2020-08-08 15:47:34 +02:00
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<title>XSCHEM TUTORIAL: CREATE SYMBOL</title>
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<!-- start of slide -->
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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: Manage XSCHEM design / symbol libraries </h1>
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<p>
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There are 2 ways to describe symbols in xschem,<br>
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</p>
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<ul>
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<li>
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first approach: define a <kbd>XSCHEM_LIBRARY_PATH</kbd> that is a list of paths
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to last level directories containing .sym /.sch files
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</li>
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<li>
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second approach: define a <kbd>XSCHEM_LIBRARY_PATH</kbd> that is a list of paths
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2020-08-13 02:19:08 +02:00
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one or more levels above the directories containing .sym/.sch files
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2020-08-08 15:47:34 +02:00
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</li>
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</ul>
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<p>
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In the first approach a '<kbd>npn.sym</kbd>' symbol placed in a schematic will be
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saved as '<kbd>npn.sym</kbd>' in the .sch file, when loading back the parent
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2020-08-13 02:19:08 +02:00
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schematic xschem will go through the elements of <kbd>XSCHEM_LIBRARY_PATH</kbd> and look for
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2020-08-08 15:47:34 +02:00
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a directory containing <kbd>npn.sym</kbd>.
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</p>
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<p>
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In the second approach the '<kbd>npn.sym</kbd>' will be saved as
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'<kbd>devices/npn.sym</kbd>' (assuming <kbd>devices/</kbd> is the directory containing this
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symbol) . This is because the <kbd>XSCHEM_LIBRARY_PATH</kbd> is pointing to
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something like <kbd>/some/path/xschem_library/</kbd>
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and <kbd>xschem_library/</kbd> contains <kbd>devices/</kbd> (names are just given as
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examples, any dir name is allowed for <kbd>xschem_library/</kbd> and <kbd>devices/</kbd>)
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</p>
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<p>
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The first approach is preferred by pcb hobbysts, people working on
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small designs.
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the second approach is preferred for big designs where a one or more directory level
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indirection is desired for symbols, so any symbol in xschem is given
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as '<kbd>libname/symname.sym</kbd>' (one level directory specification in symbol references)
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or '<kbd>libgroup/libname/symname.sym</kbd>' (2 level directory specification in symbol references)
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instead of just '<kbd>symname.sym</kbd>'<br>
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</p>
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<p>
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In any case the real path of the symbol reference is obtained by prepending
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the XSCHEM_LIBRARY_PATH paths to the symbol reference until the resulting file is found in
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the machine filesystem.
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</p>
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2020-08-08 15:47:34 +02:00
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2020-08-13 02:19:08 +02:00
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<p>
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2020-08-08 15:47:34 +02:00
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For VLSI / big designs I <b>strongly</b> suggest using the second approach,
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just as an example i have the following dirs:
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</p>
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<pre class="code">
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~/share/xschem/xschem_library/
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containing:
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devices/
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TECHLIB/
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~/xschem_library/
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containing:
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stdcell_stef/
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~/share/doc/xschem/
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containing:
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library_t9/
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dram/
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</pre>
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<p>
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then in my xschemrc i have the following:
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</p>
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<p>
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<kbd>set XSCHEM_LIBRARY_PATH \ <br>
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$env(HOME)/share/xschem/xschem_library:$env(HOME)/share/doc/xschem/:$env(HOME)/xschem_library</kbd><br>
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</p>
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<h3>
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You may choose either method, but please be consistent throughout your design.
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</h3>
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