1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969
|
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Author : Frederic Petrot
% Modified by : Olivier Sirol
% Modified by : Ludovic Jacomme
% $Id: overview.tex,v 1.8 2009/08/26 14:01:53 jpc Exp $
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\documentclass{article}
\usepackage[latin1]{inputenc}
%\usepackage{t1enc,isolatin1}
\usepackage{t1enc}
\usepackage{palatino,graphicx}
\textheight 9.0in
\textwidth 6.0in
\topmargin -0.0in
\oddsidemargin +0.3in
\evensidemargin -0.3in
\marginparwidth +0.5in
\parskip 8pt plus 2pt minus 2pt % space beetween paragraphe
\parindent 0em % indentation of the first line
\topsep 0pt % space beetween list and text
\parsep 8pt % space beetween 2 par.
\partopsep 0pt % space beetween 2 par.
\itemsep 0pt % space beetween 2 items
\raggedbottom
\begin{document}
%\psdraft
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{center}
\Large \textbf{Alliance}: A Complete CAD System for \textbf{VLSI} Design\\
\vspace*{1cm}
\large
quipe Achitecture des Systmes et Micro-lectronique\\
Laboratoire d'Informatique de Paris 6\\
Universit Pierre et Marie Curie\\
4, Place Jussieu 75252 Paris Cedex 05,\\
France\\
\texttt{http://www-asim.lip6.fr/alliance/}\\*
\texttt{ftp://ftp-asim.lip6.fr/pub/alliance/}\\*
\texttt{mailto:alliance-users@asim.lip6.fr}\\*
\end{center}
%%%%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section*{\centerline{Abstract}}
\begin{quote}\em
The \textbf{Alliance} package is a complete set of CAD tools for the
specification, design and validation of digital \textbf{VLSI} circuits.
Beside the tools, \textbf{Alliance} includes also a set of cell
libraries, from standard cells for automatic place and route tools,
to custom block generators to be used in high performance circuits.
This package is used in more than 250 universities worldwide.
Each \textbf{Alliance} tool can operate as a standalone program as
well as a part of the complete design framework.
After introducing briefly the design methodology, we outline the
functionnality of the tools.
Experimental results conclude the presentation.
\textbf{Alliance} runs on any \textbf{Unix} system and has been also
ported to Windows using \textbf{Cygwin} environment.
It is freely available on \texttt{ftp}, and includes binaries, leaf
cells libraries, on-line documentation, and tutorials.
\rm\end{quote}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%
\section{Introduction}
The \textbf{Alliance} package is the result of a ten years effort
spent at the \textbf{LIP6} Laboratory (formerly \textbf{MASI})
of the Pierre et Marie Curie University (UPMC), in Paris.
During these years, our major goal was to provide our undergraduate
and graduate students with a complete CAD framework, designed to
assist them in digital \textbf{VLSI} \textbf{CMOS} course.
The \textit{Architecture} team at \textbf{LIP6} focuses its activity on
two key issues: computer architectures using high complexity ASICs,
and innovative CAD tools for \textbf{VLSI} design.
Strong interaction exists between the people working on computer
architectures and the one working on CAD tools.
The main CAD action aims at fulfilling both the needs of experienced
designers by providing practical answers to state-of-the-art problems
(logic synthesis, procedural generation, layout verification, test and
interoperability), and novice designers, by providing a simple and
consistent set of tools.
Our \textbf{VLSI} design flow is therefore based on both advanced CAD tools
that are not available within commercial CAD systems, such as
functional abstraction or static timing
analysis, and standard design/validation tools.
\textbf{Alliance} VLSI CAD System is free software. Binaries, source code and
cells libraries are freely available under the GNU General Public Licence (\textbf{GPL}).
You are welcome to use the software package even for commercial designs whithout
any fee. You are just required to mention : "Designed with Alliance LIP6/Universit
Pierre et Marie Curie". For any questions please mail to :
\texttt{alliance-users@asim.lip6.fr}.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Process independence}
To be useful, a CAD system must provide a way to the silicon,
therefore \textbf{Alliance} provides a large set of cell libraries
also available at the layout level.
The target technologies of \textbf{Alliance} is \textbf{CMOS}.
The layout libraries rely on a symbolic layout approach that provides
process independence in order to allow the designers to easily
port their designs from one silicon supplier to another.
The main point in this approach is that the pitch matching constraints
in both \textit{x} and \textit{y} direction are kept through
technological retargetting.
The translation, fully automated, relies on a technological file
suited to a given process.
These files can be generated directly from the process design rules.
Also technological files for several processes are available through
the CMP and EuroPractice services, provided you signed a NDA for the
process.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Software portability}
The \textbf{Alliance} package has been designed so to run on an
heterogeneous network of workstations.
The only requirements are a \textbf{C} compiler and a \textbf{Unix} system.
For the graphical applications, the XWindow library is used.
Several hardware platforms, from Intel 386 based computers to
SparcStations and DEC Stations, are supported.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Modularity}
According to the interoperability constraints, each \textbf{Alliance}
tool can operate as a standalone program as well as a part of the
complete \textbf{Alliance} design framework.
Each \textbf{Alliance} tool therefore supports several standard \textbf{VLSI}
description formats : \textbf{SPICE}, \textbf{EDIF}, \textbf{VHDL}, \textbf{CIF},
\textbf{GDS2}.
In that respect, the tools ouputs are fully usable under the
\textbf{Compass} and \textbf{Cadence Opus} environnement, provided these
tools have the necessary configuration files.
The \textbf{Alliance} tools support a zero-default top-down design
methodology with not only construction tools --- layout editor, automatic
place \& route --- but also validation tools, from design rule checker to
functional abstraction and formal proof.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Compactness}
Unlike commercially available CAD systems, the \textbf{Alliance} CAD
Framework suits the limited ressources of low-cost workstations.
For small educational projects --- 5000 gates ---, a \textbf{Unix}
system with 8 to 20 Mbytes of memory, appropriate disk storage (30
Mbytes per user), and graphic capabilities (X-Window) is sufficient.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Easiness}
All tools and the proposed design flow are simple to teach and to
learn.
In any situation, easiness and simplicity have been prefered to
sophisticated approaches.
To each tool correspond a unique behavior and utility.
Each step of the design methodology corresponds to the use of one or a
few tools, for which the usage is well identified.
From a pratical point of view, both on-line documentation (\textbf{Unix}
\texttt{man}) and paper are available with each tool of the
\textbf{Alliance} package.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Alliance design flow}
We refer to the term "design flow" as a sequenced set of
operations performed when realizing a \textbf{VLSI} circuit.
In the design flow, we rely on a strict definition of all the
objects and design functions found in the process of designing a
\textbf{VLSI} chip.
The design flow is based on the Mead-Conway model and is
characterized by its top-down aspect.
Below we introduce the major steps of the basic design methodology.
It emphasizes the top-down aspect of the design flow, and points out
that our methodology is breaked up into 5 distinct parts, the latter
being not available yet within \textbf{Alliance}:
\begin{itemize}
\item capture and simulation of the behavioral view,
\item capture and validation of the structural view,
\item physical implementation of the design,
\item layout verification,
\item test and coverage evaluation.
\end{itemize}
The design flow also includes miscellaneous tools like layout editor
for the design of the cell libraries, and a PostScript plotter for
documentation.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Capture and simulation of the behavioral view}
Like we just saw, the capture of the behavioral view is the
very first step of our design flow.
Within \textbf{Alliance}, any \textbf{VLSI} design begins with a timing
independent description of the circuit with a subset of \textbf{VHDL}
behavior primitives.
This subset of \textbf{VHDL}, called \texttt{vbe}, is fairly
restricted: it is the data-flow subset of this language.
It is not very easy to modelize an architecture using this subset,
but it has the great advantage of allowing simulation, logic synthesis
and bit level formal proof on the same files.
A \textbf{VHDL} analyzer called \texttt{vasy} can be used to
automatically convert most common \textbf{VHDL} descriptions
(using for example IEEE 1164 packages) to the
restricted Alliance subsets (\texttt{vbe} and \texttt{vst}).
Patterns, \textbf{VHDL} simulation stimuli, are described in a specific
formalism that can be captured using a dedicated language \texttt{genpat}.
Once a \textbf{VHDL} behavioral description written and a set of test vectors
have been determined, a functional simulation is ran.
The behavioral \textbf{VHDL} simulator is called \texttt{asimut}.
It validates the input behavior, according to the input/output vectors.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Capture and validation of the structural view}
The structural view can be captured once the data flow description
is validated.
The actual capture of the netlist relies either on specific
description languages, \texttt{genlib} for standard cells or \texttt{dpgen}
for data-path, or on direct synthesis from the data flow using the
\texttt{boom} tool for optimization and the \texttt{boog} tool to map
on a cell library.
\texttt{Genlib} and \texttt{dpgen} are netlist-oriented libraries of C
functions.
In the design methodology, it is essential for the students to get
acquainted with the \textbf{C} language basics.
The advantage of such an approach is that designers do not have to
learn several language with specific syntax and semantics.
Usually, the main behavior is partitionned in several sub-behaviors.
Some are described recursively using the \texttt{genlib} language
and the other ones can be directly synthesized from a \textbf{VHDL}
description of the corresponding sub-behaviors.
The \texttt{boog} tool takes an \textbf{RTL} description and
generates a netlist of standard cell gates.
An other subset of \textbf{VHDL} allows to capture finite state machines.
This subset, called \texttt{fsm}, can be translated into a
\textbf{RTL} description using the tool \texttt{syf}, and then the
resulting description optimized using \texttt{boom} and finally
syntesized as a netlist using once more \texttt{boog}.
Since \texttt{asimut} can operate on both \textbf{RTL} and structural views,
the structural description is checked against the behavioral
description by using the same set of patterns that has been used for
behavioral validation.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Physical design}
Once the circuit netlist has been captured and validated, each leaf of
the hierarchy has to be physically implemented.
A netlist issued from \texttt{boog} is usually placed and routed using
the over cell router \texttt{nero}.
If the netlist has been captured using \texttt{genlib} and if it has a
high degree of regularity, it can be placed manually for optimisation
using other \texttt{genlib} functions.
The different parts can be placed and assembled together using
\texttt{ocp} and routed using overcell router called \texttt{nero},
and this generates what we call a \textit{core}.
The circuit core is now ready to be connected to external pads.
The core-to-pads router, \texttt{ring}, aims at doing this operation
automatically, provided the user has given an appropriate netlist and
some indications on pad placement.
The last stage of the physical implementation is the translation of
the symbolic layout to a foundry compliant layout using the
\texttt{s2r} tool.
After that, the tape containing the circuit can be processed by the
silicon supplier.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Verification}
In our \textbf{VLSI} class, we intend to show that \textbf{VLSI}
verification is at least as important as \textbf{VLSI} physical
design.
For that reason, we have introduced in the design flow powerful tools
to perform behavior, netlist and layout verifications.
The correctness of the design rules is checked using the design rule
checker \texttt{druc}.
An extracted netlist can be obtained from the resulting layout.
\texttt{Cougar}, the layout extractor operates on both hierarchical and
flattened layout and can output both flattened netlists (transistor
netlist) and hierarchical netlists.
The transistor netlist can be the input of a spice simulator.
When extracted hierarchically, the resulting netlist can be compared
with the original netlist by using the \texttt{lvx} tool.
\texttt{lvx}, that stands for Logical Versus Extracted, is a netlist
comparator that matches every design object found in both netlists.
The critical path of the circuit is evaluated using a commercial
static timming analyzer, as \textbf{Alliance} doesn't provided one.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Test and coverage evaluation}
For now, the fault coverage provided by the functional patterns is
evaluated using a commercial fault simulator, as \textbf{Alliance}
doesn't provide one yet.
%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Tools and layout libraries of the \textbf{Alliance} package}
Every \textbf{Alliance} tool has been designed to simply interface with
each other, in order to support the proposed design flow.
Nevertheless, each tool can also be used independently, thanks to the
multiple standard formats used for input and output files.
One of the most important characteristics of the \textbf{Alliance} system is
that it provides a common internal data structure to represent the
three basic views of a chip:
\begin{itemize}
\item the behavioral view,
\item the structural view,
\item the physical view.
\end{itemize}
Figure~\ref{tools} details how all the \textbf{Alliance} tools are linked
together around the basic behavioral, structural and physical
data structures.
\begin{figure}\center
%\leavevmode
\includegraphics[width=\linewidth]{tools.eps}
\caption{\label{tools}How the tools are linked on the data structures.}
\end{figure}
The process independence goal is achieved with a thin fixed-grid
symbolic layout approach.
All the library of the system use this approach successfully.
Layouts have been targetted to ES2 2$\mu$m, 1.5$\mu$m, 1.2$\mu$m,
1.0$\mu$m and 0.7$\mu$m technologies, the AMS 1.2$\mu$m technology and
SGS-Thomson 0.5$\mu$m, 0.35$\mu$m technologies.
Chips have been fabricated successfully through the \textbf{CMP} services on
these technologies.
%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Tools}
\begin{itemize}
\item \texttt{vasy} is a \textbf{VHDL} analyzer and convertor.
The supported \textbf{VHDL} subset is closed to commercial synthesizer
tools such as Synopsys. It converts automatically \textbf{VHDL}
descriptions to the restricted \textbf{VHDL} subsets of Alliance tools.
\item \texttt{asimut} is a \textbf{VHDL} logic simulator.
The supported \textbf{VHDL} subset allows both structural and behavioral
data-flow description (without timing information).
Complex systems and microprocessors, including \textbf{INTEL} 8086 and
\textbf{MIPS} R3000 have been successfully simulated with \texttt{asimut}.
\texttt{Asimut} is based on an event-driven algorithm and powerful
representation of boolean functions using binary decision
diagrams.
\item \texttt{genpat} is a language interpreter dedicated to efficient
descriptions of simulation stimuli.
It generates an \textbf{ASCII} file that can act as an input of
\texttt{asimut}.
A \texttt{genpat} file format to \textbf{MSA} translator allows the
generation of appropriate simulation patterns for the Tektronix
LV500 tester.
This allows to perform functional tests when the circuits comes
back from the foundry.
\item \texttt{loon} is a gate level netlist optimizer.
If the output of the logic synthesis takes into account the
internal delays of the cells during the mapping phase, it
doesn't take into account the fan-out problems.
\texttt{Netoptim} work is to ensure that the drive capabilities of
all cells are correct, and to try to minimize the delays on the
critical pathes in inserting buffers where appropriate.
\item \texttt{genlib} is a procedural language for netlist capture and
placement description (there is no schematic editor in the
\textbf{Alliance} system).
\texttt{Genlib} provides a consistent set of \textbf{C}
primitives, giving the designers the ability to describe
\textbf{VLSI} circuit netlists in terms of terminals, signals
and instances, or circuit topologies in terms of placement of
abutment boxes.
\texttt{Genlib} is mainly used to build parameterized netlist and
layout generators.
\item \texttt{dpgen} is a language that has moreorless the same
functionalities as \texttt{genlib}, but it is dedicated to datapath
description.
Its primary difference with \texttt{genlib} is that it allows to
manipulate vectors of cells, like 32 two inputs \texttt{nand} gates
or a 32 bits adder.
It contains many primitives that greatly simplify the
description of operative parts, in an optimized manner.
\texttt{dpgen} has been recently merged with \texttt{genlib}.
\item \texttt{boom} is a logic optimizer and logic synthesis tool.
The input file is a behavioral description of the circuit using
the same \textbf{VHDL} subset as the logic simulator.
The boolean equations described in \textbf{VHDL} are optimized so
to minimize the number of boolean operators.
The output is a new, optimized, data flow description.
\item \texttt{boog} is a logic synthesis tool.
The output is a netlist of gates.
\texttt{boog} can map a data-flow description on any
standard-cell library, as long as a \textbf{VHDL} data-flow
description is provided with each cell.
\item \texttt{syf} is a finite state machine synthesizer.
More precisely, \texttt{syf} assigns values to the symbolic states
used for the automaton description, and aims at minimizing the
resulting logic for both state transistion and output generation.
The input is a \texttt{fsm} description, using a dedicated subset
of \textbf{VHDL} that includes process description.
The output is a behavioral description of the circuit using
the same \textbf{VHDL} subset as the logic simulator.
The output of \texttt{syf} is to be synthesized into a netlsit of
gates using \texttt{boog}.
\item \texttt{ocp} is a placer for standard-cells.
The placement system is based on simulated annealing.
\item \texttt{nero} is an over cell router. The input is a netlist of gates
and a placement file.
The output is an hierarchical chip core
layout without external pads.
A specialized router is used for core to pad routing.
\item \texttt{Ring} is a specific router dedicated to the final routing
of chip core and input/output pads.
\texttt{Ring} takes into account the various problems of pad
placement optimization, power and ground distribution.
A set of symbolic pads is included in the package.
\item \texttt{S2r} is the ultimate tool used in our design flow to
perform process mapping.
\texttt{S2r} stands for "symbolic to real", and translates the
hierarchical symbolic layout description into physical layout
required by a given silicon supplier.
The translation process involves complex operations such as
denotching, oversizing, gap-filling and layer adaptation.
Output formats are either \textbf{CIF} or \textbf{GDSII}.
\texttt{S2r} requires a parameter file for each technology aimed at.
This file is shared with \texttt{druc}, \texttt{cougar}, \texttt{graal}
and \texttt{dreal}.
From an implementation point of view, these tools use a
bin-based data-structure that has very good performances.
\item \texttt{druc} is a design rule checker.
The input file is a - possibly hierarchical - symbolic layout.
It checks that a layout is correct regarding the set of symbolic
design rules.
This correctness must be ensured in order for \texttt{s2r} to
produce a layout compatible with the target silicon foundry.
\item \texttt{Cougar} is a layout extractor.
The input is a - possibly hierarchical - layout.
The layout can be either symbolic or real.
The output is an extracted netlist with parasitic capacitances
and optionally resistors.
The resulting netlist can either be hierarchical or flattened
(up to transistor level netlist).
\item \texttt{Lvx} is a logical versus extracted net-compare tool.
The result of a run indicates if the two netlist match together,
or if there are different.
Note that \texttt{lvx} doesn't work at the transistor level.
\item \texttt{proof} performs a formal comparison between two data
flow \textbf{VHDL} descriptions that share the same register set.
\texttt{Proof} supports the same subset of \textbf{VHDL} as
\texttt{asimut}, \texttt{boom}, \texttt{boog}.
\item \texttt{graal} is an hierarchical symbolic layout editor.
It requires a X-Window graphical environment and the Motif libraries.
\texttt{Graal} is used for cell layout design or hierarchical
block construction.
It provides an on-line \textbf{DRC} and automatic display of
equipotential nets.
Editing a cell under \texttt{graal} is shown figure~\ref{graal}.
\begin{figure}\center
% \leavevmode
\includegraphics[width=5cm]{graal.eps}
\caption{\label{graal}Editing some custom layout using \texttt{graal}.}
\end{figure}
\item \texttt{dreal} is a real layout editor (rectangles in micron) .
It requires a X-Window graphical environment and the Motif libraries.
\item there are many other tools not described here.
\end{itemize}
%%%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Cell libraries}
The \textbf{Alliance} package provide a wide range of libraries, either
static, ie. fixed cells, or dynamic, as the block is produced by
running a parameterized generator.
These libraries are compatible with any two metals/one polysilicon
technology.
Each object in the library has, for static ones, or produces, for
dynamics ones, three views at least :
\begin{itemize}
\item the symbolic layout, that describes the cell topology.
\item the netlist, in terms of transistor interconnections.
\item the behavior, specified in \textbf{VHDL} data flow form.
\end{itemize}
%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsubsection{Standard cell library}
The \texttt{sxlib} library contains boolean functions, buffers, mux,
latches, flip-flops, $\ldots$ (around 100 cells).
All cells have the same heightare and N times the width, where N is
the number of pitches. That is the only physical information given in
the cell list below. Power supplies are in horizontal ALU1 and have the
same width. Connectors are inside the cells, placed on a 5x5 grid.
Half layout design rules are a warranty for any layer on any face,
except for the power supply and NWELL.Cells can be abutted in all directions
whenever the supply is well connected and connectors are always placed on
the 5x5 grid.
They are supposed to be used with a usual standard cells place and
route tools, such as \textbf{Alliance}'s \texttt{ocp} and \texttt{nero},
\textbf{Compass} or \textbf{Cadence}.
These cells are to be used primary for glue logic, since optimized
operators can be obtained using dedicated generators, as stated
paragraph~\ref{gene}.
The \texttt{logic} tool can map a behaviral VHDL onto this library.
%%%%%%%%%%%%%%%%%%
%%
%%%%%%%%%%
\subsubsection{Datapath libraries: (This part of the document is not up to date !)}
\label{gene}
There are two kinds of datapath libraries:
\begin{itemize}
\item \texttt{dp\_sxlib} is a cell library dedicated to high density data-paths.
It must be used in conjunction with the data-path tool
\texttt{dpgen}.
The cells in \texttt{dp\_sxlib} have the same functionnalities as the
ones in \texttt{sxlib}, but have a topology that is usable only
within a datapath.
\texttt{Boog} can also map a behavior onto the \texttt{dp\_sxlib}
library.
\item \texttt{fplib} is a set of above 30 regular functions that are
useful in the design of a datapath.
These functions range from a \textit{n} inputs \texttt{nand} gate to
a \textit{n $times$ m} register file.
\end{itemize}
Here the cells share the power and ground lines in metal2.
A powerful dedicated over the cell router can route custom
blocks and logic glue in the same structure.
Among the \texttt{fplib} functionnalities, four optimized blocks
generators should be presented in more details, as they reflect the
quality of this library.
All the generators are build with a tiler using a dedicated leaf cell
library.
Their output is a symbolic layout, a \textbf{VHDL} behavior, a set of
pattern for test purpose, a netlist, an icon, and a datasheet
indicating size and timing estimation for a given technology.
The structural parameters varies according to their functionalities.
\begin{itemize}
\item optimized generators for datapath operators:
\begin{description}
\item[\tt rsa\rm ,] a fast adder generator, with propagation time
in log \textit{nb} and size in \textit{nb\/ \rm log \it nb},
where \textit{nb} is the number of bits.
Its has 2 or 3 input buses, and if needed a carry input.
It may be used as a substractor or adder/substractor.~\\
\begin{tabular}{|p{7ex}|p{45ex}|p{15ex}|}
\hline
Params & Meaning & Range \\
\hline
nb & number of bits & 3 to 128\\
cin & carry in & true or false\\
csa & three inputs adder & true or false\\
ovr & overflow flag & true or false\\
\hline
\end{tabular}
\item[\tt rfg\rm ,] a static register file generator.
It has one write address , and one or two read address.
It may be operated as a set of level-sensitive latches
or edge triggered flip-flops.~\\
\begin{tabular}{|p{7ex}|p{45ex}|p{15ex}|}
\hline
Params & Meaning & Range \\
\hline
nb & number of bits & 2 to 64\\
nw & number of words & 2 to 256\\
bus & number of read bus & 1 or 2\\
op & mode of operation & latch or flip-flop\\
low power & reduce power consumption & true or false\\
\hline
\end{tabular}
\item[\tt bsg\rm ,] a barrel shifter generator.
Possible operations are :
\begin{itemize}
\item logical right shift
\item arithmetical right shift
\item logical left shift
\item arithmetical left shift
\item right rotation
\item left rotation
\end{itemize}
\begin{tabular}{|p{7ex}|p{45ex}|p{15ex}|}
\hline
Params & Meaning & Range \\
\hline
nb & number of bits & 3 to 64\\
\hline
\end{tabular}
\item[\tt amg\rm ,] an integer modified booth algorithm array
multiplier.
the \textit{x} and \textit{y\/} inputs are independent,
and pipeline stages can be inserted in the circuit.~\\
\begin{tabular}{|p{7ex}|p{45ex}|p{15ex}|}
\hline
Params & Meaning & Range \\
\hline
nx & number of bits of the \textit{x} operand & 8 to 64\\
ny & number of bits of the \textit{y} operand & 8 to 64\\
ps & number of pipeline stages to be inserted in the
circuit & 0 to min($\frac{\rm nx}{\rm 2}$\rm,
$\frac{\rm ny}{\rm 2}$)-\rm 1\\
\hline
\end{tabular}
\end{description}
\end{itemize}
%%%%%%%%%%%%%%%%%%
%%
%%%%%%%%%%
\subsubsection{Custom libraries}
Two full-custom parameterized generators are also available.
They produce stand-alone blocks, that are to be routed only at the
floorplan level with other blocks, using either \texttt{bbr} or better
\texttt{xcheops}.
\begin{itemize}
\item \textit{ROM} and \textit{RAM\/} generators:
\begin{description}
\item[\tt grog\rm ,] a generic \textit{ROM} generator.
The interface is an address bus, a clock and an output
enable signal, and a data out bus.
The coding format to specify the \textit{ROM} contents
is a limited subset of VHDL.~\\
\begin{tabular}{|p{7ex}|p{45ex}|p{15ex}|}
\hline
Params & Meaning & Range \\
\hline
nb & number of bits & 1 to 64\\
nw & number of words & 64, 128, 256,
\textit{n~\rm 512,~1~$\leq$~\it n~$\leq$~\rm 8}\\
hz & tri-state output & true or false\\
\hline
\end{tabular}
\item[\tt rage\rm ,] a \textit{RAM} generator.
The interface has a read/write address, a write signal
indicating if a read or a write is to be performed, and a
clock.~\\
\begin{tabular}{|p{7ex}|p{45ex}|p{15ex}|}
\hline
Params & Meaning & Range \\
\hline
nb & number of bits & 2 to 128\\
nw & number of words & 128 to 4096\\
aspect & aspect ratio & narrow, medium or large\\
ud & unidirectional, ie share the same bus for data in
and out & true or false\\
\hline
\end{tabular}
\end{description}
\end{itemize}
All these generators have been designed using the \textbf{Alliance} CAD
tools, for both design and verification phases.
%%%%%%%%%%%%%%%%%%
%%
%%%%%%%%%%
\subsubsection{Pad library}
\textbf{Alliance} provides also a \texttt{padlib} library.
This library also uses a symbolic layout approach, and therefore a
whole chip can be targeted on several technology without even the core
to pad routing.
A very robust approach has been enforced, as the pads are subject to
electrostatic discharge, and also more sensible to latch-up than the
other parts of the circuit due to the amount of current that flows
through them.
Chips using these pads have been fabricated on ES2 1.0$\mu$m,
AMS 1.2$\mu$m and SGS-Thomson 0.5$\mu$m technology and work as
expected.
%%%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Supported exchange formats}
The \textbf{Alliance} CAD system handles many file formats.
They are summarized here.
A file can be either read, using a \textit{parser}, or written, using a
\textit{driver}.
\begin{itemize}
\item Behavioral view:
\begin{itemize}
\item dataflow \textbf{VHDL} parser and driver.
\end{itemize}
\item Structural view:
\begin{itemize}
\item \textbf{VHDL} parser and driver.
\item \textbf{EDIF} parser and driver.
\item \textbf{Spice} parser and driver.
\item \textbf{Compass} parser and driver.
\item \textbf{Alliance} parser and driver.
\item \textbf{Hilo} driver
\end{itemize}
\item Physical view:
\begin{itemize}
\item \textbf{Alliance} parser and driver, for symbolic layout.
\item \textbf{Compass} parser and driver, for symbolic layout.
\item \textbf{Modgen} parser and driver, for symbolic layout.
\item \textbf{CIF} parser and driver, for real layout.
\item \textbf{GDSII} parser and driver, for real layout.
\end{itemize}
\end{itemize}
Being able to understand and write many file formats is a must.
First, in a development environment, as it allows to check the
validity of tools on other CAD systems.
Second, because some tools are not available or desirable within
\textbf{Alliance}, but may be useful however: it is possible to feed an
other software with a design in that situation.
The experience showa that many of these formats are used daily.
For example, the design that we fabricate through the CMP
services are transmitted using the \textbf{GDSII} format.
The final \textbf{DRC} on these files are performed using \textbf{Cadence}
\texttt{pdverify}.
An other example: \textbf{Alliance} does not have a fault simulator yet.
However this kind of tool is very useful to evaluate the fault
coverage of a set of vectors and must be introduced in a \textbf{VLSI}
class.
This is hopefully easilly done using the \textbf{Hilo} output of
\textbf{Alliance} that feed the \texttt{hifault} simulator.
%%%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{\textbf{Alliance} internal organization}
The complete \textbf{Alliance} CAD system contains about 600 000
lines of C code, and over 600 leaf cells.
It compiles and runs on most \textbf{Unix} system, and requires the basic
X-Window library X11 plus Motif.
The distribution tape shows that there are three kinds of files:
\begin{itemize}
\item common data structures and manipulation primitives.
\item parsers/drivers to read and write external file formats.
\item actual tools.
\end{itemize}
\textbf{Alliance} as been developed in order to simplify cooperative
work between the CAD tool designers.
The existence of a common data structure framework releaves the
developer of many burdens: reading and writing many file format,
conceptualizing the VLSI objects, writing classical high level and
nevertheless complex functions, ...
All the \textbf{Alliance} tools share these data structures and their
related functions.
So each tool communicates with the other ones smoothly, by construction.
%%%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Use of \textbf{Alliance} inside our laboratory}
\textbf{Alliance} is used for both educational and research purposes.
We relate our experience below.
\subsection*{Educational aspects}
The \textbf{Alliance} System has been extensively used during the past
fifteen academic years (1989-2004) as a practical support of two
undergraduate courses: one on \textbf{CMOS} \textbf{VLSI} design, the other
one on \textbf{advanced computer architecture}.
These initiation courses lasts 13 weeks with a 2 hours lecture and 4
hours spent using the \textbf{Alliance} system per week, and involves 60
students and 3 teachers.
The `\textbf{VLSI} design' course is for students that have no previous
knowledge on \textbf{VLSI} design and mainly come from two distinct
channels:
"computer science" and "electrical engineering" masters of sciences.
During this course, students are required to design and implement an
\textbf{AMD2901} compatible processor, starting from a commercial data-sheet.
The chip, with a complexity of about 2000 transistors, is designed by
groups of 2 or 3 students.
The main interest in this course is to teach the design methodology.
Most of the \textbf{Alliance} tools are used during this class.
The `architecture' course focuses on the way processor architecture, from
the system point of view and not from an implementation one.
Typical \textbf{CISC} and \textbf{RISC} processors are studied, and part of
them modelized using our \textbf{VHDL} subset.
In that class, only the \texttt{asimut} simulator is used.
\textbf{Alliance} is also used in an intensive graduate course, for the
design of the 32 bits microprocessor \texttt{MIPS} \textbf{RISC} processor
-- 30000 transistors --.
This course lasts two months, and aims only at the implementation~:
the high level behavioral model of the processor is given to the
students.
During that period of time, all the \textbf{Alliance} tools are
used.
\subsection*{Research projects}
These projects range from medium complexity ASICs developed in 6
months by a couple of designers \textbf{Data-safe}, \textbf{TNT},
\textbf{Smal}, \textbf{Rf264},etc... to high complexity circuits
(\textbf{FRISC}, \textbf{Multick}, \textbf{StaCS}, \textbf{Rapid2}, \textbf{Rcube})
developed by a team of PhD students.
\begin{figure}\center
\begin{tabular}{|c|c|l|}
\hline
Project & transistors & Functionality\\
\hline
\textbf{Smal} & 17 000 & one bit processor for SIMD architectures\\
\hline
\textbf{Data-safe} & 35 000 & dynamic data encryption chips\\
\hline
\textbf{TNT} & 60 000 & switch-router for T800 transputerss\\
\hline
\textbf{FRISC} & 200 000 & floating-point \textbf{RISC} microprocessor\\
\hline
\textbf{StaCS} & 875 000 & Very Long Instruction Word processor\\
\hline
\textbf{Rapid2} & 650 000 & SIMD systolic and associative processor\\
\hline
\textbf{Rcube} & 350 000 & Message router for parallel machines\\
\hline
\end{tabular}
\caption{\label{chip}Various chips designed with \textbf{Alliance}.}
\end{figure}
\begin{figure}\center
%\leavevmode
\includegraphics[width=5cm]{stacs.eps}
\caption{\label{stacs} The 875 000 VLIW StaCS processor.}
\end{figure}
The three largest circuits described in table~\ref{chip} use not only
standard-cells but also parameterized generators for regular blocks
like \textit{RAM}s, data-paths, or floating-point operators.
The \textbf{FRISC} and \textbf{TNT} projects successfully used the
\textbf{Cadence} and \textbf{Compass} place and route tools, and
therefore prove the interoperability of the \textbf{Alliance} system.
A picture of the \textbf{StaCS} processor is shown figure~\ref{stacs}.
%%%%%%%%%%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Conclusion}
We are very satisfied to use a set of tools of our own for teaching
\textbf{CMOS} \textbf{VLSI} design for two good reasons.
First, we simply can't afford 50 high end workstations to run
commercial CAD systems like \textbf{Synopsys}, \textbf{Mentor Graphics} or
\textbf{Cadence}.
Second, both the \textbf{Synopsys} and \textbf{Cadence} system have been
used in research project at \textbf{LIP6}.
They are powerful and sophisticated environments but are much too
complex for novice undergraduate students.
The great advantage of the \textbf{Alliance} CAD system is that we
have done our best to stick to the basic yet powerful concepts of
\textbf{VLSI} design.
To each tool correspond a unique functionnality, that cannot be
changed or worked around by parameter files.
At last, we experienced that the technology migration and process
independence are key issues.
Hence, it is crucial to rely on a portable library at the symbolic
layout level.
The \textbf{Alliance} package is now in use all over the world, and more
than 250 sites have registered today.
It is available through anonymous \texttt{ftp} at
\texttt{ftp://ftp-asim.lip6.fr/pub/alliance/} \texttt{distribution/},
or through a \texttt{Web} browser at
\texttt{http://www-asim.lip6.fr/pub/alliance/} \texttt{distribution/}.
There is an \textbf{Alliance} mailing list, where users can share their
views and problems, and our team is always ready to answer questions.
The address of this mailing list is
\texttt{alliance-users@asim.} \texttt{lip6.fr}.
%%%%%%%%%%%%%%%%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\bibliography{/users/cao4/fred/tex/articles/bib/article,/users/cao4/fred/tex/articles/padp/pplace,./thesis}
%\bibliography{/users/cao4/fred/faq}
%\bibliographystyle{unsrt}
\end{document}
|