Arbiter Using Blurred Age Values for Subset Arbitration
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Solution Overview
Problem
The complexity of microprocessor scheduler circuitry increases with the number of instructions, making it difficult to achieve timely and efficient arbitration between multiple requests for resources, especially when exact priority is required.
Innovation Solution
An arbiter that uses relative age values and blurred age values to simplify the arbitration process by dividing entries into subsets, where relative age values are used within subsets and blurred age values represent multiple relative age values between different subsets, reducing the circuitry complexity and accelerating the arbitration process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of instructions in the scheduler increases to improve throughput, then productivity is improved, but device complexity increases making arbitration timing difficult to meet
Solution Approach 1:
The patent divides the set of instructions in the scheduler into multiple subsets. Each subset is arbitrated independently using simplified arbitration logic. This segmentation reduces the complexity of the arbitration circuitry while maintaining the ability to handle a large number of instructions, thereby resolving the contradiction between improved throughput and increased device complexity.
2Reliability
If exact arbitration based on relative age values is used to ensure correct instruction dispatch, then reliability is improved, but device complexity increases and timing parameters cannot be met
Solution Approach 1:
By segmenting instructions into subsets and performing independent arbitration on each subset, the patent reduces the complexity of the grant logic. The segmented approach maintains sufficient arbitration accuracy for correct instruction dispatch while avoiding the need for complex exact arbitration logic across all instructions, thus resolving the contradiction between reliability and device complexity.
Solution Approach 2:
The patent changes the arbitration parameter from exact relative age comparison to a simplified age-based selection within subsets. This parameter change reduces the computational complexity of the grant logic while maintaining adequate arbitration accuracy, allowing timing parameters to be met without sacrificing essential reliability.
3Reliability
If complex arbitration logic is used to ensure exact priority servicing, then reliability is improved, but speed of arbitration decreases making it difficult to meet timing criteria
Solution Approach 1:
The segmentation of instructions into multiple subsets enables parallel or faster sequential arbitration of smaller groups. This reduces the arbitration time for each subset while maintaining overall priority servicing reliability through the structured subset approach, thereby resolving the contradiction between reliability and arbitration speed.
Data Source
AI summary
An arbiter that performs accelerated arbitration by approximating relative ages including a memory, blur logic, and grant logic. Multiple entries arbitrate for one or more resources. The memory stores age values each providing a relative age between each pair of entries, and further stores blurred age values. The entries are divided into subsets in which each entry belongs to only one subset. The blur logic determines each blurred age value to indicate a relative age between an entry of a first subset and an entry of a different subset for each pair of subsets. The grant logic grants access by an entry to a resource based on relative age using corresponding age values when comparing relative age between entries within a common subset, and using corresponding blurred age values when comparing relative age between entries in different subsets. Each blurred age value represents multiple age values to simplify arbitration.