Low cost test for core-based system-on-a-chip
The availability of high level integration leads to building of millions of gates systemson- a-chip (SOC). Due to the high complexity of SOCs, testing them is becoming increasingly difficult. In addition, if the current test practises are maintained, the high cost of test will lead to a considerable production cost increase. To alleviate the test cost problem, this research investigates methods which lead to low-cost test of core-based systems-on-a-chip based on test resource partitioning and without changing the embedded cores. Analysing the factors which drive the continuous increase in test cost, this thesis identifies a number of factors which need to be addressed in order to reduce the cost of test. These include volume of test data, number of pins for test, bandwidth requirements and the cost of test equipment. The approaches proposed to alleviate the cost of test problem have been validated using academic and industrial benchmark cores. To reduce the volume of test data and the number of pins for test, the new Variablelength Input Huffman Coding (VIHC) test data compression method is proposed, which is capable of simultaneously reducing the volume of test data, the test application time and the on-chip area overhead, when compared to previously reported approaches. Due to the partitioning of resources among the SOC and the test equipment, various synchronisation issues arise. Synchronisation increases the cost of test equipment and hence limits the effectiveness of test resource partitioning schemes. Therefore, the synchronisation issues imposed by test data compression methods are analysed and an on-chip distribution architecture is proposed which in addition to accounting for the synchronisation issues also reduces the test application time. The cost of test equipment is related to the amount of test memory, and therefore efficient exploitation of this resource is of great importance. Analysing the memory requirements for core based SOCs, useless test data is identified as one contributor to the total amount of allocated memory, leading to inefficient memory usage. To address this problem a complementary approach to test data compression is proposed to reduce the test memory requirements through elimination of useless test data. Finally, a new test methodology is proposed which combines the approaches proposed in this thesis into an integrated solution for SOC test. The proposed solution leads to reduction in volume of test data, test pins, bandwidth requirements and cost of test equipment. Furthermore, the solution provides seamless integration with the design flow and refrains from changing the cores. Hence, it provides a low-cost test solution for corebased SOC using test resource partitioning.