gEDA-user: Prototyping with SMTs

["Samuel A. Falvo II" <sam.falvo@xxxxxxxxx>]

I'm old-school.  Whenever and whereever possible, I prefer to
prototype what I'm working on incrementally.  For example, my Kestrel
1 computer is a clear demonstration of this.  It's built on one of
those cheesy Radio Shack breadboards, runs at 4MHz (although the
oscillator used in the pictures on the website is 1MHz), and took me
about two weeks to build.

I would place the board's power first, then test.  Once that test
works, then I'd place the CPU, along with a NOP generator so that it
has some (bogus) instructions to fetch.  Test.  Once that passed, I'd
place the address decoder -- test.  Then the RAM itself -- test.  Etc.
 I simply would not advance to the next stage without fully testing
the first stage.

The problem with SMTs is that they're very poor at allowing someone to
incrementally build with them.  Wire-wrap sockets for SMT chips are
expensive if you can find them, and they are usually quite limited in
the number of pins they support.  One could perhaps find commercial
SMT-to-DIP or to PLCC conversion modules, thus allowing for easier
wire-wrapping, but you're still pretty much limited to 68 pins.  Good
luck trying to do this with a 144-pin FPGA.

You could always make your own PCBs that break out all the pins of a
chip onto a bunch of 40-pin headers, I suppose.  However, even this
has the problem of being very expensive when you think about it, as
PCB runs of these kinds of boards is typically done in very small
quantity.

What are your approaches to dealing with this problem?  Thanks.

--
Samuel A. Falvo II