Functional Mockup Units (FMUs)
##############################

The following sections explain the use of **FMUs** in **MTF**.
The full documentation can be found in the following locations:

+ `GitHub project page <https://github.com/modelica/reference-fmus>`_ 
+ `FMI documentation page <https://fmi-standard.org>`_ 
+ `FMI v2.x specification <https://fmi-standard.org/assets/releases/FMI_for_ModelExchange_and_CoSimulation_v2.0.pdf>`_ 
+ `FMI v3.x specification <https://fmi-standard.org/docs/3.0/>`_ 


Introduction
************

A **Functional Mockup Unit (FMU)** is a tool-independent, self-contained program (part) or library along with specifications and definitions how the binary code is to be executed.

For more detailed information check the `FMI introduction <https://fmi-standard.org/docs/3.0/#_introduction>`_.

The **Functional Mockup Interface (FMI)** defines the various *APIs* needed to develop the *FMUs* themselves as well as the tool that can execute them.

FMU and FMI
===========

In general the term **FMU** defines the *ZIP-archive* containing the binary code as well as the specifications, definitions, and APIs, whereas **FMI** is the interface how the specifications and definitions have to be organized and laid out in order for the **FMU** to be correctly executed.

FMI v2.x vs FMI v3.x
====================

In order to fix some problems of the **CoSimulation concept** the following features were added:

+ Event mode
+ Early return
+ Intermediate Update Model

Additionally the **Scheduled Execution** model has been added in FMI-3.0.

For detailed information check the `respective FMI documentation <https://fmi-standard.org/docs/3.0/#fmi-whats-new>`_.

Execution models (CS vs SE)
===========================

Whereas the **FMUs** based on the **CoSimulation** model must provide the solution method and algorithms additionally to their model description algorithms, the **Scheduled Execution** lets the master govern the time progression during the simulation. This provides some distinct advantages especially for concurrent simulation.

Fore more information check the `CoSimulation <https://fmi-standard.org/docs/3.0/#fmi-for-co-simulation>`_ and `Scheduled Execution <https://fmi-standard.org/docs/3.0/#fmi-for-scheduled-execution>`_ documentation.