Parallel Logic Paths for Fast ALU Metadata Generation

Solution Overview

Problem

The generation of flags or metadata associated with arithmetic operations in microprocessors is serially dependent on the primary result, leading to constraints in processor performance and increased latency, which can result in stalls and reduced efficiency, especially in pipelined architectures.

Innovation Solution

A microprocessor architecture with parallel logic paths is introduced, where a secondary logic path is configured to determine metadata with fewer stages and lower latency than the primary logic path, allowing metadata to be generated at least as early as the primary result, potentially enabling earlier action based on characteristics and reducing power consumption by disabling the main path if only the flag is of interest.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a serial process is used to generate flags after calculating the primary result, then the logic path is simple and device complexity is reduced, but the latency increases and processor performance is constrained

Engineering Contradiction:

Improvelogic path complexityVSAvoidflag generation latency

Core Design Contradiction:

Device complexityVSLoss of time

Solution Approach 1:

The execution logic is divided into multiple parallel logic paths: a first logic path for calculating the primary result and a second logic path for generating flags/metadata. This segmentation allows independent parallel execution of result calculation and flag generation, eliminating the serial dependency that caused latency while maintaining manageable complexity through modular organization of each path's functions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The second logic path performs flag generation in advance by operating in parallel with the first logic path during the same clock cycle. By preparing the flag information simultaneously with the primary result calculation rather than sequentially after, the system eliminates waiting time and reduces overall latency without increasing the critical path duration.

Inventive Principle:

Principle #10Preliminary action

2Device complexity

If a serial process is used where the primary result is first calculated and then sent through downstream logic to determine flags, then device complexity is minimized, but processor performance and instruction-level parallelism are reduced

Engineering Contradiction:

Improveexecution logic structureVSAvoidprocessor performance

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The system transitions from a one-dimensional serial execution model to a two-dimensional parallel execution model by introducing multiple logic paths that operate simultaneously. The first logic path handles primary result calculation while the second logic path handles flag generation in parallel, effectively adding a temporal dimension of concurrency to the execution architecture, thereby improving productivity without proportionally increasing structural complexity.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If additional downstream logic is added to generate flags after the primary result, then flag determination accuracy is ensured, but device complexity increases and latency is extended

Engineering Contradiction:

Improveflag determination accuracyVSAvoiddownstream logic stages

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The execution logic is divided into multiple parallel logic paths: a first logic path for calculating the primary result and a second logic path for generating flags/metadata. This segmentation allows independent parallel execution of result calculation and flag generation, eliminating the serial dependency that caused latency while maintaining manageable complexity through modular organization of each path's functions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The second logic path performs flag generation in advance by operating in parallel with the first logic path during the same clock cycle. By preparing the flag information simultaneously with the primary result calculation rather than sequentially after, the system eliminates waiting time and reduces overall latency without increasing the critical path duration.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS8838665B2Fast condition code generation for arithmetic logic unit

Publication Date: 2014.09.16 NVIDIA CORP

AI summary

In one embodiment, a microprocessor includes fetch logic for retrieving an instruction, decode logic configured to identify a plurality of operands and a multiply operation specified in the instruction, and execution logic configured to receive the plurality of operands and the multiply operation. The execution logic includes a first logic path configured to perform the multiply operation on the plurality of operands and output a result, and a second logic path, arranged in parallel with the first logic path, configured to output metadata associated with the result of the multiply operation.