% -*- Mode:Text -*-

 \chapter{System organization}\label{sect.sys}

A complete \cam\ system consists of a three-dimensional array of \cam\
{\em boxes} driven by a {\em host} via a tree-shaped network
called the {\em \bus}, as sketched in \fig{cam-system} (where only two
dimensions of the array are shown).
	\figonegiven{cam-system}{\psfig{file=fig/cam-system.ps}}{A \cam\ system
consists of an array of \cam\ boxes ({\em \cam\ machine}) driven
by a \sparcstation\ ({\em host\/}). The {\em \cam\ controller} interfaces the
host's Sbus with the machine's \bus.}

\noindent In the current implementation, the host is a \sun\ \sparcstation,
which features a high-performance external bus called the \sbus.  The
\bus\ is driven at the root by the \bus\ {\em controller}---a small
custom board plugged into one of the \sbus\ slots. From this board, a
short cable---which represents the \bus\ trunk---leads
directly to one of the boxes, located on a corner of the array. From
this {\em corner box} the \bus\ branches out through the rest of the array.
We shall call \cam\ {\em machine} the interconnected array of \cam\ boxes,
when viewed as distinct from the host and the \cam\ controller.

Besides implementing, by means of eight separate printed-circuit
boards called {\em modules}, a functional {\em block} of eight sectors
(see \chapt{block}), a box provides mechanical and electrical support
to the modules themselves (motherboard, enclosure, power supply and
cooling), as well as \bus\ routing and buffering and some other
support circuitry.

In turn, each module contains, besides conventional \dram\ and \sram\
chips, sixteen copies of the {\em \chip}---a custom {\sc vlsi} chip
that one may view as embodying the \cam\ architecture. In fact, each
\chip\ has complete control over one \dram\ chip's data and
control lines; and, collectively, the sixteen \chip{}s have complete
control over the \sram\ chips' data and control lines---as well as
over transactions over the \bus. Thus, the \chip{}s repesent the
``glue'' that turns plain electronic commodities into sophisticated
computing resources.

\medskip

The present Part II discusses the \cam\
system at four levels of the design hierarchy, namely,
 \begin{enumerate}
	\item the \cam\ machine with its controller,
	\item the \cam\ box,
	\item the \cam\ module, and
	\item the \chip.
 \end{enumerate}
	For each level, detailed interface specifications
(pinout and signal description) with the level above it are given.

Part III describes in detail the internals of the \chip.

\medskip

One may view the host \sparcstation\ as representing a further Level 0.  Its
relevant hardware and system-software aspects are documented by \sun\
Microsystems.  \Cam\ specific software is documented in the \cam\ {\em
Programmer's guide} and {\em User's guide}.

