The real-time control system of NAOMI

The Nasmyth Adaptive Optics for Multi-purpose Instrumentation (NAOMI) is the common-user Adaptive Optics (AO) system on the 4.2m William Herschel Telescope (WHT) operated by the Isaac Newton Group of Telescopes (ING). The system contains a 76-element Deformable Mirror (DM) containing 228-degrees of freedom with Strain Gauge (SG) feedback capabilities and an 8x8 Shack Hartmann Wavefiront Sensor (ATS). The wavefront corrector and wavefront sensor are controlled and coordinated by the third key component of the adaptive optics system, the Real-Time Control System (RTCS). The RTCS manages and processes interrupts and inputs including WFS image data and SG feedback signals. It also provides calculated drive signals for the system's DM and Fast Steering Mirror (FSM) as well as debug, visualisation and logging data to the user's workstation. This paper contains a description of both the control hardware and software architecture of the RTCS including the WFS and SG real-time control loops. Each loop contains 8 Texas Instrument TMS320C44 digital signal processors, housed on DBV44 cards seated inside the NAOMI Real-Time Control Rack (RTCR) VME crate. A description of the complete processor architecture and ring structure is provided, detailing each processor's connections and external hardware communications. The described software architecture incorporates Bulk Synchronisation Parallelism (BSP) methodology, Interrupt Service Routines (ISRs), "General Purpose" (GP) messaging, Lovetrains, Cowcatchers, the Data Transfer Mechanism (DTM) and Parameter Block Transactions (PBT). The paper concludes with revealing planned enhancements to the current RTCS.