Computer Aids for VLSI Design
Steven M. Rubin
Copyright © 1994
Appendix C: GDS II Format
Appendix 3 of 7
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 owned subsidiary of General Electric Company, U.S.A.). For many years, this format was the only one of its kind and many other vendors accepted it in their systems. Although Calma has updated the format as their CAD systems have developed, they have maintained backward compatibility so that no GDS II files become obsolete. This is important becau GDS II is a binary format that makes assumptions about integer and floating-point reprentations.
A GDS II circuit description is a collection of cells that may contain geometry or other cell references. The cells, called structures in GDS II parlance, have alphanumeric names up to 32 characters long.
A library of the structures is contained in a file that consists of a library header, a quence of structures, and a library tail. Each structure in the quence consists of a structure header, a quence of elements, and a structure tail. There are ven kinds of elements: boundary defines a filled polygon, path defines a wire, structure reference invokes a subcell, array reference invokes an array of subcells, text2021年四级考试答案
is for documentation, node defines an electrical path, and box places rectangular geometry.
C.1 Record Format
In order to understand the preci format of the above GDS II components, it is first necessary to describe the general record format. Each GDS II record has a
4-byte header that specifies the record size and function. The first 2 bytes form a 16-bit integer that contains the record length in bytes. This length includes the 4-byte header and must always be an even number. The end of a record can contain a single null byte if the record contents is an odd number of bytes long. The third byte of the header contains the type of the record and the fourth byte contains the type of the data. Since the data type is constant for each record type, this 2-byte field defines the possible records as shown in Figs. C.1 and C.2.
File Header Records:Bytes 3 and 4 Parameter Type
HEADER0002 2-byte integer
BGNLIB0102 12 2-byte integers
LIBNAME0206 ASCII string
REFLIBS1F06 2 45-character ASCII strings
FONTS2006 4 44-character ASCII strings
ATTRTABLE2306 44-character ASCII string
GENERATIONS2202 2-byte integer
FORMAT3602 2-byte integer
大一英语期末考试试题MASK3706 ASCII string
ENDMASKS3800 No data
UNITS0305 2 8-byte floats
File Tail Records:Bytes 3 and 4Parameter Type
ENDLIB0400 No data
Structure Header Records: Bytes 3 and 4Parameter Type
BGNSTR0502 12 2-byte integers
STRNAME0606 Up to 32-characters ASCII string
Structure Tail Records:Bytes 3 and 4Parameter Type
ENDSTR0700 No data
FIGURE C.1 GDS II header record types.
Magnetic tapes containing GDS II files will have 2048 byte blocks that contain the records. The block size is standardized but has no bearing on record length or position. There is also a capability for circuits that require multiple reels of tape.
百万英镑英文版Element Header Records:Bytes 3 and 4 Parameter Type
BOUNDARY0800 No data
PATH0900 No data
SREF0A00 No data
AREF0B00 No data
TEXT0C00 No data
NODE1500 No data
BOX2D00 No data
Element Contents Records: Bytes 3 and 4Parameter Type
ELFLAGS2601 2-byte integer
PLEX2F03 4-byte integer
LAYER0D02 2-byte integers大学英语b级
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DATATYPE0E02 2-byte integer现大洋
XY1003 Up to 200 4-byte integer pairs
PATHTYPE2102 2-byte integer
WIDTH0F03 4-byte integer
SNAME1206 Up to 32-character ASCII string STRANS1A01 2-byte integer
MAG1B05 8-byte float
ANGLE1C05 8-byte float
COLROW1302 2 2-byte integers
TEXTTYPE1602 2-byte integer
PRESENTATION1701 2-byte integer
ASCII STRING1906 Up to 512-character string
NODETYPE2A02 2-byte integer
BOXTYPE2E02 2-byte integer
FIGURE C.2 GDS II element record types.
C.2 Library Head and Tail
A GDS II file header always begins with a HEADER record the parameter of which contains the GDS II version number ud to write the file. For example, the bytes 0, 6, 0, 2, 0, 1 at the start of the file constitute the header record for a version-1 file. Following the HEADER comes a BGNLI
youjizz是什么B record that contains the date of the last modification and the date of the last access to the file. Dates take six 2-byte integers to store the year, month, day, hour, minute, and cond. The third record of a file is the LIBNAME, which identifies the name of this library file. For example, the bytes 0, 8, 2, 6, "C", "H", "I", "P" define a library named "CHIP." Following the LIBNAME record there may be any of the optional header records: REFLIBS to name up to two reference libraries, FONTS to name up to four character fonts, ATTRTABLE to name an attribute file, GENERATIONS to indicate th
e number of old file copies to keep, and FORMAT to indicate the nature of this file. The strings in the REFLIBS, FONTS, and ATTRTABLE records must be the specified length, padded with zero bytes.
The parameter to FORMAT has the value 0 for an archived file and the value 1 for a filtered file. Filtered files contain only a subt of the mask layers and that subt is described with one or more MASK records followed by an ENDMASK record. The string parameter in a MASK record names layers and quences of layers; for example, "1 3 5-7."
The final record of a file header is the UNITS record and it is not optional. The parameters to this record contain the number of ur units per databa unit (typically less than 1 to allow granularity of ur specification) and the number of meters per databa unit (typically much less than 1 for IC specifications). Eight-byte floating-point numbers have a sign at the top of the first byte, a 7-
bit exponent in the rest of that byte, and 7 more bytes that compo a mantissa (all to the right of an implied decimal point). The exponent is a factor of 16 in excess-64 notation (that is, the mantissa is multiplied by 16 raid to the true value of the exponent, where the true value is its integer reprentation minus 64).
Following the file header records come the structure records. After the last structure has been define
d, the file terminates with a simple ENDLIB record. Note that there is no provision for the specification of a root structure to define a circuit; this must be tracked by the designer.
C.3 Structure Head and Tail
Each structure has two header records and one tail record that sandwich an arbitrary list of elements. The first structure header is the BGNSTR record, which contains the creation date and the last modification date. Following that
is the STRNAME record, which names the structure using any alphabetic or numeric characters, the dollar sign, or the underscore. The structure is then open and any of the ven elements can be listed.
annexThe last record of a structure is the ENDSTR. Following it must be another BGNSTR or the end of the library, ENDLIB.
C.4 Boundary Element
The boundary element defines a filled polygon. It begins with a BOUNDARY record, has an optional ELFLAGS and PLEX record, and then has required LAYER, DATATYPE, and XY records.
The ELFLAGS record, which appears optionally in every element, has two flags in its parameter to indicate template data (if bit 16 is t) or external data (if bit 15 is t). This record should be ignored on input and excluded from output. Note that the GDS II integer has bit 1 in the leftmost or most significant position so the two flags are in the least significant bits.
The PLEX record is also optional to every element and defines element structuring by aggregating tho that have common plex numbers. Although a 4-byte integer is available for plex numbering, the high byte (first byte) is a flag that indicates the head of the plex if its least significant bit (bit 8) is t.
The LAYER record is required to define which layer (numbered 0 to 63) is to be ud for this boundary. The meaning of the layers is not defined rigorously and must be determined for each design environment and library.
The DATATYPE record contains unimportant information and its argument should be zero.
The XY record contains anywhere from four to 200 coordinate pairs that define the
mingle
outline of the polygon. The number of points in this record is defined by the record length. Note that boundaries must be clod explicitly, so the first and last coordinate values must be the same.
C.5 Path Element
A path is an open figure with a nonzero width that is typically ud to place wires. This element is initiated with a PATH record followed by the optional ELFLAGS and PLEX records. The LAYER record must follow to identify the desired path material. Also, a DATATYPE record must appear and an XY record to define the coordinates of the path. From two to 200 points may be given in a path.
Prior to the XY record of a path specification there may be two optional records called PATHTYPE and WIDTH. The PATHTYPE record describes the nature of the path gment ends, according to its parameter value. If the value is 0, the gments will have square ends that terminate at the path vertices. The value 1 indicates rounded ends and the value 2 indicates square ends that overlap their vertices by one-half of their width. The width of the path is defined by the optional WIDTH record. If the width value is negative, then it will be independent of any structure scaling (from MAG records, e next ction).
C.6 Structure Reference Element
Hierarchy is achieved by allowing structure references (instances) to appear in other structures. The SREF record indicates a structure reference and is followed by the optional ELFLAGS and PLEX rec
ords. The SNAME record then names the desired structure and an XY record contains a single coordinate to place this instance.
It is legal to make reference to structures that have not yet been defined with STRNAME.
Prior to the XY record there may be optional transformation records. The STRANS record must appear first if structure transformations are desired. Its parameter has bit flags that indicate mirroring in x before rotation (if bit 1 is t), the u of absolute magnification (if bit 14 is t), and the u of absolute
rotation (if bit 15 is t). The magnification and rotation amounts may then be specified in the optional MAG and ANGLE records. The rotation angle is in counterclockwi degrees.
C.7 Array of Structures Element
For convenience, an array of structure instances can be specified with the AREF record. Following the optional ELFLAGS and PLEX records comes the SNAME to identify the structure being arrayed. Next, the optional transformation records STRANS, MAG, and ANGLE give the orientation of the instances. A COLROW record must follow to specify the number of columns and the number of rows in the array. The final record is an XY with three points: the coordinate of the corner
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