Lightweight Processor Core Delay Fields for Data Hazard Mitigation
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Solution Overview
Problem
Data hazards in RISC processors, such as data not being available in time for computations, are inefficiently managed by existing methods that incur significant area overhead or reduce instruction throughput.
Innovation Solution
Implementing a delay field in instruction words to statically schedule wait times, allowing for NOP insertion or dynamic adjustment, reduces data hazards without increasing hardware area and improves throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hazard detection hardware is implemented to compare current instruction decode with register pipeline indices, then data hazards are detected and mitigated, but hardware area increases significantly
Solution Approach 1:
The patent extracts the hazard detection function from hardware and relocates it to software/compiler. The compiler analyzes dependencies between instructions and inserts NOPs accordingly, removing the need for complex hardware comparison circuits while maintaining hazard detection capability
Solution Approach 2:
The patent replaces the mechanical/hardware-based hazard detection system with a software-based solution. Instead of using hardware circuits to compare register indices, the compiler performs dependency analysis and generates appropriate delay instructions, substituting electronic computation with software logic
2Reliability
If NOP instructions are inserted to prevent data hazards, then hazards are avoided, but program memory space increases
Solution Approach 1:
The patent applies partial action by inserting NOPs only where necessary based on compiler analysis of actual data dependencies, rather than inserting NOPs after every instruction. This selective approach prevents hazards while minimizing memory usage compared to conservative fixed-delay approaches
Solution Approach 2:
The patent changes the parameter of delay insertion from a fixed conservative value to a variable value determined by compiler analysis. The compiler calculates the actual number of NOPs needed based on instruction dependencies, allowing optimization of memory space while maintaining hazard prevention
3Reliability
If a fixed execution time is implemented for all instructions to avoid worst-case hazards, then data hazards are prevented, but instruction throughput decreases severely
Solution Approach 1:
The patent introduces dynamics by allowing variable instruction execution times based on actual dependencies. Instead of forcing all instructions to take the maximum possible time, the compiler analyzes each instruction's actual requirements and inserts only the necessary delay, enabling the pipeline to operate closer to its full capacity while maintaining correctness
4Reliability
If hardware comparison circuits are used to monitor destination and source registers, then data hazards are detected, but device complexity increases
Solution Approach 1:
The patent extracts the complex comparison and dependency analysis function from the hardware circuit and transfers it to the compiler. The compiler performs the detailed analysis of source and destination register dependencies and generates appropriate code, simplifying the hardware to only need basic instruction execution and NOP insertion capability
Data Source
AI summary
Integrated circuits that include lightweight processor cores are provided. Each processor core may be configured to execute a series of instructions. At least one of the instructions may include an embedded delay field with a value specifying the amount of time that instruction needs to wait before proceeding to the next instruction to avoid a data hazard. The value of the delay field may be determined by a compiler during software compile time. Such delay field may also be used in conjunction with branch instructions to specify a number of no-operations (NOPs) for one or more associated branch delay slots and may also be used to reduce data forwarding cost.