DmpDelayCalc.cc

// OpenSTA, Static Timing Analyzer
// Copyright (c) 2021, Parallax Software, Inc.
// 
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 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, see <https://www.gnu.org/licenses/>.

#include "DmpDelayCalc.hh"

#include "TableModel.hh"
#include "TimingArc.hh"
#include "Liberty.hh"
#include "Sdc.hh"
#include "Parasitics.hh"
#include "DcalcAnalysisPt.hh"
#include "GraphDelayCalc.hh"
#include "DmpCeff.hh"

namespace sta {

// PiElmore parasitic delay calculator using Dartu/Menezes/Pileggi
// effective capacitance and elmore delay.
class DmpCeffElmoreDelayCalc : public DmpCeffDelayCalc
{
public:
  DmpCeffElmoreDelayCalc(StaState *sta);
  virtual ArcDelayCalc *copy();
  virtual void gateDelay(const LibertyCell *drvr_cell,
			 TimingArc *arc,
			 const Slew &in_slew,
			 float load_cap,
			 Parasitic *drvr_parasitic,
			 float related_out_cap,
			 const Pvt *pvt,
			 const DcalcAnalysisPt *dcalc_ap,
			 // Return values.
			 ArcDelay &gate_,
			 Slew &drvr_slew);
  virtual void loadDelay(const Pin *load_pin,
			 ArcDelay &wire_delay,
			 Slew &load_slew);
};

ArcDelayCalc *
makeDmpCeffElmoreDelayCalc(StaState *sta)
{
  return new DmpCeffElmoreDelayCalc(sta);
}

DmpCeffElmoreDelayCalc::DmpCeffElmoreDelayCalc(StaState *sta) :
  DmpCeffDelayCalc(sta)
{
}

ArcDelayCalc *
DmpCeffElmoreDelayCalc::copy()
{
  return new DmpCeffElmoreDelayCalc(this);
}

void
DmpCeffElmoreDelayCalc::gateDelay(const LibertyCell *drvr_cell,
				  TimingArc *arc,
				  const Slew &in_slew,
				  float load_cap,
				  Parasitic *drvr_parasitic,
				  float related_out_cap,
				  const Pvt *pvt,
				  const DcalcAnalysisPt *dcalc_ap,
				  // Return values.
				  ArcDelay &gate_delay,
				  Slew &drvr_slew)
{
  DmpCeffDelayCalc::gateDelay(drvr_cell, arc, in_slew,
			      load_cap, drvr_parasitic, related_out_cap,
			      pvt, dcalc_ap,
			      gate_delay, drvr_slew);
}

void
DmpCeffElmoreDelayCalc::loadDelay(const Pin *load_pin,
				  ArcDelay &wire_delay,
				  Slew &load_slew)
{
  ArcDelay wire_delay1 = 0.0;
  Slew load_slew1 = drvr_slew_;
  bool elmore_exists = false;
  float elmore = 0.0;
  if (drvr_parasitic_)
    parasitics_->findElmore(drvr_parasitic_, load_pin, elmore, elmore_exists);
  if (elmore_exists) {
    if (input_port_) {
      // Input port with no external driver.
      if (parasitics_->isReducedParasiticNetwork(drvr_parasitic_))
	dspfWireDelaySlew(load_pin, elmore, wire_delay1, load_slew1);
      else {
	// The elmore delay on an input port is used for the wire
	// delay and the load slew is the same as the driver slew.
	wire_delay1 = elmore;
	load_slew1 = drvr_slew_;
      }
    }
    else
      loadDelaySlew(load_pin, elmore, wire_delay1, load_slew1);
  }
  thresholdAdjust(load_pin, wire_delay1, load_slew1);
  wire_delay = wire_delay1;
  load_slew = load_slew1 * multi_drvr_slew_factor_;
}

////////////////////////////////////////////////////////////////

// PiPoleResidue parasitic delay calculator using Dartu/Menezes/Pileggi
// effective capacitance and two poles/residues.
class DmpCeffTwoPoleDelayCalc : public DmpCeffDelayCalc
{
public:
  DmpCeffTwoPoleDelayCalc(StaState *sta);
  virtual ArcDelayCalc *copy();
  virtual Parasitic *findParasitic(const Pin *drvr_pin,
				   const RiseFall *rf,
				   const DcalcAnalysisPt *dcalc_ap);
  virtual ReducedParasiticType reducedParasiticType() const;
  virtual void inputPortDelay(const Pin *port_pin,
			      float in_slew,
			      const RiseFall *rf,
			      Parasitic *parasitic,
			      const DcalcAnalysisPt *dcalc_ap);
  virtual void gateDelay(const LibertyCell *drvr_cell,
			 TimingArc *arc,
			 const Slew &in_slew,
			 float load_cap,
			 Parasitic *drvr_parasitic,
			 float related_out_cap,
			 const Pvt *pvt,
			 const DcalcAnalysisPt *dcalc_ap,
			 // Return values.
			 ArcDelay &gate_delay,
			 Slew &drvr_slew);
  virtual void loadDelay(const Pin *load_pin,
			 ArcDelay &wire_delay,
			 Slew &load_slew);

private:
  void loadDelay(Parasitic *pole_residue,
		 double p1,
		 double k1,
		 ArcDelay &wire_delay,
		 Slew &load_slew);
  float loadDelay(double vth,
		  double p1,
		  double p2,
		  double k1,
		  double k2,
		  double B,
		  double k1_p1_2,
		  double k2_p2_2,
		  double tt,
		  double y_tt);

  bool parasitic_is_pole_residue_;
  float vth_;
  float vl_;
  float vh_;
  float slew_derate_;
};

ArcDelayCalc *
makeDmpCeffTwoPoleDelayCalc(StaState *sta)
{
  return new DmpCeffTwoPoleDelayCalc(sta);
}

DmpCeffTwoPoleDelayCalc::DmpCeffTwoPoleDelayCalc(StaState *sta) :
  DmpCeffDelayCalc(sta),
  parasitic_is_pole_residue_(false),
  vth_(0.0),
  vl_(0.0),
  vh_(0.0),
  slew_derate_(0.0)
{
}

ArcDelayCalc *
DmpCeffTwoPoleDelayCalc::copy()
{
  return new DmpCeffTwoPoleDelayCalc(this);
}

Parasitic *
DmpCeffTwoPoleDelayCalc::findParasitic(const Pin *drvr_pin,
				       const RiseFall *rf,
				       const DcalcAnalysisPt *dcalc_ap)
{
  // set_load has precidence over parasitics.
  if (!sdc_->drvrPinHasWireCap(drvr_pin)) {
    Parasitic *parasitic = nullptr;
    const ParasiticAnalysisPt *parasitic_ap = dcalc_ap->parasiticAnalysisPt();
    if (parasitics_->haveParasitics()) {
      // Prefer PiPoleResidue.
      parasitic = parasitics_->findPiPoleResidue(drvr_pin, rf,
						 parasitic_ap);
      if (parasitic)
	return parasitic;

      parasitic = parasitics_->findPiElmore(drvr_pin, rf, parasitic_ap);
      if (parasitic)
	return parasitic;

      Parasitic *parasitic_network =
	parasitics_->findParasiticNetwork(drvr_pin, parasitic_ap);
      if (parasitic_network) {
	parasitics_->reduceToPiPoleResidue2(parasitic_network, drvr_pin,
					    dcalc_ap->operatingConditions(),
					    dcalc_ap->corner(),
					    dcalc_ap->constraintMinMax(),
					    parasitic_ap);
	parasitic = parasitics_->findPiPoleResidue(drvr_pin, rf, parasitic_ap);
	reduced_parasitic_drvrs_.push_back(drvr_pin);
	return parasitic;
      }
    }

    const MinMax *cnst_min_max = dcalc_ap->constraintMinMax();
    Wireload *wireload = sdc_->wireloadDefaulted(cnst_min_max);
    if (wireload) {
      float pin_cap, wire_cap, fanout;
      bool has_wire_cap;
      graph_delay_calc_->netCaps(drvr_pin, rf, dcalc_ap,
				 pin_cap, wire_cap, fanout, has_wire_cap);
      parasitic = parasitics_->estimatePiElmore(drvr_pin, rf, wireload,
						fanout, pin_cap,
						dcalc_ap->operatingConditions(),
						dcalc_ap->corner(),
						cnst_min_max,
						parasitic_ap);
      // Estimated parasitics are not recorded in the "database", so
      // it for deletion after the drvr pin delay calc is finished.
      if (parasitic)
	unsaved_parasitics_.push_back(parasitic);
      return parasitic;
    }
  }
  return nullptr;
}

ReducedParasiticType
DmpCeffTwoPoleDelayCalc::reducedParasiticType() const
{
  return ReducedParasiticType::pi_pole_residue2;
}

void
DmpCeffTwoPoleDelayCalc::inputPortDelay(const Pin *port_pin,
					float in_slew,
					const RiseFall *rf,
					Parasitic *parasitic,
					const DcalcAnalysisPt *dcalc_ap)
{
  parasitic_is_pole_residue_ = parasitics_->isPiPoleResidue(parasitic);
  DmpCeffDelayCalc::inputPortDelay(port_pin, in_slew, rf, parasitic, dcalc_ap);
}

void
DmpCeffTwoPoleDelayCalc::gateDelay(const LibertyCell *drvr_cell,
				   TimingArc *arc,
				   const Slew &in_slew,
				   float load_cap,
				   Parasitic *drvr_parasitic,
				   float related_out_cap,
				   const Pvt *pvt,
				   const DcalcAnalysisPt *dcalc_ap,
				   // Return values.
				   ArcDelay &gate_delay,
				   Slew &drvr_slew)
{
  parasitic_is_pole_residue_ = parasitics_->isPiPoleResidue(drvr_parasitic);
  const LibertyLibrary *drvr_library = drvr_cell->libertyLibrary();
  const RiseFall *rf = arc->toTrans()->asRiseFall();
  vth_ = drvr_library->outputThreshold(rf);
  vl_ = drvr_library->slewLowerThreshold(rf);
  vh_ = drvr_library->slewUpperThreshold(rf);
  slew_derate_ = drvr_library->slewDerateFromLibrary();
  DmpCeffDelayCalc::gateDelay(drvr_cell, arc, in_slew,
			      load_cap, drvr_parasitic,
			      related_out_cap, pvt, dcalc_ap,
			      gate_delay, drvr_slew);
}

void
DmpCeffTwoPoleDelayCalc::loadDelay(const Pin *load_pin,
				   ArcDelay &wire_delay,
				   Slew &load_slew)
{
  // NEED to handle PiElmore parasitic.
  ArcDelay wire_delay1 = 0.0;
  Slew load_slew1 = drvr_slew_;
  Parasitic *pole_residue = 0;
  if (parasitic_is_pole_residue_)
    pole_residue = parasitics_->findPoleResidue(drvr_parasitic_, load_pin);
  if (pole_residue) {
    size_t pole_count = parasitics_->poleResidueCount(pole_residue);
    if (pole_count >= 1) {
      ComplexFloat pole1, residue1;
      // Find the 1st (elmore) pole.
      parasitics_->poleResidue(pole_residue, 0, pole1, residue1);
      if (pole1.imag() == 0.0
	  && residue1.imag() == 0.0) {
	float p1 = pole1.real();
	float k1 = residue1.real();
	if (input_port_) {
	  float elmore = 1.0F / p1;
	  // Input port with no external driver.
	  if (parasitics_->isReducedParasiticNetwork(drvr_parasitic_))
	    dspfWireDelaySlew(load_pin, elmore, wire_delay1, load_slew1);
	  else {
	    // For RSPF on an input port the elmore delay is used for the
	    // wire delay and the load slew is the same as the driver slew.
	    wire_delay1 = elmore;
	    load_slew1 = drvr_slew_;
	  }
	}
	else {
	  if (pole_count >= 2)
	    loadDelay(pole_residue, p1, k1, wire_delay1, load_slew1);
	  else {
	    float elmore = 1.0F / p1;
	    wire_delay1 = elmore;
	    load_slew1 = drvr_slew_;
	  }
	}
      }
    }
  }
  thresholdAdjust(load_pin, wire_delay1, load_slew1);
  wire_delay = wire_delay1;
  load_slew = load_slew1 * multi_drvr_slew_factor_;
}

void
DmpCeffTwoPoleDelayCalc::loadDelay(Parasitic *pole_residue,
				   double p1, double k1,
				   ArcDelay &wire_delay,
				   Slew &load_slew)
{
  ComplexFloat pole2, residue2;
  parasitics_->poleResidue(pole_residue, 1, pole2, residue2);
  if (!delayZero(drvr_slew_)
      && pole2.imag() == 0.0
      && residue2.imag() == 0.0) {
    double p2 = pole2.real();
    double k2 = residue2.real();
    double k1_p1_2 = k1 / (p1 * p1);
    double k2_p2_2 = k2 / (p2 * p2);
    double B = k1_p1_2 + k2_p2_2;
    // Convert tt to 0:1 range.
    float tt = delayAsFloat(drvr_slew_) * slew_derate_ / (vh_ - vl_);
    double y_tt = (tt - B + k1_p1_2 * exp(-p1 * tt)
		   + k2_p2_2 * exp(-p2 * tt)) / tt;
    wire_delay = loadDelay(vth_, p1, p2, k1, k2, B, k1_p1_2, k2_p2_2, tt, y_tt)
      - tt * vth_;

    float tl = loadDelay(vl_, p1, p2, k1, k2, B, k1_p1_2, k2_p2_2, tt, y_tt);
    float th = loadDelay(vh_, p1, p2, k1, k2, B, k1_p1_2, k2_p2_2, tt, y_tt);
    load_slew = (th - tl) / slew_derate_;
  }
}

float
DmpCeffTwoPoleDelayCalc::loadDelay(double vth,
				   double p1,
				   double p2,
				   double k1,
				   double k2,
				   double B,
				   double k1_p1_2,
				   double k2_p2_2,
				   double tt,
				   double y_tt)
{
  if (y_tt < vth) {
    // t1 > tt
    // Initial guess.
    double t1 = log(k1 * (exp(p1 * tt) - 1.0) / ((1.0 - vth) * p1 * p1 * tt))/p1;
    // Take one newton-raphson step.
    double exp_p1_t1 = exp(-p1 * t1);
    double exp_p2_t1 = exp(-p2 * t1);
    double exp_p1_t1_tt = exp(-p1 * (t1 - tt));
    double exp_p2_t1_tt = exp(-p2 * (t1 - tt));
    double y_t1 = (tt - k1_p1_2 * (exp_p1_t1_tt - exp_p1_t1)
		   - k2_p2_2 * (exp_p2_t1_tt - exp_p2_t1)) / tt;
    double yp_t1 = (k1 / p1 * (exp_p1_t1_tt - exp_p1_t1)
		    - k2 / p2 * (exp_p2_t1_tt - exp_p2_t1)) / tt;
    double delay = t1 - (y_t1 - vth) / yp_t1;
    return static_cast<float>(delay);
  }
  else {
    // t1 < tt
    // Initial guess based on y(tt).
    double t1 = vth * tt / y_tt;
    // Take one newton-raphson step.
    double exp_p1_t1 = exp(-p1 * t1);
    double exp_p2_t1 = exp(-p2 * t1);
    double y_t1 = (t1 - B + k1_p1_2 * exp_p1_t1
		   + k2_p2_2 * exp_p1_t1) / tt;
    double yp_t1 = (1 - k1 / p1 * exp_p1_t1
		    - k2 / p2 * exp_p2_t1) / tt;
    double delay = t1 - (y_t1 - vth) / yp_t1;
    return static_cast<float>(delay);
  }
}

} // namespace