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Revise Defining Constants

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Rob Bocchino 2025-11-02 12:10:05 -08:00
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108
docs/fpp-users-guide.html
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@ -467,6 +467,7 @@ body.book #toc,body.book #preamble,body.book h1.sect0,body.book .sect1>h2{page-b
</li>
<li><a href="#Defining-Constants_Multiple-Definitions-and-Element-Sequences">3.4. Multiple Definitions and Element Sequences</a></li>
<li><a href="#Defining-Constants_Multiline-Definitions">3.5. Multiline Definitions</a></li>
<li><a href="#Defining-Constants_Framework-Constants">3.6. Framework Constants</a></li>
</ul>
</li>
<li><a href="#Writing-Comments-and-Annotations">4. Writing Comments and Annotations</a>
@ -1829,6 +1830,111 @@ is not legal:</p>
</div>
</div>
</div>
<div class="sect2">
<h3 id="Defining-Constants_Framework-Constants">3.6. Framework Constants</h3>
<div class="paragraph">
<p>Certain constants defined in FPP have a special meaning in the
F Prime framework.
These constants are called <strong>framework constants</strong>.
For example, the constant <code>Fw.DpCfg.CONTAINER_USER_DATA_SIZE</code>
defines the size of the user data field in a data product container.
(Data products are an F Prime feature that we describe
<a href="#Defining-Components_Data-Products">in a later section of this manual</a>.)
You typically set these constants by overriding configuration
files provided in the directory <code>default/config</code> in the F Prime repository.
For example, the file <code>default/config/DpCfg.fpp</code> provides a default value for
<code>Fw.DpCfg.CONTAINER_USER_DATA_SIZE</code>.
You can override this default value by providing your own version of
the file <code>DpCfg.fpp</code>.
The
<a href="https://fprime.jpl.nasa.gov/devel/docs/user-manual/framework/configuring-fprime/,">F
Prime User Manual</a>
explains how to do this configuration.</p>
</div>
<div class="paragraph">
<p>The FPP analyzer does not require that framework constants be defined
unless they are used.
For example, the following model is valid, because it neither defines nor users
<code>Fw.DpCfg.CONTAINER_USER_DATA_SIZE</code>:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code data-lang="fpp">constant a = 0</code></pre>
</div>
</div>
<div class="paragraph">
<p>The following model is valid because it defines and uses <code>Fw.DpCfg.CONTAINER_USER_DATA_SIZE</code>:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code data-lang="fpp">module Fw {
module DpCfg {
constant CONTAINER_USER_DATA_SIZE = 10
}
}
constant a = Fw.DpCfg.CONTAINER_USER_DATA_SIZE</code></pre>
</div>
</div>
<div class="paragraph">
<p>The following model is invalid, because it uses <code>Fw.DpCfg.CONTAINER_USER_DATA_SIZE</code>
without defining it:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code data-lang="fpp">constant a = Fw.DpCfg.CONTAINER_USER_DATA_SIZE</code></pre>
</div>
</div>
<div class="paragraph">
<p>If framework constants are defined in the FPP model, then
then they must conform to certain rules.
These rules are spelled out in detail in the
<a href="https://nasa.github.io/fpp/fpp-spec.html#Definitions_Framework-Definitions"><em>The
FPP Language Specification</em></a>.
For example, <code>Fw.DpCfg.CONTAINER_USER_DATA_SIZE</code> must have an integer type.
So this model is invalid:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code data-lang="fpp">module Fw {
module DpCfg {
constant CONTAINER_USER_DATA_SIZE = "abc"
}
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>Here is what happens when you run this model through <code>fpp-check</code>:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>% fpp-check
module Fw {
module DpCfg {
constant CONTAINER_USER_DATA_SIZE = "abc"
}
}
^D
fpp-check
stdin:5.5
constant CONTAINER_USER_DATA_SIZE = "abc"
^
error: the F Prime framework constant Fw.DpCfg.CONTAINER_USER_DATA_SIZE must have an integer type</pre>
</div>
</div>
</div>
</div>
</div>
<div class="sect1">
@ -15894,7 +16000,7 @@ serialized according to its
</div>
<div id="footer">
<div id="footer-text">
Last updated 2025-10-30 17:21:37 -0700
Last updated 2025-11-02 12:09:14 -0800
</div>
</div>
<script src="code-prettify/run_prettify.js"></script>

98
docs/users-guide/Defining-Constants.adoc
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@ -737,3 +737,101 @@ is not legal:
constant
a = 1
--------
=== Framework Constants
Certain constants defined in FPP have a special meaning in the
F Prime framework.
These constants are called *framework constants*.
For example, the constant `Fw.DpCfg.CONTAINER_USER_DATA_SIZE`
defines the size of the user data field in a data product container.
(Data products are an F Prime feature that we describe
<<Defining-Components_Data-Products,in a later section of this manual>>.)
You typically set these constants by overriding configuration
files provided in the directory `default/config` in the F Prime repository.
For example, the file `default/config/DpCfg.fpp` provides a default value for
`Fw.DpCfg.CONTAINER_USER_DATA_SIZE`.
You can override this default value by providing your own version of
the file `DpCfg.fpp`.
The
https://fprime.jpl.nasa.gov/devel/docs/user-manual/framework/configuring-fprime/,[F
Prime User Manual]
explains how to do this configuration.
The FPP analyzer does not require that framework constants be defined
unless they are used.
For example, the following model is valid, because it neither defines nor users
`Fw.DpCfg.CONTAINER_USER_DATA_SIZE`:
[source,fpp]
----
constant a = 0
----
The following model is valid because it defines and uses `Fw.DpCfg.CONTAINER_USER_DATA_SIZE`:
[source,fpp]
----
module Fw {
module DpCfg {
constant CONTAINER_USER_DATA_SIZE = 10
}
}
constant a = Fw.DpCfg.CONTAINER_USER_DATA_SIZE
----
The following model is invalid, because it uses `Fw.DpCfg.CONTAINER_USER_DATA_SIZE`
without defining it:
[source,fpp]
--------
constant a = Fw.DpCfg.CONTAINER_USER_DATA_SIZE
--------
If framework constants are defined in the FPP model, then
then they must conform to certain rules.
These rules are spelled out in detail in the
https://nasa.github.io/fpp/fpp-spec.html#Definitions_Framework-Definitions[_The
FPP Language Specification_].
For example, `Fw.DpCfg.CONTAINER_USER_DATA_SIZE` must have an integer type.
So this model is invalid:
[source,fpp]
--------
module Fw {
module DpCfg {
constant CONTAINER_USER_DATA_SIZE = "abc"
}
}
--------
Here is what happens when you run this model through `fpp-check`:
----
% fpp-check
module Fw {
module DpCfg {
constant CONTAINER_USER_DATA_SIZE = "abc"
}
}
^D
fpp-check
stdin:5.5
constant CONTAINER_USER_DATA_SIZE = "abc"
^
error: the F Prime framework constant Fw.DpCfg.CONTAINER_USER_DATA_SIZE must have an integer type
----