Hacking the Xbox

APPENDIX D
Getting Started
with FPGAs
Integration is the bane of hardware hackers. We like to take things apart,
modify them, and improve them, but the trend has been to cram everything
into one or two ASICs (Application Specific Integrated Circuit).
This kind of integration is out of the reach of mere mortals, as the cost
of a set of masks used for defining the features on chips is rapidly
approaching one million dollars. That’s one million dollars per unique
revision of the chip. If a mistake is made that requires a new mask set, you
have to spend yet another million dollars to fix it.
Fortunately, a million dollars cash upfront for a chip is too much even for
many corporations, and this has created a market for FPGAs — generalpurpose,
programmable (“reconfigurable”) hardware devices that can be
used in place of an ASIC in many applications.
What Is an FPGA?
FPGA stands for field programmable gate array. In other words, it is an
array of gates that can be programmed in the field by end users. You can
think of FPGAs as custom silicon that you can build in the comfort of
your own home, although the trend toward partial reconfigurability and
context-sensitive reconfiguration adds a dimension to FPGAs that is not
found in ASICs. While ASICs are cheaper per unit in volume, and they
can have much higher clock speed performance, FPGAs have established
themselves as the tool of choice for low to moderate volume applications
and for prototyping.
The FPGA’s basic architecture is that of an array of hardware primitives
embedded in a flexible routing network. The power of the FPGA comes
from the fact that complex computations can be broken down into a