Zero-Overhead Operand Copy in VLIW Processor Register Files
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Solution Overview
Problem
VLIW processor architectures face scalability limitations due to the need for multiple access ports in shared register files, leading to quadratic growth and performance penalties, particularly in distributed register file architectures where register-to-register copies incur significant overhead.
Innovation Solution
Implementing a distributed register file architecture with result-path multiplexers and switching circuitry that allows for zero-overhead operand copies by performing register-to-register copies concurrently with instruction execution, using pass-control bits or encoded operation codes to control the selection between function unit outputs and register-file operands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a shared register file architecture is used to support multiple function units, then the processor can execute parallel operations, but the register file size grows quadratically with the number of access ports required
Solution Approach 1:
The patent divides the shared register file into multiple distributed register files, each serving a subset of function units. This segmentation reduces the size of individual register files and the number of access ports required in each, while maintaining the overall parallel execution capability through coordinated access across the distributed structure.
Solution Approach 2:
The patent introduces a new dimension to the register file architecture by adding a register file index dimension. Instead of a single large register file with quadratic port growth, the system uses multiple smaller register files indexed by a additional dimension, allowing logarithmic port growth while maintaining access to all operands.
2Quantity of substance
If a distributed register file architecture is used to reduce register file size, then scalability is improved, but register-to-register copy operations incur significant performance overhead
Solution Approach 1:
The patent performs register-to-register copy operations in advance, during the same cycle that the source operand is read. By preparing the destination register file with the required operand before it is needed by the destination function unit, the system eliminates the need for separate copy cycles and maintains instruction execution speed.
Solution Approach 2:
The patent ensures that the operand copy operation continues concurrently with the normal instruction execution pipeline. The source function unit reads its operand while the destination register file simultaneously receives the copied data, ensuring that the useful action of instruction execution continues without interruption.
3Productivity
If multiple access ports are added to the register file to support more function units, then parallel execution capability is enhanced, but the die area and complexity increase quadratically
Solution Approach 1:
The patent segments the register file access ports across multiple distributed register files, so that each individual register file requires fewer ports. The total number of function units is supported by coordinating access across the segmented structure, reducing the quadratic complexity of any single register file.
Solution Approach 2:
The patent introduces a register file indexing mechanism as an intermediary between function units and the distributed register files. This intermediary translates function unit requests into appropriate register file accesses, managing the complexity of supporting multiple function units without requiring quadratic port growth in any single register file.
Data Source
AI summary
A processor having a zero-overhead operand copy capability. The processor includes multiple execution units to execute instructions in parallel and multiple register files each associated with one or more of the execution units. The processor further includes circuitry to select either an instruction execution result from a first one of the execution units or content of a register within a first one of the register files associated with the first one of the execution units to be stored within a register within a second one of the register files.