Single-event upsets (SEUs) pose great threats to avionic systems' state machine control logic, which are frequently used to control sequence of events and to qualify protocols. The risks of SEUs manifest in two ways: (a) the state machine's state information is changed, causing the state machine to unexpectedly transition to another state; (b) due to the asynchronous nature of SEU, the state machine's state registers become metastable, consequently causing any combinational logic associated with the metastable registers to malfunction temporarily. Effect (a) can be mitigated with methods such as triple-modular redundancy (TMR). However, effect (b) cannot be eliminated and can degrade the effectiveness of any mitigation method of effect (a).
Although there is no way to completely eliminate the risk of SEU-induced errors, the risk can be made very small by use of a combination of very fast state-machine logic and error-detection logic. Therefore, one goal of two main elements of the present method is to design the fastest state-machine logic circuitry by basing it on the fastest generic state-machine design, which is that of a one-hot state machine. The other of the two main design elements is to design fast error-detection logic circuitry and to optimize it for implementation in a field-programmable gate array (FPGA) architecture: In the resulting design, the one-hot state machine is fitted with a multiple-input XNOR gate for detection of illegal states. The XNOR gate is implemented with lookup tables and with pipelines for high speed.
In this method, the task of designing all the logic must be performed manually because no currently available logic-synthesis software tool can produce optimal solutions of design problems of this type. However, some assistance is provided by a script, written for this purpose in the Python language (an object-oriented interpretive computer language) to automatically generate hardware description language (HDL) code from state-transition rules.
This work was done by Martin Le, Xin Zheng, and Sunant Katanyoutant of Caltech for NASA's Jet Propulsion Laboratory.
NPO-42401
This Brief includes a Technical Support Package (TSP).
Using Pipelined XNOR Logic To Reduce SEU Risks in State Machines
(reference NPO-42401) is currently available for download from the TSP library.
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Overview
The document titled "Using Pipelined XNOR Logic to Reduce SEU Risks in State Machines" is a technical support package developed by the Jet Propulsion Laboratory (JPL) under NASA's Commercial Technology Program. It addresses the challenges posed by Single Event Upsets (SEUs) in finite state machines, which are critical components in avionic control systems.
The overview of the document outlines several key sections, including background information, asynchronous SEU analysis, existing mitigation methods, and future outlooks. The primary focus is on the innovative use of pipelined XNOR logic as a method to enhance the reliability of state machines against SEUs, which can occur due to radiation exposure in space environments.
The document begins with a background section that explains the significance of finite state machines in aerospace applications and the potential risks associated with SEUs. It then delves into an analysis of asynchronous SEUs, detailing how these events can disrupt the normal operation of state machines.
Existing mitigation methods are reviewed, highlighting various strategies that have been employed to protect against SEUs. The document emphasizes the limitations of these methods and introduces the concept of using a one-hot encoding scheme combined with pipelined XNOR logic. This approach aims to improve fault tolerance and reduce the likelihood of SEUs affecting the state machine's performance.
A Python script automation section is included, which discusses how automation can streamline the testing and implementation of the proposed mitigation strategies. Test results are presented to demonstrate the effectiveness of the pipelined XNOR logic in real-world scenarios, showcasing its potential to significantly reduce SEU risks.
The document concludes with a future outlook, suggesting further research and development opportunities to enhance the resilience of state machines in aerospace applications. It emphasizes the importance of continued innovation in this field to ensure the safety and efficiency of avionic systems.
Overall, this technical support package serves as a valuable resource for engineers and researchers working on aerospace technologies, providing insights into advanced techniques for mitigating SEU risks and enhancing the reliability of critical systems in challenging environments.
