Comparison of hardware based and software based stress testing of memory IO interface

Abstract

In post-silicon testing and validation of circuit functionality, an effective IO stress pattern can identify bugs quickly and provide adequate test coverage. A lot of work has been done to identify the right stress patterns specific to each IO interface. While some patterns can be generic enough to apply to all IOs, other patterns are interface topology specific. In addition to identifying the worst-case pattern, tradeoffs between test-time and test coverage must be made depending on the test goals. Pseudo Random Bit Stream (PRBS) generators are commonly used to generate test patterns because of the adequate frequency content in the PRBS patterns, the ease of implementation, and minimal gate count. This paper introduces an Advanced Pattern Generator and Checker (APGC) based on PRBS that retains all the aforementioned advantages. The APGC was implemented for a DDR memory interface where different LFSRs beat against each other spatially on neighboring IO lanes while rotating this form of aggressor-victim pattern in time. The results of the APGC stress patterns are compared to a form of advanced software-based learning algorithm based patterns that exhaustively search this complete parameter space. The comparison of APGC to software showed that the measured bit error rate (BER) plotted on a Q-scale of both methods is similar for the Receiver side. On the Transmitter side, APGC showed less eye opening than the software. In addition to the margin comparison, on the test execution side, APGC can speed up the test and validation execution time compared to the software by 32 to 2048 times depending on aggressor victim lane width of 8 to 64 lanes.