SSD Overlap Table Handling for Write-Protected Read Conflicts
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Solution Overview
Problem
Existing solid state devices (SSDs) face inefficiencies when handling command overlaps, particularly in managing read-overwrite conflicts and write-protected ranges, leading to increased firmware overhead and complex command processing flows.
Innovation Solution
The firmware monitors the overlap table instead of both overlap read commands and write-protected write commands, allowing the controller to process read commands normally and pass write overlaps into the data path, reducing firmware monitoring to only when the data path clears the overlap table.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the firmware monitors both overlap read commands and write-protected write commands, then command processing correctness is ensured, but firmware overhead increases and processing efficiency decreases
Solution Approach 1:
The patent extracts the monitoring function from the firmware and relocates it to hardware components. Specifically, the overlap detection is performed by dedicated hardware logic that monitors the overlap table, while the firmware only needs to handle the results of this detection. This separation removes the burden of continuous monitoring from the firmware, improving its processing efficiency while maintaining correct command handling.
Solution Approach 2:
The patent introduces an intermediary overlap table and associated hardware logic that mediates between the command queue and the execution units. This intermediary structure automatically tracks overlapping commands and write-protected ranges, providing the necessary correctness guarantees without requiring the firmware to actively monitor each command. The firmware interacts with this intermediary rather than directly managing overlap detection.
2Reliability
If the device waits for overlapped write command to complete before executing read command, then data consistency is maintained, but command execution speed decreases
Solution Approach 1:
The patent performs preliminary actions by pre-marking ranges as write-protected and pre-detecting potential overlaps before commands are executed. The overlap table is populated in advance with information about write-protected ranges and pending write commands. When a read command arrives, the hardware quickly checks this pre-prepared information to determine if waiting is necessary, enabling faster decision-making compared to real-time monitoring during command execution.
Solution Approach 2:
The patent implements dynamic command handling where the execution path is determined based on real-time overlap detection. Instead of a static approach where all overlapping commands must wait, the system dynamically evaluates each read command against the current state of the overlap table and write-protected ranges. This allows non-conflicting commands to proceed immediately while only blocking specific commands that would actually cause data inconsistency, thereby improving overall execution speed.
Data Source
AI summary
Instead of the firmware (FW) monitoring for both an overlap read command and a write protected (WP) overlapped write command, the FW can monitor the overlap table only. The controller will receive a read command or an overlap read command. If the command is not an overlap read command, then the controller will process the command normally. If the command is an overlap read command, then the controller will look for the write command that is being overlapped. When passing the write overlap of write protect (WP) into the data path instead of the exception queue, the FW is limited to monitoring the overlap table. As such, when the WP command is completed the entry is removed by the data path. As a result, the FW can limit monitoring to when the data path clears the overlap table.