devices/res: use model parameter `r' and `res' as default for instances w/o value

and set minimal resistor value to 1 mOhm

src/spicelib/devices/res/res.c

@@ -54,7 +54,8 @@ IFparm RESmPTable[] = { /* model parameters */
     IOPQ(  "kf",     RES_MOD_KF,       IF_REAL,"Flicker noise coefficient"),
     IOPQ(  "af",     RES_MOD_AF,       IF_REAL,"Flicker noise exponent"),
     IOPXU( "tnom",   RES_MOD_TNOM,     IF_REAL,"Parameter measurement temperature"),
-    IP(    "r",      RES_MOD_R,        IF_FLAG,"Device is a resistor model")
+    IOP(   "r",      RES_MOD_R,        IF_REAL,"Resistor model default value"),
+    IOPR(  "res",    RES_MOD_R,        IF_REAL,"Resistor model default value")
 };
 
 char *RESnames[] = {

src/spicelib/devices/res/resdefs.h

@@ -104,6 +104,7 @@ typedef struct sRESmodel {       /* model structure for a resistor */
     double RESshort;        /* amount by which device is shorter than drawn */
     double RESfNcoef;       /* Flicker noise coefficient */
     double RESfNexp;        /* Flicker noise exponent */
+    double RESres;          /* Default model resistance */
     unsigned REStnomGiven       :1; /* flag to indicate nominal temp. was given */
     unsigned REStc1Given        :1; /* flag to indicate tc1 was specified */
     unsigned REStc2Given        :1; /* flag to indicate tc2 was specified */
@@ -114,6 +115,7 @@ typedef struct sRESmodel {       /* model structure for a resistor */
     unsigned RESshortGiven      :1; /* flag to indicate short effect given */
     unsigned RESfNcoefGiven     :1; /* flag to indicate kf given */
     unsigned RESfNexpGiven      :1; /* flag to indicate af given */
+    unsigned RESresGiven        :1; /* flag to indicate model resistance given */
 } RESmodel;
 
 /* device parameters */

src/spicelib/devices/res/resmask.c

@@ -60,6 +60,9 @@ RESmodAsk(CKTcircuit *ckt, GENmodel *inModel, int which, IFvalue *value)
             else
                 value->rValue = 0.0;
             return(OK);
+        case RES_MOD_R:
+            value->rValue = model->RESres;
+            return(OK);
         default:
             return(E_BADPARM);
     }

src/spicelib/devices/res/resmpar.c

@@ -59,8 +59,10 @@ RESmParam(int param, IFvalue *value, GENmodel *inModel)
         model->RESfNexpGiven = TRUE;
         break;
     case RES_MOD_R:
-        /* just being reassured by user that this is a resistor model */
-        /* no-op */
+        if ( value->rValue > 1e-03 ) {
+            model->RESres = value->rValue;
+            model->RESresGiven = TRUE;
+        }
         break;
     default:
         return(E_BADPARM);

src/spicelib/devices/res/resparam.c

@@ -29,8 +29,7 @@ RESparam(int param, IFvalue *value, GENinstance *inst, IFvalue *select)
         break;
     case RES_RESIST:
         /* 0 valued resistor causes ngspice to hang -- can't solve for initial voltage */
-        if ( AlmostEqualUlps( value->rValue, 0, 3 ) ) value->rValue = 0.001; /* 0.0001 should be sufficiently small */
-        /* it's the value that smartspice uses */
+        if ( AlmostEqualUlps( value->rValue, 0, 3 ) ) value->rValue = 0.001; /* 0.001 should be sufficiently small */
         here->RESresist = value->rValue;
         here->RESresGiven = TRUE;
         break;

src/spicelib/devices/res/restemp.c

@@ -62,14 +62,17 @@ REStemp(GENmodel *inModel, CKTcircuit *ckt)
             if(!here->RESmGiven)       here->RESm      = 1.0;
             if(!here->RESnoisyGiven)   here->RESnoisy  = 1;
             if(!here->RESresGiven)  {
-                if(model->RESsheetResGiven && (model->RESsheetRes != 0) &&
-                        (here->RESlength != 0)) {
+                if(here->RESlength * here->RESwidth * model->RESsheetRes > 0.0) {
                     here->RESresist = model->RESsheetRes * (here->RESlength -
                                                             model->RESshort) / (here->RESwidth - model->RESnarrow);
                 } else {
-                    SPfrontEnd->IFerror (ERR_WARNING,
-                                         "%s: resistance = 0 ohm, set to 1000 ohm",&(here->RESname));
-                    here->RESresist=1000;
+                    if(model->RESresGiven) {
+                        here->RESresist = model->RESres;
+                    } else {
+                        SPfrontEnd->IFerror (ERR_WARNING,
+                                             "%s: resistance to low, set to 1 mOhm", &(here->RESname));
+                        here->RESresist = 1e-03;
+                    }
                 }
             }