| 摘要 |
A CPU or other graphics processor provides a pixel data stream to a graphics controller over a system bus. The pixel data stream includes a graphics controller address as well as a pixel type tag, which in the presently preferred embodiment comprises 4 bits. In addition to the graphic controller address and pixel type tag, a pixel address and pixel data are provided. The pixel type tag identifies the "type" of pixel data in the data stream supplied to the graphics controller. If the data identified by the pixel type tag corresponds to the type of data which the frame buffer is configured for, then the data provided over the system bus is simply passed through the graphics controller and written at the appropriate pixel address in the frame buffer. If, however, the pixel type tag indicates that the data is not of the same type as that for which the frame buffer is configured, then the graphic controller executes a conversion algorithm to convert the pixel data to a single pixel type acceptable to the frame buffer, and the data is then written into the frame buffer at the pixel address identified by the pixel address. Pixel type tagging is accomplished, in the preferred embodiment, in bits 27:24 of the physical address used to write pixels into the frame buffer. The CPU, or other graphics engine source, affixes the tag to the pixel data, thereby identifying its format. In the present embodiment, MDA tagging applies only to pixel write commands and not to commands reading from the frame buffer. Accordingly, the use of a pixel type tag field in the pixel data permits a graphics system to utilize a variety of standard pixel types by a CPU, graphics controller or other graphics source, while permitting the frame buffer to utilize a single pixel type to be stored in the frame buffer for subsequent display.
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