USB Universal Floppy Disk controller

[Tony Duell]

> 
> Tony wrote:
> > So not much better then. The FPGAs have presumably become more complex as
> > the PCs to compile them get faster...
> [...]
> > Oh yes. But the point it is took many, many, compiles to get the darn
> > thing to work. I am sure I could have hand-wired it in less time than
> > that.
> 
> For a Spartan 3 FPGA (XC3S400), in less than five minutes I can
> compile a design that includes a 32-bit RISC processor core, a VGA
> controller, a PS/2 mouse controller, and an SDRAM interface.

And how long did it take you to design all those parts? (If you're just 
sticking pre-designed modules together, that's little more than PC 
assembling, and doesn't count :-)). I find I can design and debug _as I 
wire_.


> 
> If I wanted to build the equivalent out of SSI/MSI chips, it would
> take me weeks if not months.

I suspect that the actual time in going from idea to working prototype is 
much the same in both cases. Or at least it was when I had to use FPGAs. 

> 
> > If you need to make a change to a hand-wired design, it takes,
> > perhaps, 5 minutes. To do it to the FPGA design means another overnight
> > compile.
> 
> Depends on the change.  If it's simple, the times might be comparable.
> For a complex change, doing it on the FPGA is much faster.  For instance,
> suppose I decide that I want to change the load and store byte
> instructions to be little-endian rather than big-endian.  With an HDL

That's not a change, it's a redesign :-). Seriously, I do like to have 
some idea of what I am trying to build before I start building it.

> IF I want to do things like experiment with adding extra pipeline stages,
> the FPGA is an even bigger win.

And when it doesn't work, and you can't probe the relevant signal in the 
FPGA, the board of TTL/ECL is a much bigger win...

-tony