2021-10-12 18:03:39 +02:00
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<title>XSCHEM TUTORIAL: Translate GEDA gschem/lepton-schematic schematics and symbols to xschem</title>
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<div class="content">
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<a href="xschem_man.html" class="home">UP</a>
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<!-- slide title -->
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<h1>TUTORIAL: Translate GEDA gschem/lepton-schematic schematics and symbols to xschem</h1>
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<p>
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The <kbd>gschemtoxschem.awk</kbd> utility (installed in <kbd>(install_root)/share/xschem</kbd>) generates xschem
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schematic and symbol files from their GEDA equivalents.
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</p>
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<p>
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First of all, note that xschem comes with all geda symbols already translated to xschem.
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</p>
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<p>
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Create an empty directory where you want your xschem schematics/symbols, inside this directory create an <kbd>xschemrc</kbd> file
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with the following path added, if not already done in your <span style="white-space: nowrap;"><kbd>~/.xschem/xschemrc</kbd></span> file:
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</p>
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<pre class="code">
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append XSCHEM_LIBRARY_PATH :${XSCHEM_SHAREDIR}/../doc/xschem/gschem_import/sym
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</pre>
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<p>
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Next, in this directory create a <kbd>convert.sh</kbd> script and make it executable:
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</p>
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<pre class="code">
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#!/bin/bash
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# remove empty glob specifications *.sym or *.sch
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shopt -s nullglob
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for file in directory_with_geda_files/*.{sym,sch}
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do
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/path_to_xschem_install_root/share/xschem/gschemtoxschem.awk $file > $(basename -- $file)
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done
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</pre>
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<p>
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Note that you have to set the correct path for <kbd>gschemtoxschem.awk</kbd> depending on your xschem installation
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and set the correct path for the directory (<kbd>directory_with_geda_files</kbd> in above example) containing the geda files.
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<br>
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The current directory will be populated with xschem schematics/symbols with the same name as their GEDA equivalents.
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Incidentally xschem and gschem use the same file extensions (.sym, .sch), so be careful not to mix xschem and gschem files.
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</p>
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<p>
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Below an example of a schematic and a symbol shown both in xschem and lepton-schematic (gschem fork)
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</p>
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2021-10-13 17:33:10 +02:00
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<img src = "tutorial_gschemtoxschem_01.png">
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<br>
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<img src = "tutorial_gschemtoxschem_02.png">
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<h3> Notes for schematics targeted for spice simulations </h3>
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<p>
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Most of geda schematics do not define precise rules for spice netlisting.
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2021-10-12 23:13:59 +02:00
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primitive symbols are symbols that do not have a schematic representation,
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examples are the nmos and pmos transistors in first schematic.
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They should have a <kbd>format</kbd> property
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that defines how the symbol should be translated to spice netlist.
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See the relevant <a href="symbol_property_syntax.html">schem manual page</a>.
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<br>
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Subcircuit symbols are symbols that translate to spice as a .subckt calls.
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An example is the LATESN symbol in above picture.
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Xschem convention is that subcircuit symbol instances have a name
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attribute that begins with 'X' or 'x'. As with primitive symbols they also have a
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<kbd>format</kbd> global attribute, but the <kbd>type=subcircuit</kbd> attribute
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states it is a subcircuit instance. After producing the instance call
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(for example <kbd>X1 net1 net2 net3 ... subcircuit_name)</kbd>) for all instances
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of this symbol a .subckt expansion is also produced:
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</p>
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<pre class="code">
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.subckt subcircuit_name pin1 pin2 pin3 ...
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...
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...
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.ends
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</pre>
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<p>
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2021-10-12 23:13:59 +02:00
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After doing the conversion with <kbd>gschemtoxschem.awk</kbd> you should check your
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schematics and symbols and make the necessary corrections.<br>
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In particular you should check that schematic pins match symbol pins, regarding pin name and direction.
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Xschem standard way is to use
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<kbd>ipin.sym, opin.sym, iopin.sch</kbd> for input, output, inout pins, respectively.
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Following image shows the original converted schematic and the hand-modified schematic with the
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proper pins. Note that VDD/GND pins have been removed
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since the LATESN symbol does not have such supply pins.<br>
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In spice netlist VDD/GND to the subcircuit is in this particular case passed via net-assign.
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</p>
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<img src = "tutorial_gschemtoxschem_03.png">
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<br>
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<!-- end of slide -->
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