Multimedia system employing timers to properly allocate bus...

Details Multimedia system employing timers to properly allocate bus... Multimedia system employing timers to properly allocate bus...

1994-12-19

2001-01-23

Donaghue, Larry D. (Department: 2783)

Electrical computers and digital data processing systems: input/

Intrasystem connection

Bus access regulation

C710S117000, C710S113000

Reexamination Certificate

active

06178475

ABSTRACT:

BACKGROUND OF THE INVENTION
When many devices are connected to a data bus, such as in a multi-media application, conflicts will occur where two devices request access to the bus at the same time. To resolve these conflicts, arbiters have been developed to grant bus access to the device having the highest priority. Thus, when two devices are in contention for the bus, the arbiter first gives access to the device with the higher priority of the two and subsequently gives access to the device with the lower priority.
In a system with such an arbiter, a device with a very high priority will get frequent access to the bus while a device with a low priority will get infrequent access to the bus. This can present a problem when the devices are assigned their priorities during system initialization or boot-up such that the relative priorities of the devices do not change over time. A situation can exist where a low priority device needs access to the bus in order to continue functioning but cannot obtain access because a high priority device which does not necessarily need access happens to be requesting bus access coincidentally. Thus, although the system is granting access on a priority basis, inefficiencies can result where low priority devices experience idle time or malfunction.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to improve the efficiency of systems where multiple devices request access to a data bus by providing an arbiter with a capability for updating the priority of the respective devices during processing. More specifically, the arbiter of the present invention will utilize timers corresponding to each device. The timers will indicate an elapsed time since each device last had access to the bus. The arbiter will then grant access to the bus based on the values of the timers.
It is a further object of the present invention to provide a method of granting bus access to a plurality of devices via a bus arbiter which determines priority based upon the time since each device last had access to the bus.
It is a further object of the invention to provide an arbiter which calculates the priority of each device based not only on the time since each device last had access to the bus, but also on the amount of data needed by the device.
It is a further object of the invention to provide an arbiter which calculates the priority of each device based not only on the time since each device last had access to the bus and on the amount of data needed by the device, but also on the data transfer rate of each device.
One embodiment of the present invention comprises a bus connected to a plurality of devices through an arbiter. At least one of the devices has a corresponding timer indicating a value representing the elapsed time since the device last accessed the bus. The arbiter thus grants access to the bus based on the value of the timer. This embodiment can be expanded to associate a timer with each device. This embodiment can also be expanded to include a minimum access interval for one or more of the devices. The timer can then either count up to the minimum access interval from zero, or count down to zero from the minimum access interval. The arbiter can then determine the relative priority for each device based on the time since the device last had access to the bus and the minimum access interval for the device.


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IBMTechnical Disclosure Bulletin, vol. 37, No. 10, 10/94, pp. 461-462.

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