Printed 12/16/85 1

EXT(5) Berkeley CAD Tools User's Manual EXT(5)

NAME
ext - format of .ext files produced by Magic's hierarchical
extractor

DESCRIPTION
Magic's extractor produces a .ext file for each cell in a
hierarchical design. The .ext file for cell name is
name.ext. This file contains three kinds of information:
environmental information (scaling, timestamps, etc), the
extracted circuit corresponding to the mask geometry of cell
name, and the connections between this mask geometry and the
subcells of name.

A .ext file consists of a series of lines, each of which
begins with a keyword. The keyword beginning a line deter-
mines how the remainder of the line is interpreted. The
following set of keywords define the environmental informa-
tion:

tech techname
Identifies the technology of cell name as techname,
e.g, nmos, cmos.

timestamp time
Identifies the time when cell name was last modified.
The value time is the time stored by Unix, i.e, seconds
since 00:00 GMT January 1, 1970. Note that this is not
the time cell was extracted, but rather the timestamp
value stored in the .mag file. The incremental extrac-
tor compares the timestamp in each .ext file with the
timestamp in each .mag file in a design; if they
differ, that cell is re-extracted.

version version
Identifies the version of .ext format used to write
name.ext. The current version is 4.0.

scale rscale cscale lscale
Sets the scale to be used in interpreting resistance,
capacitance, and linear dimension values in the
remainder of the .ext file. Each resistance value must
be multiplied by rscale to give the real resistance in
milliohms. Each capacitance value must be multiplied
by cscale to give the real capacitance in attofarads.
Each linear dimension (e.g, width, height, transform
coordinates) must be multiplied by lscale to give the
real linear dimension in centimicrons. Also, each area
dimension (e.g, transistor channel area) must be multi-
plied by scale*scale to give the real area in square
centimicrons. At most one scale line may appear in a
.ext file. If none appears, all of rscale, cscale, and
lscale default to 1.

resistclasses r1 r2 ...
Sets the resistance per square for the various resis-
tance classes appearing in the technology file. The
values r1, r2, etc. are in milliohms; they are not
scaled by the value of rscale specified in the scale
line above. Each node in a .ext file has a perimeter
and area for each resistance class; the values r1, r2,
etc. are used to convert these perimeters and areas
into actual node resistances. See ``Magic Tutorial #8:
Circuit Extraction'' for a description of how resis-
tances are computed from perimeters and areas by the
program ext2sim.

The following keywords define the circuit formed by the mask
information in cell name. This circuit is extracted
independently of any subcells; its connections to subcells
are handled by the keywords in the section after this one.

node name R C x y a1 p1 a2 p2 ... aN pN [attrs]
Defines an electrical node in name. This node is
referred to by the name name in subsequent equiv lines,
connections to the terminals of transistors in fet
lines, and hierarchical connections or adjustments
using merge or adjust. The node has a total capaci-
tance to ground of C attofarads, and a lumped resis-
tance of R milliohms. For purposes of going back from
the node name to the geometry defining the node, (x,y)
is the coordinate of a point inside the node. The
values a1, p1, ... aN, pN are the area and perimeter
for the material in each of the resistance classes
described by the resistclasses line at the beginning of
the .ext file; these values are used to compute
adjusted hierarchical resistances more accurately. If
there were any labels ending in the character ``@''
attached to geometry in this node, they are considered
to be node attributes and appear in the comma-separated
list attrs, minus their trailing ``@'' characters.

equiv node1 node2
Defines two node names in cell name as being
equivalent: node1 and node2. In a collection of node
names related by equiv lines, exactly one must be
defined by a node line described above.

fet type xl yl xh yh area perim sub GATE T1 T2 ...
Defines a transistor in name. The kind of transistor
is type, a string that comes from the technology file
and is intended to have meaning to simulation programs.
The coordinates of a square entirely contained in the
gate region of the transistor are (xl, yl) for its
lower-left and (xh, yh) for its upper-right. All four
coordinates are in the name's coordinate space, and are
subject to scaling as described in scale above. The
gate region of the transistor has area area square cen-
timicrons and perimeter perim centimicrons. The sub-
strate of the transistor is connected to node sub,
which is defined in the technology file for this type
of transistor.

The remainder of a fet line consists of a series of
triples: GATE, T1, .... Each describes one of the ter-
minals of the transistor; the first describes the gate,
and the remainder describe the transistor's non-gate
terminals (e.g, source and drain). Each triple con-
sists of the name of a node connecting to that termi-
nal, a terminal length, and an attribute list. The
terminal length is in centimicrons; it is the length of
that segment of the channel perimeter connecting to
adjacent material, such as polysilicon for the gate or
diffusion for a source or drain.

The attribute list is either the single token ``0'',
meaning no attributes, or a comma-separated list of
strings. The strings in the attribute list come from
labels attached to the transistor. Any label ending in
the character ``^'' is considered a gate attribute and
appears on the gate's attribute list, minus the trail-
ing ``^''. Gate attributes may lie either along the
border of a channel or in its interior. Any label end-
ing in the character ``$'' is considered a non-gate
attribute. It appears on the list of the terminal
along which it lies, also minus the trailing ``'fB$''.
Non-gate attributes may only lie on the border of the
channel.

The keywords in this last section describe the subcells used
by name, and how it makes connections to and between them.

use def use-id TRANSFORM
Specifies that cell def with instance identifier use-id
is a subcell of cell name. If cell def is arrayed,
then use-id will be followed by two bracketed subscript
ranges of the form: [lo,hi,sep]. The first range is
for x, and the second for y. The subscripts for a
given dimension are lo through hi inclusive, and the
separation between adjacent array elements is sep cen-
timicrons.

TRANSFORM is a set of six integers that describe how
coordinates in def are to be transformed to coordinates
in the parent name. It is used by ext2sim(1) in
transforming transistor locations to coordinates in the
root of a design. The six integers of TRANSFORM
(ta, tb, tc, td, te, tf) are interpreted as components
in the following transformation matrix, by which all
coordinates in def are post-multiplied to get coordi-
nates in name:

ta td 0
tb te 0
tc tf 1

merge path1 path2 C a1 p1 a2 p2 ... aN pN
Used to specify a connection between two subcells, or
between a subcell and mask information of name. Both
path1 and path2 are hierarchical node names. To refer
to a node in cell name itself, its pathname is just its
node name. To refer to a node in a subcell of name,
its pathname consists of the use-id of the subcell (as
it appeared in a use line above), followed by a
slash (/), followed by the node name in the subcell.
For example, if name contains subcell sub with use
identifier sub-id, and sub contains node n, the full
pathname of node n relative to name will be sub-id/n.

Connections between adjacent elements of an array are
represented using a special syntax that takes advantage of
the regularity of arrays. A use-id in a path may optionally
be followed by a range of the form [lo:hi] (before the fol-
lowing slash). Such a use-id is interpreted as the elements
lo through hi inclusive of a one-dimensional array. An ele-
ment of a two-dimensional array may be subscripted with two
such ranges: first the y range, then the x range.

Whenever one path in a merge line contains such a subscript
range, the other must contain one of comparable size. For
example,

merge sub-id[1:4,2:8]/a sub-id[2:5,1:7]/b

is acceptable because the range 1:4 is the same size as 2:5,
and the range 2:8 is the same size as 1:7.

When a connection occurs between nodes in different cells,
it may be that some resistance and capacitance has been
recorded redundantly. For example, polysilicon in one cell
may overlap polysilicon in another, so the capacitance to
substrate will have been recorded twice. The values C, a1,
p1, etc. in a merge line provide a way of compensating for
such overlap. Each of a1, p1, etc. (usually negative) are
added to the area and perimeter for material of each resis-
tance class to give an adjusted area and perimeter for the
aggregate node. The value C attofarads (also usually nega-
tive) is added to the sum of the capacitances (to substrate)
of nodes path1 and path2 to give the capacitance of the
aggregate node.

cap node1 node2 C
Defines a capacitor between the nodes node1 and node2,
with capacitance C. This construct is used to specify
both internodal capacitance within a single cell and
between cells.

AUTHOR
Walter Scott