Automatic Checking of Students’ Designs Using Built-In Selftest Methods
Norman Hendrich · 2002
While distance learning is attractive for many reasons, it also incurs some specific problems. One of them is the lack of direct interaction between teaching staff and the students, another one the large number of students for some courses. Therefore, the checking and correction of the homework submitted by the students often takes a lot of time and effort. This is especially true for digital logic design exercises, where a variety of functionally equivalent designs is possible. In this paper we show how to apply the signature analysis technique based on linear-feedback shift-registers, well known from built-in selftest (BIST) research, to the automatic checking of the circuits designed by the students. As the selftest is run on the students’ own PC or workstation, the system provides immediate feedback about whether a circuit is working, and it allows to reduce the number of false solutions submitted by the students. 1 WebAssign and Hades Several management systems have been proposed to ease the distribution and correction of exercises for distance learning. One of these is the WebAssign system [1], built since 1997 in a cooperation of several German universities. Among the functions provided by WebAssign is a module for automatic checking of students’ homework solutions, which are represented as HTML documents. This module currently allows to check (and correct) numerical values and the answers to simple yes-no or multiple-choice questions. Unfortunately, none of these functions is even remotely sufficient to check or rate the solutions to digital design assignments. We therefore tried to integrate a means to automate the checking of digital logic homework assignments as far as possible. While several digital simulators suited to teaching are available (e.g. Diglog [2]), we selected Hades [3], a Java-based framework for digital system simulation and visualization. First, the Hades system is available free of charge for eductional use. Second, the software is very portable and runs on Windows, Linux, Solaris, Macintosh systems, and it can also be used as an applet. Third, the simulator provides all the simulation models required, including a complete set of gate-level models, and the linear-feedback shift registers and BILBO registers [4] used for running the selftests. Fourth, the networking functionality provided by Java allows the easy integration into the WebAssign system, which itself is also implemented in Java.