ON-LINE TESTING AND DIAGNOSIS OF MICROCONTROLLERS

摘要

During its lifetime, a digital system is tested and diagnosed on numerous occasions. For the system to perform its intended mission with high availability, testing and diagnosis must be quick and effective. A sensible way to ensure this is to specify testing as one of the system functions- in other words, self-test. Reliability, availability, and serviceability (RAS) are the major factors for consideration in system design to provide continuous correct operation [1]. Since faults cannot be completely eliminated, critical systems always employ fault tolerance techniques to guarantee high reliability and availability. Fault tolerance (FT) techniques try to keep the system operational despite the presence of faults [2]. FT can be achieved through hiding the occurrence of faults and preventing it from generating errors (fault-masking), or through fault detection and fault repairing. Technological advances have made it possible to integrate on a single chip enormous numbers of transistors, thus allowing the inclusion on a single chip of entire systems, including microprocessors (MP), microcontroller (MC), memories, ASICs, and peripherals. The development of this new class of systems is called Systems on Chip (SoCs) [3]. Testing is a crucial issue in the SoC development and production processes. The internal structure of a MP is based on a sequentially complex decode and control unit that decodes the instructions and sends the appropriate control signals to a large data-path, which may include hard-to-test elements such as multipliers and dividers [4]. Here, the decode and control unit can be seen as a complex finite state machine (FSM) and its test requires suitable sequences to traverse its state graph to excite and observe possible faults. Therefore, its test is mainly a sequential problem. Finally, test sequence generation for MP necessarily requires knowledge of the processor instruction set and instruction format, since only correct programs can internally perform meaningful operations.