TCAM Atomicity via Parallel Cache and Segmented Banks
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Solution Overview
Problem
In ternary content-addressable memory (TCAM) systems, the stacked cell configuration leads to significant downtime during write operations due to the requirement of multiple non-sequential write cycles, making entries 'invisible' during the write period, which is undesirable for performance and efficiency.
Innovation Solution
A cache module is introduced that operates in parallel to the TCAM, allowing for immediate or near-immediate write operations and maintaining entry visibility by activating new entries in the cache during the write process, ensuring all TCAM entries appear visible at all times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If stacked cell configuration is used in TCAM, then power and performance are optimized, but write operation time increases significantly causing entries to be invisible during writes
Solution Approach 1:
The TCAM is divided into multiple banks (first TCAM bank, second TCAM bank, etc.), allowing write operations to be distributed across different segments simultaneously. This segmentation enables parallel write operations, reducing the overall time required for write operations while maintaining the stacked cell configuration's power efficiency.
Solution Approach 2:
A cache is introduced as an intermediary structure between the processor and the TCAM banks. The cache holds copies of TCAM entries and can be updated independently and simultaneously with the TCAM banks, providing a buffer that masks the write operation delays and maintains entry visibility throughout the write process.
2Power
If stacked cell configuration is used in TCAM, then power and performance are optimized, but entry visibility during write operations deteriorates
Solution Approach 1:
The cache is pre-loaded with copies of TCAM entries before write operations begin. When a write operation is initiated, the cache already contains the entry data, allowing it to immediately service read requests while the actual TCAM banks are being updated. This preliminary preparation ensures continuous entry visibility.
Solution Approach 2:
The cache serves as an intermediary that maintains entry visibility during TCAM write operations. While the TCAM banks are being updated (causing temporary invisibility), the cache provides the entry data to processing elements, ensuring that no information is lost or inaccessible during the write process.
3Reliability
If multiple non-sequential write cycles are used in stacked TCAM, then data integrity is maintained, but write operation efficiency decreases
Solution Approach 1:
The TCAM is segmented into multiple banks that can be written to independently and simultaneously. This allows the write operation to be divided into parallel segments rather than sequential cycles, maintaining data integrity through controlled updates while dramatically improving write operation efficiency through parallel execution.
Solution Approach 2:
Entries are copied from the TCAM to the cache (and vice versa) during write operations. This copying mechanism allows the data to be preserved and transferred across different storage structures simultaneously, maintaining integrity through verified transfers while improving efficiency by utilizing the cache's faster access characteristics.
Data Source
AI summary
A Ternary Content-Addressable Memory (TCAM) system is disclosed. In the system, writes to the memory are performed over several cycles. In order to ensure full visibility of all entries within the TCAM, a cache memory is provided. At the start of the TCAM write, the cache is written with the contents of the new entry. The cache entry is activated for the period of time that the corresponding entry in the TCAM is deactivated for rewriting. For each input value provided to the system, both the TCAM and the cache are checked for potential matches. The results of these checks are compared at output. In this manner, all entries within the TCAM can maintain full visibility even throughout a write period.