aboutsummaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--DigDes.tex7
-rw-r--r--build/DigDes.pdfbin89638 -> 102338 bytes
-rw-r--r--tex/docmacros.sty7
-rw-r--r--tex/statemachines.tex12
-rw-r--r--tex/testbench.tex99
-rw-r--r--tex/vhdl.tex15
6 files changed, 120 insertions, 20 deletions
diff --git a/DigDes.tex b/DigDes.tex
index b9033fe..2a4dcec 100644
--- a/DigDes.tex
+++ b/DigDes.tex
@@ -10,6 +10,7 @@
%% TODO: publish to CTAN
\usepackage{tex/hsrstud}
+\usepackage{tex/docmacros}
%% Language configuration
\usepackage{polyglossia}
@@ -72,11 +73,11 @@
% \newpage
\twocolumn
-\section{Development model and Hardware}
+\section{Development model}
+\section{Hardware}
\input{tex/vhdl}
\input{tex/statemachines}
-
-\section{Testbench}
+\input{tex/testbench}
\end{document}
diff --git a/build/DigDes.pdf b/build/DigDes.pdf
index 2b23d7c..916f9ae 100644
--- a/build/DigDes.pdf
+++ b/build/DigDes.pdf
Binary files differ
diff --git a/tex/docmacros.sty b/tex/docmacros.sty
new file mode 100644
index 0000000..9fc0325
--- /dev/null
+++ b/tex/docmacros.sty
@@ -0,0 +1,7 @@
+\NeedsTeXFormat{LaTeX2e}
+\ProvidesPackage{docmacros}[2021/05/22 v0.1 Document Macros]
+
+\newcommand{\ph}[1]{\textrm{\textit{#1}}}
+\newcommand{\reqph}[1]{\textrm{\textlangle\,\ph{#1}\,\textrangle}}
+\newcommand{\optionalph}[1]{\textrm{[\,\ph{#1}\,]}}
+\newcommand{\vhdl}[1]{\lstinline[language=vhdl]{#1}}
diff --git a/tex/statemachines.tex b/tex/statemachines.tex
index 9fb47e2..967737b 100644
--- a/tex/statemachines.tex
+++ b/tex/statemachines.tex
@@ -1,5 +1,4 @@
\section{State Machines}
-There are 3 types of state machines.
\begin{figure}[h]
\centering
\ttfamily
@@ -65,21 +64,20 @@ There are 3 types of state machines.
\end{figure}
\subsection{Encoding the state}
-This is typical for Mealey and Moore machines.
+For Mealey and Moore machines it is typical to write:
\begin{lstlisting}[language=vhdl]
type state_type is (st_rst, st_a, st_b, st_c, ...);
signal present_state, next_state : state_type;
\end{lstlisting}
-The encoding of the state is left automatically to the synthesizer or
-configured in the graphical interface of the tool. If a custom encoding is
-required (Medwedjew), adding the following generates a custom encoding.
+The encoding of the state is left to the synthesizer or can be configured in
+the graphical interface of the tool. If a custom encoding is required
+(Medwedjew), adding the following generates a custom encoding.
\begin{lstlisting}[language=vhdl]
attribute enum_encoding : string;
attribute enum_encoding of state_type:
type is "0001 0010 0100 ...";
\end{lstlisting}
-
-Or alternatively a completely different approach is using a vector type.
+Or an equivalent approach is to use a vector subtype and constants.
\begin{lstlisting}[language=vhdl]
subtype state_type is bit_vector(3 downto 0);
diff --git a/tex/testbench.tex b/tex/testbench.tex
new file mode 100644
index 0000000..b555feb
--- /dev/null
+++ b/tex/testbench.tex
@@ -0,0 +1,99 @@
+\section{Testing}
+To simulate a digial circuit it is possible to write test benches using VHDL.
+The code in this section may no longer be synthetisable, and is usually
+written by a \emph{test designer}.
+
+\subsection{Simulator}
+VHDL simulates digital systems using \emph{delta cycles}.
+%% TODO: notes on how delta cycles work
+
+\subsection{Transport delay}
+To model a time delay of a signal there are two ways:
+\begin{lstlisting}[language=vhdl]
+y <= transport `\reqph{expression}` after `\reqph{time}`;
+y <= inertial `\reqph{expression}` after `\reqph{time}`;
+\end{lstlisting}
+When \vhdl{transport} is used, the output changes only exactly after the
+specified time, the simulator simply waits. With \vhdl{inertial}, the output is
+also delayed, but only if the input lasts more than the specified time. This
+means that for example with a time of \vhdl{10 ns} a pulse of \vhdl{5 ns} will
+be ignored. This is much more typical and realistic, thus when unspecified,
+\vhdl{after} is interpreted as \vhdl{inertial ... after}.
+\begin{lstlisting}[language=vhdl]
+y <= `\reqph{expression}` after `\reqph{time}`;
+\end{lstlisting}
+
+\subsection{Generate stimuli}
+Simple stimuli (signals) are generated using processes. For example a clock
+signal done in three ways:
+\begin{lstlisting}[language=vhdl]
+-- declaration
+constant f : integer := 1000;
+constant T : time := 1 sec/f;
+signal clk0, clk1, clk2 : std_ulogic;
+\end{lstlisting}
+\begin{lstlisting}[language=vhdl]
+-- concurrent
+clock0: process
+begin
+ clk <= '1'; wait for (T/2);
+ clk <= '0'; wait for (T/2);
+end process;
+
+clock1: process
+begin
+ clk1 <= '1';
+ loop
+ wait for (T/2);
+ clk1 <= not clk1;
+ end loop;
+end process;
+
+-- lazy way
+clock2: clk2 <= not clk2 after (T/2);
+\end{lstlisting}
+One time stimuli can be modelled using the following expression. Note that the
+time is absolute.
+\begin{lstlisting}[language=vhdl]
+tb_sig <= '0',
+ '1' after 20 ns,
+ '0' after 30 ns, -- 10 ns later
+ `\reqph{value}` after `\reqph{time}`;
+\end{lstlisting}
+Repeating sequences can be created using processes.
+\begin{lstlisting}[language=vhdl]
+sequence: process
+begin
+ tb_sig <= '0';
+ wait for 20 ns;
+ tb_sig <= '1';
+ wait for 10 ns;
+ ...
+end process;
+\end{lstlisting}
+For loops are also available, and can be synthesised if they run over a finite
+range.
+\begin{lstlisting}[language=vhdl]
+`\optionalph{label}:` for `\reqph{parameter}` in `\reqph{range}` loop
+ -- sequentail statements
+end loop `\optionalph{label}`;
+\end{lstlisting}
+A concrete example:
+\begin{lstlisting}[language=vhdl]
+-- declaration
+constant n : integer := 3;
+signal a, b : std_ulogic_vector(n-1 downto 0);
+\end{lstlisting}
+\begin{lstlisting}[language=vhdl]
+-- sequential
+for i in 0 to 2**n -1 loop
+ a <= std_ulogic_vector(
+ to_unsigned(i, n));
+ for k in 0 to 2**n - 1 loop
+ b <= std_ulogic_vector(
+ to_unsigned(k, n));
+ end loop;
+end loop;
+\end{lstlisting}
+
+\subsection{Assertions}
diff --git a/tex/vhdl.tex b/tex/vhdl.tex
index e51b357..4674f4a 100644
--- a/tex/vhdl.tex
+++ b/tex/vhdl.tex
@@ -4,12 +4,6 @@
% Hardware Description Language
}
-\newcommand{\ph}[1]{\textrm{\textit{#1}}}
-\newcommand{\reqph}[1]{\textrm{\textlangle\,\ph{#1}\,\textrangle}}
-\newcommand{\optionalph}[1]{\textrm{[\,\ph{#1}\,]}}
-
-\newcommand{\vhdl}[1]{\lstinline[language=vhdl]{#1}}
-
\subsection{Basic syntax and identifiers}
In VHDL an identifier is a case insensitive string composed of
\texttt{A-Z a-z 0-9 \_} that
@@ -67,9 +61,10 @@ an \emph{architecture}. There can be multiple architectures for a single entity.
\end{center}
Entities are declared with \vhdl{port()} that may contain a list of pins. Pins
-have a mode that can be \vhdl{in} input (only LHS), \vhdl{out} output (only
-RHS), \vhdl{inout} bidirectional or \vhdl{buffer} that can stay both on LHS and
-RHS. The usage of the latter is discourareged in favour of an internal signal.
+have a mode that can be \vhdl{in} input (only LHS\footnote{Left hand side}),
+\vhdl{out} output (only RHS\footnote{Right hand side}), \vhdl{inout}
+bidirectional or \vhdl{buffer} that can stay both on LHS and RHS. The usage of
+the latter is discourareged in favour of an internal signal.
\begin{lstlisting}[language=vhdl]
entity `\reqph{name}` is
port(
@@ -291,7 +286,7 @@ u1: flipflop
\subsubsection{Processes}
For more sophisticated logic VHDL offers a way of writing sequential statements
-called \emph{processes}.
+called \emph{process}.
\begin{lstlisting}[language=vhdl]
`\optionalph{label}:` process (`\optionalph{sensitivity list}`)
-- declarations