JPS61190640A - Access system of picture memory - Google Patents

Abstract

PURPOSE:To eliminate unnecessary access to raise the picture processing speed by determining the precedence of access in accordance with the quantity of data in an output buffer. CONSTITUTION:An access controller 1-2 monitors always the quantity of data in a buffer 1-3. When the quantity of data is smaller than n numbers of bytes of a required value, the access controller 1-2 transmits an access permitting signal to a CRT controller 3. Consequently, data is transferred to the buffer 1-3 from a picture memory 1-1 when data in the buffer 1-3 is smaller than n numbers of bytes. If the quantity of data in the buffer 1-3 is lager than n number of bytes, the access controller 1-2 transmits the access permitting signal to a central processing unit 2 and permits only the central processing unit to access.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an image memory access method, and in particular to an image memory access method when the image memory is shared and accessed by a central processing unit and a display control device. It is related to.

BACKGROUND ART Image processing using a central processing unit is being performed in many fields. This image processing involves storing image data in a central processing unit system in a serial-to-parallel conversion circuit in required units, and displaying the stored image data as a video signal on an output device, such as a CRT display device. Furthermore, when image memory is rewritten, it is generally performed by the central processing unit, so it is accessed in common with the image control device.

Therefore, there is a need for an image memory access method that allows image processing to be performed at high speed without interfering with the efficiency of the central processing unit.

[Conventional technology]

Conventionally, two methods have been adopted as means for resolving bus contention by sharing an image memory between a central processing unit and an image control apparatus.

That is, a method in which the central processing unit accesses the image memory when the image control device is not accessing the image memory, and a method in which both parties acquire the image memory, that is, the bus, respectively, during different periods of the basic clock. It is.

The central processing unit 2 image control device has no priority order of access, resulting in the inconvenience of accessing at unnecessary timing.

[Problem that the invention seeks to solve]

The conventional method described above has the disadvantage that the central processing unit 9 and the image control device have no priority order of access, and access is made at unnecessary timing.

The present invention proposes an image memory access method in which image memory is accessed according to priority order and image processing can be performed efficiently and at high speed.

[Means for solving problems]

The present invention proposes an image memory access method in which the image memory can be accessed according to the priority order. This is achieved by an image memory access method in which a buffer is provided for the image data, and a plurality of reference values are provided for the amount of data in the buffer, and priorities are determined based on the reference values.

[Effect]

The image memory access method described above determines the priority of the accessing device based on the reference value of the amount of data in the buffer, so there is no wasted access, and image processing by the central processing unit is performed at high speed and is efficient. Become.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of essential parts of an embodiment of the present invention. The image memory device 1 is composed of an image memory 1-1, an access control device 1-2, and a buffer 1-3. The image memory 1-1 is shared by the central processing unit 2 and the CRT control unit 3. The access control device 1-2 provides an image memory 1-2 for the central processing unit 2 and the CRT control device 3.
1 access permission signal is output. In response to this access permission signal, the central processing unit 2 outputs an address and processes (writes/reads) data at the corresponding address in the image memory 1-1.

On the other hand, the CRT control device 3 similarly outputs an address in response to the permission signal, and stores the data at the corresponding address in the image memory 1-1 in the buffer 1-3 since the CRT control device 3 generally does not read it. The data in buffers 1-3 is converted into a video signal and displayed as an image on a CRT display device.

The access control device 1-2 constantly monitors the amount of data in the buffer 1-3. When this amount of data becomes less than the required value n bytes, the access control device 1-2
An access permission signal is sent to the control device 3. Therefore, when the data in buffers 1-3 becomes n bytes or less,
Data will be transferred from the image memory 1-1.

If the amount of data in the buffer 1-3 is greater than n bytes, the access control device 1-2 sends an access permission signal to the central processing unit 2, and only accesses the central processing unit.

Of course, it goes without saying that the above n bytes can be set arbitrarily.

The priority order of devices that access the image memory is determined by the amount of data required for image display.

〔Effect of the invention〕

As explained above, according to the present invention, the priority of access is determined depending on the amount of data in the output buffer, and efficient image processing can be performed without wasting access, and the speed of image processing can be improved. It has many advantages.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of essential parts of an embodiment of the present invention. In the figure, ■ is an image memory device, 2 is a central processing unit,
Reference numeral 3 indicates a CRT control device, 1-1 an image memory, 1-2 an access control device, and 1-3 a buffer.

Claims (1)

[Claims] In a system in which an image memory device consisting of an image memory and an access control unit that controls access to the image memory is shared by a central processing unit and an image control device, a buffer for an output device is attached to the image memory, and a buffer for an output device is attached to the image memory. An image memory access method characterized in that a reference value is provided for the amount of data in a buffer, and access priority is determined when the data stored in the buffer exceeds the reference value.