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Added some information about the memory layout and a figure for the bit ordering in the registers.

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glm94
2025-02-03 23:12:00 -06:00
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chapter 1.tex
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@@ -3,6 +3,43 @@ This is an attempt to distill what I know about how computers work into some kin
\section{Registers}
Thirty-two general purpose registers are available for program code to use however it wishes. The base name for the general purpose registers is \quotes{r} follows by an unpadded number, such as \quotes{r28}. These numbers do not follow a zero-based index scheme, \quotes{r29} is the twenty-ninth register. Using the base name implies full width, a \quotes{word}, when reading or writing from or to the register respectively. In addition to the general purpose registers there is also a base pointer (bp), stack pointer (sp) and an instruction pointer (ip). The base pointer and the stack pointer may be set directly using the \hyperref[sec:mov]{mov} instruction, which allows the programmer to set up a stack frame. The instruction pointer can only be set with a branching operation like \hyperref[sec:jmp]{jmp} or a call to a subroutine with the \hyperref[sec:call]{call} instruction.
\begin{figure}[h]
\begin{tikzpicture}
%\draw[help lines] (-8,-3) grid (8,3);
\node [draw, fit={(-6, 0) (-1, -0.5)}, label=center:r1] (r1) {};
\node [draw=none, fit={(-6, -1) (-1, -1.5)}, label=center:...] (ellipsis) {};
\node [draw, fit={(-6, -2) (-1, -2.5)}, label=center:r32] (r32) {};
\node [draw, fit={(-3.0, 1.5) (2.0, 1.0)}, label=center:Flags Register] (flags) {};
\node [draw, fit={(0, 0) (5, -0.5)}, label=center:Instruction Pointer (ip)] (ip) {};
\node [draw, fit={(0, -1.0) (5, -1.5)}, label=center:Base Pointer (ip)] (bp) {};
\node [draw, fit={(0, -2.0) (5, -2.5)}, label=center:Stack Pointer (ip)] (sp) {};
\draw (r1);
\node at (r1.north) [above] {General Purpose};
\node at (r1.north west) [above] {31};
\node at (r1.north east) [above] {0};
\draw (ellipsis);
\draw (r32);
\draw (flags);
\node at (flags.north) [above] {Status Register};
\node at (flags.north west) [above] {31};
\node at (flags.north east) [above] {0};
\draw (ip);
\node at (ip.north) [above] {Program Status};
\node at (ip.north west) [above] {31};
\node at (ip.north east) [above] {0};
\draw (bp);
\draw (sp);
\end{tikzpicture}
\caption{Bit Ordering}
\label{fig:registerbitlayout} % https://www.overleaf.com/learn/latex/Referencing_Figures
\end{figure}
\begin{description}
\item In summary, the available registers are as follows:
\item[General Purpose] Thirty-two general purpose registers that are the width of a \textit{word} and numbered \quotes{r1} through \quotes{r32}
@@ -12,3 +49,4 @@ Thirty-two general purpose registers are available for program code to use howev
\end{description}
\section{Memory}
The memory layout is quite simple, much like many modern machines it is a linear memory map. The address bus is thrity-two bits wide, the same width of the data bus, meaning at most there is 2\textsuperscript{32} of addressable memory. Like contemprary machines the top of memory starts at address 0x00000000 and grows downward toward 0xFFFFFFFF.