From: Wouter Coene (wouter+cbmhackers_at_irdc.nl)
Date: 2006-02-28 20:06:33
According to fachat (afachat@gmx.de):
> Does anyone have experience with this or VHDL/FPGAs in general?
> Any hints on which system might be easy to use (e.g. programmable by
> RS232)?
FPGA's (which don't retain their configuration when turned off btw) are
generally programmed using JTAG or an on-board programming chip. JTAG is a
simple bit-serial protocol that can be driven from a PC's parallel port
using some 74-series logic.
Each FPGA vendor typically has its own software suite to target its devices.
The free availability of these suites (for hobbyists) depends on the whims
of the vendor in question, but Altera and Xilinx both have quite good
software freely available (I'm currently only familiar with Xilinx' FPGA's).
Xilinx has some nicely-priced development boards available for their
Spartan-3 (read: affordable for hobbyists) series:
http://xilinx.com/spartan3/
Here's a schematic for a JTAG-interface compatible with Xilinx' software:
http://www.xilinx.com/support/programr/jtag_cable.pdf
(you may not need this though; most development boards already include a
suitable cable)
Generally speaking, programmable hardware is not very easy to do. HDL might
look like software, but writing it requires an entirely different mindset.
One of the things that's often underestimated is the sheer amount of
cognitive density of HDL code. For example, the 16-bit RISC processor I
designed and wrote a while ago is only ~3800 lines (~28 kbytes) of code
(including comments and testing code), yet it kept me busy for the better
part of a month. And there are probably still bugs lurking in it somewhere.
However, having one's design _finally_ working as it should just feels so
very good :)
Hope that helps,
Wouter
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