DRAM Bank Compression for Lower Standby Power in Portable Devices
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Solution Overview
Problem
Portable computing devices face significant standby power consumption due to volatile memory, particularly in DDR memory, which affects battery life and requires lengthy sleep periods for data compression and decompression, and existing solutions are inefficient or require complex software restructuring.
Innovation Solution
A system and method that compresses DRAM content using a DRAM compression component to disable self-refresh in freed-up banks during standby mode, reducing power consumption by bypassing address interleave logic and utilizing a compression engine to manage bank states and metadata for efficient decompression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If DDR memory is put in standby power mode to conserve battery power, then power consumption is reduced, but self-refresh current still consumes significant standby power budget
Solution Approach 1:
The patent segments the DDR memory into multiple banks and selectively disables self-refresh for specific banks based on their content compression status. By dividing the memory system into independent banks, the patent can apply different power management policies to different segments, enabling fine-grained control over standby power consumption while maintaining data integrity in active banks.
Solution Approach 2:
The patent changes the operational parameters of memory banks by transitioning them between different power states (self-refresh enabled/disabled) based on compression status. This parameter change allows the system to dynamically adjust power consumption levels while maintaining the necessary functionality for data preservation in banks that require it.
2Loss of energy
If software compression is used to compress all data content in DDR memory, then standby power is reduced, but sleep period must be relatively long to accommodate compression and decompression operations
Solution Approach 1:
The patent performs preliminary compression of memory content before the device enters standby mode, and maintains compression metadata in the memory controller. This preliminary action allows the system to quickly determine which banks can have self-refresh disabled without requiring lengthy compression operations during the sleep period, thus reducing both power consumption and sleep duration.
Solution Approach 2:
The patent replaces the traditional software-based compression approach with a hardware-based compression engine integrated into the memory controller. This substitution eliminates the need for application processor involvement during compression, significantly reducing the time required for compression operations and enabling shorter sleep periods while maintaining power savings.
3Loss of energy
If hard drive is used to store compressed memory content, then standby power is reduced, but access time is long leading to long sleep or wake time
Solution Approach 1:
The patent extracts the compression and metadata management functionality from external storage systems and integrates it directly into the memory controller. By taking out the compression engine and metadata storage from the external hard drive system and embedding them in the memory controller, the patent eliminates the long access times associated with external storage while maintaining the power savings benefits of compression.
4Loss of energy
If flash memory is used to store compressed memory content, then standby power is reduced, but number of program/erase cycles is limited requiring large capacity for redundancy
Solution Approach 1:
The patent introduces an intermediary metadata structure that is maintained in the memory controller rather than in external flash storage. This metadata intermediary contains compression status information for each memory bank, allowing the system to track and manage compressed content without requiring persistent storage in flash memory, thereby eliminating the wear cycle issues and capacity redundancy requirements.
5Productivity
If memory controllers perform bank interleaving, then memory access efficiency is improved, but entire DDR content must be compressed or not at all
Solution Approach 1:
The patent maintains bank interleaving for memory access efficiency while simultaneously enabling selective compression on a per-bank basis. By segmenting the compression control into individual bank-level decisions based on compression metadata, the patent allows different banks to be in different compression states, thus preserving both the performance benefits of interleaving and the power savings of selective compression.
Data Source
AI summary
Various embodiments of systems and methods are disclosed for reducing volatile memory standby power in a portable computing device. One such method involves receiving a request for a volatile memory device to enter a standby power mode. One or more compression parameters are determined for compressing content stored in a plurality of banks of the volatile memory device. The stored content is compressed based on the one or more compression parameters to free-up at least one of the plurality of banks. The method disables self-refresh of at least a portion of one or more of the plurality of banks freed-up by the compression during the standby power mode.