Glossary
############

.. glossary::
    :sorted:

    GMB
        Global Memory Block.  The GMB is shared memory with segments on each of the four GPI computers. It is implemented as a database
        with key:value pairs, with keys prefixed by the system repsonsible for populating the values.

    RPC
        Remote Procedure Call.  The primary mechanism by which commands are sent to and between the GPI subsystems. See also: https://man7.org/linux/man-pages/man3/rpc.3.html

    CAL
        The Calibration subsystem computer. Also the subsystem itself.

    TLC
        The Top-Level Control computer.

    AOC
        The adaptive optics computer.

    IFS
        The integral field spectrograph computer (also the instrument itself).

    AO
        Adaptive Optics.

    SIM
        Simulated operation.  There exist multiple level of SIMs possible: at the :term:`MCD` level, at the Assembly level, and at the gpilib2 level.  Each of these has different impacts on what actually happens in the system when a command is sent to a simulated component. 

    MCD
        Motor Control Device.  Also the lowest level of software interfacing with (some) GPI mechanism controllers. 

    oneWire
        Device communications bus system for devices employing (unsurprisingly) a single conductor.  In GPI, the oneWire assembly includes all temperature, pressure, and humidity sensors  other than those inside the :term:`IFS` and internal to devices (primarily cameras) that have their own sensors.

    ack
        Acknowledgement of command receipt. 

    ASU
        Artificial Source Unit. The ASU can be deployed into the Gemini f/16 focus (immediately after the :term:`ADC`, after the :term:`OMSS` shutter) to provide an internal light source, used for engineering tasks and calibrations.  The ASU is equipped with three light sources: the :term:`SC` and two monochromatic lasers in the visible and IR.

    SC
        Supercontinuum source.  This is a white light laser source with a wavelength range from the visible to just past 2 microns. It can illuminate both the :term:`ASU` and the :term:`CAL Sphere`, each of which has an independent attenuator.  The SC is chromatic in power setting, and so is always run at 100% power in normal operation.  Each attenuator can be set between 2.2 and 60 dB (the latter being the nominal off setting).

    CAL Sphere
        Integrating sphere that can be deployed into the light path immediately ahead of the :term:`FPM` to provide a light source directly to the :term:`CAL`. 

    FPM
        Focal Plane mask.  The second component of the :term:`APLC`, residing in a filter wheel at a focal plane.

    APLC
        Apodized-Pupil Lyot Coronagraph.

    ADC
        Anti-dispersion corrector.

    OMSS
        Opto-Mechanical Support Structure.  GPI's skeleton. 

    apodizer
        The first component of the :term:`APLC`, residing in a filter wheel at a pupil plane.

    Lyot
        The third components of the :term:`APLC`, residing in a filter wheel at a pupil plane.

    PPM
        Pupil-plane Mask.  In GPI, this typically refers to the :term:`apodizer`.  The PPM :term:`assembly` explicitly is for control of the apodizer filter wheel only. 

    assembly
        GPI software construct grouping together control of multiple (usually) related mechanisms.  Some (notably the :term:`PPM` and :term:`FPM`) assemblies only control a single mechanism.

    IS
        Instrument Sequencer.  Highest-level software interface between observatory systems and GPI.  This exposes GPI commands that can be directly called by the observatory.

    PnC
        Pointing and Centering mirrors.  Pairs of mirrors that can be moved to produce pure pointing and/or pure centering changes. GPI has two such pairs: The first is immediately in front of the :term:`AO` :term:`WFS` (after the dichroic so only the :term:`WFS` sees the pointing and centering changes due to these mirrors. The second lies immediately before the :term:`CAL` exit and is used to steer the beam onto the :term:`IFS`.

    WFS
        Wavefront Sensor.

    OLM
        Open-Loop Model.  Multiple components have open loop models intended to automatically correct their settings in response to changes in tempreature and zenith angle (instrument orientation). These changes are only applied when a mechanism is in :term:`TRACK`.

    TRACK
        Mechanism state where settings changes (in response to an :term:`OLM` and other inputs) are continuously and automatically applied.