Arbitration means for controlling access to a bus shared by a number of modules

摘要

An arbitration mechanism comprising a request FIFO (408) for storing ones and zeros corresponding to received requests in the order that they are made. A one indicates that the request was made by the module in which the FIFO is located, and a zero indicates that the request was made by one of a number of other similar modules. The request status information from the other modules is received over signal lines (411) connected between the modules. This logic separates multiple requests into time-ordered slots, such that all requests in a particular time slot may be serviced before any requests in the next time slot. A store (409) stores a unique logical module number. An arbiter (410) examines this logical number bit-by-bit in successive cycles and places a one in a grant queue (412) upon the condition that the bit examined in a particular cycle is a zero and signals this condition over the signal lines. If the bit examined in a particular cycle is a one, the arbiter drops out of contention and signals this condition over the signal lines (411). This logic orders multiple requests within a single time slot, which requests are made by multiple modules, in accordance with the logical module numbers of the modules making the requests. The grant queue (412) stores status information (ones and zeros) corresponding to granted requests in the order that they are granted-a one indicating that the granted request was granted to the module in which the grant queue is located, and a zero indicating that the granted request was granted to one of the other modules. The granted request status information from the other modules is received over the signal lines (411). This logic separates multiple granted requests such that only one request corresponding to a particular module is at the head of any one grant queue at any one time.