Technical Library



The rtxd Project: Open Source Real-time for the Industrial Internet of Things

The markets for Internet of Thing (IoT) devices are forecast to experience phenomenal growth in the coming years, but not all IoT markets are created equal. Two of the most prominent IoT markets are the consumer IoT and the Industrial IoT (IIoT). IIoT devices are differentiated by much stricter requirements for timing, reliability and consistency as they are often critical links in control and safety systems. Between market demand and recent advances in technology, the IIoT is expected to accelerate an already impressive growth trajectory. With such increased demand for IIoT devices, more time and effort will be spent developing and validating these products, which in turn fuels the need for better tools and frameworks to increase development speed, quality and verifiability.

To fill this demand, the rtxd project was conceived of by ADI to share lessons learned and best practices from over twenty years of implementing critical real-time control systems for some of the world’s most demanding applications. ADI believe the need for these services will only increase in the coming years and that the best way to embrace this rapidly expanding market is to share best practices through this new open source project.

This whitepaper describes the fundamentals of the rtxd project and explains why it makes sense for ADI and others to invest their time and resources toward this effort.

The rtxd Project: Open Source Real-time for the Industrial Internet of Things PDF (2.9 MB)

Real-time Simulation and Model-Based-Systems- Engineering using Commercial-Off-The-Shelf (COTS) Computer Equipment

This paper presents the requirements development (including requirement creep), selection, and integration of a small commercial off the shelf (COTS) computer into existing simulation systems that are based on the Applied Dynamics ADvantage Framework. A comparison of the increased processing and modeling capability will be presented. Finally, changes in the existing process are shown with a discussion of modeling tradeoffs.

Real-time Simulation and Model-Based-Systems- Engineering using Commercial-Off-The-Shelf (COTS) Computer Equipment PDF (748 KB)

Improving the Accuracy of Intermediate-pass Outputs in Multi-pass Real-Time Integration Methods

In using multi-pass integration methods for real-time simulation of dynamic systems, it may be desirable to employ intermediate-pass state-variable calculations as real-time outputs. For example, the real-time version of 2nd-order Runge-Kutta (RTRK-2) utilizes two evaluations of each state variable per overall integration step.

However, in real-time simulations there may sometimes be a requirement for input and output data rates to be identical. This can be accomplished by using both half-frame and full frame data points as real-time outputs in the RTRK-2 simulation. When this is done, it is important to realize that the dynamic errors associated with the half-frame outputs will in general be larger than those of the full-frame outputs, which can lead to undesirable scatter in the dynamic errors of the output data points.

In this paper we introduce formulas which improve the accuracy of the intermediate output data points in multi-pass integration methods. This in turn permits the multi-pass methods to be utilized for real-time simulations with equal input and output data-point frame rates without compromising the dynamic accuracy of the simulation.

Improving the Accuracy of Intermediate-pass Outputs in Multi-pass Real-Time Integration Methods PDF (3.9 MB)

Predictor Methods in Real-Time Simulation

In real-time simulation it may sometimes be necessary to advance a data sequence {xn} by a given time interval in order to compensate for a delay of the same time interval which occurs somewhere else in the simulation. For example, it is well known that a D to A (digital-to-analog) converter that employs a zero-order hold introduces an effective delay equal to one-half the time step h associated with the data sequence driving the D to A converter. If left uncompensated, this can introduce a significant dynamic error in a closed-loop, real-time simulation. In this paper we present a number of formulas for calculating an estimated data sequence.

Predictor Methods in Real-Time Simulation PDF (4.7 MB)

RTOS versus GPOS: What is best for embedded development?

Do most embedded projects still need an RTOS? It is a good question, given the speed of today’s high-performance processors and the availability of real-time patches for Linux, Windows, and other General Purpose Operating Systems (GPOSs). By Paul N. Leroux

RTOS versus GPOS: What is best for embedded development? in PDF (374 KB)

The Expanded Reach of Simulation Based Aircraft System Verification and its Software Capability Requirements

The engineering and technology space surrounding Model Based Systems Engineering (MBSE) has been growing in scope and importance for product development companies, for at least a couple decades. Product Lifecycle Management (PLM) methodologies allow product companies to shorten development cycles, reduce cost, and refine the product offering to enable each successive version to be better, cheaper, faster. Matlab/Simulink has become the Microsoft Word of technical computing and the leading format for designing and simulating product behavior.

In the decade from 2000 to 2010, a tremendous amount of technology advancement was seen using Simulink models to design a system, and use Simulink-interfaced code generators to output C code providing the behavioral capability associated with any intelligent subsystems within the designed system. This, along with other advancements in MBSE, has allows for the more and more complexity to be designed into a system while at the same time reducing product design cycles. Added complexity to provide a larger feature set, reduce energy consumption, reduce initial and maintenance costs, improved user experience, etc. have expanded the effort associated with the system verification tasks. More and more work is being placed on the systems verification team whose role is to ensure the product does exactly what it was designed to do, and nothing else.

The MBSE world is seeing an increased investment in model based systems verification teams, facilities, software, and business process to expand what is, for many product companies, a bottleneck in their PLM business operations.

The aircraft manufacturing market is a very interesting product business. Like many product companies, aircraft manufacturing involves product certification and rigorous PLM methods. The certification of an aircraft requires that each aircraft system be tested to ensure they meet all system requirements, and meet system-specific airworthiness standards. Then systems must be integrated as incomplete and complete sets to be verification tested ahead of the Flight Test. The Flight Test Program represents the final system integration testing effort. Model based verification involves testing one or more systems interfaced with simulation in order to put the system(s) through normal and failure mode conditions that are highly representative of the complete aircraft behavior.

This activity involves a wide range of artifacts including simulation models, requirements documents, design documents, traceability matrices, test framework projects, facilities, product domain experts, test cases, verification software, real-time computer systems, and prototype aircraft systems. Each of these artifacts is being refined and is evolving through the product lifecycle. This results in a challenging management tasks in order to perform model based system verification in a timely and cost-effective manner. This paper reviews the historical trend of model based systems verification for aircraft, reviews the traditional methodologies and facilities that have become industry norms, looks at the software capabilities and requirements associated with a world-class model based verification process, reviews the MBSE verification process itself, and reviews in-detail, some of the new MBSE verification facilities being used in the aircraft manufacturing market, and discusses business process trends associated with this fast-changing area of the PLM world.

The Expanded Reach of Simulation Based Aircraft System Verification and its Software Capability Requirements PDF (2.3 MB)

Development of a Real-Time Capable Integrated Aircraft Model

AIAA Aviation, August 2013 – by Dr. Clare Savaglio, Applied Dynamics

Flight simulation models are used throughout the aircraft industry including aircraft subsystem design; control system development; training simulation; cockpit display development; accident analysis; and within avionics integration labs and iron bird labs for production and development testing of devices and software.  Although aircraft companies usually develop and maintain their own aircraft model library there is demand for an externally-developed aircraft model library by companies developing aircraft subsystems and also by emerging market aerospace companies in the process of building their set of technology assets.

In this paper we describe the design and on-going development of an integrated real-time capable aircraft model for use in aircraft system development, test and integration.   The library was developed for desktop simulation as well as real-time simulation with hardware-in-the-loop.  Several features are necessary to provide efficiency during test initialization and running.  Real-time capability is necessary for use in testing of actual aircraft subsystems such as line replaceable units, avionics, actuators and for pilot-in-the-loop applications.  Real-time capability places constraints on the model library mainly because each simulation cycle is completed in the same amount of time as the integration step-size.  The model architecture should provide good accessibility and flexibility to both the user and the developer.  Access to differential equation integrators is required for trimming and reinitializing the aircraft when the simulation is on-line.  Access to scalar and table parameters when the simulation is on-line is necessary for efficiency.  The model library must provide subsystem modules so that a developer can integrate with and replace library modules with in-house developed subsystem models and eventually with external devices under test.  The each component of the model must expose the data required to model the aircraft communication, control systems, and networking.  The structure of the model must support rapid reconfiguration for many different test scenarios and must not require recompile of the model in order to initialize test cases.  This paper explores the considerations in the design of an integrated aircraft simulation model, discusses the trade-offs, and discusses the results of our development effort.

Speeding Aircraft Development from Preliminary Design through Certification

Rapid advancements in avionics systems require moving from concept to certification as quickly and efficiently as possible. Simulation has proven to be invaluable in reducing development cycle times by enabling more efficient development work earlier in the design process.

Speeding Aircraft Development from Preliminary Design through Certification PDF (101 KB)

Jet Engine HIL Simulation for Electronic Control System Testing

Successful jet engine development depends as much on the quality of the electronic engine control system as it does on engine design. Hardware-in-the-loop testing puts an engine control system through test scenarios identical to those carried out in engine test stand testing, with substantially lower cost, reduced risk, and less burden on human and mechanical resources.

Jet Engine HIL Simulation for Electronic Control System Testing PDF (81 KB)

A momentum form of Kane’s equations for scleronomic systems

A momentum form of Kane’s equations for scleronomic systems

Distributed Electrical Aerospace Propulsion – Future Aircraft Concept

The Distributed Electrical Aerospace Propulsion (DEAP) concept aircraft combines six electric engines for main propulsion, electrical storage, and a single gas turbine engine for electrical power generation. This technology development program, led by Rolls-Royce and Airbus, looks to the future of energy-optimized aircraft with a dramatic departure from the current aircraft design paradigm. Read the entire article here:

Into the DEAP, SAE Vehicle Electrification, May 13, 2014, pg. 24-33

Simulation-centric processes for aerospace

Big aerospace and military applications represent the extreme end of embedded-systems complexity. Here’s how an embedded manager uses simulation and hardware-in-the-loop testing to break problems down to size. These guidelines can be used for any large project, or just projects that threaten to get out of hand.

Simulation-centric processes for aerospace PDF (161 KB)