ngspice/test_cases/node_collapsing/diode.c

/*
 * This file is part of the OSDI component of NGSPICE.
 * Copyright© 2022 SemiMod GmbH.
 * 
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 *
 * Author: Pascal Kuthe <pascal.kuthe@semimod.de>
 *
 * This is an exemplary implementation of the OSDI interface for the Verilog-A
 * model specified in diode.va. In the future, the OpenVAF compiler shall
 * generate an comparable object file. Primary purpose of this is example to
 * have a concrete example for the OSDI interface, OpenVAF will generate a more
 * optimized implementation.
 *
 */

#include "osdi.h"
#include "string.h"
#include <math.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>

// public interface
extern uint32_t OSDI_VERSION_MAJOR;
extern uint32_t OSDI_VERSION_MINOR;
extern uint32_t OSDI_NUM_DESCRIPTORS;
extern OsdiDescriptor OSDI_DESCRIPTORS[1];

// number of nodes and definitions of node ids for nicer syntax in this file
// note: order should be same as "nodes" list defined later
#define NUM_NODES 4
#define A 0
#define C 1
#define TNODE 2
#define CI 3

#define NUM_COLLAPSIBLE 2

// number of matrix entries and definitions for Jacobian entries for nicer
// syntax in this file
#define NUM_MATRIX 14
#define CI_CI 0
#define CI_C 1
#define C_CI 2
#define C_C 3
#define A_A 4
#define A_CI 5
#define CI_A 6
#define A_TNODE 7
#define C_TNODE 8
#define CI_TNODE 9
#define TNODE_TNODE 10
#define TNODE_A 11
#define TNODE_C 12
#define TNODE_CI 13

// The model structure for the diode
typedef struct DiodeModel
{
  double Rs;
  bool Rs_given;
  double Is;
  bool Is_given;
  double zetars;
  bool zetars_given;
  double N;
  bool N_given;
  double Cj0;
  bool Cj0_given;
  double Vj;
  bool Vj_given;
  double M;
  bool M_given;
  double Rth;
  bool Rth_given;
  double zetarth;
  bool zetarth_given;
  double zetais;
  bool zetais_given;
  double Tnom;
  bool Tnom_given;
  double mfactor; // multiplication factor for parallel devices
  bool mfactor_given;
  // InitError errors[MAX_ERROR_NUM],
} DiodeModel;

// The instace structure for the diode
typedef struct DiodeInstace
{
  double mfactor; // multiplication factor for parallel devices
  bool mfactor_given;
  double temperature;
  double rhs_resist[NUM_NODES];
  double rhs_react[NUM_NODES];
  double jacobian_resist[NUM_MATRIX];
  double jacobian_react[NUM_MATRIX];
  bool is_collapsible[NUM_COLLAPSIBLE];
  double *jacobian_ptr_resist[NUM_MATRIX];
  double *jacobian_ptr_react[NUM_MATRIX];
  uint32_t node_off[NUM_NODES];
} DiodeInstace;

#define EXP_LIM 80.0

double limexp(double x)
{
  if (x < EXP_LIM)
  {
    return exp(x);
  }
  else
  {
    return exp(EXP_LIM) * (x + 1 - EXP_LIM);
  }
}

double dlimexp(double x)
{
  if (x < EXP_LIM)
  {
    return exp(x);
  }
  else
  {
    return exp(EXP_LIM);
  }
}

// implementation of the access function as defined by the OSDI spec
void *osdi_access(void *inst_, void *model_, uint32_t id, uint32_t flags)
{
  DiodeModel *model = (DiodeModel *)model_;
  DiodeInstace *inst = (DiodeInstace *)inst_;

  bool *given;
  void *value;

  switch (id) // id of params defined in param_opvar array
  {
  case 0:
    if (flags & ACCESS_FLAG_INSTANCE)
    {
      value = (void *)&inst->mfactor;
      given = &inst->mfactor_given;
    }
    else
    {
      value = (void *)&model->mfactor;
      given = &model->mfactor_given;
    }
    break;
  case 1:
    value = (void *)&model->Rs;
    given = &model->Rs_given;
    break;
  case 2:
    value = (void *)&model->Is;
    given = &model->Is_given;
    break;
  case 3:
    value = (void *)&model->zetars;
    given = &model->zetars_given;
    break;
  case 4:
    value = (void *)&model->N;
    given = &model->N_given;
    break;
  case 5:
    value = (void *)&model->Cj0;
    given = &model->Cj0_given;
    break;
  case 6:
    value = (void *)&model->Vj;
    given = &model->Vj_given;
    break;
  case 7:
    value = (void *)&model->M;
    given = &model->M_given;
    break;
  case 8:
    value = &model->Rth;
    given = &model->Rth_given;
    break;
  case 9:
    value = (void *)&model->zetarth;
    given = &model->zetarth_given;
    break;
  case 10:
    value = (void *)&model->zetais;
    given = &model->zetais_given;
    break;
  case 11:
    value = (void *)&model->Tnom;
    given = &model->Tnom_given;
    break;
  default:
    return NULL;
  }

  if (flags & ACCESS_FLAG_SET)
  {
    *given = true;
  }

  return value;
}

// implementation of the setup_model function as defined in the OSDI spec
OsdiInitInfo setup_model(void *_handle, void *model_)
{
  DiodeModel *model = (DiodeModel *)model_;

  // set parameters and check bounds
  if (!model->mfactor_given)
  {
    model->mfactor = 1.0;
  }
  if (!model->Rs_given)
  {
    model->Rs = 1e-9;
  }
  if (!model->Is_given)
  {
    model->Is = 1e-14;
  }
  if (!model->zetars_given)
  {
    model->zetars = 0;
  }
  if (!model->N_given)
  {
    model->N = 1;
  }
  if (!model->Cj0_given)
  {
    model->Cj0 = 0;
  }
  if (!model->Vj_given)
  {
    model->Vj = 1.0;
  }
  if (!model->M_given)
  {
    model->M = 0.5;
  }
  if (!model->Rth_given)
  {
    model->Rth = 0;
  }
  if (!model->zetarth_given)
  {
    model->zetarth = 0;
  }
  if (!model->zetais_given)
  {
    model->zetais = 0;
  }
  if (!model->Tnom_given)
  {
    model->Tnom = 300;
  }

  return (OsdiInitInfo){.flags = 0, .num_errors = 0, .errors = NULL};
}

// implementation of the setup_instace function as defined in the OSDI spec
OsdiInitInfo setup_instance(void *_handle, void *inst_, void *model_,
                            double temperature, uint32_t _num_terminals)
{
  DiodeInstace *inst = (DiodeInstace *)inst_;
  DiodeModel *model = (DiodeModel *)model_;

  // Here the logic for node collapsing ist implemented. The indices in this list must adhere to the "collapsible" List of node pairs.
  if (model->Rs<1e-9){ // Rs between Ci C
    inst->is_collapsible[0] = true;
  }
  if (model->Rth<1e-9){ // Rs between Ci C
    inst->is_collapsible[1] = true;
  }

  if (!inst->mfactor_given)
  {
    if (model->mfactor_given)
    {
      inst->mfactor = model->mfactor;
    }
    else
    {
      inst->mfactor = 1;
    }
  }

  inst->temperature = temperature;
  return (OsdiInitInfo){.flags = 0, .num_errors = 0, .errors = NULL};
}

// implementation of the eval function as defined in the OSDI spec
uint32_t eval(void *handle, void *inst_, void *model_, uint32_t flags,
              double *prev_solve, OsdiSimParas *sim_params)
{
  DiodeModel *model = (DiodeModel *)model_;
  DiodeInstace *inst = (DiodeInstace *)inst_;

  // get voltages
  double va = prev_solve[inst->node_off[A]];
  double vc = prev_solve[inst->node_off[C]];
  double vci = prev_solve[inst->node_off[CI]];
  double vdtj = prev_solve[inst->node_off[TNODE]];

  double vcic = vci - vc;
  double vaci = va - vci;

  double gmin = 1e-12;
  for (int i = 0; sim_params->names[i] != NULL; i++)
  {
    if (strcmp(sim_params->names[i], "gmin") == 0)
    {
      gmin = sim_params->vals[i];
    }
  }

  ////////////////////////////////
  // evaluate model equations
  ////////////////////////////////

  // temperature update
  double pk = 1.3806503e-23;
  double pq = 1.602176462e-19;
  double t_dev = inst->temperature + vdtj;
  double tdev_tnom = t_dev / model->Tnom;
  double rs_t = model->Rs * powf(tdev_tnom, model->zetars);
  double rth_t = model->Rth * powf(tdev_tnom, model->zetarth);
  double is_t = model->Is * powf(tdev_tnom, model->zetais);
  double vt = t_dev * pk / pq;

  // derivatives w.r.t. temperature
  double rs_dt = model->zetars * model->Rs *
                 powf(tdev_tnom, model->zetars - 1.0) / model->Tnom;
  double rth_dt = model->zetarth * model->Rth *
                  powf(tdev_tnom, model->zetarth - 1.0) / model->Tnom;
  double is_dt = model->zetais * model->Is *
                 powf(tdev_tnom, model->zetais - 1.0) / model->Tnom;
  double vt_tj = pk / pq;

  // evaluate model equations and calculate all derivatives
  // diode current
  double id = is_t * (limexp(vaci / (model->N * vt)) - 1.0);
  double gd = is_t / vt * dlimexp(vaci / (model->N * vt));
  double gdt = -is_t * dlimexp(vaci / (model->N * vt)) * vaci / model->N / vt /
                   vt * vt_tj +
               1.0 * exp((vaci / (model->N * vt)) - 1.0) * is_dt;

  // resistor
  double irs = 0;
  double g = 0;
  double grt = 0;
  if (!inst->is_collapsible[0]) {
    irs = vcic / rs_t;
    g = 1.0 / rs_t;
    grt = -irs / rs_t * rs_dt;
  }


  // thermal resistance
  double irth = 0;
  double gt = 0;
  if (!inst->is_collapsible[1]) {
    irth = vdtj / rth_t;
    gt = 1.0 / rth_t - irth / rth_t * rth_dt;
  }

  // charge
  double vf = model->Vj * (1.0 - powf(3.04, -1.0 / model->M));
  double x = (vf - vaci) / vt;
  double x_vt = -x / vt;
  double x_dtj = x_vt * vt_tj;
  double x_vaci = -1.0 / vt;
  double y = sqrt(x * x + 1.92);
  double y_x = 0.5 / y * 2.0 * x;
  double y_vaci = y_x * x_vaci;
  double y_dtj = y_x * x_dtj;
  double vd = vf - vt * (x + y) / (2.0);
  double vd_x = -vt / 2.0;
  double vd_y = -vt / 2.0;
  double vd_vt = -(x + y) / (2.0);
  double vd_dtj = vd_x * x_dtj + vd_y * y_dtj + vd_vt * vt_tj;
  double vd_vaci = vd_x * x_vaci + vd_y * y_vaci;
  double qd = model->Cj0 * vaci * model->Vj *
              (1.0 - powf(1.0 - vd / model->Vj, 1.0 - model->M)) /
              (1.0 - model->M);
  double qd_vd = model->Cj0 * model->Vj / (1.0 - model->M) * (1.0 - model->M) *
                 powf(1.0 - vd / model->Vj, 1.0 - model->M - 1.0) / model->Vj;
  double qd_dtj = qd_vd * vd_dtj;
  double qd_vaci = qd_vd * vd_vaci;

  // thermal power source = current source
  double ith = id * vaci ;
  double ith_vtj = gdt * vaci ;
  double ith_vcic = 0;
  double ith_vaci = gd * vaci + id;
  if (!inst->is_collapsible[0]) {
    ith_vcic = 2.0 * vcic / rs_t;
    ith += powf(vcic, 2.0) / rs_t;
    ith_vtj -= - powf(vcic, 2.0) / rs_t / rs_t * rs_dt;
  }

  id += gmin * vaci;
  gd += gmin;

  double mfactor = inst->mfactor;

  ////////////////
  // write rhs
  ////////////////

  if (flags & CALC_RESIST_RESIDUAL)
  {
    // write resist rhs
    inst->rhs_resist[A] = id * mfactor;
    inst->rhs_resist[CI] = -id * mfactor + irs * mfactor;
    inst->rhs_resist[C] = -irs * mfactor;
    inst->rhs_resist[TNODE] = -ith * mfactor + irth * mfactor;
  }

  if (flags & CALC_REACT_RESIDUAL)
  {
    // write react rhs
    inst->rhs_react[A] = qd * mfactor;
    inst->rhs_react[CI] = -qd * mfactor;
  }

  //////////////////
  // write Jacobian
  //////////////////

  if (flags & CALC_RESIST_JACOBIAN)
  {
    // stamp diode (current flowing from Ci into A)
    inst->jacobian_resist[A_A] = gd * mfactor;
    inst->jacobian_resist[A_CI] = -gd * mfactor;
    inst->jacobian_resist[CI_A] = -gd * mfactor;
    inst->jacobian_resist[CI_CI] = gd * mfactor;
    // diode thermal
    inst->jacobian_resist[A_TNODE] = gdt * mfactor;
    inst->jacobian_resist[CI_TNODE] = -gdt * mfactor;

    // stamp resistor (current flowing from C into CI)
    inst->jacobian_resist[CI_CI] += g * mfactor;
    inst->jacobian_resist[CI_C] = -g * mfactor;
    inst->jacobian_resist[C_CI] = -g * mfactor;
    inst->jacobian_resist[C_C] = g * mfactor;
    // resistor thermal
    inst->jacobian_resist[CI_TNODE] = grt * mfactor;
    inst->jacobian_resist[C_TNODE] = -grt * mfactor;

    // stamp rth flowing into node dTj
    inst->jacobian_resist[TNODE_TNODE] = gt * mfactor;

    // stamp ith flowing out of T node
    inst->jacobian_resist[TNODE_TNODE] -= ith_vtj * mfactor;
    inst->jacobian_resist[TNODE_CI] = (ith_vcic - ith_vaci) * mfactor;
    inst->jacobian_resist[TNODE_C] = -ith_vcic * mfactor;
    inst->jacobian_resist[TNODE_A] = ith_vaci * mfactor;
  }

  if (flags & CALC_REACT_JACOBIAN)
  {
    // write react matrix
    // stamp Qd between nodes A and Ci depending also on dT
    inst->jacobian_react[A_A] = qd_vaci * mfactor;
    inst->jacobian_react[A_CI] = -qd_vaci * mfactor;
    inst->jacobian_react[CI_A] = -qd_vaci * mfactor;
    inst->jacobian_react[CI_CI] = qd_vaci * mfactor;

    inst->jacobian_react[A_TNODE] = qd_dtj * mfactor;
    inst->jacobian_react[CI_TNODE] = -qd_dtj * mfactor;
  }

  return 0;
}

// TODO implementation of the load_noise function as defined in the OSDI spec
void load_noise(void *inst, void *model, double freq, double *noise_dens,
                double *ln_noise_dens)
{
  // TODO add noise to example
}

#define LOAD_RHS_RESIST(name) \
  dst[inst->node_off[name]] += inst->rhs_resist[name];

// implementation of the load_rhs_resist function as defined in the OSDI spec
void load_residual_resist(void *inst_, double *dst)
{
  DiodeInstace *inst = (DiodeInstace *)inst_;

  LOAD_RHS_RESIST(A)
  LOAD_RHS_RESIST(CI)
  LOAD_RHS_RESIST(C)
  LOAD_RHS_RESIST(TNODE)
}

#define LOAD_RHS_REACT(name) dst[inst->node_off[name]] += inst->rhs_react[name];

// implementation of the load_rhs_react function as defined in the OSDI spec
void load_residual_react(void *inst_, double *dst)
{
  DiodeInstace *inst = (DiodeInstace *)inst_;

  LOAD_RHS_REACT(A)
  LOAD_RHS_REACT(CI)
}

#define LOAD_MATRIX_RESIST(name) \
  *inst->jacobian_ptr_resist[name] += inst->jacobian_resist[name];

// implementation of the load_matrix_resist function as defined in the OSDI spec
void load_jacobian_resist(void *inst_)
{
  DiodeInstace *inst = (DiodeInstace *)inst_;
  LOAD_MATRIX_RESIST(A_A)
  LOAD_MATRIX_RESIST(A_CI)
  LOAD_MATRIX_RESIST(A_TNODE)

  LOAD_MATRIX_RESIST(CI_A)
  LOAD_MATRIX_RESIST(CI_CI)
  LOAD_MATRIX_RESIST(CI_C)
  LOAD_MATRIX_RESIST(CI_TNODE)

  LOAD_MATRIX_RESIST(C_CI)
  LOAD_MATRIX_RESIST(C_C)
  LOAD_MATRIX_RESIST(C_TNODE)

  LOAD_MATRIX_RESIST(TNODE_TNODE)
  LOAD_MATRIX_RESIST(TNODE_A)
  LOAD_MATRIX_RESIST(TNODE_C)
  LOAD_MATRIX_RESIST(TNODE_CI)
}

#define LOAD_MATRIX_REACT(name) \
  *inst->jacobian_ptr_react[name] += inst->jacobian_react[name] * alpha;

// implementation of the load_matrix_react function as defined in the OSDI spec
void load_jacobian_react(void *inst_, double alpha)
{
  DiodeInstace *inst = (DiodeInstace *)inst_;
  LOAD_MATRIX_REACT(A_A)
  LOAD_MATRIX_REACT(A_CI)
  LOAD_MATRIX_REACT(CI_A)
  LOAD_MATRIX_REACT(CI_CI)

  LOAD_MATRIX_REACT(A_TNODE)
  LOAD_MATRIX_REACT(CI_TNODE)
}

#define LOAD_MATRIX_TRAN(name) \
  *inst->jacobian_ptr_resist[name] += inst->jacobian_react[name] * alpha;

// implementation of the load_matrix_tran function as defined in the OSDI spec
void load_jacobian_tran(void *inst_, double alpha)
{
  DiodeInstace *inst = (DiodeInstace *)inst_;

  // set dc stamps
  load_jacobian_resist(inst_);

  // add reactive contributions
  LOAD_MATRIX_TRAN(A_A)
  LOAD_MATRIX_TRAN(A_CI)
  LOAD_MATRIX_TRAN(CI_A)
  LOAD_MATRIX_TRAN(CI_CI)

  LOAD_MATRIX_TRAN(A_TNODE)
  LOAD_MATRIX_TRAN(CI_TNODE)
}

// implementation of the load_spice_rhs_dc function as defined in the OSDI spec
void load_spice_rhs_dc(void *inst_, double *dst, double *prev_solve)
{
  DiodeInstace *inst = (DiodeInstace *)inst_;
  double va = prev_solve[inst->node_off[A]];
  double vci = prev_solve[inst->node_off[CI]];
  double vc = prev_solve[inst->node_off[C]];
  double vdtj = prev_solve[inst->node_off[TNODE]];

  dst[inst->node_off[A]] += inst->jacobian_resist[A_A] * va +
                            inst->jacobian_resist[A_TNODE] * vdtj +
                            inst->jacobian_resist[A_CI] * vci -
                            inst->rhs_resist[A];

  dst[inst->node_off[CI]] += inst->jacobian_resist[CI_A] * va +
                             inst->jacobian_resist[CI_TNODE] * vdtj +
                             inst->jacobian_resist[CI_CI] * vci -
                             inst->rhs_resist[CI];

  dst[inst->node_off[C]] += inst->jacobian_resist[C_C] * vc +
                            inst->jacobian_resist[C_CI] * vci +
                            inst->jacobian_resist[C_TNODE] * vdtj -
                            inst->rhs_resist[C];

  dst[inst->node_off[TNODE]] += inst->jacobian_resist[TNODE_A] * va +
                                inst->jacobian_resist[TNODE_C] * vc +
                                inst->jacobian_resist[TNODE_CI] * vci +
                                inst->jacobian_resist[TNODE_TNODE] * vdtj -
                                inst->rhs_resist[TNODE];
}

// implementation of the load_spice_rhs_tran function as defined in the OSDI
// spec
void load_spice_rhs_tran(void *inst_, double *dst, double *prev_solve,
                         double alpha)
{

  DiodeInstace *inst = (DiodeInstace *)inst_;
  double va = prev_solve[inst->node_off[A]];
  double vci = prev_solve[inst->node_off[CI]];
  double vdtj = prev_solve[inst->node_off[TNODE]];

  // set DC rhs
  load_spice_rhs_dc(inst_, dst, prev_solve);

  // add contributions due to reactive elements
  dst[inst->node_off[A]] +=
      alpha * (inst->jacobian_react[A_A] * va +
               inst->jacobian_react[A_CI] * vci +
               inst->jacobian_react[A_TNODE] * vdtj);

  dst[inst->node_off[CI]] += alpha * (inst->jacobian_react[CI_CI] * vci +
                                      inst->jacobian_react[CI_A] * va +
                                      inst->jacobian_react[CI_TNODE] * vdtj);
}

// structure that provides information of all nodes of the model
OsdiNode nodes[NUM_NODES] = {
    {.name = "A", .units = "V", .is_reactive = true},
    {.name = "C", .units = "V"},
    {.name = "dT", .units = "K"},
    {.name = "CI", .units = "V", .is_reactive = true},
};

// boolean array that tells which Jacobian entries are constant. Nothing is
// constant with selfheating, though.
bool const_jacobian_entries[NUM_MATRIX] = {};
// these node pairs specify which entries in the Jacobian must be accounted for
OsdiNodePair jacobian_entries[NUM_MATRIX] = {
    {CI, CI},
    {CI, C},
    {C, CI},
    {C, C},
    {A, A},
    {A, CI},
    {CI, A},
    {A, TNODE},
    {C, TNODE},
    {CI, TNODE},
    {TNODE, TNODE},
    {TNODE, A},
    {TNODE, C},
    {TNODE, CI},
};
OsdiNodePair collapsible[NUM_COLLAPSIBLE] = {
    {CI, C},
    {TNODE, NUM_NODES},
};

#define NUM_PARAMS 12
// the model parameters as defined in Verilog-A, bounds and default values are
// stored elsewhere as they may depend on model parameters etc.
OsdiParamOpvar params[NUM_PARAMS] = {
    {
        .name = (char *[]){"$mfactor"},
        .num_alias = 0,
        .description = "Verilog-A multiplication factor for parallel devices",
        .units = "",
        .flags = PARA_TY_REAL | PARA_KIND_INST,
        .len = 0,
    },
    {
        .name = (char *[]){"Rs"},
        .num_alias = 0,
        .description = "Ohmic res",
        .units = "Ohm",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
    {
        .name = (char *[]){"Is"},
        .num_alias = 0,
        .description = "Saturation current",
        .units = "A",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
    {
        .name = (char *[]){"zetars"},
        .num_alias = 0,
        .description = "Temperature coefficient of ohmic res",
        .units = "",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
    {
        .name = (char *[]){"N"},
        .num_alias = 0,
        .description = "Emission coefficient",
        .units = "",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
    {
        .name = (char *[]){"Cj0"},
        .num_alias = 0,
        .description = "Junction capacitance",
        .units = "F",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
    {
        .name = (char *[]){"Vj"},
        .num_alias = 0,
        .description = "Junction potential",
        .units = "V",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
    {
        .name = (char *[]){"M"},
        .num_alias = 0,
        .description = "Grading coefficient",
        .units = "",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
    {
        .name = (char *[]){"Rth"},
        .num_alias = 0,
        .description = "Thermal resistance",
        .units = "K/W",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
    {
        .name = (char *[]){"zetarth"},
        .num_alias = 0,
        .description = "Temperature coefficient of thermal res",
        .units = "",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
    {
        .name = (char *[]){"zetais"},
        .num_alias = 0,
        .description = "Temperature coefficient of Is",
        .units = "",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
    {
        .name = (char *[]){"Tnom"},
        .num_alias = 0,
        .description = "Reference temperature",
        .units = "",
        .flags = PARA_TY_REAL | PARA_KIND_MODEL,
        .len = 0,
    },
};

// fill exported data
uint32_t OSDI_VERSION_MAJOR = OSDI_VERSION_MAJOR_CURR;
uint32_t OSDI_VERSION_MINOR = OSDI_VERSION_MINOR_CURR;
uint32_t OSDI_NUM_DESCRIPTORS = 1;
// this is the main structure used by simulators, it gives access to all
// information in a model
OsdiDescriptor OSDI_DESCRIPTORS[1] = {{
    // metadata
    .name = "diode_va",

    // nodes
    .num_nodes = NUM_NODES,
    .num_terminals = 3,
    .nodes = (OsdiNode *)&nodes,

    // matrix entries
    .num_jacobian_entries = NUM_MATRIX,
    .jacobian_entries = (OsdiNodePair *)&jacobian_entries,
    .const_jacobian_entries = (bool *)&const_jacobian_entries,

    // memory
    .instance_size = sizeof(DiodeInstace),
    .model_size = sizeof(DiodeModel),
    .residual_resist_offset = offsetof(DiodeInstace, rhs_resist),
    .residual_react_offset = offsetof(DiodeInstace, rhs_react),
    .node_mapping_offset = offsetof(DiodeInstace, node_off),
    .jacobian_resist_offset = offsetof(DiodeInstace, jacobian_resist),
    .jacobian_react_offset = offsetof(DiodeInstace, jacobian_react),
    .jacobian_ptr_resist_offset = offsetof(DiodeInstace, jacobian_ptr_resist),
    .jacobian_ptr_react_offset = offsetof(DiodeInstace, jacobian_ptr_react),

    // node collapsing
    .num_collapsible = NUM_COLLAPSIBLE,
    .collapsible = collapsible,
    .is_collapsible_offset = offsetof(DiodeInstace, is_collapsible),

    // noise
    .noise_sources = NULL,
    .num_noise_src = 0,

    // parameters and op vars
    .num_params = NUM_PARAMS,
    .num_instance_params = 1,
    .num_opvars = 0,
    .param_opvar = (OsdiParamOpvar *)&params,

    // setup
    .access = &osdi_access,
    .setup_model = &setup_model,
    .setup_instance = &setup_instance,
    .eval = &eval,
    .load_noise = &load_noise,
    .load_residual_resist = &load_residual_resist,
    .load_residual_react = &load_residual_react,
    .load_spice_rhs_dc = &load_spice_rhs_dc,
    .load_spice_rhs_tran = &load_spice_rhs_tran,
    .load_jacobian_resist = &load_jacobian_resist,
    .load_jacobian_react = &load_jacobian_react,
    .load_jacobian_tran = &load_jacobian_tran,
}};