Restore the deleted unused params to be backword compatible. Handle the case where the d_process instance has a null in vector, so that N_din is zero. This allows the model to be just a pattern generator. Add include to cmproto.h to avoid a forward ref. to an enum type.

src/include/ngspice/cmproto.h

@@ -49,6 +49,7 @@ NON-STANDARD FEATURES
 #include  <stdio.h>
 #include "ngspice/cmtypes.h"
 #include "ngspice/cktdefs.h"
+#include "ngspice/cpextern.h"
 
 
 void cm_climit_fcn(double in, double in_offset, double cntl_upper, 

src/xspice/icm/digital/d_process/cfunc.mod

@@ -80,9 +80,6 @@ MODIFICATIONS
         For Windows VisualC and Mingw the pipes use binary mode, and
         named pipes or fifos are not supported.
 
-     8 October 2023 Brian Taylor
-        Remove reset_delay param from ifspec.ifs since the clk_delay
-        is used with synchronous reset.
 
 REFERENCED FILES
 
@@ -191,7 +188,11 @@ static void dprocess_exchangedata(Process_t * process, double time, uint8_t din[
     int wlen = 0;
     packet_t packet;
     packet.time = time;
+    if (process->N_din > 0) {
         memcpy(packet.din, din, process->N_din);
+    } else {
+        packet.din[0] = 0;
+    }
 
 #if defined(_MSC_VER) || defined(__MINGW64__)
     wlen = _write(process->pipe_to_child, &packet, sizeof(double) + process->N_din);
@@ -338,6 +339,12 @@ void cm_d_process(ARGS)
 #endif
         sendheader(local_process, PORT_SIZE(in), PORT_SIZE(out));
 
+        if (PORT_SIZE(in) == 0) {
+            if (local_process->N_din != 0) {
+                fprintf(stderr, "Error: in port size mismatch\n");
+                exit(1);
+            }
+        }
         for (i=0; i<PORT_SIZE(in); i++) {
             LOAD(in[i]) = PARAM(input_load);
         }
@@ -377,11 +384,13 @@ void cm_d_process(ARGS)
         }
 
         if (*clk != *clk_old && ONE == *clk) {
-            uint8_t *dout, *din;
+            uint8_t *dout = NULL, *din = NULL;
             uint8_t b;
             dout = (uint8_t *)malloc(local_process->N_dout * sizeof(uint8_t));
+            if (local_process->N_din > 0) {
                 din = (uint8_t *)malloc(local_process->N_din * sizeof(uint8_t));
                 memset(din, 0, local_process->N_din);
+            }
 
             for (i=0; i<PORT_SIZE(in); i++) {
                 switch(INPUT_STATE(in[i])) {
@@ -411,8 +420,8 @@ void cm_d_process(ARGS)
                     OUTPUT_CHANGED(out[i]) = FALSE;
                 }
             }
-            free(din);
+            if (din) free(din);
-            free(dout);
+            if (dout) free(dout);
         }
         else {
             for (i=0; i<PORT_SIZE(out); i++) {

src/xspice/icm/digital/d_process/ifspec.ifs

@@ -34,7 +34,7 @@ Default_Type:        d              d
 Allowed_Types:       [d]            [d]
 Vector:              yes            no
 Vector_Bounds:       -              -
-Null_Allowed:        no             no
+Null_Allowed:        yes            no
 
 
 PORT_TABLE:
@@ -47,21 +47,21 @@ Default_Type:        d              d
 Allowed_Types:       [d]            [d]
 Vector:              no             yes
 Vector_Bounds:       -              [1 -]
-Null_Allowed:        yes            no
+Null_Allowed:        yes            yes
 
 
 
 PARAMETER_TABLE:
 
 
-Parameter_Name:     clk_delay
+Parameter_Name:     clk_delay           reset_delay
-Description:        "delay from CLK"
+Description:        "delay from CLK"    "delay from reset"
-Data_Type:          real
+Data_Type:          real                real
-Default_Value:      1.0e-9
+Default_Value:      1.0e-9              1.0e-9
-Limits:             -
+Limits:             -                   -
-Vector:             no
+Vector:             no                  no
-Vector_Bounds:      -
+Vector_Bounds:      -                   -
-Null_Allowed:       yes
+Null_Allowed:       yes                 yes
 
 
 PARAMETER_TABLE:
@@ -93,6 +93,19 @@ Null_Allowed:       yes
 PARAMETER_TABLE:
 
 
+Parameter_Name:     reset_state
+Description:        "default state on RESET & at DC"
+Data_Type:          int
+Default_Value:      0
+Limits:             -
+Vector:             no
+Vector_Bounds:      -
+Null_Allowed:       no
+
+
+PARAMETER_TABLE:
+
+
 Parameter_Name:     input_load
 Description:        "input loading capacitance (F)"
 Data_Type:          real