The scanning microwave limb sounder (SMLS) will use technological improvements in low-noise mixers to provide precise data on the Earth’s atmospheric composition with high spatial resolution. This project focuses on the design and implementation of a real-time control system needed for airborne engineering tests of the SMLS. The system must coordinate the actuation of optical components using four motors with encoder readback, while collecting synchronized telemetric data from a GPS receiver and 3-axis gyrometric system. A graphical user interface for testing the control system was also designed using Python.

Although the system could have been implemented with an FPGA(field-programmable gate array)-based setup, a processor development kit manufactured by XMOS was chosen. The XMOS architecture allows parallel execution of multiple tasks on separate threads, making it ideal for this application. It is easily programmed using XC (a subset of C). The necessary communication interfaces were implemented in software, including Ethernet, with significant cost and time reduction compared to an FPGA-based approach.

A simple approach to control the chopper, calibration mirror, and gimbal for the airborne SMLS was needed. The XMOS board allows for multiple threads and real-time data acquisition. The XC-2 development kit is an attractive choice for synchronized, real-time, event-driven applications. The XMOS is based on the transputer microprocessor architecture developed for parallel computing, which is being revamped in this new platform.

The XMOS device has multiple cores capable of running parallel applications on separate threads. The threads communicate with each other via user-defined channels capable of transmitting data within the device. XMOS provides a C-based development environment using XC, which eliminates the need for custom tool kits associated with FPGA programming. The XC-2 has four cores and necessary hardware for Ethernet I/O.

This work was done by Robert F. Jarnot of Caltech and William J. Bowden of the University of British Columbia for NASA’s Jet Propulsion Laboratory.

The software used in this innovation is available for commercial licensing. Please contact Daniel Broderick of the California Institute of Technology at This email address is being protected from spambots. You need JavaScript enabled to view it.. NPO-48054


This Brief includes a Technical Support Package (TSP).
XMOS XC-2 Development Board for Mechanical Control and Data Collection

(reference NPO-48054) is currently available for download from the TSP library.

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This article first appeared in the December, 2011 issue of NASA Tech Briefs Magazine.

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