| 摘要 |
The shared computer system memory is partitioned between system memory and frame buffer memory. The memory controller and the graphics controller share access to the computer system memory through a single interface bus. An arbitration unit is provided to arbitrate competing usage requests to the memory from the memory controller and the graphics controller. The arbitration unit may form a portion of the memory controller or may be configured as a stand alone unit. In either case, the arbitration unit resolves competing usage requests by applying a prioritization protocol. The arbitration unit grants control of the memory to either the memory controller or the graphics controller depending upon which has asserted a higher priority request. Once the graphics controller has been granted control of the memory, the arbitration unit cannot revoke control from the graphics controller. Rather, the arbitration unit requests that the graphics controller relinquish control. In one embodiment, communication between the arbitration unit and the graphics controller utilizes only two signal lines, a request line and a grant line. A two-wire protocol is disclosed which allows the graphics controller to assert two different levels of priority requests using the single request line. Method and apparatus embodiments of the invention are disclosed.
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