Nested Loop Controller Predicate FIFO Pipelined Execution
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Solution Overview
Problem
Modern digital signal processors (DSPs) face challenges in efficiently executing nested loops in a pipelined fashion, particularly with imperfectly nested loops, due to difficulties in determining whether to execute instructions associated with outer loops.
Innovation Solution
A nested loop controller is introduced, which includes registers for inner and outer loop counters and a predicate FIFO. This controller advances loop counters and populates the predicate FIFO based on loop thresholds, allowing for efficient determination of whether to execute outer loop instructions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If nested loops are executed in a pipelined fashion to improve DSP performance, then execution speed and productivity are improved, but the complexity of determining predicate values for outer loop instructions increases
Solution Approach 1:
A predicate FIFO buffer is introduced as an intermediary mechanism between the loop counter and the predicate determination logic. The buffer stores predicate values in a first-in-first-out manner, allowing the pipelined execution to access previous predicate values without complex real-time calculations, thus reducing the complexity of predicate determination while maintaining high execution speed
Solution Approach 2:
The system pre-calculates and stores predicate values in the FIFO buffer before they are needed during pipelined execution. By preparing predicate values in advance based on loop counter thresholds, the system eliminates the need for complex predicate calculations during the critical execution path, resolving the contradiction between speed and complexity
2Reliability
If multiple registers are used to track loop counters and predicates for pipelined execution, then execution accuracy is improved, but register overhead and device complexity increase
Solution Approach 1:
The patent combines multiple functions into a unified nested loop controller structure. The loop counters, predicate generation logic, and FIFO buffer management are merged into a single integrated unit, reducing the total number of separate registers needed while maintaining execution accuracy through coordinated operation of the combined components
Data Source
AI summary
A nested loop controller includes a first register having a first value initialized to an initial first value, a second register having a second value initialized to an initial second value, and a third register configured as a predicate FIFO, initialized to have a third value. The second value is advanced in response to a tick instruction during execution of a loop. In response to the second value reaching a second threshold, the second register is reset to the initial second value. The nested loop controller further includes a comparator coupled to the second register and to the predicate FIFO and configured to provide an outer loop indicator value as input to the predicate FIFO when the second value is equal to the second threshold, and provide an inner loop indicator value as input to the predicate FIFO when the second value is not equal to the second threshold.