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verilog.rst

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Verilog on Fomu

“Hello world!” - Blink a LED

The canonical “Hello, world!” of hardware is to blink a LED. The directory verilog/blink contains a Verilog example of a blink project. This takes the 48 MHz clock and divides it down by a large number so you get an on/off pattern.

Enter the verilog/blink directory and build the demo by using make:

Make sure you set the FOMU_REV value to match your hardware! See :ref:`required-hardware`.

.. session:: shell-session

   $ make FOMU_REV=$FOMU_REV
   ...
   Info: Max frequency for clock 'clk': 73.26 MHz (PASS at 12.00 MHz)

   Info: Max delay posedge clk -> <async>: 3.15 ns

   Info: Slack histogram:
   Info:  legend: * represents 1 endpoint(s)
   Info:          + represents [1,1) endpoint(s)
   Info: [ 69683,  70208) |**
   Info: [ 70208,  70733) |
   Info: [ 70733,  71258) |**
   Info: [ 71258,  71783) |**
   Info: [ 71783,  72308) |**
   Info: [ 72308,  72833) |**
   Info: [ 72833,  73358) |
   Info: [ 73358,  73883) |**
   Info: [ 73883,  74408) |*
   Info: [ 74408,  74933) |**
   Info: [ 74933,  75458) |**
   Info: [ 75458,  75983) |*
   Info: [ 75983,  76508) |*
   Info: [ 76508,  77033) |**
   Info: [ 77033,  77558) |**
   Info: [ 77558,  78083) |*
   Info: [ 78083,  78608) |
   Info: [ 78608,  79133) |*************************
   Info: [ 79133,  79658) |**
   Info: [ 79658,  80183) |***
   22 warnings, 0 errors
   icepack blink.asc blink.bit
   cp blink.bit blink.dfu
   dfu-suffix -v 1209 -p 70b1 -a blink.dfu
   dfu-suffix (dfu-util) 0.9

   Copyright 2011-2012 Stefan Schmidt, 2013-2014 Tormod Volden
   This program is Free Software and has ABSOLUTELY NO WARRANTY
   Please report bugs to http://sourceforge.net/p/dfu-util/tickets/

   Suffix successfully added to file
   $

You can then load blink.dfu onto Fomu by using the same dfu-util -D command we’ve been using so far. You should see a blinking pattern of varying color on your Fomu, indicating your bitstream was successfully loaded.

Reading Input

There is another small example in verilog/blink-expanded which shows how to read out some given pins. Build and flash it like described above and see if you can enable the blue and red LED by shorting pins 1+2 or 3+4 on your Fomu (the pins are the exposed contacts sticking out of the USB port).