Example how to mke OUTFF devices in IOBs.

examples/outff.v

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+/*
+ * Copyright (c) 1998-1999 Stephen Williams (steve@icarus.com)
+ *
+ *    This source code is free software; you can redistribute it
+ *    and/or modify it in source code form under the terms of the GNU
+ *    General Public License as published by the Free Software
+ *    Foundation; either version 2 of the License, or (at your option)
+ *    any later version.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU General Public License for more details.
+ *
+ *    You should have received a copy of the GNU General Public License
+ *    along with this program; if not, write to the Free Software
+ *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+/*
+ * IVL should generate an AND gate, and should make an OBUF and two
+ * IBUF objects, along with the PAD objects.
+ *
+ * To compile this for XNF, try a command like this:
+ *
+ *    verilog -X -fpart=XC4010XLPQ160 -fncf=outff.ncf outff.v
+ *
+ * That command causes an outff.xnf and outff.ncf file to be created.
+ * Next, make the outff.ngd file with the command:
+ *
+ *    xnf2ngd -l xilinxun -u outff.xnf outff.ngd
+ *
+ * Finally, map the file to fully render it in the target part. The
+ * par command is the step that actually optimizes the design and tries
+ * to meet timing constraints.
+ *
+ *    map -o map.ngd outff.ngd
+ *    par -w map.ncd outff.ncd
+ *
+ * At this point, you can use the FPGA Editor to edit the outff.ncd
+ * file to see that the AND gate is in a CLB and the IOB for pin 150
+ * has its flip-flop in use.
+ */
+
+module main;
+
+   wire clk, iclk;
+   wire i0, i1;
+   wire out;
+   reg o0;
+
+      // This simple logic gate get turned into a function unit.
+      // The par program will map this into a CLB F or G unit.
+   and (out, i0, i1);
+
+      // This is mapped to a DFF. Since o0 is connected to a PAD, it
+      // is turned into a OUTFF so that it get placed into an IOB.
+   always @(posedge clk) o0 = out;
+
+      // These attribute commands assign pins to the listed wires.
+      // This can be done to wires and registers, as internally both
+      // are treated as named signals.
+   $attribute(o0,  "PAD", "o150");
+   $attribute(i0,  "PAD", "i152");
+   $attribute(i1,  "PAD", "i153");
+   $attribute(iclk,"PAD", "i154");
+
+endmodule /* main */