Index: 10_forge_imp.html
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--- 10_forge_imp.html	(revision 8156)
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@@ -42,3 +42,47 @@
 the value of attribute rail, because of suba). The last two operations
 ensure connect exists as an array type attribute and appends the new
 connection to it.
+
+<h2> 10.1. cschem implementation - stances and build options </h2>
+<p>{imp10:5}
+Suppose the current project of 3 sheets is of an MCU controlled board with
+various sensors. The MCU, the interface circuity and some of the
+sensors are mandatory, but some of the more expensive sensors are optional.
+A design decision is made so that there are models <i>standard</i>,
+<i>advanced</i> and <i>professinal</i>. There is only one PCB is made
+for all options, but different components are DNP'd for the different options.
+
+<p>{imp10:6}
+The implementation in cschem is:
+<ul>
+	<li> set up the possible values for the <i>model</i> stance to a list of: <i>standard</i>, <i>advanced</i> and <i>professinal</i>
+	<li> set the value of the model stance to one of them, e.g. <i>advanced</i>
+	<li> for each abstract component that is not present on all three models, visit the symbol(s) contributing to that component and add a conditional forge attribute that creates a pcb/dnp attribute if the component should not be populated on the pcb for a given stance
+</ul>
+
+<p>{imp10:7}
+For example take a sensor that should be on <i>advanced</i> and <i>professinal</i>
+but not on <i>standard</i>. Create the array type attribute
+<i>forge-if/model-dnp</i> (the model-dnp part is arbitrary) with this
+content (each line is an array element):
+<pre>
+(project.stance != "advanced") || (project.stance != "professinal")
+scalar,pcb/dnp
+sub,^.*$,DNP,pcb/dnp
+</pre>
+
+<p>{imp10:8}
+The condition specifies when the component is DNP. Alternatively
+it could be written as (project.stance == "standard").
+
+<p>{imp10:9}
+The rest of the forge is setting the pcb/dnp attribute to DNP. The value
+could be anything, as long as the attribute exists and is non-empty, the
+export mechanism should take it as true. Using DNP is practical for
+dyntext printing the attribute value on the sheet.
+
+<p>{imp10:10}
+Note: stances and lists of possible stance values shall be stored in the
+project file (e.g. project role configuration) and not on sheet level
+because it affects the abstract model, which uses all sheets of the project.
+