\chapter[chap:introduction]{Introduction}
-\fixme{No chapter number?}
This thesis describes the result and process of my work during my
-Master's assignment. In these pages, I will try to introduce the world
+Master's assignment. In these pages, I will introduce the world
of hardware descriptions, the world of functional languages and
compilers and introduce the hardware description language Cλash that will
connect these worlds and puts a step towards making hardware programming
on the whole easier, more maintainable and generally more pleasant.
-\section{Research goals}
+This assignment has been performed in close cooperation with Christiaan
+Baaij, whose Master's thesis \cite[baaij09] has been completed at the
+same time as this thesis. Where this thesis focuses on the
+interpretation of the Haskell language and the compilation process,
+\cite[baaij09] has a more thorough study of the field, explores more
+advanced types and provides a case study.
+
+% Use \subject to hide this section from the toc
+\subject{Research goals}
This research started out with the notion that a functional program is very
easy to interpret as a hardware description. A functional program typically
- does no assumptions about evaluation order and does not have any side
+ makes no assumptions about evaluation order and does not have any side
effects. This fits hardware nicely, since the evaluation order for hardware
is simply everything in parallel.
- As a motivating example, consider the following simple functional
- program:\footnote[notfinalsyntax]{Note that this example is not in the final
- Cλash syntax}
-
-\starttyping
-notword :: [Bit] -> [Bit]
-notword = map not
-\stoptyping
+ As a motivating example, consider the simple functional program shown in
+ \in{example}[ex:AndWord]\footnote[notfinalsyntax]{This example is not in the final
+ Cλash syntax}. This is a very natural way to describe a lot of parallel not
+ ports, that perform a bitwise not on a bitvector. The example also shows an
+ image of the architecture described.
- This is a very natural way to describe a lot of parallel not ports, that
- perform a bitwise not on a bitvector. The architecture described would look
- like the following:
+ \startbuffer[AndWord]
+ notword :: [Bit] -> [Bit]
+ notword = map not
+ \stopbuffer
\startuseMPgraphic{AndWord}
% Create objects
% Draw a dotted line between the middle operations
ncline(a2)(a3) "linestyle(dashed withdots)", "arrows(-)";
\stopuseMPgraphic
- \useMPgraphic{AndWord}
- \todo{Float graphic?}
-
- Slightly more complicated is the following incremental summation of
- values:\note[notfinalsyntax]
-
-\starttyping
-sum :: [Int] -> [Int]
-sum = sum' 0
-
-sum' :: Int -> [Int] -> [Int]
-sum' acc [] = []
-sum' acc (x:xs) = acc' : (sum' acc' xs)
- where acc' = x + acc
-\stoptyping
-
- Here we see a recursive function \hs{sum'} that recurses over a list and
- takes an accumulator argument that stores the sum so far. On each step of
- the recusion, another number from the input vector is added to the
+ \placeexample[here][ex:AndWord]{Simple architecture that inverts a vector of bits.}
+ \startcombination[2*1]
+ {\typebufferlam{AndWord}}{Haskell description of the architecture.}
+ {\boxedgraphic{AndWord}}{The architecture described by the Haskell description.}
+ \stopcombination
+
+ Slightly more complicated is the incremental summation of
+ values show in \in{example}[ex:RecursiveSum]\note[notfinalsyntax].
+
+ In this example we see a recursive function \hs{sum'} that recurses over a
+ list and takes an accumulator argument that stores the sum so far. On each
+ step of the recusion, another number from the input vector is added to the
accumulator and each intermediate step returns its result.
- So, this is a nice description of a series of sequential adders that produce
+ This is a nice description of a series of sequential adders that produce
the incremental sums of a vector of numbers. For an input list of length 4,
- this is the corresponding architecture:
+ the corresponding architecture is show in the example.
+
+ \startbuffer[RecursiveSum]
+ sum :: [Int] -> [Int]
+ sum = sum' 0
- \startMPcode
+ sum' :: Int -> [Int] -> [Int]
+ sum' acc [] = []
+ sum' acc (x:xs) = acc' : (sum' acc' xs)
+ where acc' = x + acc
+ \stopbuffer
+
+ \startuseMPgraphic{RecursiveSum}
save inp, a, zero, out;
% Create objects
newCircle.inp(btex $\overrightarrow{input}$ etex) "framed(false)";
ncline(a3)(a4);
ncline(a4)(out);
drawObj(out);
- \stopMPcode
+ \stopuseMPgraphic
+
+ \placeexample[here][ex:RecursiveSum]{A recursive description that sums values.}
+ \startcombination[2*1]
+ {\typebufferlam{RecursiveSum}}{Haskell description of the architecture.}
+ {\boxedgraphic{RecursiveSum}}{The architecture described by the Haskell description.}
+ \stopcombination
+
Or... is this the description of a single accumulating adder, that will add
- one element of each input each clock cycle and has a reset value of 0? In
- that case, we would have described this architecture:
+ one element of each input each clock cycle and has a reset value of
+ {\definedfont[Serif*normalnum]0}? In
+ that case, we would have described the architecture show in \in{example}[ex:RecursiveSumAlt]
- \startMPcode
+ \startuseMPgraphic{RecursiveSumAlt}
save reg, inp, a, out;
newReg.reg("") "dx(4mm)", "dy(6mm)", "reflect(true)";
newCircle.inp(btex $input$ etex) "framed(false)";
% reg.out to a
nccurve(reg)(a) "posA(out)", "angleA(180)", "angleB(-30)";
ncline(a)(out);
- \stopMPcode
+ \stopuseMPgraphic
+
+ \placeexample[here][ex:RecursiveSumAlt]{An alternative interpretation of the description in \in{example}[ex:RecursiveSum]}
+ {\boxedgraphic{RecursiveSumAlt}}
The distinction in possible interpretations we see here, is an important
distinction in this research. In the first figure, the recursion in the code
efficient way to describe hardware.
This leads us to the following research question:
- \todo{Include Haskell in questions?}
% Slightly bigger font, some extra spacing.
\setupquotation[style=tfb,spacebefore=5mm]
\startitemize
\item How to interpret recursion in descriptions?
\item How to interpret polymorphism?
- \item How to interpret higher order descriptions?
+ \item How to interpret higher-order descriptions?
\stopitemize
- \todo{Introduce Cλash?}
-
In addition to looking at designing a hardware description language, we
- will also implement a prototype to test drive our ideas. This prototype will
+ will also implement a prototype to test ideas. This prototype will
translate hardware descriptions written in the Haskell functional language
to simple (netlist-like) hardware descriptions in the \VHDL language. The
reasons for choosing these languages are detailed in section
\in{}[sec:prototype:input] and \in{}[sec:prototype:output] respectively.
-\section{Outline}
-
-\fxnote{This section needs updating}
+ \placeintermezzo{}{
+ \startframedtext[width=8cm,background=box,frame=no]
+ \startalignment[center]
+ {\tfa The name Cλash}
+ \stopalignment
+ \blank[medium]
+ The name Cλash more-or-less expands to CAES language for hardware
+ descriptions, where CAES refers to the research chair where this
+ project was undertaken (Computer Architectures for Embedded
+ Systems). The lambda in the name is of course a reference to the
+ lambda abstraction, which is an essential element of most functional
+ languages (and is also prominent in the Haskell logo).
+ \stopframedtext
+ }
+
+ The result of this research will thus be a prototype compiler and a language
+ that it can compile, to which we will refer to as the Cλash system and Cλash
+ language for short, or simply Cλash.
+
+% Use \subject to hide this section from the toc
+\subject{Outline}
In the first chapter, we will sketch the context for this research.
The current state and history of hardware description languages will be
briefly discussed, as well as the state and history of functional
-programming. Since we're not the first to have merged these approaches,
+programming. Since we are not the first to have merged these approaches,
a number of other functional hardware description languages are briefly
described.
of the hardware description proved non-scalable. These transformations and
their application are the subject of the fourth chapter.
-The final chapter sketches ideas for further research, which are many. Some of
+The next chapter sketches ideas for further research, which are many. Some of
them have seen some initial exploration and could provide a basis for future
work in this area.
+
+Finally, we present our conclusions.
+
+% vim: set sw=2 sts=2 expandtab:
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