circuit level, if the software determines that a time-out error has occurred, it will not be possible to match between the hardware and software as to whether the transfer has been performed normally. Because. As a result, there is a possibility that the same data is retransmitted.

The second problem is that each agent must prepare a dedicated circuit for data assurance (the contact / separation notice circuit, the contact / separation latch circuit, the latch reset circuit, and the retransfer circuit shown in FIG. 8). It must be.

It is an object of the present invention to provide a data transfer control system and a data transfer control method capable of changing the connection mode of a system while guaranteeing data even during data transfer.

It is another object of the present invention to provide a data transfer control system and a data transfer control method which do not require a circuit dedicated to data transfer in a device to which data is transferred.

[0010]

A first data transfer control system according to the present invention is a data transfer control system in which a hot-swappable device is subjected to data transfer. It is characterized in that the reliability of data transferred between the host computer and the device is guaranteed even when the connection mode is changed.

According to a second data transfer control system of the present invention, in a data transfer control system in which a hot-swappable device is a target of data transfer, even if the device is disconnected from the system, the device can be identified. As long as the information is stored in the system, in response to a data transfer request from an application, the disconnection state of the device is not shown, so that a timeout error is not noticed, and when the device is reconnected within a predetermined time, The interrupted data transfer is continued using the stored device identification information.

According to a third data transfer control system of the present invention, in a data transfer control system in which a hot-swappable device is subjected to data transfer, identification information of the device, a command to be issued to the device, and A storage unit for storing a connection state of the device, and when the device is connected, the identification information of the device is obtained from the device and compared with the stored identification information. Device connection processing means for erasing the transmitted command and stopping the disconnection timer because it is a reconnection if they match, and instructing the device to resend the command, or activated by a data transfer request from the application to the device or the resending instruction The device is connected according to the contents stored in the storage means. Command execution processing means for executing the command to delete the stored command, and returning a status of "executing" to the application if the connection information is not connected but identification information is stored; and When disconnected, the connection state is set to unconnected, a device disconnection processing unit that activates a disconnection timer processing unit, a time-out period is set, and a timeout is awaited. Disconnection timer processing means for discarding the set command and erasing the stored device identification information when the timeout occurs.

Further, a preferred embodiment of the data transfer control system according to the present invention is characterized in that the time from disconnecting the device to reconnecting the device can be externally set.

According to the data transfer control method of the present invention, in the data transfer control method in which a hot-swappable device is subjected to data transfer, identification information of the device, a command to be issued to the device, and the device And a storage procedure for storing the connection state of the device, and when the device is connected, obtains the identification information of the device from the device and compares it with the stored identification information. Device connection processing procedure for stopping the disconnection timer and instructing a command resend, and resuming the connection if the match is made, or a data transfer request from the application to the device, or activated by the resend instruction. If the device is connected according to the stored contents, A command execution processing procedure for executing the command to erase the stored command, and returning a status of “executing” to the application if the connection information is not connected but the identification information is stored, and the device is disconnected. Then, the connection state is set to unconnected, a device disconnection processing procedure for activating a disconnection timer processing procedure, a time-out period is set, and a timeout is awaited. And a disconnection timer processing procedure for deleting the stored command and deleting the stored device identification information when the timeout occurs.

More specifically, the data transfer control system according to the present invention comprises a command queue (51 in FIG. 1) as storage means for a command packet to be issued to a connected device (2 in FIG. 1); A command execution unit (FIG. 1-41) as a packet execution unit, a device connection processing unit (43 in FIG. 1) as a device connection recognition unit, and a device connection flag (FIG. 1) as a device connection state storage unit. 53), device disconnection processing means (44 in FIG. 1) as recognition means for device disconnection, ID buffer (52 in FIG. 1) as means for storing device identification information, and time after device disconnection. It consists of a disconnection timer processing means (42 in FIG. 1) as a means for measuring, and stores when a device is disconnected and reconnected within a predetermined time. Using the identification information, by recognizing the cut device operates to continue the interrupted data transfer.

Further, in the data transfer control system of the present invention, a timer value register (54 in FIG. 6) as storage means for recognizing reconnection of a device to the above-mentioned data transfer control system, and a time can be set. An input device (6 in FIG. 6) is provided as input means so that the user can set the time for recognizing reconnection.

[0017]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, in the first embodiment of the present invention, a host computer 1 includes a device control device 4 and a storage device 5. Host computer 1
Is connected to the device 2 of the data transfer destination, and the application 3 uses the device control device 4 to operate the device 2. The device 2 is a peripheral device of the host computer 1 having an interface capable of hot-swapping, and a plurality of devices can be connected to the host computer 1.

The device control device 4 includes command execution processing means 41, disconnection timer processing means 42, device connection processing means 43, and device disconnection processing means 44. The storage device 5 includes a command queue 51 and an ID
A buffer 52 and a device connection flag 53 are provided.

Each of these means operates roughly as follows. The command queue 51 is a storage unit of a command to be issued to the device 2, and stores a plurality of commands including an address of a device to be transferred, a data transfer direction, a data size, and a data address.

The command execution processing means 41 reads a command from the command queue 51 and executes the command. The execution result is indicated by a status such as success, failure, or being executed, and is returned to the application 3.

The device connection processing means 43 reads the configuration of the connected device 2. Further, by reading out the serial number of the device 2 and comparing it with the contents of the ID buffer 52 which is a means for storing the identification information of the device, it is determined whether or not to initialize after connecting the device. In the present embodiment, the serial number of the device is stored in the ID buffer 52.

The device disconnection processing means 44 activates the disconnection timer processing means 42 and measures time after the occurrence of device disconnection.

After a lapse of a predetermined time, the disconnection timer processing means 42 determines that the reconnection of the device 2 has not been performed, and erases the contents of the ID buffer 52.

Next, the operation of the present embodiment will be described with reference to FIG. 1 and the flowcharts of FIGS.

When the device 2 is disconnected or connected to the host computer 1, the host computer 1 can activate the device control device 4 by generating an interrupt. The activated device control device 4 determines an internal process to be executed according to the connection state of the device.

(1) Device Connection Process The device connection process will be described with reference to the configuration diagram of FIG. 1 and the flowchart of FIG.

When the device 2 is connected to the host computer 1, the host computer 1 generates an interrupt and calls the device connection processing means 43. The device connection processing unit 43 acquires the configuration information possessed by the device 2 (Step A1). The configuration information is, for example, a device such as a USB, and is configured with information such as whether a logical channel for data communication is for data input or data output, and the size of a data packet.

Next, a logical channel for data communication is initialized based on the configuration information (step A2). At the time of initialization, state setting is performed such that the packet number for error correction is set to an initial value so that data synchronization with the communication target device can be achieved.

Next, the serial number of the connected device is obtained from the device 2 (step A3). This is because serial numbers are usually not duplicated and are therefore convenient for use in identifying individual devices.

Next, the read serial number of the device 2 is compared with the contents of the ID buffer 52 (step A).
4). As a result of this comparison, the serial number of device 2 and I
If the contents of the D buffer 52 match, the device 2
Determines that it has been reconnected. Then, as described later, the timer started by the disconnection timer processing unit 42 is stopped, and the time measurement by the disconnection timer is stopped (step A).
5).

Next, an instruction is issued to retransmit the interrupted command to the device 2 (step A6). With this instruction, the command execution processing unit 41 is started.

On the other hand, in step A4, the device 2
If the serial number does not match the contents of the ID buffer 52, it is determined that a new device has been connected. In this case, the contents of the command queue 51 are deleted, and the commands received thereafter are those after the connection of the device (step A7).

Next, the device connection flag 53 is set,
The fact that the device is currently connected is made known by the device control device 4 (step A8).

Next, the serial number of the device is stored in the ID buffer 52 so that it can be referred to at the time of the next device connection (step A9).

(2) Command execution processing Next, using the configuration diagram of FIG. 1 and the flowchart of FIG.
The command execution processing will be described.

When the application 3 requests data transfer to the device 2, a command execution process is executed. At this time, the request from the application 3 is stored in the command queue 51.

The command execution processing means 41 reads a command packet from the command queue 51 (step B).
1).

Next, the command execution process 41 determines the current connection state of the device 2 from the device connection flag 53 (step B2). As a result, if the device 2 is not connected, it is checked whether a serial number is stored in the ID buffer 52 to determine whether there is a possibility of reconnection (step B3). If,
If it is, the disconnection has not timed out and the status of the command
The process ends (step B4).

On the other hand, if the serial number is not stored, the same device has not been connected before, and there is no need to continue the command, so that the status of the command is set to "failed" (step B5). ). In this case, since this command has been processed, it is discarded from the command queue (step B10).

In step B2, if the device 2 is in the connected state, the command execution processing means 41
Is executed (step B6). Specifically, a procedure such as writing a data byte of a command to a register provided in the device 2 is performed.

Next, the command execution result is read from the device 2 and the result is determined (step B7). As a result, if the command is executed correctly, it is determined that the data transfer process accompanying the command is also successful, and the status of “success” is set (step B8).

On the other hand, if the command is not correctly executed, for example, if the contents of the register read from the device 2 are invalid, the status of "failure" is set (step B).
9). If the command is executed in step B8 or B9, the command is discarded from the command queue 51 (step B10).

The command execution status set by the above-described command execution processing is notified to the application 3.

(3) Device disconnection processing Next, using the configuration diagram of FIG. 1 and the flowchart of FIG.
The device disconnection processing will be described.

When the device 2 is disconnected from the host computer 1, the host computer 1 generates an interrupt,
The device disconnection processing means 44 is called.

The device disconnection processing means 44 updates the device connection flag 53 so that the device 2 is not connected (step C1).

Next, the disconnection timer processing means 42 is started (step C2). After the disconnection of the device 2, the disconnection timer processing unit 42 starts measuring the time during which reconnection is permitted.

(4) Disconnect Timer Processing Next, using the configuration diagram of FIG. 1 and the flowchart of FIG.
The disconnection timer process will be described.

The disconnection timer processing means 42 is started by the device disconnection processing means 44 and controls the flow chart of FIG.

The disconnection timer processing means 42 sets a time-out period (step D1) and waits for the activated timer to time-out (step D2). During this time, if the device 2 is connected and the device connection processing means 43 is executed, the timer is stopped as described above, so that the command is discarded from the command queue 51 and the process is terminated ( Step D6).

On the other hand, if a time-out occurs in step D3, the contents of the ID buffer 52 are deleted (step D4) so that the execution of the command is not continued even when the device 2 is reconnected. I do. This is because the answer in step A4 in FIG. 2 is NO, and the process does not proceed to step A6, so that the command execution processing unit 41 is not activated. Then, the status of the command which is still set to "executing" is set to "failure" (step D5), and the command is discarded from the command queue 51 (step D6).

(5) Embodiment when Device is Disconnected and Reconnected The following is an example of a case where the device 2 is newly connected, disconnected during data transfer, and then reconnected.
The flow of the entire process will be described.

When the device 2 is newly connected, the device connection processing means 43 is executed. That is, the configuration information of the device 2 is obtained (Step A1 in FIG. 2), and the logical channel of the data communication is initialized based on the configuration information (Step A2). Next, the serial number of the connected device is obtained from the device 2 (step A3), and the read serial number is compared with the contents of the ID buffer 52 (step A4). At this point, since the device 2 has been newly connected, no serial number is stored in the ID buffer 52. Therefore, the command queue 5
1 is deleted (step A7), the device connection flag 53 is set to the connected state (step A8), and the read serial number is stored in the ID buffer 52 (step A9).

In this way, the device connection processing of FIG. 2 is completed, and the application 3 can operate the device 2. The command requested from the application 3 to the device 2 is written in the command queue 51, and the command execution processing unit 41 is executed.

The command execution processing means 41 reads command data from the packet queue (Step B1 in FIG. 3). Since the device connection flag 53 is still set to the connection state, the command is executed (step B6). As a result (step B7), the status is set to success or failure (step B7).
8, B9). Next, since the command has been executed, it is discarded from the command queue 51 (step B10).

When the device 2 is disconnected from the host computer 1 at this timing, the device disconnection processing means 4
4 is called. The device disconnection process updates the device connection flag 53 to an unconnected state (step C in FIG. 4).
1), start the disconnection timer processing means 42 (step C)
2).

In the disconnection timer process, a timeout period is set, and a timeout is waited for (step D in FIG. 5).
1, D2). During the timeout waiting state, the command to the device 2 is not discarded even if written into the command queue 51, and the status of "executing" is returned (step B4 in FIG. 3). Therefore, the application 3 is treated as a state waiting for the completion of data transfer.

In this example, the device 2 is connected while waiting, and the device connection processing means 43 is executed again. The device connection processing unit 43 acquires the configuration information,
A logical channel for data communication is initialized based on the configuration information (steps A1 and A2 in FIG. 2). Next, the serial number of the connected device is obtained from the device 2 (step A3), and the read serial number is stored in the ID buffer 5.
2 (step A4). ID buffer 5
Since the serial number of the device 2 is stored in 2, the timer started by the disconnection timer processing unit 42 is stopped (step A5), and it is determined that the disconnected device 2 has been reconnected.

Next, an instruction is given to retransmit the interrupted command to the device 2 (step A6). In response to this instruction, the command execution processing means 41 is activated again, and the command is executed this time. At this time, the status is also “success” or “failure” (step B in FIG. 3).
8, B9) Commands are discarded from the command queue 51 (step B10).

As described above, the data transfer is completed, and the application 3 is released from the data transfer completion waiting state.

(6) Embodiment when Device is Disconnected and Reconnected After Timeout The following is an explanation of the flow of the entire processing in an example where the device 2 is disconnected during data transfer and then reconnected. I do.

The procedure for waiting for a timeout is as follows:
The processing is the same as that described above. If a time-out has occurred, in step D4 of FIG.
2 is erased so that the execution of the command is not continued even when the device 2 is reconnected (No in step A4 in FIG. 2).

Next, the command set as "executing" is set to "failure" (step D5 in FIG. 5), and the command is discarded from the command queue 51 (step D6).
With this process, the command that has been “executing” completes the process.

In this example, it is assumed that after these processes, the device 2 is reconnected and the device connection processing means 43 is executed. The device connection processing means 43 acquires the configuration information of the device 2 and initializes a logical channel for data communication based on the configuration information (steps A1 and A2 in FIG. 2).
2) Enter the serial number of the connected device to Device 2.
(Step A3), and the read serial number is compared with the content of the ID buffer 52. Since the serial number of the device 2 is not stored in the ID buffer 52, the content of the command queue 51 is deleted (step A3). Step A7). Next, the device connection flag 53 is set to the device connection state (step A8), and the read serial number of the device is stored in the ID buffer 52 in preparation for the next device disconnection (step A9).

Next, a second embodiment of the present invention will be described with reference to the drawings.

Referring to FIG. 6, the second embodiment of the present invention includes a device control device 40 and a storage device 50 in a host computer 10. The host computer 10 is connected to a device 2 to which data is transferred and an input device 6 for inputting a timer value. The application 3 uses the device control device 4 to operate the device 2. . The device 2 is a peripheral device of the host computer 1 having an interface capable of hot-swapping, and a plurality of devices can be connected to the host computer 1.

The device control device 4 includes a command execution processing means 41, a disconnection timer processing means 45, a device connection processing means 43, and a device disconnection processing means 44. Further, the storage device 50 stores the command queue 51 and the I
A D buffer 52, a device connection flag 53, and a timer value register 54 are provided. The device control device 40 of FIG.
Are the same as the processing units having the same reference numbers shown in FIG. 1 except for the disconnection timer processing unit 45.

FIG. 6 shows the disconnection timer processing means 45.
This will be described with reference to the block diagram of FIG.

When the disconnection timer processing means 45 is activated by the device disconnection processing means 44, the timer value register 54
Is read out (step E in FIG. 7).
1) Set a time-out period (step E)
2) Wait for the activated timer to time out (step A3). During this time, if the device 2 is connected and the device connection processing means 43 is executed, the timer is stopped as in the first embodiment.
The command is discarded from the command queue 51, and the process ends (step E7).

On the other hand, if a time-out occurs (step E4), the contents of the ID buffer 52 are deleted (step E5) so that the execution of the command is not continued even if the device 2 is reconnected. I do. This is NO at step A4 in FIG. 2 and does not proceed to step A6.
Is not started. Then, the status of the command which has been set to "executing" is set to "failed" (step E6), and the command is discarded from the command queue 51 (step D7).

The input device 6 accepts the user's time setting input, and stores the timeout time in the timer value register 54.

A unique effect of this embodiment is that the time from disconnection of a device to reconnection can be made variable. For example, in order to change the connection mode of the device, the user disconnects and reconnects the device. It is possible to provide a system that can continue data transfer even when performing an operation that requires a relatively long time in terms of computer processing, such as performing a computer process.

On the other hand, it may be inconvenient for another user that commands are continuously executed on the device despite disconnection and reconnection of the device. For example, in a device such as a printer that performs a data transfer for executing drawing by a series of data strings continuing, if the data transfer is continued, it may cause erroneous printing. In this case, setting the timer value 54 to a smaller value has the effect of avoiding the problem.

A program for causing a computer to execute the data transfer control method described above is stored in a computer-readable recording medium such as a semiconductor memory or a magnetic disk, and is read and executed by the host computer 1. You may. This program controls the host computer 1 to execute the above-described method.

[0076]

A first effect of the present invention is that an error can be avoided even if software has a timeout judgment for data transfer. The reason is that even if the device is disconnected, the command execution processing means returns the status of “executing” to the application as long as the identification information of the device is stored in the ID buffer,
Don't show applications disconnected hardware
This is because it is possible to hide the error.

As a result, for example, a USB (Universal S
(Erial Bus), if all devices connected to the hub are in use and you want to connect more devices, disconnect some devices,
Although it is necessary to replace the hub with an additional hub, data transfer can be continued even in the case of such a work requiring a long time.

The second effect is that each device does not need to prepare a dedicated circuit for data assurance.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a flowchart of a connection process according to the first embodiment of the present invention;

FIG. 3 is a flowchart of a command execution process according to the first embodiment of the present invention.

FIG. 4 is a flowchart of a disconnection process according to the first embodiment of the present invention.

FIG. 5 is a flowchart of a disconnection timer process according to the first embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 7 is a flowchart of a disconnection timer process according to the second embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration of an example of a conventional data transfer system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Host computer 2 Device 3 Application 4 Device control device 5 Storage device 10 Host computer 40 Device control device 41 Command execution processing means 42 Disconnection timer processing means 43 Device connection processing means 44 Device disconnection processing means 45 Disconnection timer processing means 51 Command queue 52 ID buffer 53 Device connection flag 54 Timer value register

Claims (8)

[Claims] In a data transfer control system in which a hot-swappable device is a target of data transfer, even when a connection state of the system is changed due to the insertion / removal of the device,
A data transfer control system for guaranteeing the reliability of data transferred between a host computer and said device. 2. A data transfer control system in which a hot-swappable device is a target of data transfer, even if the device is disconnected from the system, as long as the identification information of the device is stored in the system.
In response to a data transfer request from an application, the disconnection state of the device is not shown, and a timeout error is not considered.When the device is reconnected within a predetermined time, the saved device identification information is used. A data transfer control system for continuing interrupted data transfer. 3. A data transfer control system in which a hot-swappable device is a target of data transfer, a storage means for storing identification information of the device, a command to be issued to the device, and a connection state of the device. When the device is connected, the identification information of the device is obtained from the device and compared with the stored identification information.If there is no match, the stored command is deleted because it is a new connection, and if there is a match, Device connection processing means for stopping the disconnection timer and instructing a command retransmission because of the reconnection, and a data transfer request to the device from an application or activated by the retransmission instruction, and according to the storage content of the storage means, If the device is connected, execute the command and execute the command. Command execution processing means for erasing a command that has been disconnected, and returning a status of "executing" to the application if the connection information is not connected but identification information is stored, and the connection state is not connected when the device is disconnected. The device disconnection processing means for activating the disconnection timer processing means, the time-out period being set, and waiting for the timeout,
Disconnection timer processing means for discarding the stored command when the device connection processing means is executed during this time, and for deleting the stored device identification information when the timeout occurs. Data transfer control system. 4. The data transfer control system according to claim 2, wherein a time from disconnection of the device to reconnection of the device can be externally set. 5. The device according to claim 2, wherein the identification information of the device is a serial number of the device.
The data transfer control system according to any one of the above. 6. A data transfer control method in which a hot-swappable device is subjected to data transfer, a storage procedure for storing identification information of the device, a command to be issued to the device, and a connection state of the device. When the device is connected, the identification information of the device is obtained from the device and compared with the stored identification information.If there is no match, the stored command is deleted because it is a new connection, and if there is a match, The device connection processing procedure for stopping the disconnection timer and instructing a command retransmission because of the reconnection, and a data transfer request from the application to the device, or activated by the retransmission instruction and according to the stored content, If the device is connected, execute the command to execute the stored command. A command execution processing procedure for erasing the password and returning a status of “executing” to the application if the connection information is not connected but the identification information is stored, and the connection state is set to unconnected when the device is disconnected. , Set the device disconnection processing procedure that starts the disconnection timer processing procedure, and the time-out period, wait for the timeout,
A disconnection timer processing procedure for discarding the stored command when the device connection processing procedure is executed during this time, and for deleting the stored device identification information when the timeout occurs. Data transfer control method. 7. The data transfer control method according to claim 6, further comprising a step of externally setting a time from disconnection of said device to reconnection of said device. 8. A data transfer control method in which a hot-swappable device is a target of data transfer, wherein the storage device stores identification information of the device, a command to be issued to the device, and a connection state of the device. Procedure, when the device is connected, obtains the identification information of the device from the device, compares the identification information with the stored identification information, and if there is a mismatch, deletes the stored command because it is a new connection; and If they match, it is a reconnection, so that the disconnection timer is stopped and a command for retransmitting the command is sent to the device connection processing procedure. If the device is connected, execute the command to execute the stored command. A command execution processing procedure for erasing the password and returning a status of “executing” to the application if the connection information is not connected but the identification information is stored, and the connection state is set to unconnected when the device is disconnected. , Set the device disconnection processing procedure that starts the disconnection timer processing procedure, and the time-out period, wait for the timeout,
A disconnection timer processing procedure for discarding the stored command when the device connection processing procedure is executed during this time, and for deleting the stored device identification information when the timeout occurs. A computer-readable recording medium storing a program for causing a computer to execute the data transfer control method.