Memory request and control unit including a mechanism for issuing and

Abstract

The present invention is directed to a display FIFO module for use in DRAM interface that includes a DRAM controller sequencer which prioritizes requests for DRAM access received from various modules, such as a CPU, a blit engine module, and a half frame buffer logic module, etc. The display FIFO module is connected between the DRAM controller sequencer and a display pipeline which is connected to a display device. The display FIFO module issues low and high priority requests for DRAM access to the DRAM controller sequencer for loading the FIFO with display data to be transferred to the display device. The low priority request is issued at the earliest time when the display FIFO is capable of accepting new data without overwriting unread data. This is determined by comparing the FIFO data level against a predetermined low threshold value. The low priority request is issued when the FIFO data level falls below or is equal to the low threshold value. A high priority request is issued when the FIFO mug receive new data or FIFO underrun will occur. This is determined by comparing the FIFO data level against a predetermined high threshold value. The high priority request is issued when the FIFO data level falls below or is equal to the high threshold value.