Controller-area-network bus control and monitor system for a radio astronomy interferometer

Abstract

We describe the design and implementation of a controller-area-network bus (CANbus) monitor and control system for a millimeter wave interferometer. The Combined Array for Research in Millimeter-wave Astronomy (CARMA) is a 15-antenna connected-element interferometer for astronomical imaging, created by the merger of two university observatories. Its new control system relies on a central computer supervising a variety of subsystem computers, many of which control distributed intelligent nodes over CANbus. Subsystems are located in the control building and in individual antennas and communicate with the central computer via Ethernet. Each of the CAN modules has a very specific function, such as reading an antenna encoder or tuning an oscillator. Hardware for the modules was based on a core design including a commercial CANbus-enabled single-board computer and some standard circuitry for interfacing to peripherals. Hardware elements were added or changed as necessary for the specific module types. Similarly, a base set of embedded code was implemented for essential common functions such as CAN message handling and time keeping and extended to implement the required functionality for the different hardware. Using a standard CAN messaging protocol designed to fit the requirements of CARMA and a well-defined interface to the high-level software allowed separate development of high-level code and embedded code with minimal integration problems. Over 30 module types have been implemented and successfully deployed in CARMA, which is now delivering excellent new science data.

COMAP Early Science. II. Pathfinder Instrument

“…Much of the antenna-based monitor control system electronics were taken directly from CARMA (Woody et al 2004), with some additional components based on a control system for Argus (Sieth et al 2014). A VERSAmodule Eurocard crate with a CPU running Linux (CentOS 6.5, 32 bit) acts as a master in a controller-area-network bus (CANbus) 18 distributed system, with a protocol developed for CARMA (Woody et al 2007). CANbus modules include encoder and drive interfaces, environmental monitoring, calibration vane interface, cryogenic compressor monitoring, etc.…”

COMAP Early Science: II. Pathfinder Instrument

“…Much of the antenna-based monitor control system electronics were taken directly from CARMA (Woody et al 2004), with some additional components based on a control system for Argus (Sieth et al 2014). A VME crate with a CPU running Linux (CentOS 6.5, 32 bit) acts as a master in a controller-area-network bus (CANbus) (Marsh 2002) distributed system, with a protocol developed for CARMA (Woody et al 2007). CANbus modules include encoder and drive interfaces, environmental monitoring, calibration vane interface, cryogenic compressor monitoring, etc.…”

Software in the CARMA heterogeneous millimeter-wave array

“…At the lowest levels in the antennas and central electronics, embedded microprocessors (Philips C-167) are directly interfaced to the hardware. These are programmed in C by the hardware engineering staff and communicate over a 1 Mbps Controller-Area-Network bus (CANbus) as described by Woody, et al (2007) 2 . In general these microprocessors do not communicate with each other but with a CANbus master host computer that coordinates the activity of all the micros.…”

“…Access to any monitor point is through a specific accessor (or hierarchy of accessors), and not through a generic accessor using a string to represent a monitor point name, thus preventing runtime exceptions. An example of a hierarchical monitor point name is Ovro3.Drive.Track.requestedAzimuth which would be accessed by monitorSystem.ovro (2).drive().track().requestedAzimuth() Within a subsystem, monitor data are sent every frame from threads and processes producing monitor data to a process responsible for collecting the subsystem monitor data. These data are sent using a CORBA method call on the subsystem collection process.…”