An evaluation and acceptance of COTS software for FPGA-based controllers in NPPS

A High-Throughput Vernier Time-to-Digital Converter on FPGAs with Improved Resolution Using a Bi-Time Interpolation Scheme

A novel ring oscillator-based Vernier-type time interpolation method, known as the fine-timestamp maker, is proposed for field programmable gate array (FPGA)-based time-to-digital converters (TDCs). This method determines lower measurement dead time and improves resolution by using a bi-time interpolation scheme, first presented in this paper. Additionally, a group of cascaded delay units are packaged as an intellectual property core (DU-IP) to form a ring delay line and to adjust its length via the engineering change order (ECO) tool, which makes the adjustment of the ring oscillator’s frequency more linear and less position dependent. A prototype TDC was implemented on a Kintex-7 FPGA. The experimental results demonstrate that a single TDC channel only consumes 35 DFFs, 31 LUTs, and 16 CARRY4 logics after specific adjustment. The results, with a time resolution of 20 ps, dead time of 58 ns, and a root-mean-square error of 15–20 ps, show a significant performance improvement compared to traditional Vernier-type TDCs.

Criticality analysis for safety-critical software in nuclear power plant distributed control system

Software criticality analysis examines the degree of contribution that each individual failure mode of a software component has on the reliability of software. Higher safety integrity levels are assigned to software modules whose failures cause an unacceptable impact on the operation of the system, and these levels require the implementation of more rigorous software quality assurance measures as defined in IEEE Std 1012 and in the customer’s system requirements specification. In this paper, a novel software criticality analysis method is proposed, the results of which can be used to guide the development of newly developed software and the procurement of Commercial-Off-The-Shelf (COTS) software. The software structure is first analyzed and the software is divided into modules according to their functions. Then the criticality levels of software components are preliminarily classified by means of a safety criticality preliminary analysis tree, followed by their verification through the software hazard and operability analysis (HAZOP). Finally, the target Safety Integrity Level (SIL) of each software module is determined based on its criticality level and the overall safety objective (i. e., SIL) of the system it resides in. As an example, this proposed method is applied to a nuclear power plant safety-critical system to demonstrate the detail application process and to verify the feasibility of the method. Compared with the existing software criticality analysis methods, this method has better operability and verifiability, and can be utilized as a technical guidance for the software criticality analysis of nuclear power plant digital control systems.