Content Addressable Memory Test Mode for Data Processing Device Verification
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Solution Overview
Problem
Modern data processing devices are complex, making it difficult to test all portions using general test patterns, particularly for memory and associated devices, as existing testing methods often fail to comprehensively validate the device's behavior across all possible states.
Innovation Solution
A content addressable memory (CAM) within the data processing device operates in both normal and test modes, allowing flexible application of test signals to generate match values that are used to determine test results, enabling comprehensive testing by controlling the CAM through a control module and applying test patterns to verify the device's functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If general test patterns are used to test memory and associated devices, then the testing process is simple, but the coverage of possible states tested is insufficient
Solution Approach 1:
The CAM device is designed to operate in multiple modes (normal mode and test mode) within a single device structure. The same CAM hardware that performs content-addressable matching in normal operation is repurposed to generate match signals for testing functional modules, eliminating the need for separate dedicated test equipment and achieving comprehensive state coverage without proportionally increasing device complexity
Solution Approach 2:
The CAM acts as an intermediary component between the functional module under test and the test pattern generation system. By storing test patterns in the CAM and using its match output to generate test signals, the system achieves comprehensive testing capability while maintaining a relatively simple overall architecture. The CAM mediates between the input data and the functional module, enabling thorough validation without directly complicating the test infrastructure
2Reliability
If multiple test patterns are applied to increase the number of possible states tested, then the testing coverage improves, but the testing time and complexity increase
Solution Approach 1:
Test patterns are pre-loaded into the CAM device before the actual testing process begins. This preliminary action allows the CAM to quickly retrieve and apply multiple test patterns during testing without requiring complex real-time pattern generation, thereby reducing testing time while maintaining comprehensive state coverage
Solution Approach 2:
The testing process applies multiple test patterns in a systematic, periodic sequence through the CAM. By organizing test pattern application as periodic operations with defined sequences, the system achieves thorough coverage of possible states while maintaining efficient and predictable testing timing, avoiding the chaos of ad-hoc pattern application
Data Source
AI summary
A content addressable memory (CAM) of a data processing device can operate in a normal mode or a test mode. In the normal mode, the CAM provides a match value in response to determining that a received data value matches one of a plurality of values stored at memory locations of the CAM. In a test mode of operation, a plurality of test signals are applied to the CAM, and the CAM provides a match value in response to assertion of one of the test signals. The match value is applied to a functional module associated with the CAM to determine a test result. Accordingly, the test signals applied to the CAM provide a flexible way to generate match values and apply those values to the functional module during testing of the data processing device.