electric - a VLSI design system

electric [-c] [-geom WxH+X+Y] [-i MACROFILE] [-m] [-n] [-t technology] [library]

Electric is a general purpose system for all electrical design. It currently knows about nMOS, CMOS, Bipolar, artwork, schematics, printed-circuit boards, and many other technologies. Its has a large set of tools including multiple design-rule checkers (both incremental and hierarchical), an electrical rules checker, over a dozen simulator interfaces, multiple generators (PLA and pad frame), multiple routers (stitching, maze, river), network comparison, compaction, compensation, a VHDL compiler, and a silicon compiler that places-and-routes standard cells.

If a library disk file is mentioned on the command line, that file is read as the initial design for editing. In addition, the following switches are recognized:

-c

requests that the initial ".cadrc" file be ignored (not recommended).

-geom

requests that the initial edit window be of the specified size and location.

-i

requests that the file MACROFILE be used as the initial macro file (not recommended).

-m

specifies there may be multiple monitors and that Electric should look for them.

-n

requests that no session logging be done.

-t

specifies an initial technology. The argument must be a technology name such as "nmos", "cmos", "mocmossub", "schematic", "artwork", etc.

Circuits are represented as networks that contain nodes and connecting arcs. The nodes are electrical components such as transistors, logic gates, and contacts. The arcs are simply wires that connect the nodes. In addition, each node has a set of ports which are the sites of arc connection. A technology, then, is simply a set of primitive nodes and arcs that are the building blocks of circuits designed in that environment.

Collections of nodes and arcs can also be aggregated into facets of cells which can be used higher in the hierarchy to act as nodes. These user-defined nodes have ports that come from internal nodes whose ports have been converted to exports. Facets are collected in libraries which contain a hierarchically consistent design.

Arcs have properties that help constrain the design. For example, an arc may rotate arbitrarily or be held in a fixed angle. Arcs can also be stretchable or rigid under modification of their connecting nodes. These constraints propagate hierarchically from the bottom-up.

A large set of technologies is provided in Electric. These can be modified with the technology editor, or completely new technologies can be created. The following paragraphs describe some of the basic technologies.

The nMOS technologies have arcs available in Metal, Polysilicon, and Diffusion. The primitive nodes include normal contacts, buried contacts, transistors, and "pins" for making arc corners. Transistors may be serpentine and the pure layer nodes may be have an outline to form any shape. The "nmos" technology has the standard Mead&Conway design rules.

The CMOS technologies have arcs available in Metal, Polysilicon, and Diffusion. The Diffusion arcs may be found in a P-well implant or in a P+ implant. Thus, there are two types of metal-to-diffusion contacts, two types of diffusion pins, and two types of transistors: in P-well and in P+ implant. As with nMOS, the transistors may be serpentine and the pure layer primitives may take on any shape. The "cmos" technology has the standard design rules according to Griswold; the "mocmos" technology has design rules for the MOSIS CMOS process (double metal); the "mocmossub" technology has design rules for the MOSIS CMOS Submicron process (double poly and up to 6 metal); the "rcmos" technology has round geometry for the MOSIS CMOS process.

The "schematic" technology provides basic symbols for doing schematic capture. It contains the logic symbols: BUFFER, AND, OR, and XOR. Negating bubbles can be placed by negating a connecting arc. There are also more complex components such as flip-flop, off-page-connector, black-box, meter, and power source. Finally, there are analog components: transistor, resistor, diode, capacitor, and inductor. Two arc types exist: normal wires and variable-width busses.

The "artwork" technology is a sketching environment for doing general-purpose graphics. Components can be placed with arbitrary color and shape.

The "generic" technology exists for those miscellaneous purposes that do not fall into the domain of other technologies. It has the universal arc and pin which can connect to ANY other object and are therefore useful in mixed-technology designs. The invisible arc can be used for constraining two nodes without making a connection. The unrouted arc can be used for electrical connections that are to be routed later with real wires. The facet-center primitive, when placed in a facet, defines the cursor origin on instances of that facet.

The incremental design-rule checker is normally on and watches all changes made to the circuit. It does not correct but prints error messages when design rules are violated. Hierarchy is not handled, so the contents of subfacets are not checked.

The hierarchical checker looks all the way down the circuit for all design-rules. Another option allows an input deck to prepared for ECAD's Dracula design-rule checker.

The compactor attempts to reduce the size of a facet by removing unnecessary space between elements. When invoked it will compact in the vertical and horizontal directions until it can find no way to compact the facet any further. It does not do hierarchical compaction, does not guarantee optimal compaction, nor can it handle non-manhattan geometry properly. The compactor will also spread out the facet to guarantee no design-rule violations, if the "spread" option is set.

There are many simulator interfaces: ESIM (the default simulator: switch-level for nMOS without timing), RSIM (switch-level for MOS with timing), RNL (switch-level for MOS with timing and LISP front-end), MOSSIM (switch-level for MOS with timing), COSMOS (switch-level for MOS with timing), VERILOG (Cadence simulator), TEXSIM (a commercial simulator), SILOS (a commercial simulator), ABEL (PAL generator/simulator for schematic), and SPICE (circuit level). MOSSIM, COSMOS, VERILOG, TEXSIM, SILOS, and ABEL do not actually simulate: they only write an input deck of your circuit.

In preparation for most simulators, it is necessary to create exports at points that you wish to manipulate or examine. You must also make exports for power and ground.

In preparation for SPICE simulation, you must make exports for power and ground signals and explicitly connect them to source nodes. The source should then be parameterized to indicate the amount and whether it is voltage or current. For example, to make a 5 volt supply, create a source node and set the SPICE fragment to: "DC 5". Next, exports must be created at all inputs and they must be connected to the positive side of sources. Next, all exports must be created at all points that are being plotted and there must be meter nodes placed on them. The node should have the top and bottom ports connected appropriately.

There are two PLA generators, one specific to nMOS layout, and another specific to CMOS layout. The nMOS PLA generator reads a single personality table and generates the array and all driving circuitry including power and ground connections. The CMOS PLA generator reads two personality tables (AND and OR) and also reads a library of PLA helper components (called "pla_mocmos") and generates the array.

A pad frame generator reads a disk file that describes the pads, their placement, and their connection to a core facet.

The router is able to do river routing, maze routing, and simple facet stitching (the explicit wiring of implicitly connected nodes that abut). River routing runs a bus of wires between the two opposite sides of a routing channel. The connections on each side must be in a line so that the bus runs between two parallel sets of points. You must use the Unrouted arc from the Generic technology to indicate the ports to be connected. The river router can also connect wires to the perpendicular sides of the routing channel if one or more Unrouted wires cross these sides.

The maze router also requires Unrouted wires, and it converts them to real geometry.

There are two stitching modes: auto stitching and mimic stitching. In auto stitching, all ports that physically touch will be stitched. Mimic stitching watches arcs that are created by the user and adds similar ones at other places in the facet.

The network tool is able to compare the networks in the two facets being displayed on the screen. Once compared, nodes in one facet can be equated with nodes in the other. If the two networks are automorphic or otherwise difficult to distinguish, equivalence information can be specified prior to comparison by selecting a component in the first facet then selecting a component in the second facet.

Steven M. Rubin
   Static Free Software
   4119 Alpine Road
   Portola Valley, Ca 94028

Also a cast of thousands: Philip Attfield (Queens University): Polygon merging, facet dates Ron Bolton (University of Saskatchewan): Miscellaneous help Mark Brinsmead (Calgary): Apollo porting Stefano Concina (Schlumberger): Polygon clipping Peter Gallant (Queen's University): ALS simulation T. J. Goodman (University of Canterbury) TEXSIM simulation D. Guptill (Technical University of Nova Scotia): X-window interface Robert Hon (Columbia University): CIF input Sundaravarathan Iyengar (Case Western Reserve University): nMOS PLA generator Allan Jost (Technical University of Nova Scotia): X-window interface Wallace Kroeker (University of Calgary): Digital filter technology, CMOS PLA generator Andrew Kostiuk (Queen's University): QUISC 1.0 Silicon compiler Glen Lawson (S-MOS Systems): GDS-II input David Lewis (University of Toronto): Short circuit checker John Mohammed (Schlumberger): Miscellaneous help Mark Moraes (University of Toronto): X-window interface Sid Penstone (Queens University): many technologies, GDS-II output, SPICE improvements, SILOS simulation, GENERIC simulation J. P. Polonovski (Ecole Polytechnique, France): Memory management improvement Kevin Ryan (Technical University of Nova Scotia): X-window interface Nora Ryan (Schlumberger): Technology translation, Compaction Brent Serbin (Queen's University): ALS Simulator Lyndon Swab (Queen's University): Northern Telecom CMOS technologies Brian W. Thomson (University of Toronto): Mimic stitcher, RSIM interface Burnie West (Schlumberger): Network maintainer help, bipolar technology Telle Whitney (Schlumberger): River router Rob Winstanley (University of Calgary): CIF input, RNL interface Russell Wright (Queen's University): Lots of help David J. Yurach (Queen's University): QUISC 2.0 Silicon compiler

Rubin, Steven M., "A General-Purpose Framework for CAD Algorithms", IEEE Communications, Special Issue on Communications and VLSI, May 1991.

Rubin, Steven M., Computer Aids for VLSI Design, Addison-Wesley, Reading, Massachusetts, 1987.

Rubin, Steven M., "An Integrated Aid for Top-Down Electrical Design", Proceedings, VLSI '83 (Anceau and Aas, eds.), North Holland, Amsterdam, 1983.

Mead, C. and Conway, L., Introduction to VLSI Systems, Addison-Wesley, 1980.

Electrical User's Guide.

Electric Internals manual.

l l. ~/.cadrc Personal startup file *.elib Binary input/output files *.txt Text input/output files *.cif CIF input/output files *.gds GDS input/output files *.pla PLA personality input files *.map Color map files *.mac Macro files *.sim ESIM, RSIM, RNL, and COSMOS simulation output *.spi SPICE simulation output *.v VERILOG simulation output *.ntk MOSSIM simulation output *.sil SILOS simulation output *.tdl TEXSIM simulation output *.pal ABLE PAL simulation output

/usr/local/bin/spice Circuit level simulator: SPICE