Programmable Logic

Programmable Logic Educating Assurance Engineers NASA Glenn Research Center Kalynnda Berens (PI) Jackie Somos (Course designer)

What is Programmable Logic • Programmable Logic Controllers (PLC) • Programmable Logic Devices • Field Programmable Gate Array (FPGA) • Application Specific Integrated Circuit (ASIC) • System-on-chip (SOC) • Complex PLD (CPLD) • Others • FAA calls these “Complex Electronic Hardware” SAIC @ NASA Glenn Research Center

The Hardware/Software Boundary SOC Reconfig. Computing SAIC @ NASA Glenn Research Center

Issues • ASICs and FPGAs have been used to avoid the rigors of the software approval process. • Fundamental verification issues are bypassed • Devices are designed and programmed by engineers • Often without QA oversight or configuration management (CM) control of the designs. • The development process may not be well defined (e.g. ad-hoc). • Tool-induced design errors occur and can be difficult to detect. • Meaningful verification requires the person performing verification to be knowledgeable. SAIC @ NASA Glenn Research Center

Issues (2) • ASICs, FPGAs, and System on Chip (SoC) can contain embedded microprocessor cores with user-supplied software. • Combine electronics and firmware into one chip. • The presence of this firmware (i.e. software) is not always obvious to assurance personnel. • Complex programmable logic functionality cannot be completely simulated, nor the resulting chip completely tested. • High-level languages (e.g. C, C++) are now being used to define PLD designs (in whole or in part). SAIC @ NASA Glenn Research Center

Issues (3) • It can be difficult to detect faulty operation of Programmable Logic (PL). • Design errors • Tool-induced errors • Unexpected interactions • Defects in the silicon • Due to extremely small ASIC geometries, certain analog and transmission line phenomena occur internal to the ASIC, generating failures that are data-sensitive. • Designers and tools may not account for these effects • The effects can easily escape notice during test. SAIC @ NASA Glenn Research Center

Issues with Assurance Activities • Hardware QA may not be fully cognizant of the functions, potential problems, and issues with these devices. • Software Assurance personnel are currently not trained to understand programmable logic devices, and may not be able to provide effective oversight and assurance. • At NASA, • Software assurance personnel are not usually involved with PLCs, even for software hazard controls for the facility/system. • Hardware QA will usually only verify that testing was performed. There is little verification or analysis of requirements, design, and implementation processes for these devices. • NASA is using these devices in flight and ground hardware and facilities SAIC @ NASA Glenn Research Center

Recommendations - PLCs • Treat PLC programming languages (e.g. LadderLogic) as software • Apply Software Assurance (SA) • Train Software Assurance personnel to understand and assure this software • All should have basic understanding • At least one should be an “expert” SAIC @ NASA Glenn Research Center

Recommendations - PLDs • Define boundary between simple and complex electronics • Develop complex electronics checklist for Hardware Quality Assurance (QA) to use • Use Design/Process Assurance with Complex Programmable Logic • Both QA and Software Assurance should be involved in assurance of complex electronics SAIC @ NASA Glenn Research Center

Recommendations – PLDs (2) • Train Software Assurance in understanding complex electronics • All should have basic understanding • At least one should be an “expert” • Train QA in understanding and applying process assurance • Apply techniques from software to complex electronics • Apply techniques from hardware to software SAIC @ NASA Glenn Research Center

Year 1 of Research • Surveys on the usage and assurance of programmable logic to all Centers. • Survey results showed • SA involved in less than 1/3 of the projects • Projects performed their own verifications • SA knowledge of these devices is limited SAIC @ NASA Glenn Research Center

Year 2 of Research • What is industry and other government agencies doing for assurance and verification? • An intensive literature search of white papers, manuals, standards, and other documents that illustrated what various organizations were doing. • Focused interviews with industry practitioners. Interviews were conducted with assurance personnel (both hardware and software) and engineering practitioners in various industries, including biomedical, aerospace, and control systems. • Meeting with FAA representatives. Discussions with FAA representatives lead to a more thorough understanding of their approach and the pitfalls they have encountered along the way. • Position paper, with recommendations for NASA Code Q SAIC @ NASA Glenn Research Center

Current Effort • Implement some of the recommendations • Develop coursework to educate software and hardware assurance engineers • Three courses • PLCs for Software Assurance personnel • PLDs for Software Assurance personnel • Process Assurance for Hardware QA • Guidebook • Other recommendations • For Code Q to implement if desired • Follow-up CSIP to try software-style assurance on complex electronics SAIC @ NASA Glenn Research Center

Course 1: PLCs for Software Assurance Engineers SAIC @ NASA Glenn Research Center

PLC Course: Clip 2 SAIC @ NASA Glenn Research Center

Future Work • Complete PLC course • Create PLD and Process Assurance Courses • Course Review • If you can help, please contact Kalynnda.Berens@grc.nasa.gov • Courses available on Solar Try out the PLC class at the tool demo! SAIC @ NASA Glenn Research Center

Programmable Logic