[Oberon] Cheap FPGAs and cheap boards

[skulski at pas.rochester.edu]

Paul:

you said :
> I just looked at Digilent's recommended replacement
> for the Spartan 3 Board, which is the Nexys 4,
> with a huge increase of complexity for the
> same price; however, it does claim to have
> 600KB of on-chip block RAM.
> Still expensive and complicated compared
> to today's ARM boards though...

The trick with FPGAs is to choose the cheapest one. To this end, the
Spartan-6 family whose lifecycle has been inofficially extended by at
least a decade offers two lowest members in TQFP-144, which can be
soldered by hand. All the newer Series-7 and beyond are BGA which cannot
be assembled at home. So lets stay with these lowest Spartan-6 in
TQFP-144. Both have 102 I/O pins. I made both the OrCAD schematic symbol
and the OrCAD Layout footprint, if anyone wants to design a board. Below
is the speed grade 2 pricing from Digikey.

XC6SLX4-2TQG144C BRAM kbits = 216 BRAM kB=24 Digikey $10.91
XC6SLX9-2TQG144C BRAM kbits = 576 BRAM kB=64 Digikey $15.69

Note that kB = kbits/9 because the ECC bits are not very useful.

Actually, one does not have to design these boards because one can buy
them on Ebay from China. Just type XC6SLX9 into the search field.

1. XILINX Spartan-6 XC6SLX9 FPGA Developement Board $31.34
2. XILINX FPGA CORE Board SPARTAN-6 XC6SLX9 - SDRAM $50.00

The photographs look quite professional. The first one has no memory on
board. The 2nd one has 32 MBytes SDRAM, and 8 MB flash. Should be plenty
for running Oberon System. You guys have the SDRAM controller, don't you?

So yes, you can get a quite professional board that should allow to run
the Oberon System below $100.

Concerning the on-chip peripherals, the books by Pedroni and/or Chu have
plenty of good IP cores. Another great repository of these is the
PicoBlaze project. These are well documented.

Hope it helps,
Wojtek