/* * Copyright (c) 2000 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: link_const.cc,v 1.18 2007/04/14 03:10:51 steve Exp $" #endif # include "config.h" # include "netlist.h" # include "netmisc.h" /* * Scan the link for drivers. If there are only constant drivers, then * the nexus has a known constant value. If there is a supply net, * then the nexus again has a known constant value. */ bool Nexus::drivers_constant() const { if (driven_ == VAR) return false; if (driven_ != NO_GUESS) return true; for (const Link*cur = list_ ; cur ; cur = cur->next_) { const NetNet*sig; Link::DIR cur_dir; cur_dir = cur->get_dir(); if (cur_dir == Link::INPUT) continue; /* If this is an input or inout port of a root module, then the is probably not a constant value. I certainly don't know what the value is, anyhow. This can happen in cases like this: module main(sig); input sig; endmodule If main is a root module (it has no parent) then sig is not constant because it connects to an unspecified outside world. */ if (cur_dir == Link::PASSIVE) { const NetPins*obj = cur->get_obj(); const NetObj*as_obj = dynamic_cast(obj); if (as_obj == 0 || as_obj->scope()->parent() != 0) continue; sig = dynamic_cast(cur->get_obj()); assert(sig); if (sig->port_type() == NetNet::NOT_A_PORT) continue; if (sig->port_type() == NetNet::POUTPUT) continue; driven_ = VAR; return false; } /* If there is a supply net, then this nexus will have a constant value independent of any drivers. */ if (const NetNet*s = dynamic_cast(cur->get_obj())) switch (s->type()) { case NetNet::SUPPLY0: driven_ = V0; return true; case NetNet::SUPPLY1: driven_ = V1; return true; default: break; } if (! dynamic_cast(cur->get_obj())) { driven_ = VAR; return false; } } return true; } verinum::V Nexus::driven_value() const { switch (driven_) { case V0: return verinum::V0; case V1: return verinum::V1; case Vx: return verinum::Vx; case Vz: return verinum::Vz; case VAR: assert(0); break; case NO_GUESS: break; } const Link*cur = list_; verinum::V val = verinum::Vz; for (cur = list_ ; cur ; cur = cur->next_) { const NetConst*obj; const NetNet*sig; if ((obj = dynamic_cast(cur->get_obj()))) { val = obj->value(cur->get_pin()); } else if ((sig = dynamic_cast(cur->get_obj()))) { // If we find an attached SUPPLY0/1, the we know // from that what the driven value is. Stop now. if (sig->type() == NetNet::SUPPLY0) { driven_ = V0; return verinum::V0; } if (sig->type() == NetNet::SUPPLY1) { driven_ = V1; return verinum::V1; } // If we find an attached TRI0/1, then this is a // good guess for the driven value, but keep // looking for something better. if (sig->type() == NetNet::TRI0) { val = verinum::V0; } if (sig->type() == NetNet::TRI1) { val = verinum::V1; } } } /* Cache the result. */ switch (val) { case verinum::V0: driven_ = V0; break; case verinum::V1: driven_ = V1; break; case verinum::Vx: driven_ = Vx; break; case verinum::Vz: driven_ = Vz; break; } return val; } /* * $Log: link_const.cc,v $ * Revision 1.18 2007/04/14 03:10:51 steve * Properly account for tri0 connected to otherwise open mux input. * * Revision 1.17 2004/10/04 01:10:53 steve * Clean up spurious trailing white space. * * Revision 1.16 2003/06/21 01:21:43 steve * Harmless fixup of warnings. * * Revision 1.15 2002/08/12 01:34:59 steve * conditional ident string using autoconfig. * * Revision 1.14 2002/06/25 01:33:22 steve * Cache calculated driven value. * * Revision 1.13 2002/06/24 01:49:39 steve * Make link_drive_constant cache its results in * the Nexus, to improve cprop performance. * * Revision 1.12 2002/06/19 04:18:46 steve * Shuffle link_drivers_constant for speed. * * Revision 1.11 2001/08/25 23:50:03 steve * Change the NetAssign_ class to refer to the signal * instead of link into the netlist. This is faster * and uses less space. Make the NetAssignNB carry * the delays instead of the NetAssign_ lval objects. * * Change the vvp code generator to support multiple * l-values, i.e. concatenations of part selects. * * Revision 1.10 2001/07/25 03:10:49 steve * Create a config.h.in file to hold all the config * junk, and support gcc 3.0. (Stephan Boettcher) * * Revision 1.9 2001/07/07 03:01:37 steve * Detect and make available to t-dll the right shift. * * Revision 1.8 2001/02/16 03:27:07 steve * links to root inputs are not constant. * * Revision 1.7 2000/11/20 01:41:12 steve * Whoops, return the calculated constant value rom driven_value. * * Revision 1.6 2000/11/20 00:58:40 steve * Add support for supply nets (PR#17) * * Revision 1.5 2000/07/14 06:12:57 steve * Move inital value handling from NetNet to Nexus * objects. This allows better propogation of inital * values. * * Clean up constant propagation a bit to account * for regs that are not really values. * * Revision 1.4 2000/06/25 19:59:42 steve * Redesign Links to include the Nexus class that * carries properties of the connected set of links. * * Revision 1.3 2000/05/14 17:55:04 steve * Support initialization of FF Q value. * * Revision 1.2 2000/05/07 04:37:56 steve * Carry strength values from Verilog source to the * pform and netlist for gates. * * Change vvm constants to use the driver_t to drive * a constant value. This works better if there are * multiple drivers on a signal. * * Revision 1.1 2000/04/20 00:28:03 steve * Catch some simple identity compareoptimizations. * */