7 %% http://www.michaelshell.org/
8 %% for current contact information.
10 %% This is a skeleton file demonstrating the use of IEEEtran.cls
11 %% (requires IEEEtran.cls version 1.7 or later) with an IEEE conference paper.
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42 %% File list of work: IEEEtran.cls, IEEEtran_HOWTO.pdf, bare_adv.tex,
43 %% bare_conf.tex, bare_jrnl.tex, bare_jrnl_compsoc.tex
44 %%*************************************************************************
46 % *** Authors should verify (and, if needed, correct) their LaTeX system ***
47 % *** with the testflow diagnostic prior to trusting their LaTeX platform ***
48 % *** with production work. IEEE's font choices can trigger bugs that do ***
49 % *** not appear when using other class files. ***
50 % The testflow support page is at:
51 % http://www.michaelshell.org/tex/testflow/
55 % Note that the a4paper option is mainly intended so that authors in
56 % countries using A4 can easily print to A4 and see how their papers will
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58 % affected with changes in paper size (but the bottom and side margins will).
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62 % Also note that the "draftcls" or "draftclsnofoot", not "draft", option
63 % should be used if it is desired that the figures are to be displayed in
66 \documentclass[conference,pdf,a4paper,10pt,final,twoside,twocolumn]{IEEEtran}
67 % Add the compsoc option for Computer Society conferences.
69 % If IEEEtran.cls has not been installed into the LaTeX system files,
70 % manually specify the path to it like:
71 % \documentclass[conference]{../sty/IEEEtran}
73 % Some very useful LaTeX packages include:
74 % (uncomment the ones you want to load)
76 % *** MISC UTILITY PACKAGES ***
79 % Heiko Oberdiek's ifpdf.sty is very useful if you need conditional
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87 % The latest version of ifpdf.sty can be obtained from:
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99 % *** CITATION PACKAGES ***
102 % cite.sty was written by Donald Arseneau
103 % V1.6 and later of IEEEtran pre-defines the format of the cite.sty package
104 % \cite{} output to follow that of IEEE. Loading the cite package will
105 % result in citation numbers being automatically sorted and properly
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107 % cite.sty will become [1], [2], [5]--[7], [9] using cite.sty. cite.sty's
108 % \cite will automatically add leading space, if needed. Use cite.sty's
109 % noadjust option (cite.sty V3.8 and later) if you want to turn this off.
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130 % \DeclareGraphicsExtensions{.pdf,.jpeg,.png}
132 % or other class option (dvipsone, dvipdf, if not using dvips). graphicx
133 % will default to the driver specified in the system graphics.cfg if no
134 % driver is specified.
135 % \usepackage[dvips]{graphicx}
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159 % You can find documentation about the pdfTeX application at:
160 % http://www.tug.org/applications/pdftex
166 % *** MATH PACKAGES ***
168 %\usepackage[cmex10]{amsmath}
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189 % *** SPECIALIZED LIST PACKAGES ***
191 %\usepackage{algorithmic}
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193 % This package provides an algorithmic environment fo describing algorithms.
194 % You can use the algorithmic environment in-text or within a figure
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204 % Also of interest may be the (relatively newer and more customizable)
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211 % *** ALIGNMENT PACKAGES ***
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218 % respect to the quality of the end results, all users are strongly
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221 % latest version and documentation can be obtained at:
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225 %\usepackage{mdwmath}
227 % Also highly recommended is Mark Wooding's extremely powerful MDW tools,
228 % especially mdwmath.sty and mdwtab.sty which are used to format equations
229 % and tables, respectively. The MDWtools set is already installed on most
230 % LaTeX systems. The lastest version and documentation is available at:
231 % http://www.ctan.org/tex-archive/macros/latex/contrib/mdwtools/
234 % IEEEtran contains the IEEEeqnarray family of commands that can be used to
235 % generate multiline equations as well as matrices, tables, etc., of high
239 %\usepackage{eqparbox}
240 % Also of notable interest is Scott Pakin's eqparbox package for creating
241 % (automatically sized) equal width boxes - aka "natural width parboxes".
243 % http://www.ctan.org/tex-archive/macros/latex/contrib/eqparbox/
249 % *** SUBFIGURE PACKAGES ***
250 %\usepackage[tight,footnotesize]{subfigure}
251 % subfigure.sty was written by Steven Douglas Cochran. This package makes it
252 % easy to put subfigures in your figures. e.g., "Figure 1a and 1b". For IEEE
253 % work, it is a good idea to load it with the tight package option to reduce
254 % the amount of white space around the subfigures. subfigure.sty is already
255 % installed on most LaTeX systems. The latest version and documentation can
257 % http://www.ctan.org/tex-archive/obsolete/macros/latex/contrib/subfigure/
258 % subfigure.sty has been superceeded by subfig.sty.
262 %\usepackage[caption=false]{caption}
263 %\usepackage[font=footnotesize]{subfig}
264 % subfig.sty, also written by Steven Douglas Cochran, is the modern
265 % replacement for subfigure.sty. However, subfig.sty requires and
266 % automatically loads Axel Sommerfeldt's caption.sty which will override
267 % IEEEtran.cls handling of captions and this will result in nonIEEE style
268 % figure/table captions. To prevent this problem, be sure and preload
269 % caption.sty with its "caption=false" package option. This is will preserve
270 % IEEEtran.cls handing of captions. Version 1.3 (2005/06/28) and later
271 % (recommended due to many improvements over 1.2) of subfig.sty supports
272 % the caption=false option directly:
273 %\usepackage[caption=false,font=footnotesize]{subfig}
275 % The latest version and documentation can be obtained at:
276 % http://www.ctan.org/tex-archive/macros/latex/contrib/subfig/
277 % The latest version and documentation of caption.sty can be obtained at:
278 % http://www.ctan.org/tex-archive/macros/latex/contrib/caption/
283 % *** FLOAT PACKAGES ***
285 %\usepackage{fixltx2e}
286 % fixltx2e, the successor to the earlier fix2col.sty, was written by
287 % Frank Mittelbach and David Carlisle. This package corrects a few problems
288 % in the LaTeX2e kernel, the most notable of which is that in current
289 % LaTeX2e releases, the ordering of single and double column floats is not
290 % guaranteed to be preserved. Thus, an unpatched LaTeX2e can allow a
291 % single column figure to be placed prior to an earlier double column
292 % figure. The latest version and documentation can be found at:
293 % http://www.ctan.org/tex-archive/macros/latex/base/
297 %\usepackage{stfloats}
298 % stfloats.sty was written by Sigitas Tolusis. This package gives LaTeX2e
299 % the ability to do double column floats at the bottom of the page as well
300 % as the top. (e.g., "\begin{figure*}[!b]" is not normally possible in
301 % LaTeX2e). It also provides a command:
303 % to enable the placement of footnotes below bottom floats (the standard
304 % LaTeX2e kernel puts them above bottom floats). This is an invasive package
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307 % version and documentation can be obtained at:
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309 % Documentation is contained in the stfloats.sty comments as well as in the
310 % presfull.pdf file. Do not use the stfloats baselinefloat ability as IEEE
311 % does not allow \baselineskip to stretch. Authors submitting work to the
312 % IEEE should note that IEEE rarely uses double column equations and
313 % that authors should try to avoid such use. Do not be tempted to use the
314 % cuted.sty or midfloat.sty packages (also by Sigitas Tolusis) as IEEE does
315 % not format its papers in such ways.
321 % *** PDF, URL AND HYPERLINK PACKAGES ***
324 % url.sty was written by Donald Arseneau. It provides better support for
325 % handling and breaking URLs. url.sty is already installed on most LaTeX
326 % systems. The latest version can be obtained at:
327 % http://www.ctan.org/tex-archive/macros/latex/contrib/misc/
328 % Read the url.sty source comments for usage information. Basically,
335 % *** Do not adjust lengths that control margins, column widths, etc. ***
336 % *** Do not use packages that alter fonts (such as pslatex). ***
337 % There should be no need to do such things with IEEEtran.cls V1.6 and later.
338 % (Unless specifically asked to do so by the journal or conference you plan
339 % to submit to, of course. )
341 % correct bad hyphenation here
342 \hyphenation{op-tical net-works semi-conduc-tor}
344 % Macro for certain acronyms in small caps. Doesn't work with the
345 % default font, though (it contains no smallcaps it seems).
346 \def\acro#1{{\small{#1}}}
347 \def\VHDL{\acro{VHDL}}
349 \def\CLaSH{{\small{C}}$\lambda$a{\small{SH}}}
351 % Macro for pretty printing haskell snippets. Just monospaced for now, perhaps
352 % we'll get something more complex later on.
353 \def\hs#1{\texttt{#1}}
354 \def\quote#1{``{#1}"}
356 \newenvironment{xlist}[1][\rule{0em}{0em}]{%
358 \settowidth{\labelwidth}{#1:}
359 \setlength{\labelsep}{0.5cm}
360 \setlength{\leftmargin}{\labelwidth}
361 \addtolength{\leftmargin}{\labelsep}
362 \setlength{\rightmargin}{0pt}
363 \setlength{\parsep}{0.5ex plus 0.2ex minus 0.1ex}
364 \setlength{\itemsep}{0 ex plus 0.2ex}
365 \renewcommand{\makelabel}[1]{##1:\hfil}
370 %include polycode.fmt
375 % can use linebreaks \\ within to get better formatting as desired
376 \title{C$\lambda$aSH: Structural Descriptions \\ of Synchronous Hardware using Haskell}
379 % author names and affiliations
380 % use a multiple column layout for up to three different
382 \author{\IEEEauthorblockN{Christiaan P.R. Baaij, Matthijs Kooijman, Jan Kuper, Marco E.T. Gerards, Bert Molenkamp, Sabih H. Gerez}
383 \IEEEauthorblockA{University of Twente, Department of EEMCS\\
384 P.O. Box 217, 7500 AE, Enschede, The Netherlands\\
385 c.p.r.baaij@utwente.nl, matthijs@stdin.nl}}
387 % \IEEEauthorblockN{Homer Simpson}
388 % \IEEEauthorblockA{Twentieth Century Fox\\
390 % Email: homer@thesimpsons.com}
392 % \IEEEauthorblockN{James Kirk\\ and Montgomery Scott}
393 % \IEEEauthorblockA{Starfleet Academy\\
394 % San Francisco, California 96678-2391\\
395 % Telephone: (800) 555--1212\\
396 % Fax: (888) 555--1212}}
398 % conference papers do not typically use \thanks and this command
399 % is locked out in conference mode. If really needed, such as for
400 % the acknowledgment of grants, issue a \IEEEoverridecommandlockouts
401 % after \documentclass
403 % for over three affiliations, or if they all won't fit within the width
404 % of the page, use this alternative format:
406 %\author{\IEEEauthorblockN{Michael Shell\IEEEauthorrefmark{1},
407 %Homer Simpson\IEEEauthorrefmark{2},
408 %James Kirk\IEEEauthorrefmark{3},
409 %Montgomery Scott\IEEEauthorrefmark{3} and
410 %Eldon Tyrell\IEEEauthorrefmark{4}}
411 %\IEEEauthorblockA{\IEEEauthorrefmark{1}School of Electrical and Computer Engineering\\
412 %Georgia Institute of Technology,
413 %Atlanta, Georgia 30332--0250\\ Email: see http://www.michaelshell.org/contact.html}
414 %\IEEEauthorblockA{\IEEEauthorrefmark{2}Twentieth Century Fox, Springfield, USA\\
415 %Email: homer@thesimpsons.com}
416 %\IEEEauthorblockA{\IEEEauthorrefmark{3}Starfleet Academy, San Francisco, California 96678-2391\\
417 %Telephone: (800) 555--1212, Fax: (888) 555--1212}
418 %\IEEEauthorblockA{\IEEEauthorrefmark{4}Tyrell Inc., 123 Replicant Street, Los Angeles, California 90210--4321}}
423 % use for special paper notices
424 %\IEEEspecialpapernotice{(Invited Paper)}
429 % make the title area
435 The abstract goes here.
437 % IEEEtran.cls defaults to using nonbold math in the Abstract.
438 % This preserves the distinction between vectors and scalars. However,
439 % if the conference you are submitting to favors bold math in the abstract,
440 % then you can use LaTeX's standard command \boldmath at the very start
441 % of the abstract to achieve this. Many IEEE journals/conferences frown on
442 % math in the abstract anyway.
449 % For peer review papers, you can put extra information on the cover
451 % \ifCLASSOPTIONpeerreview
452 % \begin{center} \bfseries EDICS Category: 3-BBND \end{center}
455 % For peerreview papers, this IEEEtran command inserts a page break and
456 % creates the second title. It will be ignored for other modes.
457 \IEEEpeerreviewmaketitle
460 \section{Introduction}
461 Hardware description languages has allowed the productivity of hardware
462 engineers to keep pace with the development of chip technology. Standard
463 Hardware description languages, like \VHDL\ and Verilog, allowed an engineer
464 to describe circuits using a programming language. These standard languages
465 are very good at describing detailed hardware properties such as timing
466 behavior, but are generally cumbersome in expressing higher-level
467 abstractions. These languages also tend to have a complex syntax and a lack of
468 formal semantics. To overcome these complexities, and raise the abstraction
469 level, a great number of approaches based on functional languages has been
470 proposed \cite{T-Ruby,Hydra,HML2,Hawk1,Lava,ForSyDe1,Wired,reFLect}. The idea
471 of using functional languages started in the early 1980s \cite{Cardelli1981,
472 muFP,DAISY,FHDL}, a time which also saw the birth of the currently popular
473 hardware description languages such as \VHDL.
475 What gives functional languages as hardware description languages their merits
476 is the fact that basic combinatorial circuits are equivalent to mathematical
477 function, and that functional languages lend themselves very well to describe
478 and compose these mathematical functions.
479 \section{Hardware description in Haskell}
481 \subsection{Function application}
482 The basic syntactic elements of a functional program are functions
483 and function application. These have a single obvious \VHDL\
484 translation: each top level function becomes a hardware component,
485 where each argument is an input port and the result value is the
486 (single) output port. This output port can have a complex type (such
487 as a tuple), so having just a single output port does not create a
490 Each function application in turn becomes component instantiation.
491 Here, the result of each argument expression is assigned to a
492 signal, which is mapped to the corresponding input port. The output
493 port of the function is also mapped to a signal, which is used as
494 the result of the application itself.
496 Since every top level function generates its own component, the
497 hierarchy of of function calls is reflected in the final \VHDL\
498 output as well, creating a hierarchical \VHDL\ description of the
499 hardware. This separation in different components makes the
500 resulting \VHDL\ output easier to read and debug.
502 Example that defines the \texttt{mac} function by applying the
503 \texttt{add} and \texttt{mul} functions to calculate $a * b + c$:
506 mac a b c = add (mul a b) c
511 \subsection{Choices }
512 Although describing components and connections allows describing a
513 lot of hardware designs already, there is an obvious thing missing:
514 choice. We need some way to be able to choose between values based
515 on another value. In Haskell, choice is achieved by \hs{case}
516 expressions, \hs{if} expressions, pattern matching and guards.
518 The easiest of these are of course case expressions (and \hs{if}
519 expressions, which can be very directly translated to \hs{case}
520 expressions). A \hs{case} expression can in turn simply be
521 translated to a conditional assignment in \VHDL, where the
522 conditions use equality comparisons against the constructors in the
523 \hs{case} expressions.
525 A slightly more complex (but very powerful) form of choice is
526 pattern matching. A function can be defined in multiple clauses,
527 where each clause specifies a pattern. When the arguments match the
528 pattern, the corresponding clause will be used.
530 A pattern match (with optional guards) can also be implemented using
531 conditional assignments in \VHDL, where the condition is the logical
532 and of comparison results of each part of the pattern as well as the
535 Contrived example that sums two values when they are equal or
536 non-equal (depending on the predicate given) and returns 0
537 otherwise. This shows three implementations, one using and if
538 expression, one using only case expressions and one using pattern
542 sumif pred a b = if pred == Eq && a == b || pred == Neq && a != b
548 sumif pred a b = case pred of
552 Neq -> case a != b of
558 sumif Eq a b | a == b = a + b
559 sumif Neq a b | a != b = a + b
566 Translation of two most basic functional concepts has been
567 discussed: function application and choice. Before looking further
568 into less obvious concepts like higher-order expressions and
569 polymorphism, the possible types that can be used in hardware
570 descriptions will be discussed.
572 Some way is needed to translate every values used to its hardware
573 equivalents. In particular, this means a hardware equivalent for
574 every \emph{type} used in a hardware description is needed
576 Since most functional languages have a lot of standard types that
577 are hard to translate (integers without a fixed size, lists without
578 a static length, etc.), a number of \quote{built-in} types will be
579 defined first. These types are built-in in the sense that our
580 compiler will have a fixed \VHDL\ type for these. User defined types,
581 on the other hand, will have their hardware type derived directly
582 from their Haskell declaration automatically, according to the rules
585 \subsection{Built-in types}
586 The language currently supports the following built-in types. Of these,
587 only the \hs{Bool} type is supported by Haskell out of the box (the
588 others are defined by the \CLaSH\ package, so they are user-defined types
589 from Haskell's point of view).
593 This is the most basic type available. It is mapped directly onto
594 the \texttt{std\_logic} \VHDL\ type. Mapping this to the
595 \texttt{bit} type might make more sense (since the Haskell version
596 only has two values), but using \texttt{std\_logic} is more standard
597 (and allowed for some experimentation with don't care values)
600 This is the only built-in Haskell type supported and is translated
601 exactly like the Bit type (where a value of \hs{True} corresponds to a
602 value of \hs{High}). Supporting the Bool type is particularly
603 useful to support \hs{if ... then ... else ...} expressions, which
604 always have a \hs{Bool} value for the condition.
606 A \hs{Bool} is translated to a \texttt{std\_logic}, just like \hs{Bit}.
607 \item[\hs{SizedWord}, \hs{SizedInt}]
608 These are types to represent integers. A \hs{SizedWord} is unsigned,
609 while a \hs{SizedInt} is signed. These types are parametrized by a
610 length type, so you can define an unsigned word of 32 bits wide as
614 type Word32 = SizedWord D32
617 Here, a type synonym \hs{Word32} is defined that is equal to the
618 \hs{SizedWord} type constructor applied to the type \hs{D32}. \hs{D32}
619 is the \emph{type level representation} of the decimal number 32,
620 making the \hs{Word32} type a 32-bit unsigned word.
622 These types are translated to the \VHDL\ \texttt{unsigned} and
623 \texttt{signed} respectively.
625 This is a vector type, that can contain elements of any other type and
626 has a fixed length. It has two type parameters: its
627 length and the type of the elements contained in it. By putting the
628 length parameter in the type, the length of a vector can be determined
629 at compile time, instead of only at run-time for conventional lists.
631 The \hs{Vector} type constructor takes two type arguments: the length
632 of the vector and the type of the elements contained in it. The state
633 type of an 8 element register bank would then for example be:
636 type RegisterState = Vector D8 Word32
639 Here, a type synonym \hs{RegisterState} is defined that is equal to
640 the \hs{Vector} type constructor applied to the types \hs{D8} (The type
641 level representation of the decimal number 8) and \hs{Word32} (The 32
642 bit word type as defined above). In other words, the
643 \hs{RegisterState} type is a vector of 8 32-bit words.
645 A fixed size vector is translated to a \VHDL\ array type.
646 \item[\hs{RangedWord}]
647 This is another type to describe integers, but unlike the previous
648 two it has no specific bit-width, but an upper bound. This means that
649 its range is not limited to powers of two, but can be any number.
650 A \hs{RangedWord} only has an upper bound, its lower bound is
651 implicitly zero. There is a lot of added implementation complexity
652 when adding a lower bound and having just an upper bound was enough
653 for the primary purpose of this type: type-safely indexing vectors.
655 To define an index for the 8 element vector above, we would do:
658 type RegisterIndex = RangedWord D7
661 Here, a type synonym \hs{RegisterIndex} is defined that is equal to
662 the \hs{RangedWord} type constructor applied to the type \hs{D7}. In
663 other words, this defines an unsigned word with values from
664 0 to 7 (inclusive). This word can be be used to index the
665 8 element vector \hs{RegisterState} above.
667 This type is translated to the \texttt{unsigned} \VHDL type.
669 \subsection{User-defined types}
670 There are three ways to define new types in Haskell: algebraic
671 data-types with the \hs{data} keyword, type synonyms with the \hs{type}
672 keyword and type renamings with the \hs{newtype} keyword. \GHC\
673 offers a few more advanced ways to introduce types (type families,
674 existential typing, {\small{GADT}}s, etc.) which are not standard
675 Haskell. These will be left outside the scope of this research.
677 Only an algebraic datatype declaration actually introduces a
678 completely new type, for which we provide the \VHDL\ translation
679 below. Type synonyms and renamings only define new names for
680 existing types (where synonyms are completely interchangeable and
681 renamings need explicit conversion). Therefore, these do not need
682 any particular \VHDL\ translation, a synonym or renamed type will
683 just use the same representation as the original type. The
684 distinction between a renaming and a synonym does no longer matter
685 in hardware and can be disregarded in the generated \VHDL.
687 For algebraic types, we can make the following distinction:
691 A product type is an algebraic datatype with a single constructor with
692 two or more fields, denoted in practice like (a,b), (a,b,c), etc. This
693 is essentially a way to pack a few values together in a record-like
694 structure. In fact, the built-in tuple types are just algebraic product
695 types (and are thus supported in exactly the same way).
697 The \quote{product} in its name refers to the collection of values
698 belonging to this type. The collection for a product type is the
699 Cartesian product of the collections for the types of its fields.
701 These types are translated to \VHDL\ record types, with one field for
702 every field in the constructor. This translation applies to all single
703 constructor algebraic data-types, including those with just one
704 field (which are technically not a product, but generate a VHDL
705 record for implementation simplicity).
706 \item[Enumerated types]
707 An enumerated type is an algebraic datatype with multiple constructors, but
708 none of them have fields. This is essentially a way to get an
709 enumeration-like type containing alternatives.
711 Note that Haskell's \hs{Bool} type is also defined as an
712 enumeration type, but we have a fixed translation for that.
714 These types are translated to \VHDL\ enumerations, with one value for
715 each constructor. This allows references to these constructors to be
716 translated to the corresponding enumeration value.
718 A sum type is an algebraic datatype with multiple constructors, where
719 the constructors have one or more fields. Technically, a type with
720 more than one field per constructor is a sum of products type, but
721 for our purposes this distinction does not really make a
722 difference, so this distinction is note made.
724 The \quote{sum} in its name refers again to the collection of values
725 belonging to this type. The collection for a sum type is the
726 union of the the collections for each of the constructors.
728 Sum types are currently not supported by the prototype, since there is
729 no obvious \VHDL\ alternative. They can easily be emulated, however, as
730 we will see from an example:
733 data Sum = A Bit Word | B Word
736 An obvious way to translate this would be to create an enumeration to
737 distinguish the constructors and then create a big record that
738 contains all the fields of all the constructors. This is the same
739 translation that would result from the following enumeration and
740 product type (using a tuple for clarity):
744 type Sum = (SumC, Bit, Word, Word)
747 Here, the \hs{SumC} type effectively signals which of the latter three
748 fields of the \hs{Sum} type are valid (the first two if \hs{A}, the
749 last one if \hs{B}), all the other ones have no useful value.
751 An obvious problem with this naive approach is the space usage: the
752 example above generates a fairly big \VHDL\ type. Since we can be
753 sure that the two \hs{Word}s in the \hs{Sum} type will never be valid
754 at the same time, this is a waste of space.
756 Obviously, duplication detection could be used to reuse a
757 particular field for another constructor, but this would only
758 partially solve the problem. If two fields would be, for
759 example, an array of 8 bits and an 8 bit unsigned word, these are
760 different types and could not be shared. However, in the final
761 hardware, both of these types would simply be 8 bit connections,
762 so we have a 100\% size increase by not sharing these.
766 A very important concept in hardware it the concept of state. In a
767 stateful design, the outputs depend on the history of the inputs, or the
768 state. State is usually stored in registers, which retain their value
769 during a clock cycle. As we want to describe more than simple
770 combinatorial designs, \CLaSH\ needs an abstraction mechanism for state.
772 \section{\CLaSH\ prototype}
776 \section{Related work}
777 Many functional hardware description languages have been developed over the
778 years. Early work includes such languages as $\mu$\acro{FP}~\cite{muFP}, an
779 extension of Backus' \acro{FP} language to synchronous streams, designed
780 particularly for describing and reasoning about regular circuits. The
781 Ruby~\cite{Ruby} language uses relations, instead of functions, to describe
782 circuits, and has a particular focus on layout. \acro{HML}~\cite{HML2} is a
783 hardware modeling language based on the strict functional language
784 \acro{ML}, and has support for polymorphic types and higher-order functions.
785 Published work suggests that there is no direct simulation support for
786 \acro{HML}, and that the translation to \VHDL\ is only partial.
788 Like this work, many functional hardware description languages have some sort
789 of foundation in the functional programming language Haskell.
790 Hawk~\cite{Hawk1} uses Haskell to describe system-level executable
791 specifications used to model the behavior of superscalar microprocessors. Hawk
792 specifications can be simulated, but there seems to be no support for
793 automated circuit synthesis. The ForSyDe~\cite{ForSyDe2} system uses Haskell
794 to specify abstract system models, which can (manually) be transformed into an
795 implementation model using semantic preserving transformations. ForSyDe has
796 several simulation and synthesis backends, though synthesis is restricted to
797 the synchronous subset of the ForSyDe language.
799 Lava~\cite{Lava} is a hardware description language that focuses on the
800 structural representation of hardware. Besides support for simulation and
801 circuit synthesis, Lava descriptions can be interfaced with formal method
802 tools for formal verification. Lava descriptions are actually circuit
803 generators when viewed from a synthesis viewpoint, in that the language
804 elements of Haskell, such as choice, can be used to guide the circuit
805 generation. If a developer wants to insert a choice element inside an actual
806 circuit he will have to specify this explicitly as a component. In this
807 respect \CLaSH\ differs from Lava, in that all the choice elements, such as
808 case-statements and patter matching, are synthesized to choice elements in the
809 eventual circuit. As such, richer control structures can both be specified and
810 synthesized in \CLaSH\ compared to any of the languages mentioned in this
813 The merits of polymorphic typing, combined with higher-order functions, are
814 now also recognized in the `main-stream' hardware description languages,
815 exemplified by the new \VHDL\ 2008 standard~\cite{VHDL2008}. \VHDL-2008 has
816 support to specify types as generics, thus allowing a developer to describe
817 polymorphic components. Note that those types still require an explicit
818 generic map, whereas type-inference and type-specialization are implicit in
821 Wired~\cite{Wired},, T-Ruby~\cite{T-Ruby}, Hydra~\cite{Hydra}.
823 A functional language designed specifically for hardware design is
824 $re{\mathit{FL}}^{ect}$~\cite{reFLect}, which draws experience from earlier
825 language called \acro{FL}~\cite{FL} to la
827 % An example of a floating figure using the graphicx package.
828 % Note that \label must occur AFTER (or within) \caption.
829 % For figures, \caption should occur after the \includegraphics.
830 % Note that IEEEtran v1.7 and later has special internal code that
831 % is designed to preserve the operation of \label within \caption
832 % even when the captionsoff option is in effect. However, because
833 % of issues like this, it may be the safest practice to put all your
834 % \label just after \caption rather than within \caption{}.
836 % Reminder: the "draftcls" or "draftclsnofoot", not "draft", class
837 % option should be used if it is desired that the figures are to be
838 % displayed while in draft mode.
842 %\includegraphics[width=2.5in]{myfigure}
843 % where an .eps filename suffix will be assumed under latex,
844 % and a .pdf suffix will be assumed for pdflatex; or what has been declared
845 % via \DeclareGraphicsExtensions.
846 %\caption{Simulation Results}
850 % Note that IEEE typically puts floats only at the top, even when this
851 % results in a large percentage of a column being occupied by floats.
854 % An example of a double column floating figure using two subfigures.
855 % (The subfig.sty package must be loaded for this to work.)
856 % The subfigure \label commands are set within each subfloat command, the
857 % \label for the overall figure must come after \caption.
858 % \hfil must be used as a separator to get equal spacing.
859 % The subfigure.sty package works much the same way, except \subfigure is
860 % used instead of \subfloat.
863 %\centerline{\subfloat[Case I]\includegraphics[width=2.5in]{subfigcase1}%
864 %\label{fig_first_case}}
866 %\subfloat[Case II]{\includegraphics[width=2.5in]{subfigcase2}%
867 %\label{fig_second_case}}}
868 %\caption{Simulation results}
872 % Note that often IEEE papers with subfigures do not employ subfigure
873 % captions (using the optional argument to \subfloat), but instead will
874 % reference/describe all of them (a), (b), etc., within the main caption.
877 % An example of a floating table. Note that, for IEEE style tables, the
878 % \caption command should come BEFORE the table. Table text will default to
879 % \footnotesize as IEEE normally uses this smaller font for tables.
880 % The \label must come after \caption as always.
883 %% increase table row spacing, adjust to taste
884 %\renewcommand{\arraystretch}{1.3}
885 % if using array.sty, it might be a good idea to tweak the value of
886 % \extrarowheight as needed to properly center the text within the cells
887 %\caption{An Example of a Table}
888 %\label{table_example}
890 %% Some packages, such as MDW tools, offer better commands for making tables
891 %% than the plain LaTeX2e tabular which is used here.
892 %\begin{tabular}{|c||c|}
902 % Note that IEEE does not put floats in the very first column - or typically
903 % anywhere on the first page for that matter. Also, in-text middle ("here")
904 % positioning is not used. Most IEEE journals/conferences use top floats
905 % exclusively. Note that, LaTeX2e, unlike IEEE journals/conferences, places
906 % footnotes above bottom floats. This can be corrected via the \fnbelowfloat
907 % command of the stfloats package.
912 The conclusion goes here.
917 % conference papers do not normally have an appendix
920 % use section* for acknowledgement
921 \section*{Acknowledgment}
924 The authors would like to thank...
930 % trigger a \newpage just before the given reference
931 % number - used to balance the columns on the last page
932 % adjust value as needed - may need to be readjusted if
933 % the document is modified later
934 %\IEEEtriggeratref{8}
935 % The "triggered" command can be changed if desired:
936 %\IEEEtriggercmd{\enlargethispage{-5in}}
940 % can use a bibliography generated by BibTeX as a .bbl file
941 % BibTeX documentation can be easily obtained at:
942 % http://www.ctan.org/tex-archive/biblio/bibtex/contrib/doc/
943 % The IEEEtran BibTeX style support page is at:
944 % http://www.michaelshell.org/tex/ieeetran/bibtex/
945 \bibliographystyle{IEEEtran}
946 % argument is your BibTeX string definitions and bibliography database(s)
947 \bibliography{IEEEabrv,clash.bib}
949 % <OR> manually copy in the resultant .bbl file
950 % set second argument of \begin to the number of references
951 % (used to reserve space for the reference number labels box)
952 % \begin{thebibliography}{1}
954 % \bibitem{IEEEhowto:kopka}
955 % H.~Kopka and P.~W. Daly, \emph{A Guide to \LaTeX}, 3rd~ed.\hskip 1em plus
956 % 0.5em minus 0.4em\relax Harlow, England: Addison-Wesley, 1999.
958 % \end{thebibliography}
966 % vim: set ai sw=2 sts=2 expandtab: