In the design of integrated circuits, the most popular format for interchange is the Calma GDS II stream format (GDS II is a trademark of Calma Company, a wholly . Portions of the GDSII Stream Format Manual, Documentation No. B97E, Feb. , reprinted with permission of Cadence Design Systems, Inc., River. GDS II is a database file format which is the de facto industry standard for . The GDSII or Stream file format stores its information in records.
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GDSII – LayoutEditor Wiki
It is a binary file format representing planar geometric shapes, text labels, and other information about the layout in hierarchical form.
Formag data can be used to reconstruct all or formt of the artwork to be used in sharing layouts, transferring artwork between different tools, or creating photo masks. Despite its limited set of features and low data density, it became the industry’s default format for transfer of IC layout data between design tools of different vendors, all of which at that time operated with often incompatible and proprietary data formats. Currently, the format is owned by Cadence Design Systems.
GDS II files were originally placed on magnetic tapes. This moment was fittingly called “tape out” though it is not the original root of the term. Objects contained in a GDS II file are grouped by assigning numerical attributes to them including “layer number”, “datatype” or “texttype”. While these attributes were designed to correspond to the “layers of material” used in manufacturing an integrated circuit, their meaning rapidly became more abstract to reflect the way that the physical layout is designed.
This enables fast performance and avoids any unecessary conversion.
GDS II files can be read as normal files or gzip compressed files without an external decompresser. By default the LayoutEditor keeps this number untouched. This can tormat done gesii the SetupDialog or via a macro.
The LayoutEditor can store layer names by a non-standard extension see below. The technical limit of the file format structure is points, which is allowed in version 7. This limit can be set via the setup dialog or via a macro. If a polygon exceeds this limit, it will be split into two or more polygons when saving the file.
The default setting is As a bdsii it is possible to save polygons in multi-records and avoid that limit. This is not part of the GDS standard, but supported by some viewers.
Activate ‘gdsMultiXYRecord’ to use it and avoid splitting any polygons. By activating this option via the setup dialog or via a macro, all saved GDS II files will be padded to this length by adding a 0 at the end of the file. This option is rarely needed and the default ofrmat this function is off. After activating this option with the SetupDialog or via a macro, all box elements will be saved as a polygon.
By default fprmat option is turned off. Save Path as Polygon Path elements with a width greater than 0 will be saved as a polygon.
This option is useful, if the mask vendor does not accept shapes other than polygons. Therefore, text elements may look different with other viewers and are often ignored in mask production. By activating this option via the SetupDialog or via a macro, all text elements will be saved as polygons.
The current design in memory is modified as well with any save operation. To convert scale-independent text elements as well, select a non-zero default text size value for this option in the setup.
By default the Save Text as Polygon option is turned off. A polygon exceeding this limit will be split by default.
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However it is possible to save such large polygon in multiple blocks. This method will allow an unlimited number of polygon points. The names of the layers and its appearance in the design is not stored. This is done by adding an additional cell to the design with the name LayerNames that contains a text elements on each layer with flrmat layer names. Colors, and style of the layer are stored as attributes of the text element. If this option is activated, that additional cell rormat not be visible in the LayoutEditor.
However, it will not interference with any other GDSII tool as long as no cell with the mentioned named is used in the design. Validate File A file validation is performed after any save operation. This is done by calculation a SHA1 checksum during the save process.
This checksum is validated for the stored file in a second step to ensure that the GDSII file is correctly stored. It can be used to validate the file with common checksum checkers like sha1sum.
Each record starts with two bytes containing fkrmat length of the record. After the length record follows a record type and a foramt type byte.
The GDSII specification includes the description of 69 different record types, but less than the half are normally used. Seven stream data types are defined. Each record type must have the specified data type. The following data types are supported: