2

Higher circuit densities in system-on-chip designs have led to drastic increase in test data volume. Larger test data size demands not only higher memory requirements, but also an increase in testing time. Test data compression addresses this problem by reducing the test data volume without affecting the overall system performance. The major contributions of this paper are as follows: 1 it develops an efficient bitmask selection technique for test data in order to create maximum matching patterns; 2 it develops an efficient dictionary selection method which takes into account the bitmask based compression; and 3. it proposes a test compression technique using efficient dictionary and bitmask selection to significantly reduce the testing time and memory requirements. If the bit-stream contains consecutive repeating bit sequences, the bitmask-based compression encodes such patterns using same repeated compressed words, whereas our approach replaces such repetitions using a bitmask of “00”. In this example, the first occurrence will be encoded as usual; whereas the remaining repetitions will be encoded using our method i.e. run length encoding of these sequences may yield a better compression result. Interestingly, to represent such encoding no extra bits are needed. Note that bitmask value 0 is never used, because this value means that it is an exact match and would have encoded using zero bitmasks. Using this as a special marker, these repetitions can be encoded without changing the code format of bitmask-based compression. Keywords:bitmasking,dictionary,encoding,compression,dec ompressio