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Added documentation for the attribute labels in the "label" command 

description, because otherwise it only appears in the tech file
reference, where it doesn't really belong since the labels are a
user-level feature, even if they do affect extraction.  The new
feature of using gate attributes for parameters was added to the
command description.  I noticed that the tech file reference made
mention of a gate label in the form of ":ext <name>=<value>", but
this seems not to be implemented anywhere.  At any rate, the method
just committed supercedes that.
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R. Timothy Edwards 2026-03-18 19:28:23 -04:00
parent 37db9e453b
commit 66faf1d907
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doc/html/label.html
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@ -87,6 +87,50 @@ Place a label in the layout
to another layer. <P>
</BLOCKQUOTE>
<BLOCKQUOTE>
<B>Attribute labels:</B> <P>
A handful of labels are referred to as "attribute" labels. These
label types are placed on devices and affect how the device is
extracted. <P>
A label that is placed inside a device (e.g., a MOSFET gate) which
ends with the character "<B>^</B>" is a <I>gate attribute</I>. A
gate attribute in the form of "<I>name</I><B>=</B><I>value</I><B>^</B>"
specifies an extra parameter to be passed to the device in addition
to the standard parameters calculated for that device. This is used
to capture parameters which cannot easily be inferred from the layout.
For example, an RF device model might be distinguished from a non-RF
device model by a parameter such as <B>rfmode=1</B>. Whether or not
a device is intended for RF use is not easily guessed from the layout,
and so "tagging" the gate with the parameter allows the correct model
parameters to be used for the device. <P>
A gate attribute that is not in the form of a parameter will be used
as the device's instance index in the netlist; e.g., a label of
"<B>1^</B>" on a MOSFET gate extracted as a MOSFET device would be an
entry "<B>M1</B>" in the netlist. This can be used to better track
device indexes between a schematic and layout. <P>
A label that is placed on the <I>edge</I> a device, specificlly a
MOSFET gate, and which ends with the character "<B>$</B>", is a
<I>terminal attribute</I>. The only terminal attributes recognized
by magic are <B>S$</B> and <B>D$</B>, which specify which side of the
gate is to be considered the source and which is to be considered the
drain. Generally, MOSFET devices are symmetric, and their use in a
simulation does not depend on which side is in the position of the
"source" and which is in the position of the "drain". To the extent
that it matters, the terminal attributes can be used to ensure that
the source and drain connections appear in the netlist in their
intended orientation. <P>
Labels ending with "<B>@</B>" are <I>node attributes</I>. There is
currently no functional application for node attributes. When one
is applied, it will appear in the output netlist in a SPICE comment
line indicating the node and attribute. This could be used, say,
by a post-processing script, but as it is in a comment line, it has
no impact on simulation or LVS.
</BLOCKQUOTE>
<H3>Implementation Notes:</H3>
<BLOCKQUOTE>
<B>label</B> is implemented as a built-in command in <B>magic</B>.