Programmable Exception Processing Latency in Digital Processors
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Solution Overview
Problem
Digital processors face challenges in managing interrupt latency, particularly in handling variable execution times of instructions, which leads to latency jitter and inefficient interrupt response times, especially in CPUs with deep instruction pipelines.
Innovation Solution
A digital processor with programmable exception processing latency, featuring a control register that allows operation in two modes: fixed and variable latency modes, enabling dynamic switching based on software applications and predefined thresholds, and incorporating a counter for stalling or inserting no-operation instructions to adjust latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed exception processing latency is implemented to eliminate latency jitter, then interrupt response time stability is improved, but interrupt response time is worsened due to wasted time accommodating longest instructions
Solution Approach 1:
The patent implements dynamic exception processing latency by allowing the latency value to vary based on the current instruction being executed. The system automatically adjusts the preamble length according to instruction execution time characteristics, transitioning from fixed to variable latency mode. This resolves the contradiction by making the latency parameter adaptive rather than static, thereby eliminating wasted time while maintaining stability through controlled variation.
Solution Approach 2:
The patent changes the latency parameter from a fixed value to a variable value that depends on the instruction type and execution time. By implementing parameter changes based on instruction characteristics, the system optimizes interrupt response time for each specific instruction scenario rather than using a worst-case fixed latency for all instructions, thereby reducing overall time loss while maintaining reliable response characteristics.
2Stability of the object's composition
If long exception processing preamble is used to accommodate longest instruction for fixed latency, then latency consistency is improved, but processor performance is worsened due to deep instruction pipeline restrictions
Solution Approach 1:
The patent makes the exception processing preamble length dynamic by adjusting it according to the specific instruction being executed. Instead of using a fixed long preamble to accommodate the longest possible instruction, the system now uses variable-length preambles matched to actual instruction requirements. This resolves the contradiction by eliminating unnecessary pipeline restrictions while maintaining latency consistency for each instruction type through adaptive preamble length.
Solution Approach 2:
The patent applies local quality by tailoring the exception processing preamble length to match the specific characteristics of each instruction type. Rather than applying a uniform long preamble to all instructions, the system assigns appropriate preamble lengths based on local instruction requirements. This resolves the contradiction by optimizing processor performance for each instruction scenario while maintaining consistency within each instruction category.
3Adaptability or versatility
If variable execution time instructions are supported, then processor versatility is improved, but interrupt latency varies introducing latency jitter
Solution Approach 1:
The patent implements dynamic latency adjustment where the exception processing latency varies based on the instruction execution time. The system automatically adapts the preamble length to match the actual instruction being executed, thereby maintaining reliability through consistent latency for each instruction type while supporting variable execution time instructions. This resolves the contradiction by making latency adaptive rather than fixed, eliminating jitter while preserving versatility.
Solution Approach 2:
The patent uses feedback from instruction execution characteristics to adjust the exception processing latency. The system monitors or determines the execution time of the current instruction and uses this feedback to set appropriate latency parameters. This feedback mechanism resolves the contradiction by ensuring latency consistency matches actual instruction behavior, thereby maintaining reliability while supporting versatile instruction execution.
Data Source
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AI summary
A digital processor with programmable exception processing latency, may have a central processing unit (CPU) of a digital processor, an exception controller coupled with said CPU, and a control register coupled with said CPU, wherein the control register is operable to set the operation mode of said CPU in at least one of two modes, wherein in the first mode the CPU has a fixed exception processing latency time, and in a second mode the CPU has a variable exception processing latency time.