Memory Controller Power-Gating Latency Reduction
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Solution Overview
Problem
Conventional power management methods for computer systems, such as power-gating and frequency reduction in memory controllers, are limited by time constraints due to high entry and exit latencies, making deep power-saving states unreachable due to excessive timing latency, which is not transparent to memory access agents.
Innovation Solution
A centralized sequencing mechanism that manages real-time system latency tolerances, controls multiple chip mechanisms, and utilizes local storage of pre-computed and calibrated power-state contexts for efficient transitions between active and low-power states, as well as frequency changes, minimizing latency and maximizing time spent in power-saving states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If deep power-gating and frequency reduction are applied to the memory controller, then power savings are maximized, but entry and exit latencies exceed timing constraints
Solution Approach 1:
The patent pre-computes and stores calibration data for multiple frequency states in on-die storage before power-gating occurs. When exiting a low-power state, the appropriate calibration data is already available, eliminating the need for time-consuming recalibration and reducing exit latency to meet timing constraints while maintaining deep power savings
Solution Approach 2:
The patent implements dynamic frequency changing capability that allows the memory controller to transition between multiple frequency states (e.g., 500MHz, 1GHz, 1.5GHz) with pre-computed calibration data for each state. This dynamic adaptation enables the system to select optimal frequency levels based on real-time performance requirements while maintaining low exit latency through pre-stored calibration parameters
2Loss of energy
If the memory controller is powered off and restored to achieve deep power savings, then energy consumption is reduced, but the resulting latency is not transparent to memory access agents
Solution Approach 1:
The patent stores multiple pre-computed calibration contexts in on-die storage corresponding to different power states and frequency levels before the memory controller is powered off. Upon restoration, the appropriate pre-computed context is rapidly restored, making the power state transition transparent to memory access agents by eliminating recalibration delays
Solution Approach 2:
The patent creates and stores copies of calibration data for multiple frequency and power states in on-die storage. These copied calibration contexts can be rapidly restored without time-consuming recalculation, enabling transparent transitions that maintain timing constraints while achieving deep power savings
Data Source
AI summary
A method for managing a memory controller comprising selecting a low-power state from a plurality of low-power states. The method further comprises transitioning to the low-power and entering the low-power state when the transition is complete, provided a wake-event has not been received. An apparatus comprises a controller configured to select a power state for transition, a state-machine configured to execute steps for transitions between power states of a memory controller connected by a bus to a memory, a storage configured to store at least one context, and a context engine configured to stream, at the direction of the state-machine engine, the at least one context to the memory controller. Streaming comprises communicating N portions of context data as a stream to N registers in the memory controller. A context comprises a plurality of calibrations corresponding to a state selected for transition.