FPGA LOADABLE CODE GENERATOR FOR Icarus Verilog

  Copyright 2001 Stephen Williams
  $Id: fpga.txt,v 1.2 2001/09/06 04:28:40 steve Exp $

The FPGA code generator supports a variety of FPGA devices, writing
XNF or EDIF depending on the target. You can select the architecture
of the device, and the detailed part name. The architecture is used to
select library primitives, and the detailed part name is written into
the generated file for the use of downstream tools.

INVOKING THE FPGA TARGET

The code generator is invoked with the -tfpga flag to iverilog. It
understands the part= and the arch= parameters, which can be set with
the -p flag of iverilog:

	iverilog -parch=virtex -fpart=v50-pq240-6 -tfpga foo.vl

This example selects the virtext architecture, and give the detailed
part number as v50-pq240-6. The output is written into a.out unless a
different output file is specified with the -o flag.

The following is a list of architecture types that this code generator
supports.

* arch=generic-edif

This is generic EDIF code. It doesn't necessarily work because the
external library is not available to the code generator. But, what it
does is generate generic style gates that a portability library can
map to target gates if desired.

* arch=generic-xnf

If this is selected, then the output is formatted as an XNF file,
suitable for most any type of device. The devices that it emits
are generic devices from the unified library. Some devices are macros,
you will may need to further resolve the generated XNF to get working
code for your part.

* arch=virtex

If this is selected, then the output is formatted as an EDIF 200 file,
suitable for Virtex class devices. This is supposed to know that you
are targeting a Virtex part, so can generate primitives instead of
using external macros. It includes the VIRTEX internal library, and
should work properly for any Virtex part.


XNF ROOT PORTS

When the output format is XNF, the code generator will generate "SIG"
records for the signals that are ports of the root module. The name is
declared as an external pin that this macro makes available.

The name given to the macro pin is generated from the base name of the
signal. If the signal is one bit wide, then the pin name is exactly
the module port name. If the port is a vector, then the pin number is
given as a vector. For example, the module:

	module main(out, in);
	    output out;
	    input [2:0] in;
	    [...]
	endmodule

leads to these SIG, records:

	SIG, main/out, PIN=out
	SIG, main/in<2>, PIN=in2
	SIG, main/in<1>, PIN=in1
	SIG, main/in<0>, PIN=in0


EDIF ROOT PORTS

The EDIF format is more explicit about the interface into an EDIF
file. The code generator uses that control to generate an explicit
interface definition into the design. (This is *not* the same as the
PADS of a part.) The generated EDIF interface section contains port
definitions, including the proper direction marks.



---
$Log: fpga.txt,v $
Revision 1.2  2001/09/06 04:28:40  steve
 Separate the virtex and generic-edif code generators.

Revision 1.1  2001/09/02 23:58:49  steve
 Add documentation for the code generator.