16 Mar
2005
16 Mar
'05
6 p.m.
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.
If I wanted to build the equivalent out of SSI/MSI chips, it would
take me weeks if not months.
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
and FPGA, that's a simple change to somewhere between one and four lines
of code, depending on the design style. With a hand-wired design it's at
least 32 signals to be rewired, assuming that the relevant data path isn't
used for anything else. If the data path is shared, it might require the
addition of more buffers and the control logic to drive them.
IF I want to do things like experiment with adding extra pipeline stages,
the FPGA is an even bigger win.
Eric