Jmo34 at 18:54, 20 June 2008

2008-06-20T18:54:56Z

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{{Infobox file format
| name = Caltech Intermediate Form(at)
| extension = .cif
| mime =
| owner =
| creatorcode = strubin
| genre = [[electronic design automation|EDA]] file format
| containerfor =
| containedby =
| extendedfrom =
| extendedto =
}}

'''Caltech Intermediate Form''' ('''CIF''') is a [[file format]] for describing [[integrated circuit]]s.
CIF provides a limited set of graphics primitives that are useful for describing the two-dimensional
shapes on the different layers of a chip.
The format allows hierarchical description, which makes the representation concise.
In addition, it is a terse but [[human-readable]] text format.

== Overview ==

Each statement in CIF consists of a keyword or letter followed by parameters and terminated
with a semicolon.
Spaces must separate the parameters but there are no restrictions on the number of statements
per line or of the particular columns of any field.
Comments can be inserted anywhere by enclosing them in parenthesis.

There are only a few CIF statements and they fall into one of two categories: geometry or control.
The geometry statements are: <CODE>LAYER</CODE> to switch mask layers, <CODE>BOX</CODE> to draw a
rectangle, <CODE>WIRE</CODE> to draw a path, <CODE>ROUNDFLASH</CODE> to draw a circle, <CODE>POLYGON</CODE> to draw an arbitrary
figure, and <CODE>CALL</CODE> to draw a subroutine of other geometry statements.
The control statements are <CODE>DS</CODE> to start the definition of a subroutine, <CODE>DF</CODE> to finish the
definition of a subroutine, <CODE>DD</CODE> to delete the definition of subroutines, <CODE>0</CODE> through <CODE>9</CODE> to
include additional user-specified information, and <CODE>END</CODE> to terminate a CIF file.
All of these keywords are usually abbreviated to one or two letters that are unique.

== Geometry ==

The <CODE>LAYER</CODE> statement (or the letter <CODE>L</CODE>) sets the mask layer to be used
for all subsequent geometry until the next such statement.
Following the <CODE>LAYER</CODE> keyword comes a single layer-name parameter.
For example, the command:
L CC;
sets the layer to be the CMOS contact cut (see Fig. B.1 for some typical MOS layer names).

<CENTER><TABLE BORDER=1><TR><TD><TABLE>
<TR><TD ALIGN=LEFT><CODE>NM</CODE></TD><TD ALIGN=LEFT>nMOS metal</TD></TR>
<TR><TD ALIGN=LEFT><CODE>NP</CODE></TD><TD ALIGN=LEFT>nMOS polysilicon</TD></TR>
<TR><TD ALIGN=LEFT><CODE>ND</CODE></TD><TD ALIGN=LEFT>nMOS diffusion</TD></TR>
<TR><TD ALIGN=LEFT><CODE>NC</CODE></TD><TD ALIGN=LEFT>nMOS contact</TD></TR>
<TR><TD ALIGN=LEFT><CODE>NI</CODE></TD><TD ALIGN=LEFT>nMOS implant</TD></TR>
<TR><TD ALIGN=LEFT><CODE>NB</CODE></TD><TD ALIGN=LEFT>nMOS buried</TD></TR>
<TR><TD ALIGN=LEFT><CODE>NG</CODE></TD><TD ALIGN=LEFT>nMOS overglass</TD></TR>
<TR><TD COLSPAN=2></TD></TR>
<TR><TD ALIGN=LEFT><CODE>CMF</CODE></TD><TD ALIGN=LEFT>CMOS metal 1</TD></TR>
<TR><TD ALIGN=LEFT><CODE>CMS</CODE></TD><TD ALIGN=LEFT>CMOS metal 2</TD></TR>
<TR><TD ALIGN=LEFT><CODE>CPG</CODE></TD><TD ALIGN=LEFT>CMOS polysilicon</TD></TR>
<TR><TD ALIGN=LEFT><CODE>CAA</CODE></TD><TD ALIGN=LEFT>CMOS active</TD></TR>
<TR><TD ALIGN=LEFT><CODE>CSG</CODE></TD><TD ALIGN=LEFT>CMOS select</TD></TR>
<TR><TD ALIGN=LEFT><CODE>CWG</CODE></TD><TD ALIGN=LEFT>CMOS well</TD></TR>
<TR><TD ALIGN=LEFT><CODE>CC</CODE></TD><TD ALIGN=LEFT>CMOS contact</TD></TR>
<TR><TD ALIGN=LEFT><CODE>CVA</CODE></TD><TD ALIGN=LEFT>CMOS via</TD></TR>
<TR><TD ALIGN=LEFT><CODE>COG</CODE></TD><TD ALIGN=LEFT>CMOS overglass</TD></TR>
</TABLE></TD></TR><TR><TD><B>FIGURE B.1 </B>CIF layer names for MOS processes.</TD></TR></TABLE></CENTER>

The <CODE>BOX</CODE> statement (or the letter <CODE>B</CODE>) is the most commonly used way of
specifying geometry.
It describes a rectangle by giving its length, width, center position, and an optional rotation.
The format is as follows:
B length width xpos ypos [rotation] ;
Without the rotation field, the four numbers specify a box the center of which is
at (''xpos'', ''ypos'') and is ''length'' across in x and ''width'' tall in y.
All numbers in CIF are integers that refer to centimicrons of distance, unless subroutine
scaling is specified (described later).
The optional ''rotation'' field contains two numbers that define a vector endpoint
starting at the origin.
The default value of this field is (1, 0), which is a right-pointing vector.
Thus the rotation clause <CODE>10 5</CODE> defines a 30-degree counterclockwise rotation from the normal.
Similarly, <CODE>10 -10</CODE> will rotate clockwise by 45 degrees.
Note that the magnitude of this rotation vector has no meaning.

[[Image:CIFfigb02.gif|thumb|333px|right|FIGURE B.2 A sample CIF "wire" statement. The statement is: W25 100 200 100 100 200 200 300 200;]]

The <CODE>WIRE</CODE> statement (or the letter <CODE>W</CODE>) is used to construct a
path that runs between a set of points.
The path can have a nonzero width and has rounded corners.
After the <CODE>WIRE</CODE> keyword comes the width value and then an arbitrary
number of coordinate pairs that describe the endpoints.
Figure B.2 shows a sample wire.
Note that the endpoint and corner rounding are implicitly handled.

The <CODE>ROUNDFLASH</CODE> statement (or the letter <CODE>R</CODE>) draws a filled
circle, given the diameter and the center coordinate. For example, the statement:
R 20 30 40;
will draw a circle that has a radius of 10 (diameter of 20), centered at (30, 40).

[[Image:CIFfigb03.gif|thumb|175px|right|FIGURE B.3 A sample CIF "polygon" statement. The statement is: P 150 100 200 200 200 300 100 300 100 200;]]

The <CODE>POLYGON</CODE> statement (or the letter <CODE>P</CODE>) takes a series of
coordinate pairs and draws a filled polygon from them.
Since filled polygons must be closed, the first and last coordinate points are
implicitly connected and need not be the same.
Polygons can be arbitrarily complex, including concavity and self-intersection.
Figure B.3 illustrates a polygon statement.

== Hierarchy ==

The <CODE>CALL</CODE> statement (or the letter <CODE>C</CODE>) invokes a collection
of other statements that have been packaged with <CODE>DS</CODE> and <CODE>DF</CODE>.
All subroutines are given numbers when they are defined and these numbers are used in
the <CODE>CALL</CODE> to identify them.
If, for example, a <CODE>LAYER</CODE> statement and a <CODE>BOX</CODE> statement are
packaged into subroutine 4, then the statement:
C 4;
will cause the box to be drawn on that layer.

In addition to simply invoking the subroutine, a <CODE>CALL</CODE> statement can include
transformations to affect the geometry inside the subroutine.
Three transformations can be applied to a subroutine in CIF: translation, rotation, and mirroring.
Translation is specified as the letter <CODE>T</CODE> followed by an x, y offset.
These offsets will be added to all coordinates in the subroutine, to translate its
graphics across the mask.
Rotation is specified as the letter <CODE>R</CODE> followed by an x, y vector endpoint
that, much like the rotation clause in the <CODE>BOX</CODE> statement, defines a line to the origin.
The unrotated line has the endpoint (1, 0), which points to the right.
Mirroring is available in two forms: <CODE>MX</CODE> to mirror in x and <CODE>MY</CODE> to mirror in y.
Mirroring is a bit confusing, because <CODE>MX</CODE> causes a negation of the x
coordinate, which effectively mirrors about the y axis.

[[Image:CIFfigb04.gif|thumb|262px|right|FIGURE B.4 The transformations of a CIF "call": (a) Subroutine 10: BOX 100 200 50 50; WIRE 10 50 50 100 150; (b) Invocation: C 10 T -50 0 MX MY; (c) Invocation: C 10 R 0 -1 MX; (d) Invocation: C 10 MX R 0 -1;]]

Any number of transformations can be applied to an object and their listed order
is the sequence that will be used to apply them.
Figure B.4 shows some examples, illustrating the importance of ordering the
transformations (notice that Figs. B.4c and B.4d produce different results by
rearranging the transformations).

Defining subroutines for use in a <CODE>CALL</CODE> statement is quite simple.
The statements to be packaged are enclosed between <CODE>DS</CODE> (definition
start) and <CODE>DF</CODE> (definition finish) statements.
Arguments to the <CODE>DS</CODE> statement are the subroutine number and a subroutine scaling factor.
There are no arguments to the <CODE>DF</CODE> statement.
The scaling factor for a subroutine consists of a numerator followed by a denominator
that will be applied to all values inside the subroutine.
This scaling allows large numbers to be expressed with fewer digits and allows ease
of rescaling a design.
The scale factor cannot be changed for each invocation of the subroutine since it
is applied to the definition.
As an example, the subroutine of Fig. B.4 can be described formally as follows:
DS 10 20 2;
B10 20 5 5;
W1 5 5 10 15;
DF;
Note that the scale factor is 20/2, which allows the trailing zero to be dropped
from all values inside the subroutine.

Arbitrary depth of hierarchy is allowed in CIF subroutines.
Forward references are allowed provided that a subroutine is defined before it is used.
Thus the sequence:
DS 10;
...
C 11;
DF;
DS 11;
...
DF;
C 10;
is legal, but the sequence:
C 11;
DS 11;
...
DF;
is not. This is because the actual invocation of subroutine 11 does
not occur until after its definition in the first example.

== Control ==

CIF subroutines can be overwritten by deleting them and then redefining them.
The <CODE>DD</CODE> statement (delete definition) takes a single parameter and
deletes every subroutine that has a number greater than or equal to this value.
The statement is useful when merging multiple CIF files because designs can be
defined, invoked, and deleted without causing naming conflicts.
However, it is not recommended for general use by CAD systems.

Extensions to CIF can be done with the numeric statements <CODE>0</CODE> through <CODE>9</CODE>.
Although not officially part of CIF, certain conventions have evolved for the
use of these extensions (see Fig. B.5).

<CENTER><TABLE BORDER=1><TR><TD><TABLE>
<TR><TD ALIGN=LEFT><CODE>0</CODE> x y layer <CODE>N</CODE> name<CODE>;</CODE></TD><TD ALIGN=LEFT>Set named node on specified layer and position</TD></TR>
<TR><TD ALIGN=LEFT><CODE>0V</CODE> x1 y1 x2 y2 ... xn yn<CODE>;</CODE></TD><TD ALIGN=LEFT>Draw vectors</TD></TR>
<TR><TD ALIGN=LEFT><CODE>2A</CODE> "msg" <CODE>T</CODE> x y<CODE>;</CODE></TD><TD ALIGN=LEFT>Place message above specified location</TD></TR>
<TR><TD ALIGN=LEFT><CODE>2B</CODE> "msg" <CODE>T</CODE> x y<CODE>;</CODE></TD><TD ALIGN=LEFT>Place message below specified location</TD></TR>
<TR><TD ALIGN=LEFT><CODE>2C</CODE> "msg" <CODE>T</CODE> x y<CODE>;</CODE></TD><TD ALIGN=LEFT>Place message centered at specified location</TD></TR>
<TR><TD ALIGN=LEFT><CODE>2L</CODE> "msg" <CODE>T</CODE> x y<CODE>;</CODE></TD><TD ALIGN=LEFT>Place message left of specified location</TD></TR>
<TR><TD ALIGN=LEFT><CODE>2R</CODE> "msg" <CODE>T</CODE> x y<CODE>;</CODE></TD><TD ALIGN=LEFT>Place message right of specified location</TD></TR>
<TR><TD ALIGN=LEFT><CODE>4A</CODE> lowx lowy highx highy<CODE>;</CODE></TD><TD ALIGN=LEFT>Declare cell boundary</TD></TR>
<TR><TD ALIGN=LEFT><CODE>4B</CODE> instancename<CODE>;</CODE></TD><TD ALIGN=LEFT>Attach instance name to cell</TD></TR>
<TR><TD ALIGN=LEFT><CODE>4N</CODE> signalname x y<CODE>;</CODE></TD><TD ALIGN=LEFT>Labels a signal at a location</TD></TR>
<TR><TD ALIGN=LEFT><CODE>9</CODE> cellname<CODE>;</CODE></TD><TD ALIGN=LEFT>Declare cell name</TD></TR>
<TR><TD ALIGN=LEFT><CODE>91</CODE> instancename<CODE>;</CODE></TD><TD ALIGN=LEFT>Attach instance name to cell</TD></TR>
<TR><TD ALIGN=LEFT><CODE>94</CODE> label x y<CODE>;</CODE></TD><TD ALIGN=LEFT>Place label in specified location</TD></TR>
<TR><TD ALIGN=LEFT><CODE>95</CODE> label length width x y<CODE>;</CODE></TD><TD ALIGN=LEFT>Place label in specified area</TD></TR>
</TABLE></TD></TR><TR><TD><B>FIGURE B.5 </B>Typical user extensions to CIF.</TD></TR></TABLE></CENTER>

The final statement in a CIF file is the <CODE>END</CODE> statement (or the letter <CODE>E</CODE>).
It takes no parameters and typically does not include a semicolon.

== References ==
*[http://www.rulabinsky.com/cavd/text/chapb.html Computer Aids for VLSI Design - Appendix B: Caltech Intermediate Format by Steven M. Rubin]
*Hon, Robert W. and Sequin, Carlo H., "A Guide to LSI Implementation," 2nd Edition, Xerox Palo Alto Research Center technical memo SSL-79-7, January 1980.

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Jmo34 at 18:54, 20 June 2008