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For those of you who wish to use Icarus Verilog, in combination with
the Xilinx back end (Foundation or Alliance), it can be done. I have
run some admittedly simple (2300 equivalent gates) designs through this
setup, targeting a Spartan XCS10.
Older versions of Icarus Verilog (like 19990814) couldn't synthesize
logic buried in procedural (flip-flop) assignment. Newer versions
(like 20000120) don't have this limitation.
Procedural assignments have to be given one at a time, to be
"found" by xnfsyn. Say
always @ (posedge Clk) Y = newY;
always @ (posedge Clk) Z = newZ;
rather than
always @ (posedge Clk) begin
Y = newY;
Z = newZ;
Steve's xnf.txt covers most buffer and pin constructs, but I had reason
to use a global clock net not connected to an input pin. The standard
Verilog for a buffer, combined with a declaration to turn that into a
BUFG, is:
buf BUFG( your_output_here, your_input_here );
I use post-processing on my .xnf files to add "FAST" attributes to
output pins.
Running ivl:
The -F switches are important. The following order seems to robustly
generate valid XNF files, and is used by "verilog -X":
-Fsynth -Fnodangle -Fxnfio
Generating .pcf files:
The ngdbuild step seems to lose pin placement information that ivl
puts in the XNF file. Use xnf2pcf to extract this information to
a .pcf file, which the Xilinx place-and-route software _will_ pay
attention to. Steve says he now makes that information available
in an NCF file, with -fncf=<path>, but I haven't tested that.
Running the Xilinx back end:
You can presumably use the GUI, but that doesn't fit in Makefiles :-).
Here is the command sequence in pseudo-shell-script:
ngdbuild -p $part $1.xnf $1.ngd
map -p $part -o map.ncd $1.ngd
xnf2pcf <$1.xnf >$1.pcf # see above
par -w -ol 2 -d 0 map.ncd $1.ncd $1.pcf
bitgen_flags = -g ConfigRate:SLOW -g TdoPin:PULLNONE -g DonePin:PULLUP \
-g CRC:enable -g StartUpClk:CCLK -g SyncToDone:no \
-g DoneActive:C1 -g OutputsActive:C3 -g GSRInactive:C4 \
-g ReadClk:CCLK -g ReadCapture:enable -g ReadAbort:disable
bitgen $1.ncd -l -w $bitgen_flags
The Xilinx software has diarrhea of the temp files (14, not including
.xnf, .pcf, .ngd, .ncd, and .bit), so this sequence is best done in a
dedicated directory. Note in particular that map.ncd is a generic name.
I had reason to run this remotely (and transparently within a Makefile)
via ssh. I use the gmake rule
%.bit : %.xnf
ssh -x -a -o 'BatchMode yes' ${ALLIANCE_HOST} \
remote_alliance ${REMOTE_DIR} $(basename $@) 2>&1 < $<
and the remote_alliance script (on ${ALLIANCE_HOST})
cd $1
cat >! $2.xnf
xnf2pcf <$2.xnf >! $2.pcf
./backend $2
There is now a "Xilinx on Linux HOWTO" at
I haven't tried this yet, it looks interesting.
I use the XESS ( XSP-10 development board, which
uses the PC parallel (printer) port for downloading and interaction
with the host. They made an old version of their download program
public domain, posted it at ,
and now there is a Linux port at .
The above hints are based on my experience with Foundation 1.5 on NT
(gack) and Alliance 2.1i on Solaris. Your mileage may vary. Good luck!
- Larry Doolittle <> August 19, 1999
updated February 1, 2000