Variable Latency Instruction Pipeline Hazard Management
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Solution Overview
Problem
Modern digital signal processors face challenges in efficiently processing real-time data streams due to memory bandwidth and scheduling concerns, particularly in handling variable latency instructions and pipeline hazards, which can lead to undesired results and performance issues.
Innovation Solution
The implementation of an instruction execution pipeline with a writeback queue that adjusts latency values based on execution time and uses capture queues to manage pipeline stages, enabling correct execution and output of instructions by tracking their readiness and lifetime, thereby addressing data and structural hazards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If instructions are executed in a pipeline to increase processing rate, then productivity is improved, but pipeline hazards (data and structural hazards) occur leading to incorrect results
Solution Approach 1:
The patent implements preliminary detection of pipeline hazards before they cause incorrect results. The hazard detection logic identifies data hazards and structural hazards in advance, allowing the system to insert stalls or adjust timing before the hazard manifests, thus maintaining both high productivity and execution correctness.
Solution Approach 2:
The patent employs feedback mechanisms where the results of pipelined instructions are monitored and fed back to the control logic. This feedback allows the system to detect hazards dynamically and adjust pipeline operation accordingly, ensuring correctness while maintaining high execution rates through intelligent pipeline management.
2Device complexity
If latency values are fixed for pipeline stages, then device complexity is reduced, but variable latency instructions cannot be handled correctly
Solution Approach 1:
The patent implements dynamic latency values for pipeline stages instead of fixed latencies. The system adjusts the latency of pipeline stages based on the specific instruction being executed, allowing variable latency instructions to be handled correctly. This dynamic approach increases adaptability while managing complexity through systematic control mechanisms.
Solution Approach 2:
The patent changes the latency parameter of pipeline stages dynamically based on instruction type. By modifying the latency parameter according to the specific instruction requirements, the system can accommodate both fixed and variable latency instructions without requiring fundamentally different pipeline architectures, thus balancing complexity and versatility.
3Productivity
If multiple instructions are executed simultaneously in pipeline stages, then productivity increases, but structural hazards occur due to resource conflicts
Solution Approach 1:
The patent segments the pipeline into distinct stages with clear resource allocation boundaries. By dividing the execution process into fetch, decode, execute, memory, and writeback stages, the system can manage resource conflicts more easily while maintaining high parallel execution capability. Each stage has dedicated resources, reducing structural hazards.
Solution Approach 2:
The patent introduces intermediary control logic and buffer structures between pipeline stages to mediate resource conflicts. These intermediaries coordinate resource access between multiple simultaneous instructions, allowing parallel execution to continue while preventing structural hazards through controlled resource sharing.
Data Source
AI summary
Techniques related to executing instructions by a processor comprising receiving a first instruction for execution, determining a first latency value based on an expected amount of time needed for the first instruction to be executed, storing the first latency value in a writeback queue, beginning execution of the first instruction on the instruction execution pipeline, adjusting the latency value based on an amount of time passed since beginning execution of the first instruction, outputting a first result of the first instruction based on the latency value, receiving a second instruction, determining that the second instruction is a variable latency instruction, storing a ready value indicating that a second result of the second instruction is not ready in the writeback queue, beginning execution of the second instruction on the instruction execution pipeline, updating the ready value to indicate that the second result is ready, and outputting the second result.