Computer graphics system with dual fifo interface

Abstract

A computer system has a graphics subsystem employing a rasterizer and a frame buffer, with a digital-to-analog converter for producing drive signals to a video display. A bus interface acts as a gateway between a PCI bus and the graphics subsystem; this interface manages commands and DMAs passing between the host processor and various parts of the graphics subsystem. Within the interface, two command FIFOs are employed, one for storing commands/data sent from the host for 2D display (window management) and another for 3D applications. Using two command FIFOs eliminates the need for host semaphore, FIFO draining, and the latency associated with these operations. Timers are provided in the interface, associated with the two command FIFOs, to manage and regulate the frequency with which the system automatically switches between 2D and 3D FIFO processing. Host intervention is minimized by use of a context macro store for holding locally the sequences for context save and context restore which are used repeatedly.