Update xilinx-hints.txt from Larry.

xilinx-hint.txt

@@ -1,21 +1,14 @@
 
 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 (no arithmetic, 600 equivalent gates) designs
-through this setup, targeting a Spartan XCS10.
+run some admittedly simple (2300 equivalent gates) designs through this
+setup, targeting a Spartan XCS10.
 
 Verilog:
 
-   As of Icarus Verilog 19990814, you still can't have logic buried
-   in procedural (flip-flop) assignment.  I use a hacked workaround
-   copy of ivl that allows 1-bit wide logic.  The other approach
-   is to use temporary wires, assign them to the logic, and assign
-   the reg to that wire.  For example, instead of
-       always @ (posedge Clk) Z = ~Q1 & ~Q2 & ~Q3 & ~Q4;
-   you can write
-       wire newZ;
-       assign newZ = ~Q1 & ~Q2 & ~Q3 & ~Q4;
-       always @ (posedge Clk) Z = newZ;
+   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
@@ -27,36 +20,29 @@ Verilog:
            Z = newZ;
        end
 
-   I had reason to use a global clock net.  I used this snippet of
-   Verilog code to make it happen:
-       primitive BUFG ( O, I );
-        output O;
-        input I;
-        table
-         0:0;
-         1:1;
-        endtable
-       endprimitive
+   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 );
        $attribute(BUFG,"XNF-LCA","BUFG:O,I")
 
-   Oh, yes, you probably also want to choose I/O pins!  Try this:
-       wire d1;
-       $attribute(d1,   "PAD", "i45");    // input
-       wire vsync;
-       $attribute(vsync,  "PAD", "o67");   // output
+   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:
-      -Fxnfio -Fnobufz -Fsigfold -Fxnfsyn
+   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.
+   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:
 
@@ -76,6 +62,23 @@ Running the Xilinx back end:
    .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 < $<
+	scp ${ALLIANCE_HOST}:${REMOTE_DIR}/$@ .
+    and the remote_alliance script (on ${ALLIANCE_HOST})
+/bin/csh
+cd $1
+cat >! $2.xnf
+xnf2pcf <$2.xnf >! $2.pcf
+./backend $2
+
+   There is now a "Xilinx on Linux HOWTO" at
+         http://www.polybus.com/xilinx_on_linux.html
+   I havn't tried this yet, it looks interesting.
+
 Downloading:
 
    I use the XESS (http://www.xess.com/) XSP-10 development board, which
@@ -90,3 +93,4 @@ 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   <LRDoolittle@lbl.gov>   August 19, 1999
+                                        updated February 1, 2000