15 Jun
2006
15 Jun
'06
3:04 a.m.
Tony Duell wrote:
I think it depends on how big the item that you are designing
will end up -- and, if it stays a "one of a kind" design or if
you ever decide to make several of them.
What I find most annoying about FPGAs is they are all sole
source parts -- if you have a problem with one vendor's
part, you may have to reinvest a lot of time to switch to
another vendor's device (as well as investing in another
tool chain!)
<shrug>
[ Homebrew procrssors]
2901 really only makes sense for a "classic" CPU design.
By the time you put all of the parts together to get a complete
CPU, it is quite a large solution. Some parts (29116, etc.)
could help a little but it still was big.
If you don't need a "full" instruction set (traditional ALU, etc.)
then there were better ways of doing this. E.g., in one of my
CPUs, I needed some cascaded multiply/inverse/multiply operators.
I chose to use serial adders and multipliers instead of a more
conventional approach.
I think once the 2901 "fell from grace"
(?), this became a thing
of the past. I've designed two processors "from scratch" (TTL
Maybe, althoguh i never cared much for the 2901... with bipolar
ROMs for the microcode store) and found it quite
an interesting exercise. Not just the "logic design" but
actually thinking about what the instruction set should be
for that particular application domain, etc.
But, nowadays, I think it would be a lot less tedious if you
could do it in a big FPGA using synthesis tools. You could
Hmm... I had to use FPGAs in my last job, and I hated every darn minute
of it. Don't get me wrong, I can and will use them if somebody is paying
me to do so, but I won't chose them for my own design. I found it a lot
quicker to debug a circuit by changing things on the actual hardware
(rathen than waiting for your design to complie again, and finding the
darn compiler had removed most of your logic without warning because
you'd tiend an enable pin to the wrong state). And I wouldn't trust that
simulator as far as I could throw it ... No, for my own hobby designs,
I'll stick to boards of TTL and a logic analyser. So, is it your
opinion that the "build it" mentality is
so individualistic that the differences in attitudes towards
it between our sides of the pond are more *cultural* (of
I am not sure it is different in the UK. Very few people do any kind of
homebrewing over here any more. There are a few of us left, I guess,
that's all.