183 lines
5.1 KiB
C++
183 lines
5.1 KiB
C++
/*
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* Copyright (c) 2000 Stephen Williams (steve@icarus.com)
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*
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* This source code is free software; you can redistribute it
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* and/or modify it in source code form under the terms of the GNU
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* General Public License as published by the Free Software
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* Foundation; either version 2 of the License, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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#if !defined(WINNT) && !defined(macintosh)
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#ident "$Id: link_const.cc,v 1.12 2002/06/19 04:18:46 steve Exp $"
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#endif
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# include "config.h"
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# include "netlist.h"
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# include "netmisc.h"
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/*
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* Scan the link for drivers. If there are only constant drivers, then
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* the nexus has a known constant value. If there is a supply net,
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* then the nexus again has a known constant value.
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*/
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bool link_drivers_constant(const Link&lnk)
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{
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const Nexus*nex = lnk.nexus();
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for (const Link*cur = nex->first_nlink()
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; cur ; cur = cur->next_nlink()) {
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const NetNet*sig;
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Link::DIR cur_dir;
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if (cur == &lnk)
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continue;
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cur_dir = cur->get_dir();
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if (cur_dir == Link::INPUT)
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continue;
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/* If this is an input or inout port of a root module,
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then the is probably not a constant value. I
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certainly don't know what the value is, anyhow. This
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can happen in cases like this:
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module main(sig);
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input sig;
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endmodule
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If main is a root module (it has no parent) then sig
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is not constant because it connects to an unspecified
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outside world. */
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if (cur_dir == Link::PASSIVE) {
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const NetObj*obj = cur->get_obj();
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if (obj->scope()->parent() != 0)
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continue;
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sig = dynamic_cast<const NetNet*>(cur->get_obj());
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assert(sig);
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if (sig->port_type() == NetNet::NOT_A_PORT)
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continue;
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if (sig->port_type() == NetNet::POUTPUT)
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continue;
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return false;
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}
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if (! dynamic_cast<const NetConst*>(cur->get_obj()))
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return false;
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/* If there is a supply net, then this nexus will have a
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constant value independent of any drivers. */
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if (const NetNet*sig = dynamic_cast<const NetNet*>(cur->get_obj()))
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switch (sig->type()) {
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case NetNet::SUPPLY0:
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case NetNet::SUPPLY1:
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return true;
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default:
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break;
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}
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}
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return true;
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}
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verinum::V driven_value(const Link&lnk)
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{
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verinum::V val = lnk.get_init();
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const Nexus*nex = lnk.nexus();
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for (const Link*cur = nex->first_nlink()
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; cur ; cur = cur->next_nlink()) {
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const NetConst*obj;
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const NetNet*sig;
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if (obj = dynamic_cast<const NetConst*>(cur->get_obj())) {
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val = obj->value(cur->get_pin());
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} else if (sig = dynamic_cast<const NetNet*>(cur->get_obj())) {
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if (sig->type() == NetNet::SUPPLY0)
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return verinum::V0;
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if (sig->type() == NetNet::SUPPLY1)
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return verinum::V1;
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}
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}
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return val;
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}
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/*
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* $Log: link_const.cc,v $
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* Revision 1.12 2002/06/19 04:18:46 steve
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* Shuffle link_drivers_constant for speed.
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*
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* Revision 1.11 2001/08/25 23:50:03 steve
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* Change the NetAssign_ class to refer to the signal
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* instead of link into the netlist. This is faster
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* and uses less space. Make the NetAssignNB carry
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* the delays instead of the NetAssign_ lval objects.
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*
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* Change the vvp code generator to support multiple
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* l-values, i.e. concatenations of part selects.
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*
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* Revision 1.10 2001/07/25 03:10:49 steve
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* Create a config.h.in file to hold all the config
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* junk, and support gcc 3.0. (Stephan Boettcher)
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*
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* Revision 1.9 2001/07/07 03:01:37 steve
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* Detect and make available to t-dll the right shift.
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*
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* Revision 1.8 2001/02/16 03:27:07 steve
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* links to root inputs are not constant.
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*
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* Revision 1.7 2000/11/20 01:41:12 steve
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* Whoops, return the calculated constant value rom driven_value.
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*
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* Revision 1.6 2000/11/20 00:58:40 steve
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* Add support for supply nets (PR#17)
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*
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* Revision 1.5 2000/07/14 06:12:57 steve
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* Move inital value handling from NetNet to Nexus
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* objects. This allows better propogation of inital
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* values.
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*
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* Clean up constant propagation a bit to account
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* for regs that are not really values.
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*
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* Revision 1.4 2000/06/25 19:59:42 steve
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* Redesign Links to include the Nexus class that
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* carries properties of the connected set of links.
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*
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* Revision 1.3 2000/05/14 17:55:04 steve
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* Support initialization of FF Q value.
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*
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* Revision 1.2 2000/05/07 04:37:56 steve
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* Carry strength values from Verilog source to the
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* pform and netlist for gates.
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*
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* Change vvm constants to use the driver_t to drive
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* a constant value. This works better if there are
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* multiple drivers on a signal.
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*
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* Revision 1.1 2000/04/20 00:28:03 steve
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* Catch some simple identity compareoptimizations.
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*
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*/
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