\chapter[chap:introduction]{Introduction}
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.
+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 simple functional program shown in
- \in{example}[ex:AndWord]\footnote[notfinalsyntax]{Note that this example is not in the final
+ \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.
% Draw a dotted line between the middle operations
ncline(a2)(a3) "linestyle(dashed withdots)", "arrows(-)";
\stopuseMPgraphic
- \placeexample[here][ex:AndWord]{Simple architecture that inverts a vector of bits.}
+ \placeexample[][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].
+ values shown 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
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
+ 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]
\startuseMPgraphic{RecursiveSumAlt}
\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
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
+ 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.
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).
+
+ Cλash is pronounced like \quote{Clash}.
\stopframedtext
}
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.
-Chapter two describes the exploratory part of this research: How can we
+Chapter two describes the exploratory part of this research: how can we
describe hardware using a functional language and how can we use functional
concepts for hardware descriptions?
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