| 摘要 |
A method and apparatus for bus arbitration with weighted bandwidth allocation are described. Each bus agent is assigned a weight that governs the percentage of bus bandwidth allocated to the agent. An agent is granted control of the bus base, at least in part, upon its weight. The weight corresponds to the number of arbitration states assigned to the agent, where each state represents a grant of bus control. If a first agent is assigned a weight W and all agents together are assigned a total weight Z, an arbiter guarantees bus control to the first agent for at least W arbitrations out of Z arbitrations in which the first agent requests bus control. By employing this scheme, the first agent is guaranteed a fraction W/Z of the bus bandwidth. To ensure flexibility of bandwidth allocation, the weith may be programmed using conventional memory-mapped techniques. The arbitration scheme of the present invention can be split into multiple levels of hierarchy, where arbitration at each level is controlled by an independent state machine. When an agent wins arbitration at one level, it is passed to the next higher level where it competes with other agents at that level for bus access. A bus agent may also raise the priority of its request based upon the urgency of the request. If a low priority request is not acknowledged after the expiration of a predetermined waiting period, then the agent raises the request to a high priority request. The waiting period is selected so that the agent will be guaranteed access to the bus within a worst case latency period after asserting a request.
|
