JP2000330761A - Ring buffer control device and ring buffer control method - Google Patents

Abstract

(57) [Problem] To provide a ring buffer control device capable of dynamically changing the capacity of a ring buffer during operation. SOLUTION: When receiving an instruction to change the capacity of a ring buffer, a ring buffer bottom address holding means 101 determines whether or not the highest address can be changed.
1 and the address indicated by the write pointer stored in the write pointer holding means 1003 and the address indicated by the read pointer stored in the read pointer holding means 1007, and the highest address can be changed. When it is determined that the state is not the state, when the address indicated by the read pointer exceeds the highest address, an interrupt signal is generated from the interrupt control means 1005 to change the highest address and change the capacity of the ring buffer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring buffer control device and a ring buffer control method, and more particularly, to a method of setting the highest address of a memory area having continuous addresses as an address logically adjacent to the lowest address, and performing a cyclic operation. The present invention relates to a ring buffer control device and a ring buffer control method for controlling the size of a ring buffer configured so that writing and reading are possible.

[0002]

2. Description of the Related Art In a device such as a printer which operates in response to a command or data transmitted from a host computer, a reception buffer is used for the purpose of absorbing a difference between an operation speed and a data reception speed. As a buffer configuration, a ring buffer that can store data in a FIFO (first-in first-out) system and has a logical ring shape is used.

[0003] In addition to the above-mentioned reception buffer, the printer device also has a so-called recording buffer for storing recording image data in a format that can be handled by the recording mechanism of the printer.

[0004] Normally, the reception buffer and the recording buffer are provided on the same semiconductor and used by dividing the area.
Alternatively, it is formed as a module including a plurality of semiconductor devices, can be accessed as a continuous buffer area, and is configured to divide and use the area.

In a printer, the capacity of a ring buffer and the capacity of a recording buffer are in a trade-off relationship. That is, it is desirable to change the required capacity distribution of the ring buffer and the recording buffer according to the performance of the host computer to be connected, the amount and format of the image data to be transferred, the recording paper and the recording quality, and the like.

If the operation time of the printer or the data transfer waiting time of the host computer is to be minimized, it may be necessary to change the capacity of the ring buffer depending on the situation. For example, there is a case where it is desired to increase the capacity of the ring buffer, or a case where it is desired to reduce the capacity of the ring buffer in order to increase the capacity of the recording buffer.

In order to change the capacity of the ring buffer, it is necessary to stop writing to the ring buffer, read out all the data remaining in the buffer, empty the ring buffer, and then change its size. .

[0008]

When the capacity of the ring buffer is changed as described above, access to the data stored in the ring buffer is prohibited, leading to a decrease in system performance. .

In particular, when the size of the ring buffer is reduced in order to increase the capacity of the image buffer, it is necessary to temporarily save the data in the ring buffer to a buffer other than the ring buffer and the image buffer. This is notable because an evacuation buffer is further required.

The present invention has been made in view of the above situation, and provides a ring buffer control device and a ring buffer control method capable of dynamically changing the capacity of a ring buffer during operation. Aim.

[0011]

In order to achieve the above object, a ring buffer control device according to the present invention sets a highest address of a memory area having continuous addresses as an address logically adjacent to a lowest address, A ring buffer control device for controlling a ring buffer configured to be able to write and read cyclically, wherein a bottom address storage means for storing the highest address and a write pointer indicating an address to be written next. A write pointer storage unit, a read pointer storage unit that stores a read pointer indicating an address to be read next, and a state in which the highest address can be changed when an instruction to change the capacity of the ring buffer is received. Whether or not the highest address, the address indicated by the write pointer and the Determining means for determining from the address indicated by the read pointer; and interrupt control means for generating an interrupt signal when the address indicated by the read pointer exceeds the highest address, wherein the highest address is determined by the determining means. When it is determined that the state cannot be changed, the highest address is changed to change the capacity of the ring buffer when the interrupt signal is received.

According to the ring buffer control method of the present invention, which achieves the above object, the highest address of a memory area having continuous addresses is set as an address logically adjacent to the lowest address, and writing and reading are performed cyclically. A ring buffer control method for controlling a ring buffer configured to be capable of, a bottom address storage step of storing the highest address, and a write pointer storage step of storing a write pointer indicating an address to be written next, A read pointer storing step of storing a read pointer indicating an address to be read next, and determining whether or not the highest address can be changed when an instruction to change the capacity of the ring buffer is received. Address, the address indicated by the write pointer, and the read pointer A judging step of judging from the address indicated by the address, an interrupt control step of generating an interrupt signal when the address indicated by the read pointer exceeds the highest address, and a state in which the highest address cannot be changed by the judging step. And when the interrupt signal is received, the highest address is changed to change the capacity of the ring buffer.

That is, when an instruction to change the capacity of the ring buffer is received, whether or not the highest address can be changed is determined from the highest address, the address indicated by the write pointer, and the address indicated by the read pointer. When it is determined that the highest address cannot be changed, the highest address is changed when an interrupt signal is received, which is generated when the address indicated by the read pointer exceeds the highest address. Change the ring buffer capacity.

With this configuration, when it is determined that the capacity of the ring buffer can be changed, the capacity is changed immediately, and when it is determined that the capacity cannot be changed at present, the capacity is changed when the change becomes possible. Since the capacity can be changed by generating an interrupt signal and notifying the fact, the capacity of the ring buffer can be dynamically changed during operation without saving the data in the ring buffer.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a block diagram showing the configuration of an embodiment of a system using the ring buffer control device of the present invention. The system includes a CPU 101 that controls the entire apparatus.
A ROM 103 for storing a control program, a RAM 105 having an area used as a work memory and a ring buffer, and a ring buffer controller 104 as an embodiment of the ring buffer control device of the present invention for controlling the ring buffer. Are connected to each other.

The CPU 102 reads data stored in the ring buffer via the ring buffer controller 104. In addition, the CPU 101 accesses the various control registers of the ring buffer controller 104 via the bus 101 to control the ring buffer controller 104.

FIG. 3 is a diagram showing the structure of the ring buffer 110. The ring buffer 110 configures a ring-shaped memory area by regarding the lowest address (ring top: RT) and the highest address (ring bottom: RB) of a continuous memory area as logically adjacent to each other. Write the ring-shaped memory to the write pointer (write pointer:
WP) to write data to a position (address), and read data from an address indicated by a read pointer (read pointer: RP).

The ring buffer controller writes data to the address indicated by the current write pointer WP, and further increments the write pointer WP. If the increment exceeds the highest address RB of the ring buffer that has been set in advance, the write pointer WP is set to the lowest address RT of the buffer. The direction in which the pointer moves by increment is
It is counterclockwise as indicated by the arrow CCW in the figure.

Similarly, with respect to the read pointer RP, the read pointer RP is incremented each time the read is performed, and when the read pointer RP exceeds the highest address RB of the ring buffer,
The read pointer RP is set to the lowest address RT of the buffer. By controlling in this way, it is possible to circulate and access the one-dimensional memory in a ring shape.

FIG. 1 shows a ring buffer controller 104 according to an embodiment of the present invention.
FIG. 3 is a block diagram showing the configuration of FIG. The ring buffer controller 104 includes a write control unit 1001, a line / pointer increment unit 1002, a write pointer holding unit 1003, and a comparison unit 1004 as components related to writing, and an interrupt control unit 1005, a read pointer Increment unit 1006, read pointer holding unit 100
7. It has comparison means 1008.

The top address R of the ring buffer
As means for holding the T and the bottom address RB, a ring buffer top address holding means 1010 and a ring buffer bottom address holding means 1011 are provided.

The write control means 1001 can inhibit the write operation by monitoring and suppressing the pointer increment operation of the write pointer increment means 1002.

The interrupt control means 1005 determines that the read pointer RP is
When the data exceeds the bottom address RB held in No. 11, that is, when the data stored in the bottom address RB is read, an interrupt signal is asserted to the CPU 102. The CPU 102 can permit / prohibit the interruption to the interruption control means 1005.

The current values of the read pointer RP and the write pointer WP and the ring buffer top address RT
And the value of the bottom address RB,
Reading or setting is possible from U102.

Next, a method for expanding and reducing the size of the ring buffer in the present embodiment will be described with reference to a specific example.

As described above with reference to FIG. 3, this embodiment assumes that the ring buffer is used cyclically as a one-dimensionally continuous memory. Further, it is assumed that the read pointer RP and the write pointer WP are incremented in the direction CCW in which the buffer address increases.

Here, the description will be made assuming that the area to be deleted / added in accordance with the reduction / expansion of the ring buffer is the area on the higher address RB side of the ring buffer.

The use of the ring buffer and the size reduction / expansion processing in this embodiment are performed as follows. That is, R executed by CPU 102 in FIG.
A program in the OM 103 reads data in a ring buffer in the RAM 105 controlled by the ring buffer controller 104 and performs processing.

Writing data to the ring buffer is as follows:
The processing is performed from hardware (not shown) connected via the bus 101 in FIG. 2 via the ring buffer controller 104. The process of reducing / expanding the size of the ring buffer is started by a function call from a program executed by the CPU 102.

As described above, in this embodiment,
The ring buffer controller 104 has a read pointer R
When the address of P exceeds the address of the ring bottom RB, an interrupt is generated for the CPU 102.

That is, the data is read from the current read pointer RP by software, and an interrupt is generated at the moment when the data corresponding to the ring bottom RB has been read, whereby the interrupt processing routine is called. The interaction between the function for reducing / expanding the size of the ring buffer 110 and the interrupt processing routine realizes the reduction / expansion of the size of the ring buffer 110.

First, a method of expanding the size of the ring buffer 110 will be described with reference to FIG. FIG. 5A shows a state before expansion, and it is recognized that the ring top and the ring bottom of the ring buffer 110 are logically adjacent. Here, when expanding the size of the ring buffer 110, a continuous memory area from the address next to the current ring bottom is prepared as the ring buffer expansion area 120.

Then, as shown in FIG. 5B, the address of the new ring bottom NRB is set as the highest address of the ring buffer extension area 120, and the ring buffer 110 is moved from the ring top RT to the new ring bottom NRB. By re-recognizing the memory area as a continuous memory area up to, it can be used as a new ring buffer 110 whose size has been expanded, as shown in FIG.

Here, a function for expanding the ring buffer will be described. FIG. 7 is a flowchart showing the processing of the “ring expansion” function for expanding the size of the ring buffer. When this function is called with a new ring bottom address as an argument, this argument is stored in an argument storage area provided in the work memory.

First, in step S71, the current RP
(Read pointer) and WP (write pointer) are compared. The case where WP is equal to or larger than RP means that the ring buffer whose values match each other is empty or that data exists but data does not exist across the ring bottom position and the ring top position. Represents the case.

In this case, the ring buffer can be expanded. Therefore, the process proceeds to step S74, and the write control unit 100 of the ring buffer controller 104
1, the writing to the ring buffer is prohibited, and the highest address of the ring buffer extension area 120, which is continuous from the next address of the current ring bottom RB, is set as the new ring bottom NRB. It is set in the means 1011 (step S75).

Thereafter, the writing to the ring buffer prohibited in step S76 is permitted, and the expansion of the ring buffer is completed. In order to indicate that the operation on the ring buffer has been completed normally, a ring buffer operation completion flag prepared as a global variable is set in step S77. This flag is for reference by a ring buffer operation completion confirmation function to be described later.

On the other hand, if RP is larger than WP in step S71, the read pointer RP and the write pointer WP sandwich the current ring top RT and ring bottom RB.
Is present. In this state, expansion cannot be performed unless data is read out until the read pointer RP becomes equal to or greater than the current ring top RT address.

Therefore, the ring buffer controller 104
When the read pointer RP exceeds the address of the ring bottom RB, the CPU 1
02 is set to generate an interrupt. Further, in step S72, the case number "1" is set so that a corresponding process can be performed in an interrupt processing routine described later.
Is stored in the case storage area provided in the work memory. In the interrupt processing routine, it is necessary to divide the processing according to various cases, and thus it is necessary to hold the case numbers.

In step S73, the interrupt mask of the interrupt control means 1001 of the ring buffer controller 104 is released, and the CPU 102 is set so that an interrupt can be generated. This is so that data can be continuously read from the ring buffer until the ring buffer can be expanded.

As a result of reading data by the program,
At the moment when the read pointer RP exceeds the ring bottom RB (when data stored in the ring bottom is read), an interrupt occurs, and an interrupt processing routine described later is called.

Next, a method of reducing the size of the ring buffer will be described with reference to FIG. NRB in the figure
Indicates a new ring bottom, and is an address value in an area currently used as a ring buffer. The memory area from the address following this address to the current ring bottom address is removed from the ring buffer 110 as the ring buffer deletion area 130 as shown in FIG.

FIG. 4C shows the ring buffer deletion area 13.
This shows the state of the ring buffer 110 after 0 has been removed, and the ring buffer 110 is recognized as a ring-shaped area where the NRB and the RT are adjacent to each other.

The size of the ring buffer is reduced by calling a "ring reduction" function from a program. When calling the function, the amount of buffer to be deleted is passed as an argument. This argument is stored in the argument holding area of the work area.

In this embodiment, cases are classified according to the magnitude relationship between the addresses pointed to by the read pointer and the write pointer at the time when the ring reduction function is called, and the new ring bottom address. FIG. 6 is a diagram illustrating a state of the case 1 and the case 2 in the present embodiment.

In case 1 shown in FIG. 6A, NRB ≧ W
This is the case where P ≧ RP ≧ RT, which is indicated by hatching in the figure.
Data area 14 that has been written but not read
0, that is, the case where the area from the address indicated by the read pointer RP to the address indicated by the write pointer WP is not included in the ring buffer deletion area 130 (NRB to RB).

On the other hand, Case 2 shown in FIG.
≧ NRB and WP ≧ RP, and a part of the data area 140 that has been written but not read is the ring buffer deletion area 130 (NRB to RB).
And only the address pointed to by the write pointer RT is in the deletion area.

Next, the operation of the "ring reduction" function will be described with reference to the flowchart of FIG. First, the ring reduction function prohibits writing to the ring buffer in step S801, and then in step S802, a branch determination is made as to whether the current state of the ring buffer corresponds to case 1, case 2, or other. .

In case 1, since there is no data in the deletion area, the data can be deleted immediately. Therefore, the process proceeds to step S803, and the new ring bottom address NRB calculated from the deletion buffer amount given as an argument and the current ring bottom address RB is set in the ring buffer bottom address holding unit 1011. Thereafter, in step S804, writing to the prohibited ring buffer is permitted. Finally, in step S805, the ring buffer operation completion flag is set to complete the reduction of the ring buffer.

In case 2, the portion from the address pointed to by the write pointer RT to the ring bottom address RB in the deletion area contains no data and can be deleted. This is performed by setting the address value indicated by the current write pointer RP in the ring bottom address holding unit 1011 in step S806. In this case, even after the part that can be deleted is deleted, the write pointer R
Since data to be read exists up to the address indicated by P, it is necessary to wait for completion of data reading by the program.

Therefore, in step S807, the corresponding processing can be performed later in the interrupt processing routine.
The case number “2” is stored in a case storage area provided in the work memory. Then, in step S808, the interrupt mask is released so that an interrupt occurs when the reading of data proceeds and the read pointer RP exceeds the ring buffer bottom address RB.

Other cases that do not correspond to Case 1 or Case 2 are referred to as Case 3. In this case, since the read pointer exists at least in the ring buffer deletion area, even a part of the area cannot be deleted. Therefore, there is no choice but to wait until the read pointer reaches the ring bottom. In this case, in step S809, case number "3"
Is stored in the case storage area provided in the work memory. Then, in step S810, the data reading proceeds, and the interrupt mask is released so that an interrupt occurs when the read pointer exceeds the ring buffer bottom address.

When the processing by the ring reduction function is completed as described above, the program that has called the ring reduction function calls a ring operation end confirmation function, which will be described later, and checks the return value. At this time, if the return value is “FALSE”, it means that the delete operation has not been completed, so that the data read from the ring buffer is continued, and the ring operation end confirmation function is called periodically or as needed. You need to confirm the completion of buffer reduction.

Next, the processing in the interrupt handler will be described with reference to the flowchart in FIG. When an interrupt occurs, the contents of the case number storage area are checked in step S91, and the process branches depending on the case number. The types of interrupts in the present embodiment include a case 1 corresponding to step S72 of “ring expansion” described with reference to FIG. 7, and a case 2 corresponding to steps S807 and S809 of “ring reduction” described with reference to FIG. Case 3 is three types.

In the process for case number "1", first, writing to the ring buffer is prohibited in step S92, and in step S93, the new ring buffer bottom address NRB read from the argument storage area is stored in the ring buffer bottom address holding means 1011. And reconfigure the ring buffer. Thereafter, writing to the ring buffer, which was prohibited in step S94, is permitted. Finally, in step S92, a ring buffer operation completion flag is set to complete the expansion of the ring buffer.

In the processing for the case numbers "2" and "3", the new ring buffer bottom address NRB read from the argument storage area is set in the ring buffer bottom address holding means 1011 in step S96, and the ring buffer is reconfigured. . Thereafter, the writing into the ring buffer, which was prohibited in step S97, is permitted. Finally, in step S98, the ring buffer operation completion flag is set, and the reduction of the ring buffer is completed.

As described above, in the processing for the case numbers "2" and "3", the write to the ring buffer, which is performed in the processing for the case number "1", is not inhibited. This is step S of the ring buffer reduction function.
This is because 801 has already been prohibited.

The ring buffer operation functions such as the ring expansion function and the ring reduction function do not always complete the operation on the ring buffer at the time of return. Therefore, it is necessary to call a separately provided ring operation end confirmation function shown in FIG. 10 and confirm that the return value is “TRUE”.

In the processing by the ring operation end confirmation function, it is confirmed whether or not the ring buffer completion flag is set in step S101. If the flag is set, the process proceeds to step S102, and "TRUE" is returned as a return value. If not, the flow advances to step S103 to return "FALSE" as a return value.

According to the above-described embodiment, the size of the ring buffer is dynamically changed by generating an interrupt when the read pointer of the ring buffer exceeds the ring bottom address. This allows efficient use of the buffer.

Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus including one device (for example, a copier, a facsimile) Device).

Further, an object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and a computer (a computer) of the system or the apparatus. It is needless to say that the present invention can also be achieved by a CPU or an MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. Also,
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also the operating system (OS) running on the computer based on the instructions of the program code.
It is needless to say that a case in which the functions of the above-described embodiments are implemented by performing part or all of the actual processing.

Further, after the program code read from the storage medium is written into the memory provided in the function expansion card inserted into the computer or the function expansion unit connected to the computer, the program code is read based on the instruction of the program code. Needless to say, the CPU included in the function expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

When the present invention is applied to the above-mentioned storage medium, the storage medium described above (FIGS. 7, 8, 9 and / or
Alternatively, a program code corresponding to the flowchart (shown in FIG. 10) is stored.

[0066]

As described above in detail, according to the present invention, when it is determined that the capacity of the ring buffer can be changed, the capacity is changed immediately, and it is determined that the capacity cannot be changed at present. When a change is possible, an interrupt signal can be generated to notify the fact and the capacity can be changed, so the ring buffer can be dynamically changed during operation without saving the data in the ring buffer. There is an effect that the capacity of the data can be changed.

Particularly, in an apparatus in which a memory area is divided and used as two buffer areas, the allocation of two buffers can be changed as appropriate according to the operation state of the apparatus, the data transfer rate, and the like. It is valid.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a ring buffer controller of the present invention.

FIG. 2 is a block diagram showing the configuration of the entire system.

FIG. 3 is a diagram showing a structure of a ring buffer.

FIG. 4 is a diagram for explaining a reduction process of a ring buffer;

FIG. 5 is a diagram for explaining a process of expanding a ring buffer;

FIG. 6 is a diagram for explaining the case division when the ring buffer is reduced.

FIG. 7 is a flowchart illustrating processing of an extension function of a ring buffer.

FIG. 8 is a flowchart showing processing of a ring buffer reduction function.

FIG. 9 is a flowchart illustrating processing of an interrupt handler function.

FIG. 10 is a flowchart illustrating processing of a ring operation end confirmation function.

[Explanation of symbols]

 101 Bus 102 CPU 103 ROM 104 Ring buffer controller 105 RAM 110 Ring buffer 120 Extended area 130 Delete area 140 Data area 1001 Write control means 1002 Write pointer increment means 1003 Write pointer holding means 1004 Comparison means 1005 Interrupt control means 1006 Read pointer increment means 1007 read pointer holding means 1008 comparing means 1010 ring buffer top address holding means 1011 ring buffer bottom address holding means

Claims (11)

[Claims] 1. A ring buffer control for setting a highest address of a memory area having continuous addresses as an address logically adjacent to a lowest address, and controlling a ring buffer configured to be able to write and read cyclically. An apparatus, comprising: a bottom address storage means for storing the highest address; a write pointer storage means for storing a write pointer indicating an address to be written next; and a read pointer for storing a read pointer indicating an address to be read next. Storage means, when receiving an instruction to change the capacity of the ring buffer, determines whether or not the highest address can be changed, by determining the highest address, the address indicated by the write pointer, and the read pointer. Determining means for determining from the indicated address; Interrupt control means for generating an interrupt signal when the address indicated by the address exceeds the highest address.When the determination means determines that the highest address cannot be changed, the interrupt signal is output. The ring buffer control device is configured to change the highest address and change the capacity of the ring buffer when receiving the ring buffer. 2. The ring buffer control device according to claim 1, wherein the instruction to change the capacity of the ring buffer is transmitted together with an address to be newly set as the highest address. 3. The high-order address can be changed when an address indicated by the read pointer is larger than an address indicated by the write pointer when an instruction to expand the capacity of the ring buffer is received. 3. The ring buffer control device according to claim 1, wherein it is determined that the state is not the state. 4. The method according to claim 1, wherein when the instruction to reduce the capacity of the ring buffer is received, the address to be newly set as the highest address is equal to or greater than the address indicated by the write pointer. 3. The ring buffer control device according to claim 2, wherein when the address indicated by is higher than the address indicated by the read pointer, it is determined that the highest address can be changed. 5. When the determination means receives an instruction to reduce the capacity of the ring buffer, the address to be the new highest address is smaller than the address indicated by the write pointer, and 5. The method according to claim 4, wherein when the indicated address is equal to or greater than the address indicated by the read pointer, it is determined that the highest address cannot be changed, and the address indicated by the write pointer is set as the highest address.
3. The ring buffer control device according to item 1. 6. A memory module having a continuous memory area, wherein a memory area of the memory module is divided, one of which is used as a reception buffer for temporarily storing reception data, and the other is used for recording data. A recording device configured to be used as a recording buffer for temporarily storing, wherein the reception buffer is configured to receive the signal from the ring buffer controlled by the ring buffer control device according to any one of claims 1 to 5. A recording device, comprising: 7. A ring buffer control for setting a highest address of a memory area having continuous addresses as an address logically adjacent to a lowest address, and controlling a ring buffer configured to be capable of cyclically writing and reading. A bottom address storing step of storing the highest address, a write pointer storing step of storing a write pointer indicating an address to be written next, and a read pointer storing a read pointer indicating an address to be read next. A storage step, when receiving an instruction to change the capacity of the ring buffer, determines whether or not the highest address can be changed, by determining the highest address, the address indicated by the write pointer, and the read pointer. A determination step for determining from the indicated address; An interrupt control step of generating an interrupt signal when the address indicated by the address exceeds the highest address; and receiving the interrupt signal when the determination step determines that the highest address is not in a changeable state. An interrupt changing step of changing the highest-order address and changing the capacity of the ring buffer at the time of execution. 8. The ring buffer control method according to claim 7, wherein the instruction to change the capacity of the ring buffer is transmitted together with an address to be newly set as the highest address. 9. The method according to claim 1, wherein the determining step is configured to change the highest address when an address indicated by the read pointer is larger than an address indicated by the write pointer when an instruction to expand the capacity of the ring buffer is received. 9. The ring buffer control method according to claim 7, wherein it is determined that the state is not the state. 10. The method according to claim 1, wherein when the instruction to reduce the capacity of the ring buffer is received, the address to be newly set as the highest address is equal to or greater than the address indicated by the write pointer. 9. The ring buffer control method according to claim 8, wherein when the address indicated by is higher than the address indicated by the read pointer, it is determined that the highest address can be changed. 11. The method according to claim 11, wherein when the instruction to reduce the capacity of the ring buffer is received, the address to be the new highest address is smaller than the address indicated by the write pointer, and 11. The method according to claim 10, wherein when the indicated address is equal to or larger than the address indicated by the read pointer, it is determined that the highest address cannot be changed, and the address indicated by the write pointer is set as the highest address. 3. The ring buffer control method according to 1.