system.tex

\begin{tikzpicture}[>=latex]
  \tikzset{
    pics/cpu/.style n args={3}{
      code = {
        \draw node (#2) [draw,thick,rectangle,minimum height=1cm,
              minimum width=2cm,#3] at (0.5,1) {#1};
        \draw (0,0) node [draw,thick,rectangle,minimum height=1cm,minimum width=1cm] {ROM};
        \draw (1,0) node [draw,thick,rectangle,minimum height=1cm,minimum width=1cm] {RAM};
      }
    }
  }

  \tikzstyle{dev}=[rounded rectangle,thick, draw, minimum width=2.5cm,
    minimum height=1cm, align=left];
  \tikzstyle{edge}=[thick,->];
  \tikzstyle{dedge}=[thick,<->];
  \tikzstyle{border}=[dotted,thick]
  \tikzstyle{boxed}=[draw,thick]

  \pic at (0,0) {cpu={CPU 2}{C2}{fill=red!10}};
  \pic at (5,0) {cpu={CPU 1}{C1}{fill=blue!10}};
  \pic at (11,0) {cpu={CPU 0}{C0}{fill=green!10}};

  \draw [border] (2.5,-2.5) -- (2.5,4);
  \draw [border] (8.5,-2.5) -- (8.5,4);

  \draw node (button) [dev] at (4,2.5) {Yes/No \\ button};
  \draw node (display) [dev] at (7,2.5) {Display};

  \draw [edge] ($(C1.north east)+(-0.25,0)$) -- (display.south);
  \draw [edge] (button.south) -- ($(C1.north west)+(0.25,0)$);

  \draw node (reset) [dev] at (10,2.5) {Reset\\button};
  \draw node (led) [dev] at (13,2.5) {User/SYS\\indicator};

  \draw [edge] (reset.south) -- ($(C0.north west)+(0.25,0)$);
  \draw [edge] ($(C0.north east)+(-0.25,0)$) -- (led.south);

  \draw node (flash) [dev] at (15,1) {Flash};
  \draw [dedge] (C0.east) -- (flash.west);

  \draw [dedge] ($(C0.north west)+(0.0,-0.25)$) -- node[above] {UART} ($(C1.north east)+(0.0,-0.25)$);
  \draw [dedge] ($(C1.north west)+(0.0,-0.25)$) -- node[above] {UART} ($(C2.north east)+(0.0,-0.25)$);

  \draw [dedge] (C2.west) -- node[above] {USB} ($(C2.west)+(-2,0)$);

  \draw [edge] (C0.west) to [bend left] node[below] {Reset} (C1.east);
  \draw [edge] (C0.west) to [bend left=50] node[above] {Reset} (C2.east);
  \draw [edge] (C0.south west) to [bend left=50] node[below] {UART
    (One-way)} (C2.south east);

  \draw [boxed] (-1,-2.5) rectangle (16.5,4);

  \draw node at (1, 3.5) {\textbf{Comm domain}};
  \draw node at (6, 3.5) {\textbf{Agent domain}};
  \draw node at (12, 3.5) {\textbf{Kernel domain}};

\end{tikzpicture}