Virtual Scan Chains for Online Testing of FPGA-based Embedded Systems

While techniques for offline testing of FPGAs, either manufacturing-oriented or application-oriented, are today relatively mature, in critical applications such as avionics, space, and even numerous commercial products it is often necessary to perform online testing. In this paper, we present a technique for online testing of digital designs implemented on an FPGA. The approach enables application-oriented testing, in that it covers the subset of the FPGA which is actually used for the implemented design, and considers scenarios where the FPGA component is a part of a larger embedded system. The proposed approach is in fact based on a software framework, which acts as an abstraction layer for reconfigurable hardware resources. Essentially, the framework exposes to software applications a Register-Transfer Level view of the underlying hardware, allowing test procedures to be implemented as software programs. Our approach is especially advantageous when memory is a constraint, the case of many embedded systems. As proved by experimental results, in fact, test procedures turn out to be very compact and much more memory-efficient than conventional approaches relying on static sets of FPGA testing configurations to be stored in system memory.