ENHANCED TEXTURE MAP DATA FETCHING CIRCUIT AND METHOD

摘要

A circuit and method for increasing the processing efficiency of texture map data requests within a 3D subunit of a computer controlled graphics display system. The 3D graphics display subsystem includes a polygon engine, a texture map engine and a pixel pipeline. The texture map engine contains a texture map data access (TDA) circuit having a cache controller with a computer readable cache memory for containing recently used texture maps stored in (u, v) coordinate space. The cache controller is limited in handling only n cache miss operations simultaneously. In one embodiment, n is 1. The TDA circuit also contains a texture map address (TMA) FIFO memory unit for storing texture map addresses associated with texture data requests that hit or missed in the cache memory unit. Since the cache controller handles up to n misses, the texture engine stalls when the (n+1)<th> unprocessed texture request miss is encountered. Therefore, the TMA FIFO at any time contains at most n miss addresses therein. Processing efficiency is increased when a miss is encountered but the TMA FIFO contains unprocessed hit addresses. At this time, simultaneously with the cache controller fetching the texture data for the missed address, it can also advantageously: (1) supply data from the cache memory for the previously encountered and stored hit addresses; and (2) accept new hit addresses into the TMA FIFO thereby effectively avoiding a texture engine stall. This is quite unlike the prior art systems which process no hit addresses upon a texture miss but rather stall the texture engine.