Hacking the Xbox

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Hacking the Xbox: An Introduction to Reverse Engineering
FPGAs before taping out the final silicon. A side benefit from this
approach is that the software and hardware teams that are users of the
custom silicon can begin validating their designs using the FPGA mockup
while the custom silicon is being fabricated; a process that can
sometimes take a couple of months.
For hackers, FPGAs are sort of a panacea for all kinds of complex
projects. They are excellent choices for implementing cryptographic
functions if you are interested in doing brute-force keysearches or
encrypting large amounts of data quickly. They are also very useful for
implementing signal processing functions, especially given the existence
of free multiplier and digital filter cores. FPGAs can achieve higher
performance for less power than a DSP, and thus they have a unique
niche in applications such as battery-powered robotics. FPGAs are also
useful for embedded controller applications: A small microprocessor
core, equivalent to or better than a PIC, can easily fit in an FPGA today.
Add all your custom hardware peripherals, such as a serial port and
PWM timing generators, and you’re in business.
FPGAs are also useful in situations where the focus is not on big number
crunching. An FPGA makes a great piece of glue logic in a tight spot,
and well-placed FPGA can save you from having to ever add a wire
jumper to patch a board due to a logic design error. FPGAs also make a
cheap logic analyzer alternative for those of us who cannot afford a
$10,000 Tek TLA mainframe. The high-speed I/O capabilities of the
latest FPGAs combined with large autogenerated FIFO-configured
embedded memories make short work of designing a signal capture and
analysis system.
Finally, FPGAs have applications in mixed-signal situations that are not
immediately obvious. The most common mixed-signal application is
probably using an FPGA to drive the analog signals of a VGA monitor. A
couple of resistive dividers or a well-chosen output driver type is all you
need, and all the timing and logic necessary to generate color images can be
handled with logic inside the FPGA. FPGAs can also be trivially used as
PWM D/A converters, or even as part of a sigma-delta D/A or A/D
converters.
Where to Buy
You’re probably thinking that any tool this versatile and powerful has to
cost a fortune. While that was true about a decade ago, today you can buy
100,000 gate FPGAs for well under $50, and the design tools are often
free for educational users and/or hobbyists.
Of course, an FPGA on its own is not so useful; it needs to be mounted
to a board with the proper connections in order to be used. To this end,
a company called XESS (www.xess.com) makes a line of fairly affordable
FPGA starter kits. Their product line shifts as new FPGAs are introduced,
but the current entry-level FPGA board is the XSA-50 board that