ogma-cli: Document fprime command in README. Refs #77.

Add instructions of how the `fprime` command works.

Add entry in list of features documenting the new F' (FPrime) support.

Describe existing limitations for the command.

ogma-cli/README.md

@@ -22,6 +22,9 @@ verification framework that generates hard real-time C99 code.
 - Generating [Robot Operating System](https://ros.org) applications that use
   Copilot for monitoring data published in different topics.
 
+- Generating [F' (FPrime)](https://github.com/nasa/fprime/) components that use
+  Copilot for monitoring data published in different ports.
+
 
 <p align="center">
   <img src="https://raw.githubusercontent.com/nasa/ogma/gh-pages/images/fret-to-c.gif" alt="Conversion of requirements into C code">
@@ -45,6 +48,7 @@ verification framework that generates hard real-time C99 code.
   - [cFS Application Generation](#cfs-application-generation)
   - [Struct Interface Generation](#struct-interface-generation)
   - [ROS Application Generation](#ros-application-generation)
+  - [F' Application Generation](#f-application-generation)
 - [Contributions](#contributions)
 - [Acknowledgements](#acknowledgements)
 - [License](#license)
@@ -108,6 +112,7 @@ Available commands:
   structs                  Generate Copilot structs from C structs
   handlers                 Generate message handlers from C structs
   cfs                      Generate a complete cFS/Copilot application
+  fprime                   Generate a complete FPrime monitoring component
   fret-component-spec      Generate a Copilot file from a FRET Component
                            Specification
   fret-reqs-db             Generate a Copilot file from a FRET Requirements
@@ -442,6 +447,120 @@ be generated for any variables for which a DB entry cannot be found. At present,
 Ogma will proceed without warnings if a variable is mentioned in a requirement
 or variables file but a matching entry is not found in the variable DB.
 
+## F' Component Generation
+
+F' (FPrime) is a component-based framework for spaceflight applications.
+
+Ogma is able to generate F' monitoring components that subscribe to obtain
+the data needed by the monitors and report any violations. At present, support
+for F' component generation is considered preliminary.
+
+F' components are generated using the Ogma command `fprime`, which receives
+five main arguments:
+- `--app-target-dir DIR`: location where the F' application files must be
+  stored.
+- `--fret-file-name FILENAME`: a file containing a FRET component specification.
+- `--variable-file FILENAME`: a file containing a list of variables that must
+be made available to the monitor.
+- `--variable-db FILENAME`: a file containing a database of known variables,
+and their types.
+- `--handlers FILENAME`: a file containing a list of handlers used in the
+  specification.
+
+Not all arguments are mandatory. You should always provide either a FRET
+component specification, or both a variable file and a handlers file. If you
+provide a variables file or a handler file _and_ a FRET component
+specification, the variables/handlers file will always take precedence, and the
+variables/requirements listed in the FRET component specification file will be
+ignored.
+
+The following execution generates an initial F' component for runtime
+monitoring using Copilot:
+```sh
+$ ogma fprime --fret-file-name Export.json --variable-db fprime-variable-db --app-target-dir fprime_demo
+```
+
+The component generated by Ogma contains the following files:
+```
+fprime_demo/CMakeLists.txt
+fprime_demo/Copilot.fpp
+fprime_demo/Copilot.cpp
+fprime_demo/Copilot.hpp
+fprime_demo/Dockerfile
+fprime_demo/inline-copilot
+```
+
+For completion, the following execution should compile the produced monitoring
+component in a docker environment (assuming that the necessary `Export.json`,
+`fprime-variable-db` files exist, they have consistent information, etc.) using
+FPrime's Reference Application:
+
+```sh
+$ ogma fprime --fret-file-name Export.json --variable-db fprime-variable-db --app-target-dir fprime_demo
+$ ogma fret-component-spec --fret-file-name Export.json > Spec.hs
+$ sed -i -e 's/compile "fret"/compile "copilot"/g' Spec.hs
+$ cd fprime_demo/
+$ runhaskell ../Spec.hs
+$ docker build -t fprime .
+```
+
+### File formats
+
+The format of the variables, variable DB, and handlers file are as follows.
+
+The variables file can contain a list of variables used in a specification, one
+per line. For example, if we are working with a specification that uses three
+boolean variables called `autopilot`, `sensorLimitsExceeded`, and `pullup`, we
+can provide them to Ogma's `fprime` command in a file like the following:
+```sh
+$ cat variables
+autopilot
+sensorLimitsExceeded
+pullup
+```
+
+The variables database file contains a list of known variables and their types.
+It does not matter if there are variables that are not used for one particular
+specification, FRET file, or requirement/monitor. The only thing that matters
+is that the variables used, and their types, be listed in the file. Continuing
+with the same example, we could have:
+
+```sh
+$ cat fprime-variable-db
+("temperature", "uint8_t")
+("autopilot", "bool")
+("sensorLimitsExceeded", "bool")
+("pullup", "bool")
+("current_consumption", "float")
+```
+
+In our example, we only care about the boolean variables; it is sufficient that
+they be listed in the variable DB file.
+
+Finally, the handlers file is a list of monitor handlers that the generated
+FPrime component should restrict to monitoring. They are listed one per line:
+```sh
+$ cat handlers
+handlerpropREQ_001
+```
+
+Note that the handler name must match the one used by Copilot. Ogma transforms
+requirement names to ensure that they corresponding handlers are valid C
+identifiers. For example, the Ogma-generated monitor for a FRET requirement
+`REQ_001` would, upon violation, call a C handler `handlerpropREQ_001`. The
+transformation only applies if you are working with FRET files and not directly
+with other source languages.
+
+### Current limitations
+
+The user must place the code generated by Copilot monitors in three files,
+`fprime_demo/src/copilot.h`, `fprime_demo/src/copilot_types.h` and
+`fprime_demo/src/copilot.c`. No Copilot or C code for the monitors is generated
+by default by the `fprime` command.
+
+The code generated by default assumes that handlers receive no arguments. The
+user must modify the handlers accordingly if that is not the case.
+
 ## Struct Interface Generation
 
 A lot of the information that must be monitored in real-world C applications is