[Oberon] Digilent Spartan 3 Board

[Paul Reed]

Hi all,

>> I feel sad that Spartan 3 is becoming obsolete.
> I agree. The more recent Spartan-3E based Nexys-2 board from Digilent

A few points of background about the Digilent Spartan 3 board which may help.

First, don't be sad!  ;-)  Everything of course becomes obsolete in our
world (tech); it's actually useful that Digilent have discontinued this
board in a rather timely fashion (just after I released the binaries for
it, bang!) as a reminder that sooner-or-later, they would have done so
anyway.  As in all things (like Windows XP!) support cannot (of course) go
on forever.  Around the time I started the project, the board was even
better value for money at $109, and has gradually been creeping up in
price ever since. A clue. :(

Even though I noticed that the silk-screen says copyright 2004, I chose
this board for the project to replace the Ceres because it is simple, and
because ETH have over 200 of them which they currently use in several
courses.  They all seem to be the 200Kgate version, but (depending on
whether you believe the tools) the current RISC5 machine only just fits. 
Hence I have tended to recommend that people buy the 1000Kgate version if
they wish to experiment, as the additional cost was marginal, all things
considered.

The simplicity of the board means that it is 'just enough' (with the
addition of a small and simple do-it-yourself-daughterboard for the
SD-card hard disk, mouse and wireless network module) to implement the
Oberon system in a nice resource-constrained and understandable way. 
Porting the simplicity, rather than the system, to another board would be
quite hard.

(The RISC processor itself is relatively easy to port to other FPGA
boards.  I have had it running in various guises on Xilinx FPGA boards
made or not made by Digilent, and also on an Altera FPGA board, for
example.)

The real killer feature about the Spartan 3 board is the 1MByte
(2x256Kx16) of extremely fast (10nS) static RAM (as in, real good
old-fashioned SRAM, not pseudo-SRAM for example!).  I haven't found a
board which provides sustained, completely random-access cycles anywhere
near as fast; anything else I have seen would imply a memory interface
which would dwarf the rest of the whole design in its complexity.  Of
course, I'd be delighted to be proved wrong about this. :)

HTH
Paul