47 lines
2.4 KiB
TeX
47 lines
2.4 KiB
TeX
\chapter{Overview}
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This is an attempt to distill what I know about how computers work into some kind of emulator / simulator. I'm curious to see if what I know at the moment is enough to allow me to emulate a general purpose computer. A computer that will be big-endian, using 8-bit bytes for its char type. The memory is a 32 bit linear address space allowing for a maximum of 2\textsuperscript{32} bytes to be addressable.
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\section{Registers}
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Eight 32-bit general purpose registers are available for holding operands and memory addresses along with a Flags Register. The Flags Register is a 32-bit register allowing for 32 flags. Currently there are only arithmetic flags which are Overflow (OF), Underflow (UF), and a Zero Flag (ZF). The overflow flag is set if there is a carry. A base pointer register contains a 32 bit address that points to the start of the current stack frame, which is the first opcode of the stack frame. Therefore the first argument would be addressed as such:
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\begin{verbatim}
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mov r1, bp - sizeof(void *)
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\end{verbatim}
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Finally we have the Program Counter which contains a 32 bit address that points to the next instruction to execute.
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\def\minY{-5} \def\maxY{5}
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\def\minX{-5} \def\maxX{5}
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\begin{figure}[ht]
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\centering
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\begin{tikzpicture}[node distance=0cm]
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\node [draw, fit={(\minX, 1.0) (0, 1.5)}, label=center:Program Counter] (pc) {};
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\node [draw, fit={(\minX, 0) (0, 0.5)}, label=center:Flags] (flags) {};
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\node [draw, fit={(\minX, -1) (0, -1.5)}, label=center:r1] (r1) {};
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\node [draw, fit={(\maxX / 2, 0) (\maxX, \minY)}, label=center:Memory] (memory) {};
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\draw (pc);
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\node[above =of pc] {Status Registers};
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\node[above left =of pc] {31};
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\node[above right =of pc] {0};
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\draw (flags);
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\draw (r1);
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\node[above =of r1] {General Purpose Registers};
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\node[above left =of r1] {31};
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\node[above right =of r1] {0};
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\foreach \pos in {2,...,8} {
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\node [draw, fit={(\minX, -\pos) (0, -\pos - 0.5)}, label=center:r\pos] (r\pos) {};
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\draw (r\pos);
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}
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\draw (memory);
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\node [above =of memory] {Linear Memory (2\textsuperscript{32} Bytes)};
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\node [above right =of memory, yshift=-1em] {0};
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\node [below right =of memory, yshift=1em] {2\textsuperscript{32 - 1}};
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%\draw (memory.north east) -- (memory.south west);
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%\node at (memory.south east) {test};
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\end{tikzpicture}
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\caption{Register Bit Layout}
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\end{figure}
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\section{Memory Layout} |