JPH02291035A - Access system for graphic vram - Google Patents

Abstract

PURPOSE:To switch the picture of a graphic video RAM (VRAM) without being conscious of the operation by providing a CPU and a page table to store correspondence between a virtual page and a physical page and converting a virtual address to be sent from the CPU to a physical address by referring a page address. CONSTITUTION:A page table 3 stores the page number of the virtual address, a flag to show whether the correspondent physical page exists in the page or not and the page number of the correspondent physical page when the page exists. An address converter 2 retrieves the page table 3 according to the page number of the virtual page. When the page is correspondent to the page of a physical space, offset is synthesized with the page of the physical space and the physical address is generated. When the page is not correspondent, interruption is generated in a CPU 1. Thus, a procedure for accessing the graphic VRAM can be processed without being conscious of switching the picture of the graphic VRAM.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an access method for a graphic VRAM (video RAM), and more particularly to an access method for a graphic VRAM that allows switching between sides of the graphic VRAM without being aware of it.

(Prior Art) Conventionally, in a graphic display, a graphic V of a bit map memory of a graphic display figure is
If the plane corresponding to the display color of the RAM occupies the same address space on the main memory and only one side of the day can be accessed from the CPU at any time, then when drawing to the graphic VRAM, the side that is different from the currently accessed side At the time of accessing the page, the accessible side was switched.

(Problem to be Solved by the Invention) As described above, in the conventional method, access to the graphic VRAM is performed by switching the access surface, but graphic drawing is performed between other main memories and the graphic VRAM, and between the graphic VRAMs. When performing copying or logical operations, you must always be aware of switching the graphic VRAM surface, so copying and logical operations are performed for each combination.
The disadvantage is that routines for logical operations must be created.

(Means for solving the problem) The access method of the graphic VRAM according to the present invention is as follows:
It is equipped with a CPU, a page table that stores the correspondence between virtual pages and physical pages, and an address converter that refers to the page address and converts the virtual address sent from the CPU into a physical address, and corresponds to the display color. A plurality of surfaces of the Zuru graphic VRAM have the same physical address.

(Example) Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of a graphic VRAM access method according to the present invention.

The address converter 2 converts the virtual address sent from the C'P U 1 into a physical address. The virtual space is divided into fixed-length pages, and the virtual address is
It is composed of this page number and offset within the page.

The page table 3 stores a page number of a virtual address, a flag indicating whether a physical page corresponding to the page exists, and if so, the corresponding physical page number.

The address converter 2 searches the page table 3 using the page number of the virtual address, and if the page corresponds to a page in the physical space, the page in the physical space and the offset 1 to
to generate a physical address. Moreover, if it is not supported, an interrupt is generated to the CPU.

FIG. 2 shows the configuration of the main memory 4, and the graphic V
RAM5 occupies the space from physical addresses GVI to GV2. The physical page of this space is shifted from PGI to PGn.

As shown in Fig. 3, there are three graphic VRAMs 6 to 8 corresponding to the basic display colors of red (R), green (G), and blue (B) in the same space. are shared. When accessing this graphic VRAM, the surface to be accessed is designated by the CPU and then accessed.

FIG. 4 shows the virtual space provided by the memory management procedure M. On this space, the R side 6 of the graphic VRAM is V2 (space 10) from address ■1, and the G side 7 is address ■2.
Therefore, V3 (space 1 1 ), B side 8 occupies V4 (space 12) from address ■3. The page numbers occupied by each side are vpR, to ■PRo, ■Po1 to vp.
o. ．． ．． vp. , to vpI]. Tozuru. In the page table 3, ① PGI to PG are set as PR1 to VPRfik physical pages. vPo1 to vp.
,,, ■ Do the same from PBl to v p lIn.

Next, regarding operation, address conversion and graphic VRAM
Referring also to FIG. 5, which shows a flowchart of surface switching, procedure P is graphic ■RA. G side 7 of M
This will be explained using an example of accessing .

Procedure P generates an address VG in the range from address (2) to (3) in order to access the G plane 7 of the graphic VRAM. This address ■G is sent from the CPU 1 to the address converter 2.

The address converter 2 converts the page number VP from the address VG.
(without taking out l If it indicates that the G plane 7 is accessible (step 13), the address converter 2 accesses the corresponding physical page PGX.
is extracted and combined with the offset to generate a physical address (step 14).

If the flag for page number vPGx of page table 3 does not exist in memory, that is, it indicates that G plane 7 of graphic VRAM is inaccessible (step 13), address converter 2 generates an interrupt. let

The interrupt causes the CPUI to transfer control to the memory management procedure. The memory management procedure identifies the access to the G surface 7 of the graphic VRAM from the address VG to be converted. After identification, the accessible surface is designated as G surface 7 (step 15).

Next, page V P representing G side 7 of page table 3
o+ to vpo. The flags up to (step 16) are set to indicate "existence in memory". R
Flags from page VP n + to VPRfi without side 6, pages ■PII1 to ■P[l without side B 8
The flag at the n-ma is set to indicate that "memory F does not exist" (step 16).

After setting, the control is returned from the memory management procedure M to the procedure P, and the process is re-executed from the time when the G plane 7 of the graphic VRAM is accessed.

The same procedure is repeated when accessing other surfaces.

(Effects of the Invention) As explained above, in the present invention, the surface of the graphic VRAM is switched in the memory management procedure that controls virtual memory, so the procedure for accessing the graphic VRAM changes the surface of the graphic VRAM. This has the advantage of being able to perform processing without being aware of switching.

A block diagram showing an embodiment of the access method, FIG. 2 is a block diagram of the main memory 4 in this embodiment, and FIG. 3 is a graphic V
FIG. 4 is a configuration diagram of the RAM 5, and FIG. 5 is a configuration diagram of the virtual space 9.
The figure is a flowchart showing the processing procedure for address conversion and graphic VRAM surface switching.

1...CPU, 2...Address converter, 3...
・Page table, 4... Main memory, 5... Graphic VRAM0

Claims (1)

[Claims] It is equipped with a CPU, a page table that stores the correspondence between virtual pages and physical pages, and an address converter that refers to the page address and converts the virtual address sent from the CPU into a physical address, and corresponds to the display color. An access method for a graphic VRAM characterized in that a plurality of surfaces of the graphic VRAM have the same physical address.