Graded DRAM Refresh Scheduling to Limit Bank Blackouts
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The refresh process in DRAM systems negatively affects performance and power usage due to blackout periods during refresh commands, particularly when all-bank refresh commands are required, impacting overall throughput and quality of service.
Innovation Solution
Implementing a refresh scheduler that manages refresh commands on a per-bank basis, using graded alert levels to adapt to traffic patterns and prioritize high-priority transactions, reducing the need for all-bank refreshes by proactively managing refresh intervals and transactions based on impending refresh requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all-bank refresh commands (REFab) are issued to refresh all DRAM banks, then data integrity is maintained across all banks, but system throughput decreases due to blackout periods affecting all banks
Solution Approach 1:
The patent divides the DRAM banks into multiple groups (e.g., first bank group and second bank group) and issues refresh commands to one group at a time using per-bank refresh (REFpb) commands. This segmentation allows other bank groups to remain accessible during refresh operations, eliminating system-wide blackout periods while maintaining data integrity across all banks through sequential refreshing.
2Productivity
If per-bank refresh commands (REFpb) are used to refresh individual banks, then system throughput is improved by allowing access to other banks, but the complexity of refresh scheduling increases
Solution Approach 1:
The patent implements a periodic refresh scheduling mechanism that systematically cycles through different bank groups in predetermined intervals. The controller alternates between issuing REFpb commands to the first bank group and the second bank group in a periodic manner, providing structured management that reduces scheduling complexity while maintaining high throughput through continuous availability of at least one bank group.
Solution Approach 2:
The patent proactively monitors refresh intervals and issues REFpb commands to bank groups before their refresh deadlines approach. By anticipating refresh requirements and scheduling them in advance during periods of lower traffic, the controller prevents data corruption without causing urgent blackouts, thereby simplifying real-time scheduling decisions.
3Reliability
If refresh commands are issued during periods of high memory traffic, then refresh requirements are met timely, but performance deteriorates due to interruption of read/write operations
Solution Approach 1:
The patent enables the DRAM system to service its own refresh requirements autonomously by utilizing idle periods within bank groups. When one bank group is being accessed, the controller automatically refreshes the other bank group without external intervention, ensuring refresh compliance is met independently of traffic patterns and without requiring performance-degrading interruptions to active banks.
Data Source
AI summary
This specification describes memory controllers for dynamic random-access memory (DRAM). In one aspect, a memory system includes DRAM that includes DRAM banks. The memory system includes a memory controller for managing the DRAM. The memory controller includes a request scheduler configured to receive memory transactions and send memory request commands to the DRAM banks. The memory controller includes a refresh scheduler configured to monitor a status of a dynamically changing refresh requirement for the DRAM, determine an alert level for the DRAM based at least in part on the status of the refresh requirement, and manage, based on the determined alert level, the DRAM banks to which refresh commands are sent and the memory transactions for which memory request commands are sent by the request scheduler.