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<HTML><HEAD><TITLE>Using Electric 3-9: Libraries</TITLE></HEAD>
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<!-- PAGE BREAK --><A NAME="chap03-09"></A>
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<BR><CENTER><FONT SIZE=6><B>Chapter 3: HIERARCHY</B></FONT></CENTER><BR>
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<TD><CENTER><H2>3-9: Libraries</H2></CENTER></TD>
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A <I>library</I> is a collection of cells and facets that forms a consistent hierarchy.
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To enforce this consistency,
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Electric stores an entire library in one disk file that is read or written at one time.
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It is possible, however, to have multiple libraries in Electric.
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Only one library is the current one, and this sometimes affects commands that work at the library level.
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When there are multiple libraries, you can switch between them with the <B>Change Current Library...</B>
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command of the <B>File</B> menu.
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To see which libraries are read in, use the <B>List Libraries</B> command of the <B>Info</B> menu.
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To create a new, empty library, use the <B>New Library...</B> command of the <B>File</B> menu.
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To change the name of the current library, use the <B>Rename Library...</B> command.
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To delete a library, use the <B>Close Library</B> command.
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This removes only the memory representation, not the disk file.
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Note that library changes are too vast to be tracked by the database-change mechanism and so are not undoable.
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It is possible to link two libraries by placing an instance of a facet from one library into another
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(this is done with the <B>New Facet Instance...</B> command of the <B>Edit</B> menu).
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When this happens, the library with the instance
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(the main library) is linked to the library with the actual facet (this is the <I>reference library</I>).
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Because the reference library is needed to complete the main library,
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it will be read whenever the main library is read.
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If referenced libraries are edited independently,
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it is possible that a reference to a facet in another library will not match the actual facet in that library.
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When this happens, Electric creates a "placeholder" facet that matches the original specification.
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Thus, the link to the referenced library is broken because the facet there does not fit where the instance should be.
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To see a list of all placeholder facets that were created because of such problems,
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use the <B>List Placeholder Facets</B> subcommand of the <B>Facet Information</B> command of the
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<H3>Reading Libraries</H3>
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The <B>Open Library...</B> command of the <B>File</B> menu brings a new library into Electric from disk.
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These disk files are in a private binary format (that is, not readable outside of Electric).
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Besides Electric libraries,
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it is possible to read circuit descriptions that are in other formats with the <B>Import</B> command of the <B>File</B> menu.
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Most of these commands place the data into a new library that has the same name as the disk file.
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When reading these files,
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it is important that the current technology be set to the one in the file so that proper layer conversion can be done
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(use the <B>Change Current Technology...</B> command of the <B>Technology</B> menu).
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These formats can be read:
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<LI><B>Caltech Intermediate Format (CIF)</B> is used to describe integrated circuit layout.
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It contains no connectivity, so after the library is read,
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it does not know about transistors and contacts: just layers.
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Use the <B>CIF Options...</B> subcommand of the <B>IO Options</B> command to affect how CIF is read.
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<LI><B>Stream (GDS II)</B> is also used to describe integrated circuit layout.
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It contains no connectivity, so after the library is read,
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it does not know about transistors and contacts: just layers.
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Use the <B>GDS Options...</B> subcommand of the <B>IO Options</B> command to affect how GDS is read.
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On Windows, it is possible to select multiple files for input.
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If you do this, all of the GDS will be read into the current library.
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<LI><B>Electronic Design Interchange Format (EDIF)</B> is used to describe both schematics and layout.
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Electric reads EDIF version 2 0 0.
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<LI><B>VHDL</B> is a hardware description language that describes the structure of a circuit.
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When VHDL is read, it is not converted to layout,
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but instead is placed into a text facet with the {vhdl} view.
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<LI><B>Library Exchange Format (LEF)</B> is an interchange format that describes the cells in a library.
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The facets that are read in contain ports, but very little contents.
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<LI><B>Design Exchange Format (DEF)</B> is an interchange format that describes the contents of a library.
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DEF input often makes use of associated LEF files which must already have been read.
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Use the <B>DEF Options...</B> subcommand of the <B>IO Options</B> command to affect how DEF is read.
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<LI><B>AutoCAD DXF</B> is a solid-modeling interchange format,
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and so it may contain 3D objects that cannot be read into Electric.
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Nevertheless, Electric creates a library of artwork primitives as well as it can
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(you must switch to the Artwork technology before importing DXF).
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Use the <B>DXF Options...</B> subcommand of the <B>IO Options</B> command to affect how DXF is read.
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<LI><B>Standard Delay Format (SDF)</B> is used to read test vector parameters and place them on facets in the current library.
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Before this data can be used by the simulator, one of the three sets
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(<B>Typical</B>, <B>Minimum</B>, or <B>Maximum</B>) must be selected with the <B>Annotate Delay Data (ALS)</B>
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subcommand of the <B>Simulate</B> command of the <B>Tools</B> menu.
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<LI><B>Schematic User Environment (SUE)</B> is a schematic editor that captures a single cell in each file.
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The circuitry in SUE files is added to the current library instead of being placed in its own library
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(because many SUE files may have to be read to build up a single Electric library).
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<LI><B>Readable Dump</B> is an Electric-specific format that captures the entire database,
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but in an editable text format.
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Because it is text, it is slower to read than Electric's binary files,
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and takes up more space on disk.
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However, it can be transferred between machines more reliably and can be edited if necessary.
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See <A HREF="chap07-03.html#chap07-03">Section 7-3</A>
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for more information on external formats.
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<H3>Writing Libraries</H3>
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Writing libraries to disk is done with the <B>Save Library</B> command of the <B>File</B> menu.
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The <B>Save All Libraries</B> command of the <B>File</B> menu writes all libraries that have changed.
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If a library was read from disk, it is written back to the same file.
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If, however, you wish to write the library to a new file
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(thus preserving the original) then use the <B>Save Library As...</B> command.
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<TABLE><TR><TD VALIGN=TOP>
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The <B>Library Options...</B> subcommand of the <B>IO Options</B> command of the <B>File</B>
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menu controls the writing of libraries to disk.
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By default, saved libraries overwrite the previous libraries and no backup is created.
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If you choose "Backup of last library file",
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then the former library is renamed so that it has a "~" at the end.
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If you choose "Backup history of library files",
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then the former library is renamed so that it has its creation date as part of its name.
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You can also use this dialog to request that the database be checked when saves are done.
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</TD><TD><CENTER><IMG SRC="../images/chap03-19.png" ALT="Figure 3.19"></CENTER></TD></TR></TABLE>
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Electric can also write external format files with the <B>Export</B> command of the <B>File</B> menu.
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These formats can be written:
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<LI><B>Caltech Intermediate Format (CIF)</B> is used to describe integrated circuit layout.
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The output file contains only the current facet and any circuitry below that in the hierarchy.
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Use the <B>CIF Options...</B> subcommand of the <B>IO Options</B> command to affect how CIF is written.
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<LI><B>Stream (GDS II)</B> is also used to describe integrated circuit layout.
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The output file contains only the current facet and any circuitry below that in the hierarchy.
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Use the <B>GDS Options...</B> subcommand of the <B>IO Options</B> command to affect how GDS is written.
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<LI><B>Electronic Design Interchange Format (EDIF)</B> can write either the Netlist or the Schematic view of the circuit.
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Use the <B>EDIF Options...</B> subcommand of the <B>IO Options</B> command to affect how EDIF is written.
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Electric writes EDIF version 2 0 0.
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<LI><B>Library Exchange Format (LEF)</B> is an interchange format that describes the exports on facets in a library.
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<LI><B>Circuit Design Language (CDL)</B> is a Cadence interchange format for netlists.
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<LI><B>Eagle</B> is an interface to the Eagle schematics design system (netlist format).
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Before writing Eagle files, you must give every node the "ref_des" attribute,
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and every port on these nodes the "pin" attribute.
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If you also place the "pkg_type" attribute on the node, it overrides the cell name.
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Use the <B>Define...</B> subcommand of the <B>Attributes</B> command of the <B>Info</B> menu to create these attributes
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(see <A HREF="chap06-08.html#chap06-08">Section 6-8</A> for more information).
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Also, every network must be named.
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<LI><B>ECAD</B> is an interface to the ECAD schematics design system (netlist format).
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<LI><B>Pads</B> is an interface to the Pads schematics design system (netlist format).
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<LI><B>AutoCAD DXF</B> is a solid-modeling interchange format.
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Use the <B>DXF Options...</B> subcommand of the <B>IO Options</B> command to affect how DXF is written.
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<LI><B>L</B> is the GDT language, still appearing in some commercial systems.
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The output file contains only the current facet and any circuitry below that in the hierarchy.
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<LI><B>PostScript</B> is the Adobe printing language.
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The output file contains only a visual representation of the current facet
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(or part of that facet).
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PostScript options can be controlled with the <B>Print Options...</B> command of the <B>File</B> menu.
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<LI><B>HPGL</B> is the Hewlett-Packard printing language.
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The output file contains only a visual representation of the current facet
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(or part of that facet).
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HPGL options can be controlled with the <B>Print Options...</B> command of the <B>File</B> menu.
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<LI><B>Readable Dump</B> is an Electric-specific format that captures the entire database,
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but in an editable text format.
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Because it is text, it takes up more space on disk.
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However, it can be transferred between machines more reliably and can be edited if necessary.
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See <A HREF="chap07-03.html#chap07-03">Section 7-3</A>
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for more information on external formats.
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<H3>Standard-Cell Libraries</H3>
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Electric does not come with any useful libraries for doing design.
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However, the system is able to make use of <A HREF="http://www.artisan.com">Artisan</A> libraries.
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These libraries are free, provided that you sign an Artisan license.
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Once you are licensed, you will have standard cell libaries, pad libraries, memory libraries,
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Artisan libraries are not distributed in Electric format.
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Instead, they come in a variety of formats that can be read into Electric.
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The GDS files contain the necessary geometry, and the LEF files contain the connectivity.
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By combining them, Electric creates a standard cell library that can be placed-and-routed
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(with the silicon compiler) and can be fabricated.
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Note that the data is not node-extracted,
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so not all of Electric's capabilities can be used with this data.
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To create an Artisan library, follow these steps:
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<LI>Select the Artisan data that you want and extract the GDS and LEF files for it.
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The GDS files will have the extension ".gds2", which is not what Electric expects
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(Electric expects them to end with ".gds"), so you may want to rename them.
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<LI>Read the LEF file into Electric with the <B>LEF (Library Exchange Format)</B>
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subcommand of the <B>Import</B> command of the <B>File</B> menu.
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Keep in mind that the LEF data may come in multiple versions for different numbers of metal layers.
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<LI>Read the GDS data into Electric with the <B>GDS II (Stream)</B> subcommand of the <B>Import</B>
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command of the <B>File</B> menu.
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Note that the proper GDS layers must be established first
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(with the <B>GDS II Options...</B> subcommand of the <B>IO Options</B> command of the <B>File</B> menu).
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As an aid in this process,
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you may find it helpful to read either the file "tsmc25.txt" or "umc18.txt" in the Electric library directory
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(these are Readable Dump files that can be read with the <B>Readable Dump</B> subcommand of the <B>Import</B>
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command of the <B>File</B> menu).
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Note that there will now be two libraries in memory: one with the GDS data and one with the LEF data.
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<LI>Merge the port information from the LEF library into the GDS library.
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It is important that the GDS library be the "current library"
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(use the <B>Change Current Library...</B> command of the <B>File</B> menu if it is not).
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To merge the LEF port information, use the <B>Add Export from Library...</B> command of the <B>Export</B> menu.
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You will be prompted for a library, and should select the one with the LEF data.
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<LI>At this point, the GDS library now has standard cells in it.
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Before saving it to disk, you should probably use the <B>Facet Options...</B> command of the <B>Facets</B>
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menu and set all of the facets to be "Part of a cell-library".
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