iverilog/tgt-fpga/d-virtex2.c

/*
 * Copyright (c) 2001 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
 */
#ifdef HAVE_CVS_IDENT
#ident "$Id: d-virtex2.c,v 1.13 2003/06/25 01:49:06 steve Exp $"
#endif

# include  "device.h"
# include  "fpga_priv.h"
# include  "edif.h"
# include  "xilinx.h"
# include  <stdlib.h>
# include  <string.h>
#ifdef HAVE_MALLOC_H
# include  <malloc.h>
#endif
# include  <assert.h>


static edif_t edf = 0;
static edif_xlibrary_t xlib = 0;

/*
 * The cell_* variables below are the various kinds of devices that
 * this family supports as primitives. If the cell type is used at
 * least once, then the edif_cell_t is non-zero and will also be
 * included in the library declaration. The constants underneath are
 * pin assignments for the cell.
 */

static edif_cell_t cell_0 = 0;
static edif_cell_t cell_1 = 0;

static edif_cell_t cell_ipad = 0;
static edif_cell_t cell_opad = 0;

/*
 * This is a table of cell types that are accessible via the cellref
 * attribute to a gate.
 */
const static struct edif_xlib_celltable virtex2_celltable[] = {
      { "BUFG",     xilinx_cell_bufg },
      { "MULT_AND", xilinx_cell_mult_and },
      { 0, 0}
};
	    
/*
 * The show_header function is called before any of the devices of the
 * netlist are scanned.
 *
 * In this function, we look at the ports of the root module to decide
 * if they are to be made into ports. Modules that have PAD attributes
 * are *not* to be used as ports, they will be connected to special
 * PAD devices instead.
 */
static void virtex2_show_header(ivl_design_t des)
{
      unsigned idx;
      ivl_scope_t root = ivl_design_root(des);
      unsigned sig_cnt = ivl_scope_sigs(root);
      unsigned nports = 0, pidx;
      const char*part_str = 0;

	/* Count the ports I'm going to use. */
      for (idx = 0 ;  idx < sig_cnt ;  idx += 1) {
	    ivl_signal_t sig = ivl_scope_sig(root, idx);

	    if (ivl_signal_port(sig) == IVL_SIP_NONE)
		  continue;

	    if (ivl_signal_attr(sig, "PAD") != 0)
		  continue;

	    nports += ivl_signal_pins(sig);
      }

      edf = edif_create(ivl_scope_basename(root), nports);

      pidx = 0;
      for (idx = 0 ;  idx < sig_cnt ;  idx += 1) {
	    edif_joint_t jnt;
	    ivl_signal_t sig = ivl_scope_sig(root, idx);

	    if (ivl_signal_port(sig) == IVL_SIP_NONE)
		  continue;

	    if (ivl_signal_attr(sig, "PAD") != 0)
		  continue;

	    if (ivl_signal_pins(sig) == 1) {
		  edif_portconfig(edf, pidx, ivl_signal_basename(sig),
				  ivl_signal_port(sig));

		  assert(ivl_signal_pins(sig) == 1);
		  jnt = edif_joint_of_nexus(edf, ivl_signal_pin(sig, 0));
		  edif_port_to_joint(jnt, edf, pidx);

	    } else {
		  const char*name = ivl_signal_basename(sig);
		  ivl_signal_port_t dir = ivl_signal_port(sig);
		  char buf[128];
		  unsigned bit;
		  for (bit = 0 ;  bit < ivl_signal_pins(sig) ; bit += 1) {
			const char*tmp;
			sprintf(buf, "%s[%u]", name, bit);
			tmp = strdup(buf);
			edif_portconfig(edf, pidx+bit, tmp, dir);

			jnt = edif_joint_of_nexus(edf,ivl_signal_pin(sig,bit));
			edif_port_to_joint(jnt, edf, pidx+bit);
		  }
	    }

	    pidx += ivl_signal_pins(sig);
      }

      assert(pidx == nports);

      xlib = edif_xlibrary_create(edf, "VIRTEX2");
      edif_xlibrary_set_celltable(xlib, virtex2_celltable);


      if ( (part_str = ivl_design_flag(des, "part")) && (part_str[0] != 0) ) {
	    edif_pstring(edf, "PART", part_str);
      }

      cell_0 = edif_xcell_create(xlib, "GND", 1);
      edif_cell_portconfig(cell_0, 0, "GROUND", IVL_SIP_OUTPUT);

      cell_1 = edif_xcell_create(xlib, "VCC", 1);
      edif_cell_portconfig(cell_1, 0, "VCC", IVL_SIP_OUTPUT);

}

static void virtex2_show_footer(ivl_design_t des)
{
      unsigned idx;

      for (idx = 0 ;  idx < ivl_design_consts(des) ;  idx += 1) {
	    unsigned pin;
	    ivl_net_const_t net = ivl_design_const(des, idx);
	    const char*val = ivl_const_bits(net);

	    for (pin = 0 ;  pin < ivl_const_pins(net) ;  pin += 1) {
		  edif_joint_t jnt;
		  edif_cellref_t pad;

		  jnt = edif_joint_of_nexus(edf, ivl_const_pin(net, pin));
		  switch (val[pin]) {
		      case '0':
			pad = edif_cellref_create(edf, cell_0);
			break;
		      case '1':
			pad = edif_cellref_create(edf, cell_1);
			break;
		      default:
			assert(0);
			break;
		  }

		  edif_add_to_joint(jnt, pad, 0);
	    }
      }

      edif_print(xnf, edf);
}

/*
 * Make (or retrieve) a cell in the external library that reflects the
 * scope with its ports.
 */
static void virtex2_show_scope(ivl_scope_t scope)
{
      edif_cell_t cell;
      edif_cellref_t ref;

      unsigned port, idx;

      cell = edif_xlibrary_scope_cell(xlib, scope);
      ref = edif_cellref_create(edf, cell);

      for (idx = 0 ;  idx < ivl_scope_sigs(scope) ;  idx += 1) {
	    edif_joint_t jnt;
	    ivl_signal_t sig = ivl_scope_sig(scope, idx);

	    if (ivl_signal_port(sig) == IVL_SIP_NONE)
		  continue;

	    port = edif_cell_port_byname(cell, ivl_signal_basename(sig));
	    jnt = edif_joint_of_nexus(edf, ivl_signal_pin(sig, 0));
	    edif_add_to_joint(jnt, ref, port);
      }
}

static void virtex2_pad(ivl_signal_t sig, const char*str)
{
      unsigned idx;
      unsigned*pins;

      if (cell_ipad == 0) {
	    cell_ipad = edif_xcell_create(xlib, "IPAD", 1);
	    edif_cell_portconfig(cell_ipad, 0, "IPAD", IVL_SIP_OUTPUT);
      }

      if (cell_opad == 0) {
	    cell_opad = edif_xcell_create(xlib, "OPAD", 1);
	    edif_cell_portconfig(cell_opad, 0, "OPAD", IVL_SIP_OUTPUT);
      }

	/* Collect an array of pin assignments from the attribute
	   string passed in as str. The format is a comma separated
	   list of unsigned decimal integers. */
      pins = calloc(ivl_signal_pins(sig), sizeof(unsigned));
      for (idx = 0 ;  idx < ivl_signal_pins(sig) ;  idx += 1) {
	    char*tmp;
	    pins[idx] = strtoul(str, &tmp, 10);
	    switch (*tmp) {
		case ',':
		  tmp += 1;
		  break;
		case 0:
		  break;
		default:
		  assert(0);
	    }

	    str = tmp;
      }

	/* Now go through the pins of the signal, creating pads and
	   bufs and joining them to the signal nexus. */
      for (idx = 0 ;  idx < ivl_signal_pins(sig) ;  idx += 1) {
	    edif_joint_t jnt;
	    edif_cellref_t pad, buf;

	    const char*name_str = ivl_signal_basename(sig);
	    if (ivl_signal_pins(sig) > 1) {
		  char name_buf[128];
		  sprintf(name_buf, "%s[%u]", name_str, idx);
		  name_str = strdup(name_buf);
	    }

	    switch (ivl_signal_port(sig)) {
		case IVL_SIP_INPUT:
		  pad = edif_cellref_create(edf, cell_ipad);
		  buf = edif_cellref_create(edf, xilinx_cell_ibuf(xlib));

		  jnt = edif_joint_create(edf);
		  edif_joint_rename(jnt, name_str);
		  edif_add_to_joint(jnt, pad, 0);
		  edif_add_to_joint(jnt, buf, BUF_I);

		  jnt = edif_joint_of_nexus(edf, ivl_signal_pin(sig, idx));
		  edif_add_to_joint(jnt, buf, BUF_O);
		  break;

		case IVL_SIP_OUTPUT:
		  pad = edif_cellref_create(edf, cell_opad);
		  buf = edif_cellref_create(edf, xilinx_cell_obuf(xlib));

		  jnt = edif_joint_create(edf);
		  edif_joint_rename(jnt, name_str);
		  edif_add_to_joint(jnt, pad, 0);
		  edif_add_to_joint(jnt, buf, BUF_O);

		  jnt = edif_joint_of_nexus(edf, ivl_signal_pin(sig, idx));
		  edif_add_to_joint(jnt, buf, BUF_I);
		  break;

		default:
		  assert(0);
	    }

      }

      free(pins);
}

/*
 * This function handles the case where the user specifies the cell to
 * use by attribute.
 */
static void edif_cellref_logic(ivl_net_logic_t net, const char*def)
{
      char*str = strdup(def);
      char*pins;
      edif_cell_t cell;
      edif_cellref_t ref;
      edif_joint_t jnt;
      unsigned idx, port;

      pins = strchr(str, ':');
      assert(pins);
      *pins++ = 0;

	/* Locate the cell in the library, lookup by name. */
      cell = edif_xlibrary_findcell(xlib, str);
      assert(cell);

      ref = edif_cellref_create(edf, cell);

      for (idx = 0 ;  idx < ivl_logic_pins(net) ;  idx += 1) {
	    char*tmp;

	    assert(pins);
	    tmp = strchr(pins,',');
	    if (tmp != 0)
		  *tmp++ = 0;
	    else
		  tmp = 0;

	    port = edif_cell_port_byname(cell, pins);
	    jnt = edif_joint_of_nexus(edf, ivl_logic_pin(net, idx));
	    edif_add_to_joint(jnt, ref, port);

	    pins = tmp;
      }

      free(str);
}

static void lut_logic(ivl_net_logic_t net, const char*init3,
		      const char*init4, const char*init5)
{
      edif_cellref_t lut;
      edif_joint_t jnt;
      const char* init;

      assert(ivl_logic_pins(net) <= 5);
      assert(ivl_logic_pins(net) >= 3);

      switch (ivl_logic_pins(net)) {
	  case 3:
	    lut = edif_cellref_create(edf, xilinx_cell_lut2(xlib));
	    init = init3;
	    break;

	  case 4:
	    lut = edif_cellref_create(edf, xilinx_cell_lut3(xlib));
	    init = init4;
	    break;

	  case 5:
	    lut = edif_cellref_create(edf, xilinx_cell_lut4(xlib));
	    init = init5;
	    break;
      }

      edif_cellref_pstring(lut, "INIT", init);

      switch (ivl_logic_pins(net)) {
	  case 5:
	    jnt = edif_joint_of_nexus(edf, ivl_logic_pin(net, 4));
	    edif_add_to_joint(jnt, lut, LUT_I3);
	  case 4:
	    jnt = edif_joint_of_nexus(edf, ivl_logic_pin(net, 3));
	    edif_add_to_joint(jnt, lut, LUT_I2);
	  case 3:
	    jnt = edif_joint_of_nexus(edf, ivl_logic_pin(net, 2));
	    edif_add_to_joint(jnt, lut, LUT_I1);
      }

      jnt = edif_joint_of_nexus(edf, ivl_logic_pin(net, 1));
      edif_add_to_joint(jnt, lut, LUT_I0);

      jnt = edif_joint_of_nexus(edf, ivl_logic_pin(net, 0));
      edif_add_to_joint(jnt, lut, LUT_O);
}

static void virtex2_logic(ivl_net_logic_t net)
{
      edif_cellref_t obj;
      edif_joint_t   jnt;

      { const char*cellref_attribute = ivl_logic_attr(net, "cellref");
        if (cellref_attribute != 0) {
	      edif_cellref_logic(net, cellref_attribute);
	      return;
	}
      }

      switch (ivl_logic_type(net)) {

	  case IVL_LO_BUF:
	  case IVL_LO_BUFZ:
	    assert(ivl_logic_pins(net) == 2);

	    obj = edif_cellref_create(edf, xilinx_cell_buf(xlib));

	    jnt = edif_joint_of_nexus(edf, ivl_logic_pin(net, 0));
	    edif_add_to_joint(jnt, obj, BUF_O);

	    jnt = edif_joint_of_nexus(edf, ivl_logic_pin(net, 1));
	    edif_add_to_joint(jnt, obj, BUF_I);
	    break;

	  case IVL_LO_NOT:
	    assert(ivl_logic_pins(net) == 2);

	    obj = edif_cellref_create(edf, xilinx_cell_inv(xlib));

	    jnt = edif_joint_of_nexus(edf, ivl_logic_pin(net, 0));
	    edif_add_to_joint(jnt, obj, BUF_O);

	    jnt = edif_joint_of_nexus(edf, ivl_logic_pin(net, 1));
	    edif_add_to_joint(jnt, obj, BUF_I);
	    break;

	  case IVL_LO_AND:
	    assert(ivl_logic_pins(net) <= 5);
	    assert(ivl_logic_pins(net) >= 3);
	    lut_logic(net, "8", "80", "8000");
	    break;

	  case IVL_LO_NOR:
	    assert(ivl_logic_pins(net) <= 5);
	    assert(ivl_logic_pins(net) >= 3);
	    lut_logic(net, "1", "01", "0001");
	    break;

	  case IVL_LO_OR:
	    assert(ivl_logic_pins(net) <= 5);
	    assert(ivl_logic_pins(net) >= 3);
	    lut_logic(net, "E", "FE", "FFFE");
	    break;

	  case IVL_LO_XNOR:
	    assert(ivl_logic_pins(net) <= 5);
	    assert(ivl_logic_pins(net) >= 3);
	    lut_logic(net, "9", "69", "9669");
	    break;

	  case IVL_LO_XOR:
	    assert(ivl_logic_pins(net) <= 5);
	    assert(ivl_logic_pins(net) >= 3);
	    lut_logic(net, "6", "96", "6996");
	    break;

	  default:
	    fprintf(stderr, "UNSUPPORTED LOGIC TYPE: %u\n",
		    ivl_logic_type(net));
	    break;
      }
}

static void virtex2_generic_dff(ivl_lpm_t net)
{
      unsigned idx;

      ivl_nexus_t aclr = ivl_lpm_async_clr(net);
      ivl_nexus_t aset = ivl_lpm_async_set(net);
      const char*abits = 0;

      if (aset) {
	    ivl_expr_t avalue = ivl_lpm_aset_value(net);
	    assert(avalue);
	    abits = ivl_expr_bits(avalue);
	    assert(abits);
      }


      for (idx = 0 ;  idx < ivl_lpm_width(net) ;  idx += 1) {
	    edif_cellref_t obj;
	    ivl_nexus_t nex;
	    edif_joint_t jnt;

	      /* If there is a preset, then select an FDCPE instead of
		 an FDCE device. */
	    if (aset && (abits[idx] == '1')) {
		  obj = edif_cellref_create(edf, xilinx_cell_fdcpe(xlib));
	    } else {
		  obj = edif_cellref_create(edf, xilinx_cell_fdce(xlib));
	    }

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_q(net, idx));
	    edif_add_to_joint(jnt, obj, FDCE_Q);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, idx));
	    edif_add_to_joint(jnt, obj, FDCE_D);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_clk(net));
	    edif_add_to_joint(jnt, obj, FDCE_C);

	    if ( (nex = ivl_lpm_enable(net)) ) {
		  jnt = edif_joint_of_nexus(edf, nex);
		  edif_add_to_joint(jnt, obj, FDCE_CE);
	    }

	    if (aclr) {
		  jnt = edif_joint_of_nexus(edf, aclr);
		  edif_add_to_joint(jnt, obj, FDCE_CLR);
	    }

	    if (aset) {
		  if (abits[idx] == '1') {
			jnt = edif_joint_of_nexus(edf, aset);
			edif_add_to_joint(jnt, obj, FDCE_PRE);
		  } else {
			assert(aclr == 0);
			jnt = edif_joint_of_nexus(edf, aset);
			edif_add_to_joint(jnt, obj, FDCE_CLR);
		  }
	    }
      }
}

/*
 * The left shift is implemented as a matrix of MUX2_1 devices. The
 * matrix has as many rows as the device width, and a column for each
 * select.
 */
static void virtex2_show_shiftl(ivl_lpm_t net)
{
      unsigned width = ivl_lpm_width(net);
      unsigned nsel = 0, swid = 0;
      unsigned sdx, qdx;

      edif_cellref_t* cells;
      edif_cellref_t**table;

      edif_cellref_t pad0_cell;
      edif_joint_t pad0;


	/* First, find out how many select inputs we really need. We
	   can only use the selects that are enough to shift out the
	   entire width of the device. The excess can be used as an
	   enable for the last column. When disabled, the last column
	   emits zeros. */

      while (nsel < ivl_lpm_selects(net)) {

	    nsel += 1;

	    swid = 1 << nsel;
	    if (swid >= width)
		  break;
      }

      assert(nsel > 0);

	/* Allocate a matrix of edif_cellref_t variables. A devices
	   will be addressed by the expression table[sdx][qdx];
	   This should make the algorighm code easier to read. */
      cells = calloc(nsel * width, sizeof(edif_cellref_t));
      table = calloc(nsel, sizeof(edif_cellref_t*));

      for (sdx = 0 ;  sdx < nsel ;  sdx += 1)
	    table[sdx] = cells + sdx*width;

	/* Make a 0 valued pad bit. I wlil use this for all the shifin
	   values that are beyond the input. */
      pad0_cell = edif_cellref_create(edf, cell_0);
      pad0 = edif_joint_create(edf);
      edif_add_to_joint(pad0, pad0_cell, 0);

	/* The LUT matrix is <nsel> columns of <width> devices, with
	   the last column a LUT4 devices. The extra input of the
	   LUT4s in the last column are used as an enable to collect
	   all the excess select inputs. */

	/* Allocate the LUT devices of the matrix, and connect the
	   select inputs to I2 of all the devices of the column. */
      for (sdx = 0 ;  sdx < nsel ;  sdx += 1) {
	    const char*init_string = 0;
	    ivl_nexus_t nex = ivl_lpm_select(net,sdx);
	    edif_joint_t sdx_jnt = edif_joint_of_nexus(edf, nex);

	    edif_cell_t lut;

	    if (((sdx+1) == nsel) && (nsel < ivl_lpm_selects(net))) {
		  lut = xilinx_cell_lut4(xlib);
		  init_string = "00CA";
	    } else {
		  lut = xilinx_cell_lut3(xlib);
		  init_string = "CA";
	    }

	    for (qdx = 0 ;  qdx < width ;  qdx += 1) {
		  table[sdx][qdx] = edif_cellref_create(edf, lut);
		  edif_add_to_joint(sdx_jnt, table[sdx][qdx], LUT_I2);

		  edif_cellref_pstring(table[sdx][qdx], "INIT", init_string);
	    }
      }

	/* Connect the inputs of the SHIFTL device to the column 0 LUT
	   inputs. The slice on the low end shifts in a 0 for a select
	   input. */
      for (qdx = 0 ;  qdx < width ;  qdx += 1) {
	    ivl_nexus_t nex0, nex1;
	    edif_joint_t jnt0;
	    edif_joint_t jnt1;

	    nex0 = ivl_lpm_data(net,qdx);
	    jnt0 = edif_joint_of_nexus(edf, nex0);

	    if (qdx > 0) {
		  nex1 = ivl_lpm_data(net,qdx-1);
		  jnt1 = edif_joint_of_nexus(edf, nex1);
	    } else {
		  jnt1 = pad0;
	    }

	    edif_add_to_joint(jnt0, table[0][qdx], LUT_I0);
	    edif_add_to_joint(jnt1, table[0][qdx], LUT_I1);
      }

	/* Make the inner connections between LUT devices. Each column
	   connects to the previous column, shifted by the power of
	   the column value. If the shifted input falls off the end,
	   then pad with zero. */
      for (sdx = 1 ;  sdx < nsel ;  sdx += 1) {

	    for (qdx = 0 ;  qdx < width ;  qdx += 1) {
		  unsigned shift = 1 << sdx;
		  edif_joint_t jnt0 = edif_joint_create(edf);
		  edif_joint_t jnt1 = (qdx >= shift)
			? edif_joint_create(edf)
			: pad0;

		  edif_add_to_joint(jnt0, table[sdx][qdx], LUT_I0);
		  edif_add_to_joint(jnt1, table[sdx][qdx], LUT_I1);

		  edif_add_to_joint(jnt0, table[sdx-1][qdx], LUT_O);
		  if (qdx >= shift)
		       edif_add_to_joint(jnt1, table[sdx-1][qdx-shift], LUT_O);
	    }
      }

	/* Connect the output of the last column to the output of the
	   SHIFTL device. */
      for (qdx = 0 ; qdx < width ;  qdx += 1) {
	    ivl_nexus_t nex = ivl_lpm_q(net,qdx);
	    edif_joint_t jnt = edif_joint_of_nexus(edf, nex);

	    edif_add_to_joint(jnt, table[nsel-1][qdx], LUT_O);
      }

	/* Connect the excess select inputs to the enable inputs of
	   the LUT4 devices in the last column. */
      if (nsel < ivl_lpm_selects(net)) {
	    edif_joint_t jnt;

	      /* XXXX Only support 1 excess bit for now. */
	    assert((nsel + 1) == ivl_lpm_selects(net));

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_select(net,nsel));
	    for (qdx = 0 ;  qdx < width ;  qdx += 1)
		  edif_add_to_joint(jnt, table[nsel-1][qdx], LUT_I3);
      }

      free(cells);
      free(table);
}

/*
 * This function generates ADD/SUB devices for Virtex-II devices,
 * based on the documented implementations of ADD8/ADD16, etc., from
 * the Libraries Guide.
 *
 * Each slice of the ADD/SUB device is made from a LUT2 device, an
 * XORCY device that mixes with the LUT2 to make a full adder, and a
 * MUXCY_L to propagate the carry. The most significant slice does no
 * have a carry to propagate, so has no MUXCY_L.
 *
 * If the device is a wide adder, then the LUT2 devices are configured
 * to implement an XOR function and a zero is pumped into the least
 * significant carry input.
 *
 * If the device is really an adder, then the input is turned into an
 * XNOR, which takes a 1-s complement of the B input. Pump a 1 into
 * the LSB carry input to finish converting the B input into the 2s
 * complement.
 */
static void virtex2_add(ivl_lpm_t net)
{
      const char*ha_init = 0;
      edif_cellref_t lut, xorcy, muxcy, pad;
      edif_joint_t jnt;

      unsigned idx;

      switch (ivl_lpm_type(net)) {
	    case IVL_LPM_ADD:
	    ha_init = "6";
	    break;
	  case IVL_LPM_SUB:
	    ha_init = "9";
	    break;
	  default:
	    assert(0);
      }

	/* If this is a single bit wide, then generate only a
	   half-adder. Normally this is an XOR, but if this is a SUB
	   then it is an XNOR. */
      if (ivl_lpm_width(net) == 1) {

	    lut = edif_cellref_create(edf, xilinx_cell_lut2(xlib));

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_q(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_O);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_I0);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_I1);

	    edif_cellref_pstring(lut, "INIT", ha_init);
	    return;
      }

      assert(ivl_lpm_width(net) > 1);

      lut   = edif_cellref_create(edf, xilinx_cell_lut2(xlib));
      xorcy = edif_cellref_create(edf, xilinx_cell_xorcy(xlib));
      muxcy = edif_cellref_create(edf, xilinx_cell_muxcy_l(xlib));
      edif_cellref_pstring(lut, "INIT", ha_init);

	/* The bottom carry-in takes a constant that primes the add or
	   subtract. */
      switch (ivl_lpm_type(net)) {
	  case IVL_LPM_ADD:
	    pad = edif_cellref_create(edf, cell_0);
	    break;

	  case IVL_LPM_SUB:
	    pad = edif_cellref_create(edf, cell_1);
	    break;

	  default:
	    assert(0);
      }

      jnt = edif_joint_create(edf);
      edif_add_to_joint(jnt, pad, 0);
      edif_add_to_joint(jnt, muxcy, MUXCY_CI);
      edif_add_to_joint(jnt, xorcy, XORCY_CI);

      jnt = edif_joint_of_nexus(edf, ivl_lpm_q(net, 0));
      edif_add_to_joint(jnt, xorcy, XORCY_O);

      jnt = edif_joint_create(edf);
      edif_add_to_joint(jnt, xorcy, XORCY_LI);
      edif_add_to_joint(jnt, muxcy, MUXCY_S);
      edif_add_to_joint(jnt, lut,   LUT_O);

      jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, 0));
      edif_add_to_joint(jnt, lut,   LUT_I0);
      edif_add_to_joint(jnt, muxcy, MUXCY_DI);

      jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, 0));
      edif_add_to_joint(jnt, lut, LUT_I1);

      for (idx = 1 ;  idx < ivl_lpm_width(net) ;  idx += 1) {
	    edif_cellref_t muxcy0 = muxcy;

	    lut = edif_cellref_create(edf, xilinx_cell_lut2(xlib));
	    xorcy = edif_cellref_create(edf, xilinx_cell_xorcy(xlib));
	    edif_cellref_pstring(lut, "INIT", ha_init);

	      /* If this is the last bit, then there is no further
		 propagation in the carry chain, and I can skip the
		 carry mux MUXCY. */
	    if ((idx+1) < ivl_lpm_width(net))
		  muxcy = edif_cellref_create(edf, xilinx_cell_muxcy_l(xlib));
	    else
		  muxcy = 0;

	    jnt = edif_joint_create(edf);
	    edif_add_to_joint(jnt, muxcy0, MUXCY_O);
	    edif_add_to_joint(jnt, xorcy, XORCY_CI);
	    if (muxcy) edif_add_to_joint(jnt, muxcy, MUXCY_CI);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_q(net, idx));
	    edif_add_to_joint(jnt, xorcy, XORCY_O);

	    jnt = edif_joint_create(edf);
	    edif_add_to_joint(jnt, xorcy, XORCY_LI);
	    if (muxcy) edif_add_to_joint(jnt, muxcy, MUXCY_S);
	    edif_add_to_joint(jnt, lut,   LUT_O);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, idx));
	    edif_add_to_joint(jnt, lut,   LUT_I0);
	    if (muxcy) edif_add_to_joint(jnt, muxcy, MUXCY_DI);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, idx));
	    edif_add_to_joint(jnt, lut, LUT_I1);
      }

}

/*
 * This method handles both == and != operators, the identity
 * comparison operators.
 *
 * If the identity compare is applied to small enough input vectors,
 * it is shoved into a single LUT. Otherwise, it is strung out into a
 * row of LUT devices chained together by carry muxes. The output of
 * the comparison is the output of the last mux.
 *
 * When the compare is small, a LUT is generated with the appropriate
 * truth table to cause an == or != result.
 *
 * When the compare is too wide for a single LUT, then it is made into
 * a chain connected by a string of carry mux devices. Each LUT
 * implements == for up to two pairs of bits, even if the final output
 * is supposed to be !=. The LUT output is connected to an associated
 * MUX select input. The CO output of each muxcy is passed up to the
 * next higher order bits of the compare.
 *
 * For identity == compare, a != output from the LUT selects the DI
 * input of the muxcy, generating a 0 output that is passed up. Since
 * the next higher muxcy now gets a 0 input to both DI and CI, the
 * output of the next higher muxcy is guaranteed to be 0, and so on to
 * the final output of the carry chain. If the output from a LUT is ==,
 * then the CI input of the muxcy is selected and the truth of this
 * level depends on lower order bits. The least significant muxcy is
 * connected to GND and VCC so that its CO follows the least
 * significant LUT.
 *
 * Identity != is the same as == except that the output is
 * inverted. To get that effect without putting an inverter on the
 * output of the top muxcy pin CO (which would cost a LUT) the DI
 * inputs are all connected to VCC instead of GND, and the CI of the
 * least significant muxcy is connected to GND instead of VCC. The LUT
 * expressions for the chained compare are configured for ==, with the
 * changed CI/DI inputs performing the inversion.
 */
static void virtex_eq(ivl_lpm_t net)
{
      edif_cellref_t lut, mux, mux_prev;
      edif_joint_t jnt, jnt_di;
      unsigned idx;

	/* True if I'm implementing CMP_EQ instead of CMP_NE */
      int eq = 1;

      assert(ivl_lpm_width(net) >= 1);

      if (ivl_lpm_type(net) == IVL_LPM_CMP_NE)
	    eq = 0;

      switch (ivl_lpm_width(net)) {

	  case 1:
	    lut = edif_cellref_create(edf, xilinx_cell_lut2(xlib));
	    edif_cellref_pstring(lut, "INIT", eq? "9" : "6");

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_q(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_O);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_I0);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_I1);
	    return;

	  case 2:
	    lut = edif_cellref_create(edf, xilinx_cell_lut4(xlib));
	    edif_cellref_pstring(lut, "INIT", eq? "9009" : "6FF6");

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_q(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_O);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_I0);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_I1);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, 1));
	    edif_add_to_joint(jnt, lut, LUT_I2);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, 1));
	    edif_add_to_joint(jnt, lut, LUT_I3);
	    return;

	  default:
	    { edif_cellref_t di;
	      di = edif_cellref_create(edf, eq? cell_0 : cell_1);
	      jnt_di = edif_joint_create(edf);
	      edif_add_to_joint(jnt_di, di, 0);
	    }

	    mux_prev = 0;
	    for (idx = 0 ;  idx < ivl_lpm_width(net) ;  idx += 2) {
		  int subwid = 2;
		  if ((idx + 1) == ivl_lpm_width(net))
			subwid = 1;

		  mux = edif_cellref_create(edf, xilinx_cell_muxcy(xlib));
		  if (subwid == 2) {
			lut = edif_cellref_create(edf, xilinx_cell_lut4(xlib));
			edif_cellref_pstring(lut, "INIT", "9009");
		  } else {
			lut = edif_cellref_create(edf, xilinx_cell_lut2(xlib));
			edif_cellref_pstring(lut, "INIT", "9");
		  }

		  jnt = edif_joint_create(edf);
		  edif_add_to_joint(jnt, lut, LUT_O);
		  edif_add_to_joint(jnt, mux, MUXCY_S);

		  jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, idx));
		  edif_add_to_joint(jnt, lut, LUT_I0);

		  jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, idx));
		  edif_add_to_joint(jnt, lut, LUT_I1);

		  if (subwid > 1) {
			jnt = edif_joint_of_nexus(edf,
					       ivl_lpm_data(net, idx+1));
			edif_add_to_joint(jnt, lut, LUT_I2);

			jnt = edif_joint_of_nexus(edf,
					       ivl_lpm_datab(net, idx+1));
			edif_add_to_joint(jnt, lut, LUT_I3);
		  }

		  edif_add_to_joint(jnt_di, mux, MUXCY_DI);

		  if (mux_prev) {
			jnt = edif_joint_create(edf);
			edif_add_to_joint(jnt, mux, MUXCY_CI);
			edif_add_to_joint(jnt, mux_prev, MUXCY_O);
		  } else {
			edif_cellref_t ci;
			ci = edif_cellref_create(edf, eq? cell_1 : cell_0);
			jnt = edif_joint_create(edf);
			edif_add_to_joint(jnt, ci, 0);
			edif_add_to_joint(jnt, mux, MUXCY_CI);
		  }

		  mux_prev = mux;
	    }

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_q(net, 0));
	    edif_add_to_joint(jnt, mux_prev, MUXCY_O);
	    return;
      }
}

/*
 * Implement hardware for the device (A >= B). We use LUT devices if
 * it can handle the slices, or carry chain logic if the slices must
 * span LUT devices.
 */
static void virtex2_cmp_ge(ivl_lpm_t net)
{
      edif_cellref_t muxcy_prev;
      edif_cellref_t lut;
      edif_joint_t jnt;
      unsigned idx;

      if (ivl_lpm_width(net) == 1) {

	      /* If the comparator is a single bit, then use a LUT2
		 with this truth table:

		 Q   A B
		 --+----
		 1 | 0 0
		 0 | 0 1
		 1 | 1 0
		 1 | 1 1

		 Connect the A value to I1 and the B value to I0. */

	    lut = edif_cellref_create(edf, xilinx_cell_lut2(xlib));
	    edif_cellref_pstring(lut, "INIT", "D");

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_q(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_O);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_I1);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_I2);
	    return;
      }

	/* Handle the case where the device is two slices
	   wide. In this case, we can use a LUT4 to do all
	   the calculation. Use this truth table:

	      Q   AA BB
	      --+------
	      1 | 00 00
	      0 | 00 01
	      0 | 00 10
	      0 | 00 11
	      1 | 01 00
	      1 | 01 01
	      0 | 01 10
	      0 | 01 11
	      1 | 10 00
	      1 | 10 01
	      1 | 10 10
	      0 | 10 11
	      1 | 11 xx

	   The I3-I0 inputs are A1 A0 B1 B0 in that order. */

      assert(ivl_lpm_width(net) >= 2);

      lut = edif_cellref_create(edf, xilinx_cell_lut4(xlib));
      edif_cellref_pstring(lut, "INIT", "F731");

      jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, 0));
      edif_add_to_joint(jnt, lut, LUT_I2);

      jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, 0));
      edif_add_to_joint(jnt, lut, LUT_I0);

      jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, 1));
      edif_add_to_joint(jnt, lut, LUT_I3);

      jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, 1));
      edif_add_to_joint(jnt, lut, LUT_I1);

	/* There are only two slices, so this is all we need. */
      if (ivl_lpm_width(net) == 2) {
	    jnt = edif_joint_of_nexus(edf, ivl_lpm_q(net, 0));
	    edif_add_to_joint(jnt, lut, LUT_O);
	    return;
      }

	/* The general case requires that we make the >= comparator
	   from slices. This is an iterative design. Each slice has
	   the truth table:

	      An Bn | A >= B
	      ------+-------
	      0  0  |   CI
	      0  1  |   0
	      1  0  |   1
	      1  1  |   CI

	   The CI for each slice is the output of the compare of the
	   next less significant bits. We get this truth table by
	   connecting a LUT2 to the S input of a MUXCY. When the S
	   input is (1), it propagates its CI. This suggests that the
	   init value for the LUT be "9" (XNOR).

	   When the MUXCY S input is 0, it propagates a local
	   input. We connect to that input An, and we get the desired
	   and complete truth table for a slice.

	   This iterative definition needs to terminate at the least
	   significant bits. In fact, we have a non-iterative was to
	   deal with the two least significant slices. We take the
	   output of the LUT4 device for the least significant bits,
	   and use that to generate the initial CI for the chain. */


      muxcy_prev = edif_cellref_create(edf, xilinx_cell_muxcy_l(xlib));
      jnt = edif_joint_create(edf);

      edif_add_to_joint(jnt, lut, LUT_O);
      edif_add_to_joint(jnt, muxcy_prev, MUXCY_S);
      { edif_cellref_t p0 = edif_cellref_create(edf, cell_0);
        edif_cellref_t p1 = edif_cellref_create(edf, cell_1);

	jnt = edif_joint_create(edf);
	edif_add_to_joint(jnt, p0, 0);
	edif_add_to_joint(jnt, muxcy_prev, MUXCY_DI);

	jnt = edif_joint_create(edf);
	edif_add_to_joint(jnt, p1, 0);
	edif_add_to_joint(jnt, muxcy_prev, MUXCY_CI);
      }

      for (idx = 2 ;  idx < ivl_lpm_width(net) ;  idx += 1) {
	    edif_cellref_t muxcy;

	    lut = edif_cellref_create(edf, xilinx_cell_lut2(xlib));
	    muxcy = edif_cellref_create(edf, xilinx_cell_muxcy(xlib));
	    edif_cellref_pstring(lut, "INIT", "9");

	    jnt = edif_joint_create(edf);
	    edif_add_to_joint(jnt, lut,   LUT_O);
	    edif_add_to_joint(jnt, muxcy, MUXCY_S);

	    jnt = edif_joint_create(edf);
	    edif_add_to_joint(jnt, muxcy, MUXCY_CI);
	    edif_add_to_joint(jnt, muxcy_prev, MUXCY_O);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_data(net, idx));
	    edif_add_to_joint(jnt, lut, LUT_I0);
	    edif_add_to_joint(jnt, muxcy, MUXCY_DI);

	    jnt = edif_joint_of_nexus(edf, ivl_lpm_datab(net, idx));
	    edif_add_to_joint(jnt, lut, LUT_I1);

	    muxcy_prev = muxcy;
      }

      jnt = edif_joint_of_nexus(edf, ivl_lpm_q(net, 0));
      edif_add_to_joint(jnt, muxcy_prev, MUXCY_O);
}

const struct device_s d_virtex2_edif = {
      virtex2_show_header,
      virtex2_show_footer,
      virtex2_show_scope,
      virtex2_pad,
      virtex2_logic,
      virtex2_generic_dff,
      virtex_eq,
      virtex_eq,
      virtex2_cmp_ge,
      0,
      virtex2_add,
      virtex2_add,
      virtex2_show_shiftl, /* show_shiftl */
      0  /* show_shiftr */
};


/*
 * $Log: d-virtex2.c,v $
 * Revision 1.13  2003/06/25 01:49:06  steve
 *  Spelling fixes.
 *
 * Revision 1.12  2003/06/25 01:46:44  steve
 *  Virtex support for NOT gates.
 *
 * Revision 1.11  2003/06/24 03:55:00  steve
 *  Add ivl_synthesis_cell support for virtex2.
 *
 * Revision 1.10  2003/04/05 05:53:34  steve
 *  Move library cell management to common file.
 *
 * Revision 1.9  2003/04/05 01:35:40  steve
 *  Fix LUT function for chained NE.
 *
 * Revision 1.8  2003/04/04 06:20:29  steve
 *  Add == and some lut logic.
 *
 * Revision 1.7  2003/04/04 04:59:03  steve
 *  Add xlibrary celltable.
 *
 * Revision 1.6  2003/03/31 01:34:19  steve
 *  Wide shift of MUX was wrong.
 *
 * Revision 1.5  2003/03/31 00:25:19  steve
 *  Fix wrong input constant to bottom of GE.
 *
 * Revision 1.4  2003/03/31 00:04:21  steve
 *  Proper sliced >= comparator.
 *
 * Revision 1.3  2003/03/30 03:43:44  steve
 *  Handle wide ports of macros.
 *
 * Revision 1.2  2003/03/24 02:29:04  steve
 *  Give proper basenames to PAD signals.
 *
 * Revision 1.1  2003/03/24 00:47:54  steve
 *  Add new virtex2 architecture family, and
 *  also the new edif.h EDIF management functions.
 *
 */