Getting started with programmable logic, was Re: Cray 1 replica

Philip Pemberton classiccmp at philpem.me.uk
Mon Aug 30 19:17:32 CDT 2010


On 30/08/10 18:25, Dave McGuire wrote:
> I recommend picking up one of the Xilinx-based Digilent boards. They're
> inexpensive and very nice. Xilinx has a freely-downloadable toolchain
> (WebPACK) that works very well. It even has "real" Linux support
> nowadays. The free stuff supports all but the very largest of their FPGAs.

If you're taking the Xilinx route and want a cheap entry, the Enterpoint 
Drigmorn2 is also worth a look:

   http://www.enterpoint.co.uk/drigmorn/drigmorn2.html

It's based around a Spartan3A-700 FPGA, and has:
   256MBit x32 SDRAM,
   128Mbit SPI Flash,
   a text-based 16x2 LCD display (HD44780 controller),
   a bunch of 'traffic light' LEDs (four full R/Y/G sets and a 
standalone red)
   one 16-position hexadecimal switch and two pushbuttons
   FTDI USB Serial Port controller chip (FT232)
   25MHz onboard oscillator
   Two 20-pin 5V-tolerant GPIO ports (40 pins total) with LVDS support

Price is about £110 for board and parallel programming cable, £170 for 
board and USB programming cable, or (if memory serves) about £100 for 
board only.


If you want to go down the Altera route, the Altera Cyclone II Starter 
Board is available from DigiKey and Farnell (last I checked, DigiKey 
were significantly cheaper). That's based on a Cyclone II 2C20 FPGA, and 
the following peripherals:
   8Mbit PowerChip SDRAM (though I understand this has been swapped with 
a different part in more recent builds),
   512Kbit x16 SDRAM,
   4Mbit parallel FLASH,
   SMA external clock input (plus 24, 27 and 50MHz TTL oscillators),
   Wolfson Microelectronics WM8731 24-bit audio codec,
   Ten switches (latching on/off),
   Four pushbuttons,
   14 LEDs (10 red, 4 green),
   Four-digit segment-addressable 7seg display,
   VGA,
   RS232,
   PS/2 (keyboard-mode only, the Minimig DE1 Port project has documented 
a simple modification which adds mouse-mode),
   Two 40-pin IDC connectors with (if memory serves) 32 GPIOs each
   Built-in Altera USB Blaster cable clone

Cost is about £120 total for the Cyclone II Starter Board. It's also 
sold as the TerASIC DE1, so look out for those too (same board, but 
without the silver Altera sticker). The Minimig Amiga clone has been 
ported to the DE1 (minimig-tg68), and that's quite cool to play with for 
a while on a rainy day.

Disadvantages are you can't really do LVDS on the DE1 (so you can't hook 
up a laptop LCD panel without an external LVDS transceiver chip); the 
Drigmorn2 has a couple of switchable LVDS/GPIO pairs on the main 
connector. This is a bit specialist though; I like the pluggable modules 
on the Drigmorn2, but I like that the Altera board has >90% of what I 
need on it already (no need to make up expander boards most of the 
time). The Drigmorn2 does have Ethernet, PS/2 and USB boards available, 
which are kinda cool to play with.


If you're just starting, go with a Digilent kit board or the Altera DE1. 
I find the Altera Quartus software easier to use (and a lot less 
finicky) than the Xilinx Webpack, but that's just me. Altera also tend 
to be much more receptive to bug reports -- Xilinx are well known for 
making it almost impossible to file a bug report or contact an FAE...

Xilinx parts also tend to be harder to find than Altera parts, so bear 
that in mind if you're doing a production design. I found it much easier 
to get hold of Altera Cyclone2 parts than Xilinx Spartans... Farnell 
stock small quantities of CYC2s, and if I need more there's always DigiKey.

Put simply: you're likely to have less headaches starting with Altera. 
If you want to play with 'soft-core' CPUs, get one of the Cyclone III 
Starter Kit boards, they have more flash and RAM, but it's a DDR SDRAM 
which makes designing a memory controller harder (but there are a few 
OSS/FS ones on OpenCores). If you just want a simple entry-level board, 
look at the Cyclone II Starter Kit.

-- 
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/



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