Priority arbiter with shifting sequential priority scheme

A data processing system comprising:

• a priority device;
• a plurality of devices having shifting priorities, wherein each device within the plurality of devices has a priority relative to other devices within the plurality of devices;
• detection means for detecting requests from a number of devices within the plurality of devices for access to the shared resource;
• identification means for identifying each device within the number of devices;
• first granting means, responsive to detecting a request from the priority device, for granting the priority device to access the shared resource;
• second granting means, responsive to detecting requests from a number of devices within the plurality of devices, for granting access to a device within the number of devices having a highest priority among the number of devices from which the requests were detected;
• and
• shifting means, responsive to the second granting means granting access to a device, for shifting the priority of the device having the highest priority to a lowest priority and for shifting the priority of remaining devices within the plurality of devices having shifting priorities.

A method for arbitrating access to a shared resource among devices in a data processing system, wherein the devices include a device of a first type and a plurality of devices of a second type, the method comprising:

• monitoring the devices for requests for the shared resource;
• granting the device of the first type access to the shared resource in response to detecting a request from the first device;
• granting access to a selected device within the plurality of second devices of the second type in response to a request from the selected device and an absence of a request from the device of the first type, wherein the selected device has a greater priority than other devices within the plurality devices of the second type;
• and
• changing priorities among the plurality of devices of the second type, wherein the selected device has a lowest priority.

A data processing system comprising:

• a shared resource;
• a priority device coupled to the shared resource;
• a plurality of shifting priority devices coupled to the shared resource;
• an arbiter coupled to the shared resource, wherein the arbiter has a plurality of modes of operation including:
• a first mode of operation in which the arbiter monitors for requests for the shared resource;
• a second mode of operation, responsive to detecting at least one request for the shared resource in the first mode of operation, in which the arbiter identifies a device for each request detected;
• a third mode of operation, in response to identifying a request from the priority device, in which the arbiter grants the priority device access to the shared resource;
• a fourth mode of operation, responsive to detecting a request from a shifting priority device, in which the arbiter grants the shifting priority device access to the shared resource and shifts the shifting priority device to a lowest priority among the plurality of shifting priority devices;
• a fifth mode of operation, responsive to detecting a request from at least two shifting devices from the plurality of shifting priority devices, in which the arbiter grants access to a shifting priority device having a highest priority among the at least two shifting priority devices;
• and
• a sixth mode of operation, responsive to granting access to the shifting priority device having the highest priority, in which the arbiter assigns a lowest priority to the shifting priority device granted access to the shared resource.