Reduced-Width VLIW Processor Using Register Renaming for Atomic Commit
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Solution Overview
Problem
VLIW processors with multiple parallel execution paths increase cost, size, and power consumption while maintaining compatibility with existing VLIW code and compilers is a challenge.
Innovation Solution
A VLIW processor with fewer execution paths than the number of instructions in a VLIW packet uses a control circuit to distribute instructions and a register renaming circuit to store results in physical registers, allowing for atomic commit operations without the need for dedicated architected registers, thereby reducing power consumption and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple parallel execution paths are implemented to ensure atomic commit of all instructions in a VLIW packet, then reliability is improved, but device complexity, cost, size, and power consumption increase
Solution Approach 1:
The VLIW packet processing is segmented into multiple time periods rather than requiring all instructions to execute simultaneously. The control circuit divides the execution into phases where different subsets of instructions are executed in different time periods, allowing atomic commit without requiring parallel execution paths for every instruction.
Solution Approach 2:
The processor dynamically schedules instructions across multiple time periods based on execution path availability. The control circuit adapts the execution timeline dynamically, allowing instructions to be executed in different orders and time periods while maintaining the atomic commit property through the register renaming circuit's tracking of instruction completion status.
2Productivity
If multiple parallel execution paths are implemented to process VLIW packets, then productivity is improved, but use of energy and cost increase
Solution Approach 1:
The processor uses periodic action by executing instructions in discrete time periods rather than continuous parallel execution. Each time period processes a subset of instructions, and the control circuit orchestrates transitions between periods, maintaining throughput while reducing peak power consumption compared to sustained multi-path parallel execution.
Solution Approach 2:
The register renaming circuit automatically tracks which physical registers contain results of instructions that have not yet been committed, and manages the commit process without requiring additional parallel execution paths. This self-managing mechanism reduces the need for energy-intensive parallel hardware while maintaining productivity.
3Reliability
If multiple parallel execution paths are implemented to ensure atomic commit, then reliability is improved, but manufacturing cost increases
Solution Approach 1:
The control circuit and register renaming circuit serve multiple functions: they schedule instructions across time periods, track execution status, manage physical register allocation, and ensure atomic commit. This multi-functionality replaces the need for dedicated parallel execution paths, simplifying the processor architecture and reducing manufacturing cost while maintaining reliability.
Solution Approach 2:
The register renaming circuit acts as an intermediary between the execution paths and the architectural registers. It manages the mapping and tracking of instruction results, enabling atomic commit without requiring a separate execution path for each instruction. This intermediary mechanism reduces hardware complexity and manufacturing cost.
4Device complexity
If processor width is reduced to lower cost and power consumption, then device complexity and use of energy are improved, but the ability to process VLIW packets with more instructions than execution paths becomes problematic
Solution Approach 1:
The patent adds the time dimension to instruction execution by processing instructions across multiple time periods rather than requiring all instructions to execute in a single cycle. This temporal dimension allows a reduced-width processor to handle VLIW packets with more instructions than execution paths, maintaining compatibility with existing VLIW code while reducing processor complexity.
Solution Approach 2:
The control circuit changes the execution parameter from simultaneous multi-path execution to sequential time-period-based execution. By adjusting the execution timeline and allowing instructions to complete in different time periods, the processor maintains adaptability to existing VLIW code while using fewer execution paths, thus reducing device complexity.
Data Source
AI summary
Very long instruction word (VLIW) instruction processing using a reduced-width processor is disclosed. In a particular embodiment, a VLIW processor includes a control circuit configured to receive a VLIW packet that includes a first number of instructions and to distribute the instructions to a second number of instruction execution paths. The first number is greater than the second number. The VLIW processor also includes physical registers configured to store results of executing the instructions and a register renaming circuit that is coupled to the control circuit.