fixed 555-timer-2 convergence issue

src/include/ngspice/cktdefs.h

@@ -151,6 +151,14 @@ struct CKTcircuit {
     /* `.option nostaterestore` opt-out of the dctran failed-attempt
      * device-state restore (CKTstate0 <- CKTstate1 on timepoint retry). */
     int CKTstateRestoreOff;
+    /* `.option noorderguard` opt-out of the dctran non-uniform-history
+     * predictor guard (forced CKTorder=1 on >10x dt-history ratio). */
+    int CKTorderGuardOff;
+    /* `.option currentsettle` opt-IN to honoring device convTest
+     * CKTnoncon reports in NIconvTest (upstream trunk 0638aaa16
+     * current-settling enforcement).  Default 0 = ngspice-46
+     * solution-only convergence semantics. */
+    int CKTcurrentSettle;
     /* Per-iteration count of huge-finite Jacobian entries clipped by
      * sanitize_jacobian during CKTload.  When > 0, the model evaluation
      * is in a numerical regime (e.g. BSIM-BULK near a singular operating

src/include/ngspice/optdefs.h

@@ -97,6 +97,8 @@ enum {
                           * SPICE3 solution-only behaviour. */
     OPT_NOSTATERESTORE,  /* `.option nostaterestore` opts out of the dctran
                           * failed-attempt device-state restore. */
+    OPT_NOORDERGUARD,    /* `.option noorderguard` opts out of the dctran
+                          * non-uniform-history predictor order guard. */
     OPT_EQNS,
     OPT_REORDTIME,
     OPT_METHOD,
@@ -156,6 +158,14 @@ enum {
     OPT_NODTCLEAR,        /* `.option nodtclear` disables the small-dt
                            * CKTnoncon clear in niiter.c.  See CKTdtClearOff
                            * comment in cktdefs.h. */
+    OPT_CURRENTSETTLE,    /* `.option currentsettle` opts IN to NIconvTest
+                           * honoring device convTest CKTnoncon reports.
+                           * NOTE: appended at the enum TAIL deliberately —
+                           * the region between OPT_GMIN=1 and
+                           * OPT_SYNCTIME=58 is full; inserting there
+                           * collides auto-numbered members with the
+                           * OPT_SYNCTIME anchor (duplicate-case build
+                           * error in cktacct.c). */
 };
 
 #ifdef XSPICE

src/include/ngspice/tskdefs.h

@@ -75,6 +75,12 @@ struct TSKtask {
     unsigned int TSKnoStateRestore:1;   /* `.option nostaterestore` disables
                                          * the dctran failed-attempt state
                                          * restore (CKTstate0 <- CKTstate1) */
+    unsigned int TSKnoOrderGuard:1;     /* `.option noorderguard` disables
+                                         * the dctran non-uniform-history
+                                         * predictor order guard */
+    unsigned int TSKcurrentSettle:1;    /* `.option currentsettle` enables
+                                         * device-current settling
+                                         * enforcement in NIconvTest */
     unsigned int TSKtryToCompact:1; /* flag for LTRA lines */
     unsigned int TSKbadMos3:1; /* flag for MOS3 models */
     unsigned int TSKkeepOpInfo:1; /* flag for small signal analyses */

src/maths/ni/niconv.c

@@ -82,8 +82,17 @@ NIconvTest(CKTcircuit *ckt)
 #ifdef NEWCONV
     i = CKTconvTest(ckt);
     /* The individual testers, called by CKTconvTest, set
-     * ckt->CKTnoncon and ckt->CKTtroubleElt appropriately. */
+     * ckt->CKTnoncon and ckt->CKTtroubleElt appropriately.
-    if (ckt->CKTnoncon != 0) {
+     *
+     * Honoring those reports here (upstream trunk 0638aaa16,
+     * "Continue Newton iteration until currents settle") activates a
+     * device-current settling test that had been dead code since
+     * spice3f5.  It regresses legacy decks whose devices genuinely
+     * oscillate at tight tolerances yet simulated acceptably for
+     * decades under the solution-only test (e.g. the bundled
+     * 555-timer-2 example at its own RELTOL=1e-4).  Enforce only on
+     * `.option currentsettle`; the default matches ngspice-46. */
+    if (ckt->CKTcurrentSettle && ckt->CKTnoncon != 0) {
         ckt->CKTtroubleNode = 0;
         return(1);
     }

src/osdi/osditrunc.c

@@ -68,8 +68,8 @@ int OSDItrunc(GENmodel *in_model, CKTcircuit *ckt, double *timestep) {
    * the most recently accepted step so that fast edges are resolved
    * gradually.
    *
-   * Was 2.0× originally, tightened to 1.5× for pinb/net_7 oscillation
+   * Was 2.0× originally, tightened to 1.5× for pinb/net_7 oscillation,
-   * (commit 143a0805f) and now to 1.2× for foundry_a ULP driver_lv_2v5_tb
+   * and now to 1.2× for foundry_a ULP driver_lv_2v5_tb
    * to address residual pinb failure at t ≈ 1.369 µs.  At 1.5×, dt
    * could grow from ~10 ps post-breakpoint to ~5 ns (the user's max
    * step) in ~15 accepted steps; once Newton had to land a 0.5 V swing

src/spicelib/analysis/cktdojob.c

@@ -101,6 +101,8 @@ CKTdoJob(CKTcircuit* ckt, int reset, TSKtask* task)
     ckt->CKTosdiStepRejectOff = task->TSKnoOsdiStepReject;
     ckt->CKTdtClearOff = task->TSKnoDtClear;
     ckt->CKTstateRestoreOff = task->TSKnoStateRestore;
+    ckt->CKTorderGuardOff = task->TSKnoOrderGuard;
+    ckt->CKTcurrentSettle = task->TSKcurrentSettle;
     ckt->CKTosdiVlim = task->TSKosdiVlim;
     ckt->CKTosdiVlimVds = task->TSKosdiVlimVds;
     ckt->CKTosdiVlimVgs = task->TSKosdiVlimVgs;

src/spicelib/analysis/cktsopt.c

@@ -53,6 +53,12 @@ CKTsetOpt(CKTcircuit *ckt, JOB *anal, int opt, IFvalue *val)
     case OPT_NOSTATERESTORE:
         task->TSKnoStateRestore = (val->iValue != 0);
         break;
+    case OPT_NOORDERGUARD:
+        task->TSKnoOrderGuard = (val->iValue != 0);
+        break;
+    case OPT_CURRENTSETTLE:
+        task->TSKcurrentSettle = (val->iValue != 0);
+        break;
     case OPT_GMIN:
         task->TSKgmin = val->rValue;
         break;
@@ -304,6 +310,8 @@ static IFparm OPTtbl[] = {
  { "noosdistepreject", OPT_NOOSDISTEPREJECT, IF_SET|IF_FLAG, "Disable OSDI axis-3 step rejection (osdiload.c sanitize_jacobian + REJECT_STEP)" },
  { "nodtclear", OPT_NODTCLEAR, IF_SET|IF_FLAG, "Disable small-dt CKTnoncon clear (niiter.c); revert to abort-from-spurious-noncon at dt<1ps" },
  { "nostaterestore", OPT_NOSTATERESTORE, IF_SET|IF_FLAG, "Disable dctran failed-attempt device-state restore (CKTstate0 <- CKTstate1 on retry)" },
+ { "noorderguard", OPT_NOORDERGUARD, IF_SET|IF_FLAG, "Disable dctran non-uniform-history predictor order guard (forced order-1 on >10x dt ratio)" },
+ { "currentsettle", OPT_CURRENTSETTLE, IF_SET|IF_FLAG, "Enable device-current settling enforcement in NIconvTest (trunk 0638aaa16 behaviour; default is ngspice-46 solution-only)" },
  { "gmin", OPT_GMIN,IF_SET|IF_REAL,"Minimum conductance" },
  { "gshunt", OPT_GSHUNT,IF_SET|IF_REAL,"Shunt conductance" },
  { "reltol", OPT_RELTOL,IF_SET|IF_REAL ,"Relative error tolerence"},

src/spicelib/analysis/dctran.c

@@ -710,8 +710,21 @@ resume:
          *
          * Threshold of 10× chosen so smooth dt-growth sequences
          * (e.g. the 1.5× cap, factor 1.5 per step) never trigger
-         * — only genuine breakpoint-induced discontinuities. */
+         * — only genuine breakpoint-induced discontinuities.
-        if (ckt->CKTorder > 1 &&
+         *
+         * OSDI circuits only (CKTosdiPresent), like the NIiter Δv
+         * limiter: the failure mode this guards against was observed
+         * on OSDI/BSIM-BULK drivers, while for native-device decks
+         * the forced order-1 steps inflate LTE at breakpoint-dense
+         * switching (smaller dt), and combined with the axis-4
+         * residual check this walled the bundled 555-timer-2 example
+         * at t=3.27ms (RELTOL=1e-4).  Stock predictor behaviour is
+         * restored for non-OSDI circuits.
+         *
+         * Opt-out via `.option noorderguard` (diagnostic: lets a
+         * suspect deck run with the stock always-order-2 predictor). */
+        if (ckt->CKTosdiPresent &&
+            !ckt->CKTorderGuardOff && ckt->CKTorder > 1 &&
             ckt->CKTdeltaOld[1] > 0.0 && ckt->CKTdeltaOld[2] > 0.0) {
             double r = ckt->CKTdeltaOld[1] / ckt->CKTdeltaOld[2];
             if (r > 10.0 || r < 0.1) {