I’m currently working on some embedded systems stuff. For the documentation (written in LaTeX, of course!) I was searching for a convenient way to draw memory maps. The creation of external images using LaTeX Draw (which I like) was not a good option, as I wanted to change my memory maps in a source file and propagate the change with a single ‚typeset‘ command.

I wanted to share my solution, as I found nothing there (as a matter of fact, nobody seems to draw memory maps, which means that a lot of documentation is missing them ;__;). I use the real handy ‚bytefield‘ package (maybe the way to go for documenting registers) which is quite lightweight and convenient to use. This is an example of a basic bytefield definition:

\begin{bytefield}{32}
	\bitheader[b]{0,7,8,15,16,23,24,31}\\
	\bitbox{8}{Byte 3} \bitbox{8}{Byte 2}
	\bitbox{8}{Byte 1} \bitbox{8}{Byte 0}
\end{bytefield}

This code snipplet looks like this when typeset:

However, the supported examples made clear, that the creation of memory mappings was not the main use for this package: Memory sections have to be uniform in height. This make a memory layout much less meaningful: I wanted to state the height of every memory section independently. As a solution I hacked a real ugly new latex command \memsection which will make a LaTeX guru cry but does the job quite well. The command takes the end address, the start address, the height of the section (in lines) an a caption as its parameters. The following example shows the command in use:

\begin{bytefield}{24}
	\memsection{ffff ffff}{0040 0000}{15}{-- free --}\\
	\begin{rightwordgroup}{internal memory}
		\memsection{003f ffff}{002f c000}{4}{Special Function Registers}\\
		\memsection{002f bfff}{0007 0000}{3}{-- reseved --}\\
		\memsection{0006 ffff}{0000 0000}{8}{Internal Flash}
	\end{rightwordgroup}\\
\end{bytefield}

When typeset, it looks like this:

Note that the addresses get print with a leading ‚0x‘ and in uppercase. Note also, that the location of newlines (\\) is critcal! This is the implementation of the command:

% facilitates the creation of memory maps. Start address at the bottom, end address at the top.
% Addresses will be print with a leading '0x' and in upper case.
% syntax: \memsection{end address}{start address}{height in lines}{text in box}
\newcommand{\memsection}[4]{
	\bytefieldsetup{bitheight=#3\baselineskip}	% define the height of the memsection
	\bitbox[]{8}{
		\texttt{0x\uppercase{#1}}	 % print end address
		\\ \vspace{#3\baselineskip} \vspace{-2\baselineskip} \vspace{-#3pt} % do some spacing
		\texttt{0x\uppercase{#2}} % print start address
	}
	\bitbox{16}{#4} % print box with caption
}

What’s still missing? I would like to have a symbol to indicate skipped words in really long sections as provided with bytefields \skippedwords command. However, implementing this needs more than my current LaTeX skills.

Update:

I just removed the automatic prefix ‚0x‘ and \uppercase for addresses. That way one can create blank memory sections without any addresses: This can help make crowded layouts more readable:

Updated LaTeX command:

% facilitates the creation of memory maps. Start address at the bottom, end address at the top.
% syntax: \memsection{end address}{start address}{height in lines}{text in box}
\newcommand{\memsection}[4]{
\bytefieldsetup{bitheight=#3\baselineskip}    % define the height of the memsection
\bitbox[]{10}{
\texttt{#1}     % print end address
\\ \vspace{#3\baselineskip} \vspace{-2\baselineskip} \vspace{-#3pt} % do some spacing
\texttt{#2} % print start address
}
\bitbox{16}{#4} % print box with caption
}

Update #2: Fixed the width of the bitbox in the updated command from 8 to 10.

Feel free to share your ideas and/or solutions in the comments!