Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus access regulation
Patent
1996-09-30
2000-01-18
Sheikh, Ayaz R.
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus access regulation
710113, 710107, 710 45, G06F 1314
Patent
active
060165278
ABSTRACT:
Methods and associated apparatus for improving the fairness of bus allocation in association with standard SCSI bus arbitration. The present invention provide a plurality of time slots each of which define a delay period following the SCSI specified minimum period before arbitration is allowed to begin. Each device which requires arbitration on the SCSI bus pseudo-randomly selects one of the time slots before attempting SCSI bus arbitration. The device then delays the associated period of time before commencing SCSI bus arbitration. At any time before the end of the delay period, if the device senses that the SCSI bus has again become busy, then the device has already lost the arbitration without actually competing therefore. A second device, having selected a time slot with a shorter delay period, has won control of the SCSI bus before the first device attempted arbitration. The time slots are selected with a probability associated with each slot. To reduce the maximum added delay in arbitration, heuristic methods are applied to reduce the number of time slots and assign the probabilities to each slot for use by each SCSI. A first preferred embodiment assigns probabilities for up to seven SCSI devices sharing four time slots. A second preferred embodiment assigns probabilities for up to fourteen SCSI devices sharing five time slots. The methods of the present invention may be embodied in control programs operable within the SCSI devices or in mounting components (boards, cables and canisters) which physically and electronically connect the devices to a SCSI bus.
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Elements of Queuing Theory for System Design; A.O. Allen; 1975; pp. 161-187 .
LSI Logic Corporation
Phan Raymond N
Sheikh Ayaz R.
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