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The GDSII Stream Format

See also, for download: stream_utils

Jim Buchanan
6/11/96

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This file is for use by people having experience with GDSII format stream
files and the CAD systems that read/write them. It won't make a lot of sense
without that background.

Since knowing the library structure without knowing about records and data
types would be of marginal use, and knowing about records and data types
without knowing about the library structure would be worse, you might have
to scan through this s few times before it makes sense.

Beyond that, let me say that the stream format is quite simple. I suspect
that the people at Calma put a lot of thought into creating a file that
would be as easy to read in and parse as possible.

I suspect that they did this due to the modest computers that they had to
work with. Their results were impressive here and with the GDSII system as a
whole. A bit dated now, but in its day...

Speaking of dated, Stream Format allows records to be written out to
multiple reels of tape. Handy on those old 9 track drives. When a file was
written to a tape, it was written in 2048 byte physical blocks. The file was
padded with NULL characters so that it was always a multiple of 2048 bytes.

I've noticed that some (OK, many) stream files that were originally written
to disk using more modern software also pad the file to a multiple of 2048
bytes using NULL characters.

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A stream file consists of records.

These records are built up of 16 bit words. This means that all stream files
should have an even number of bytes.

The first two words, or four bytes, are called the "Record Header"

A record can be as small as 4 bytes long. The GDSII Stream format manual
says that a record may be infinitely long, but frankly, I don't see how it
can get over 65535 bytes long, since the first two bytes of the record
header are an unsigned integer that defines the length of the record. The
leftmost bit of the first byte is valued at 32768, the rightmost bit of the
second byte is valued at 1.

The third byte is the record type. This will tell what part of the library
this record describes. There are values for such things as the beginning of a
structure, the beginning of a boundary, the end of a structure, and so on.
There is a section below with hexadecimal values of the various record types
and a brief description of the types.

The fourth, and last, byte in the record header is the data type. This,
along with the record length, tells the parser what to expect in the rest of
the record. There may be more than one piece of data, but the rest of the
record will be of this type. You can tell how many pieces of data are in the
record by knowing the number of bytes in the record and the size of the data
type.

Actually, the data type seems redundant, since each record type has only one
valid data type. Perhaps the Calma people were thinking of future needs?
They sure did that with the layer numbers and data types. Calma allowed only
64 layers and data types, but the Stream Format has room for 65535 of each.

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There are seven data types listed in the GDSII Stream Format Manual v6.0,
one is listed as not being used at the time. I doubt anyone has had the
chutzpah to start using it since.

The first is "No data present". The code is 0x00. This means that the entire
record is 4 bytes long. An example of an element with no data would be
ENDLIB which marks the end of a library.

The second is called a "Bit array". The code is 0x01. It's simply two bytes.
The meaning of each bit depends on the record type that the bit array is
found in.

The third data type is a "Two-Byte Signed Integer". The code is 0x02. It is
an integer between -32768 and 32767. It is stored in twos complement format,
with the most significant byte first.

Some examples from the book:

0x0000 = 1
0x0020 = 2
0x0089 = 137
0xffff = -1
0xfffe = -2
0xff77 = -137

The fourth data type is a "Four-Byte Signed Integer". The code is 0x03. Same
basic thing as a two byte integer, but with four bytes.

The fifth data type is the "Four-Byte Real". The code is 0x04. This is the
one that seems to have never been used, so I'll describe the eight byte real
in a bit more detail.

Basically though, the first bit is the sign (1 = negative), the next 7 bits
are the exponent, you have to subtract 64 from this number to get the real
value. The next three bytes are the mantissa, divide by 2^24 to get the
denominator.

value = (mantissa/(2^24)) * (16^(exponent-64))

In the above, we use the actual values of the fields in the stream file for
the mantissa and exponent.

The sixth data type is the "Eight Byte Real". The code is 0x05. This one
gets a little more use.

The first (most significant) bit of the first byte is the sign, one means
negative, 0 means positive.

The 7 least significant bits of the first byte are the exponent in "excess
64" notation. You must subtract 64 to get the true value. I'll show the
subtraction in the formula below.

The remaining 7 bytes are the mantissa, with a binary point to the left of
the most significant figure. The formula below uses the unsigned integer
value of these 7 bytes as the numerator of a fraction.

value = (mantissa/(2^56)) * (16^(exponent-64))

The seventh and final data type is the "ASCII String". The code is 0x06. The
length of this string is always equal to the length of the record minus the
four bytes used for the record header. If this number is not even, a NULL
character (0x00) is added to the end. This is another artifact of the 16 bit
words that the stream file format assumes.

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This is the format of a stream file. The records shown within square
brackets '[]' are optional. The or bar '|' indicates one or the other.
The structure '{}+' is used to indicate one or more instances.
The angle brackets '<>' indicate that further definition is below. Sort of an
"include" element.

The actual stream file:

HEADER
BGNLIB
[LIBDIRSIZE]
[SRFNAME]
[LIBSECUR]
LIBNAME
[REFLIBS]
[FONTS]
[ATTRTABLE]
[GENERATIONS]
[FORMAT | FORMAT {MASK}+ ENDMASKS]
UNITS
[{BGNSTR STRNAME [STRCLASS] [{<element>}+] ENDSTR}+]
ENDLIB

An element portion of a stream file:

<boundary> | <path> | <sref> | <aref> | <text> | <node> | <box>
[{PROPATTR PROPVALUE}+] 
ENDEL

Boundary portion of an element:

BOUNDARY
[ELFLAGS]
[PLEX]
LAYER
DATATYPE
XY

Path portion of an element:

PATH
[ELFLAGS]
[PLEX]
LAYER
DATATYPE
[PATHTYPE]
[WIDTH]
[BGNEXTN]
[ENDEXTN]
XY

SREF portion of an element:

SREF
[ELFLAGS]
[PLEX]
SNAME
[STRANS [MAG] [ANGLE]]
XY

AREF portion of an element:

AREF
[ELFLAGS]
[PLEX]
SNAME 
[STRANS [MAG] [ANGLE]]
COLROW
XY

Text portion of an element:

TEXT
[ELFLAGS]
[PLEX]
LAYER
TEXTTYPE
[PRESENTATION]
[PATHTYPE]
[WIDTH]
[STRANS [MAG] [ANGLE]]
XY
STRING

Node portion of an element:

NODE
[ELFLAGS]
[PLEX]
LAYER
NODETYPE
XY

Box portion of an element:

BOX
[ELFLAGS]
[PLEX]
LAYER
BOXTYPE
XY

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A stream file may be broken up over multiple reels of tape. I haven't seen
this since the days of 9 track tapes on reels, but just in case, here we
go...

Tape 1:

HEADER
several complete stream records
TAPENUM
TAPECODE
LIBNAME

Intermediate tape(s):

TAPENUM
TAPECODE
LIBNAME
more complete stream records
TAPENUM

last tape:

TAPENUM
TAPECODE
LIBNAME
more complete stream records
ENDLIB

A concatenation of all of the tapes, without the tape id stuff (and I
presume w/o the extra LIBNAMEs) should be a valid stream file as described
above.

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OK, here's the part you've been waiting for, what the records mean...

Record type       Data type

0x00 HEADER       0x02 INTEGER_2  Start of stream, contains version number of
                                  stream file.
                                  < v3.0  0x0000    0
                                    v3.0  0x0003    3
                                    v4.0  0x0004    4
                                    v5.0  0x0005    5
                                    v6.0  0x0258  600

0x01 BGNLIB       0x02 INTEGER_2  Beginning of library, plus mod and access
                                  dates.
                                  Modification:
                                  year, month, day, hour, minute, second
                                  Last access:
                                  year, month, day, hour, minute, second
          

0x02 LIBNAME      0x06 STRING     The name of the library, supposedly following
                                  Calma DOS conventions. Using later tools,
                                  such as ISS LTL-100, it seems more flexible
                                  than that, but it won't allow any old thing
                                  you want. If memory serves, Calma DOS allowed
                                  6 characters in a file name, with a 2
                                  character extension.

0x03 UNITS        0x05 REAL_8     Size of db unit in user units, size of db
                                  unit in meters. To calculate the size of
                                  a user unit in meters, divide the second
                                  number by the first.

0x04 ENDLIB       0x00 NO_DATA    End of the library.

0x05 BGNSTR       0x02 INTEGER_2  Begin structure, plus create and mod dates in
                                  the same format as the BGNLIB record.

0x06 STRNAME      0x06 STRING     Name of a structure. Up to 32 characters in
                                  GDSII, A-Z, a-z, 0-9, _, ?, and $ are all
                                                                  legal characters.

0x07 ENDSTR       0x00 NO_DATA    End of a structure.

0x08 BOUNDARY     0x00 NO_DATA    The beginning of a BOUNDARY element.

0x09 PATH         0x00 NO_DATA    The beginning of a PATH element.

0x0a SREF         0x00 NO_DATA    The beginning of an SREF element.

0x0b AREF         0x00 NO_DATA    The beginning of an AREF element.

0x0c TEXT         0x00 NO_DATA    The beginning of a TEXT element.

0x0d LAYER        0x02 INTEGER_2  Layer specification. On GDSII this could be
                                  0 to 63, LTL allows 0 to 255. Of course a
                                  3 byte integer allows up to 65535...

0x0e DATATYPE     0x02 INTEGER_2  Datatype specification. On GDSII this could
                                  be 0 to 63, LTL allows 0 to 255. Of course a
                                  3 byte integer allows up to 65535...

0x0f WIDTH        0x03 INTEGER_4  Width specification, negative means absolute
                                  In data base units.

0x10 XY           0x03 INTEGER_4  An array of XY coordinates. An array of
                                  coordinates in data base units.
                                  Path: 2 to 200 pairs in GDSII
                                  Boundary: 4 to 200 pairs in GDSII
                                  Text: Exactly 1 pair
                                  SREF: Exactly 1 pair
                                  AREF: Exactly 3 pairs
                                         1:  Array reference point
                                         2:  column_space*columns+reference_x
                                         3:  row_space*rows+reference_y
                                  Node: 1 to 50 pairs in GDSII
                                  Box:  Exactly 5 pairs

0x11 ENDEL        0x00 NO_DATA    The end of an element.

0x12 SNAME        0x06 STRING     The name of a referenced structure.

0x13 COLROW       0x02 INTEGER_2  Columns and rows for an AREF. Two 2 byte
                                  integers. The first is the number of columns.
                                  The second is the number of rows. In an AREF
                                  of course. Neither may exceed 32767

0x14 TEXTNODE     0x00 NO_DATA    "Not currently used" per GDSII Stream Format
                                  Manual, v6.0. Would be the beginning of a
                                  TEXTNODE element if it were.

0x15 NODE         0x00 NO_DATA    The beginning of a NODE element.

0x16 TEXTTYPE     0x02 INTEGER_2  Texttype specification. On GDSII this could
                                  be 0 to 63, LTL allows 0 to 255. Of course a
                                  3 byte integer allows up to 65535...

0x17 PRESENTATION 0x01 BIT_ARRAY  Text origin and font specification.
                                  bits 15 to 0, l to r
                                  bits 0 and 1: 00 left, 01 center, 10 right
                                  bits 2 and 3: 00 top 01, middle, 10 bottom
                                  bits 4 and 5: 00 font 0, 01 font 1,
                                                10 font 2, 11 font 3,

0x18 SPACING           UNKNOWN    "Discontinued" per GDSII Stream Format
                                  Manual, v6.0.

0x19 STRING       0x06 STRING     Character string. Up to 512 char in GDSII

0x1a STRANS       0x01 BIT_ARRAY  Bits 15 to 0, l to r
                                  15=refl, 2=absmag, 1=absangle, others
                                  reserved for future use.

0x1b MAG          0x05 REAL_8     Magnification, 1 is the default if omitted.

0x1c ANGLE        0x05 REAL_8     Angular rotation factor in ccw direction.
                                  If omitted, the default is 0.

0x1d UINTEGER          UNKNOWN    User integer, used only in V2.0, when
                                  instreamed, should be converted to property
                                  attribute 126.

0x1e USTRING           UNKNOWN    User string, used only in V2.0, when
                                  instreamed, should be converted to property
                                  attribute 127.

0x1f REFLIBS      0x06 STRING     Names of the reference libraries. Starts with
                                  name of the first library and is followed by
                                  the second. There are 44 bytes in each, NULLS
                                  are used for padding, including filling in an
                                  entire unused field.

0x20 FONTS        0x06 STRING     Names of the textfont definition files. 4 44
                                  byte fields, padded with NULLS if a field is
                                  unused or less than 44 bytes.

0x21 PATHTYPE     0x02 INTEGER_2  Type of path ends.
                                  0: Square ended paths
                                  1: Round ended
                                  2: Square ended, extended 1/2 width
                                  4: Variable length extensions, CustomPlus
                                  The default is 0

0x22 GENERATIONS  0x02 INTEGER_2  Number of deleted or backed up structures to
                                  retain. Seems a bit odd in an archive...
                                  From 2-99, default is 3.

0x23 ATTRTABLE    0x06 STRING     Name of the attribute definition file. Max
                                  size 44 bytes.

0x24 STYPTABLE    0x06 STRING     "Unreleased feature" per GDSII Stream Format
                                  Manual, v6.0.

0x25 STRTYPE      0x02 INTEGER_2  "Unreleased feature" per GDSII Stream Format
                                   Manual, v6.0

0x26 ELFLAGS      0x01 BIT_ARRAY  Flags for template and exterior data.
                                  bits 15 to 0, l to r
                                  0=template, 1=external data, others unused

0x27 ELKEY        0x03 INTEGER_4  "Unreleased feature" per GDSII Stream Format
                                  Manual, v6.0.

0x28 LINKTYPE          UNKNOWN    "Unreleased feature" per GDSII Stream Format
                                  Manual, v6.0.

0x29 LINKKEYS          UNKNOWN    "Unreleased feature" per GDSII Stream Format
                                  Manual, v6.0.

0x2a NODETYPE     0x02 INTEGER_2  Nodetype specification. On GDSII this could
                                  be 0 to 63, LTL allows 0 to 255. Of course a
                                  3 byte integer allows up to 65535...

0x2b PROPATTR     0x02 INTEGER_2  Property number.

0x2c PROPVALUE    0x06 STRING     Property value. On GDSII, 128 characters max,
                                  unless an SREF, AREF, or NODE, which may
                                  have 512 characters.

0x2d BOX          0x00 NO_DATA    The beginning of a BOX element.

0x2e BOXTYPE      0x02 INTEGER_2  Boxtype specification. On GDSII this could be
                                  0 to 63, LTL allows 0 to 255. Of course a
                                  3 byte integer allows up to 65535...

0x2f PLEX         0x03 INTEGER_4  Plex number and plexhead flag. The least
                                  significant bit of the most significant byte
                                  is the plexhead flag. Because of this, you
                                                                  can "only" have 2^24 plex groups. Or is that
                                  2^24-1? I'm not sure if 0 is a valid plex
                                                                  group in a stream file.

0x30 BGNEXTN      0x03 INTEGER_4  Path extension beginning for pathtype 4 in
                                  CustomPlus. In database units, may be
                                  negative.

0x31 ENDTEXTN     0x03 INTEGER_4  Path extension end for pathtype 4 in
                                  CustomPlus. In database units, may be
                                  negative.

0x32 TAPENUM      0x02 INTEGER_2  Tape number for multi-reel stream file.

0x33 TAPECODE     0x02 INTEGER_2  Tape code to verify that the reel is from the
                                  proper set. 12 bytes that are supposed to
                                                                  form a unique tape code.

0x34 STRCLASS     0x01 BIT_ARRAY  Calma use only. In stream files created by
                                  non-Calma programs, this should be missing or
                                  all field should be 0.

0x35 RESERVED     0x03 INTEGER_4  Used to be NUMTYPES per GDSII Stream Format
                                  Manual, v6.0.

0x36 FORMAT       0x02 INTEGER_2  Archive or Filtered flag.
                                  0: Archive
                                  1: filtered

0x37 MASK         0x06 STRING     Only in filtered streams. Layers and
                                  datatypes used for mask in a filtered stream
                                  file. A string giving ranges of layers and
                                  datatypes separated by a semicolon. There may
                                  be more than one mask in a stream file.

0x38 ENDMASKS     0x00 NO_DATA    The end of mask descriptions.

0x39 LIBDIRSIZE   0x02 INTEGER_2  Number of pages in library director, a GDSII
                                  thing, it seems to have only been used when
                                  Calma INFORM was creating a new library.

0x3a SRFNAME      0x06 STRING     Sticks rule file name.

0x3b LIBSECUR     0x02 INTEGER_2  Access control list stuff for CalmaDOS,
                                  ancient. INFORM used this when creating a new
                                  library. Had 1 to 32 entries with group
                                  numbers, user numbers and access rights.

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