US 5,477,242 A · Display adapter for virtual VGA support in XGA native mode

Abstract

Method and apparatus for enabling an XGA display adapter selectively to support VGA graphics mode virtualization during native mode operation of the adapter by rendering VGA graphics assist hardware and certain VGA registers accessible. In a preferred embodiment, the invention comprises an XGA display adapter which includes a host interface for interfacing the display adapter with a central processing unit (CPU) of a personal computer (PC), VGA graphics assist hardware for performing VGA graphics assist functions, a memory controller for reading and writing a video memory of the PC as requested by the CPU during video memory accesses, and a display interface for generating control and timing signals to a display of the PC. The XGA display adapter also includes a XGA Operating Mode Register having three control bits which can be written by applications software selectively to enable or disable the virtual VGA function of the present invention. When the virtual VGA function is enabled, logic circuitry within the host interface examines the CPU address associated with each video memory access to determine whether the access comprises a virtual VGA memory access, rather than a native memory access. If so, the host interface routes CPU address and any data to be written to the video memory at that address, which performs the appropriate graphics assist operations on the address and/or data to enable the requested operation accurately to be performed on a virtual VGA memory buffer portion of the video memory by the memory controller.

Claims21

Dependent claims

An extended graphics array (XGA) controller for a computer display subsystem for selectively enabling support of virtual video graphics array (VGA) graphics modes during XGA native mode operation of said display subsystem, the XGA controller comprising:

a memory controller having an output electrically coupled to an input of a video memory for performing read or write operations on said video memory in response to requests by a central processing unit (CPU), said video memory comprising an XGA memory portion and a VGA memory portion;
VGA graphics assist hardware having an output electrically coupled to an input of said memory controller;
and
a host interface having an input electrically connected to said CPU for receiving said CPU requests, a first output electrically connected to said memory controller and a second output electrically connected to said VGA graphics assist hardware, said host interface comprising circuitry for determining whether each of said CPU requests comprises a request for an XGA memory operation or a request for a VGA memory operation and for routing XGA memory operation requests directly to said memory controller and VGA memory operation requests to said memory controller via said VGA graphics assist hardware;
wherein said VGA graphics assist hardware comprises circuitry for performing VGA graphics assist functions on an address and data of each of said VGA memory operation requests.

2 more elements

Apparatus for enabling VGA graphics mode virtualization during native mode operation of a display adapter, the apparatus comprising:

means for generating a request for an operation to be performed on a video memory means of said display adapter, said video memory comprising a native memory portion and a virtual VGA memory buffer portion;
means connected to receive said request from said generating means for comparing an address of said request with a range of addresses defining a first aperture through which said native memory portion is addressable and with a range of addresses defining a second aperture through which said virtual VGA memory buffer portion is addressable;
means for generating a first signal if said request address falls within said first memory aperture address range and a second signal if said request address falls within said second memory aperture address range;
controller means connected to said comparing means for performing read and write operations on said video memory means;
graphics assist means connected between said comparing means and said controller means for performing graphics assist functions on an address and data of each request input thereto;
means responsive to said first signal for routing said request directly to said controller means, said controller performing said requested operation on said native memory portion;
and
means responsive to said second signal for routing said request to said controller means via said graphics assist means, said controller means performing said requested operation on said virtual VGA memory buffer portion.

5 more elements

Dependencies are inferred from the claim text.

Display adapter for virtual VGA support in XGA native mode

Life of this patent

Display adapter for virtual VGA support in XGA native mode

Life of this patent

Abstract

Claims21