DEFLATE Accelerator Verification with LZ77 Bypass Switching
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Solution Overview
Problem
Conventional methods for verifying the correctness of DEFLATE compression accelerators face challenges in predictability and repeatability, particularly due to the complex nature of the LZ77 compression phase, which can lead to inconsistent results across hardware implementations.
Innovation Solution
The implementation of a software-controlled switch to disable the LZ77 compression phase, modifying the LZ77 compressor to never form matching strings or hashes across page boundaries, and using a programmable hash character size to ensure reproducible results, allowing for comprehensive testing without low-level modeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the LZ77 compression phase is enabled with full functionality, then compression ratio is improved, but predictability and repeatability of test results deteriorate
Solution Approach 1:
The patent segments the compression test into two distinct phases: a first test with LZ77 enabled to measure compression ratio, and a second test with LZ77 disabled to verify predictability and repeatability. This segmentation allows both compression performance and test reliability to be evaluated separately without interfering with each other.
Solution Approach 2:
The patent dynamically configures the LZ77 compressor based on test requirements. A control mechanism enables or disables the LZ77 phase depending on whether the test prioritizes compression ratio measurement or predictability verification, allowing the system to adapt its behavior to different testing objectives.
2Productivity
If the LZ77 compressor processes data across page boundaries, then compression efficiency is improved, but result consistency deteriorates
Solution Approach 1:
The patent extracts and removes the LZ77 compression phase from the test path when verifying predictability and repeatability. By taking out the problematic component that causes inconsistency across page boundaries, the system can verify core functionality without the interference of LZ77's non-deterministic behavior.
Solution Approach 2:
The patent performs preliminary testing without LZ77 to establish baseline predictability and repeatability before enabling LZ77 for compression ratio measurement. This preliminary action ensures that the core system functions correctly and produces consistent results before adding the variable LZ77 component.
3Measurement precision
If comprehensive testing with low-level modeling is performed, then verification accuracy is improved, but test complexity and time increase
Solution Approach 1:
The patent creates a simplified copy of the compression test that excludes the LZ77 phase. This copy allows verification of core functionality and predictability without requiring complex low-level modeling, reducing test complexity while maintaining sufficient verification accuracy for the Huffman encoding phase.
Solution Approach 2:
The patent performs partial testing by disabling LZ77 for specific verification tests. This partial action approach verifies the critical predictability and repeatability requirements without the excessive complexity of fully modeling the entire compression pipeline including LZ77's variable-length matching.
Data Source
AI summary
Embodiments of the invention are directed to a DEFLATE compression accelerator and to a method for verifying the correctness of the DEFLATE compression accelerator. The accelerator includes an input buffer and a Lempel-Ziv 77 (LZ77) compressor communicatively coupled to an output of the input buffer. A switch is communicatively coupled to the output of the input buffer and to the output of the LZ77 compressor. The switch is configured to bypass the LZ77 compressor during a compression test. The accelerator further includes a deflate Huffman encoder communicatively coupled to an output of the switch and an output buffer communicatively coupled to the deflate Huffman encoder. When the switch is not bypassed, the compressor can be modified to produce repeatable results.