Clock Grid Root Branch Gating for Processor Stall Detection
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Solution Overview
Problem
Clock grids in high-frequency micro-processors consume power even when inactive, due to their global 'on' configuration, leading to inefficiencies in power management, especially during critical stall conditions where software cannot timely identify mis-predictions or cache misses, resulting in unnecessary power consumption.
Innovation Solution
Implementing a hardware-based method to detect critical stall conditions within a processing unit's clocked components, allowing for clock-gating at the root branch of the clock grid to suspend clock signal distribution during such conditions, using a counter to monitor for response thresholds and manage power accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a clock grid is used for global clock distribution, then clock skew is reduced and computational efficiency is improved, but power consumption increases when the processor is inactive
Solution Approach 1:
The patent implements dynamic clock-gating control that automatically adjusts the clock grid state based on processor activity. A hardware monitor detects stall conditions and dynamically gates the clock signal at the root branch when stalls are detected, and ungates it when activity resumes. This dynamic adaptation allows the system to maintain high computational efficiency during active periods while reducing power consumption during inactive periods, resolving the contradiction between speed and energy use.
2Ease of operation
If traditional software-controlled power management is used, then power states can be managed explicitly, but the system cannot timely identify critical conditions such as mis-predictions or cache misses
Solution Approach 1:
The patent replaces software-controlled power management with a hardware-based monitoring system. A hardware monitor circuit continuously detects critical stall conditions (such as cache misses and mis-predictions) in real-time, eliminating the delay inherent in software polling. When a stall condition is detected, the hardware directly triggers clock-gating at the root branch without software intervention. This substitution of hardware for software mechanics achieves both ease of operation through automatic control and rapid response time by eliminating software execution delays.
3Loss of energy
If clock-gating is performed closer to the leaves in a clock grid, then local power management is improved, but more power is consumed due to increased capacitance and transistors in the grid
Solution Approach 1:
The patent extracts the clock-gating function from the distributed leaf level and concentrates it at the root branch of the clock grid. By placing a single clock-gating control point at the root, the system eliminates the need for multiple distributed gating controls at leaf nodes. This extraction approach reduces the overall grid complexity and capacitance while still achieving effective power management, as the single root-level gate can control the entire grid's clock distribution when stall conditions occur.
Data Source
AI summary
A system and method for power management by performing clock-gating at a clock source. In the method a critical stall condition is detected within a clocked component of a core of a processing unit. The core includes one or more clocked components synchronized in operation by a clock signal distributed by a clock grid. The clock grid is clock-gated to suspend distribution of the clock signal to the core during the critical stall condition.