ivl_target.h access branch terminals

Fill in the functions to add branch terminals, and add code in the
stub to check that the terminals are present and reasonable.

ivl.def

@@ -1,5 +1,7 @@
 EXPORTS
 
+ivl_branch_terminal
+
 ivl_design_const
 ivl_design_consts
 ivl_design_discipline
@@ -112,6 +114,8 @@ ivl_lval_part_off
 ivl_lval_sig
 ivl_lval_width
 
+ivl_nature_name
+
 ivl_nexus_get_private
 ivl_nexus_name
 ivl_nexus_ptrs

ivl_target.h

@@ -421,9 +421,11 @@ struct ivl_attribute_s {
 typedef const struct ivl_attribute_s*ivl_attribute_t;
 
 /* BRANCH
-*/
-extern ivl_discipline_t ivl_branch_discipline(ivl_branch_t obj);
-extern ivl_scope_t ivl_branch_scope(ivl_branch_t obj);
+ * Branches are analog constructs, a pair of terminals that is used in
+ * branch access functions. Terminal-1 is the reference node for the
+ * purposes of the access function that accesses it.
+ */
+  /* extern ivl_scope_t ivl_branch_scope(ivl_branch_t obj); */
 extern ivl_nexus_t ivl_branch_terminal(ivl_branch_t obj, int idx);
 
 /* DELAYPATH
@@ -589,6 +591,8 @@ extern ivl_dis_domain_t ivl_discipline_domain(ivl_discipline_t net);
 extern ivl_nature_t ivl_discipline_potential(ivl_discipline_t net);
 extern ivl_nature_t ivl_discipline_flow(ivl_discipline_t net);
 
+extern const char* ivl_nature_name(ivl_nature_t net);
+
 /* EVENTS
  *
  * Events are a unification of named events and implicit events

ivl_target_priv.h

@@ -58,6 +58,10 @@ struct ivl_design_s {
       const class Design*self;
 };
 
+/*
+ * A branch is a pair of terminals. The elaborator assures that the
+ * terminals have compatible disciplines.
+ */
 struct ivl_branch_s {
       ivl_nexus_t pins[2];
 };

t-dll-api.cc

@@ -31,6 +31,13 @@ static StringHeap api_strings;
 
 /* THE FOLLOWING ARE FUNCTIONS THAT ARE CALLED FROM THE TARGET. */
 
+extern "C" ivl_nexus_t ivl_branch_terminal(ivl_branch_t net, int idx)
+{
+      assert(idx >= 0);
+      assert( idx < 2);
+      return net->pins[idx];
+}
+
 extern "C" const char*ivl_design_flag(ivl_design_t des, const char*key)
 {
       return des->self->get_flag(key);
@@ -1315,6 +1322,11 @@ extern "C" ivl_signal_t ivl_lval_sig(ivl_lval_t net)
       }
 }
 
+extern "C" const char* ivl_nature_name(ivl_nature_t net)
+{
+      return net->name();
+}
+
 /*
  * The nexus name is rarely needed. (Shouldn't be needed at all!) This
  * function will calculate the name if it is not already calculated.

tgt-stub/expression.c

@@ -45,13 +45,42 @@ static void show_array_expression(ivl_expr_t net, unsigned ind)
 
 static void show_branch_access_expression(ivl_expr_t net, unsigned ind)
 {
-      fprintf(out, "%*s<Branch Access>\n", ind, "");
+      ivl_branch_t bra = ivl_expr_branch(net);
+      ivl_nature_t nature = ivl_expr_nature(net);
+      fprintf(out, "%*s<Access branch %p with nature %s>\n",
+	      ind, "", bra, ivl_nature_name(nature));
 
       if (ivl_expr_value(net) != IVL_VT_REAL) {
 	    fprintf(out, "%*sERROR: Expecting type IVL_VT_REAL, got %s\n",
 		    ind, "", vt_type_string(net));
 	    stub_errors += 1;
       }
+
+      ivl_nexus_t ta = ivl_branch_terminal(bra, 0);
+      ivl_nexus_t tb = ivl_branch_terminal(bra, 1);
+
+      ivl_discipline_t ta_disc = discipline_of_nexus(ta);
+      if (ta_disc == 0) {
+	    fprintf(out, "%*sERROR: Source terminal of branch has no discipline\n",
+		    ind, "");
+	    stub_errors += 1;
+	    return;
+      }
+
+      ivl_discipline_t tb_disc = discipline_of_nexus(tb);
+      if (ta_disc == 0) {
+	    fprintf(out, "%*sERROR: Reference terminal of branch has no discipline\n",
+		    ind, "");
+	    stub_errors += 1;
+	    return;
+      }
+
+      if (ta_disc != tb_disc) {
+	    fprintf(out, "%*sERROR: Branch terminal disciplines mismatch: %s != %s\n",
+		    ind, "", ivl_discipline_name(ta_disc),
+		    ivl_discipline_name(tb_disc));
+	    stub_errors += 1;
+      }
 }
 
 static void show_binary_expression(ivl_expr_t net, unsigned ind)

tgt-stub/priv.h

@@ -44,6 +44,8 @@ extern unsigned width_of_nexus(ivl_nexus_t nex);
 
 extern ivl_variable_type_t type_of_nexus(ivl_nexus_t nex);
 
+extern ivl_discipline_t discipline_of_nexus(ivl_nexus_t nex);
+
 /*
  * Show the details of the expression.
  */

tgt-stub/stub.c

@@ -108,6 +108,24 @@ unsigned width_of_nexus(ivl_nexus_t nex)
       return 0;
 }
 
+ivl_discipline_t discipline_of_nexus(ivl_nexus_t nex)
+{
+      unsigned idx;
+
+      for (idx = 0 ;  idx < ivl_nexus_ptrs(nex); idx += 1) {
+	    ivl_nexus_ptr_t ptr = ivl_nexus_ptr(nex, idx);
+	    ivl_signal_t sig = ivl_nexus_ptr_sig(ptr);
+
+	    if (sig != 0) {
+		  return ivl_signal_discipline(sig);
+	    }
+      }
+
+	/* ERROR: A nexus should have at least one signal to carry
+	   properties like the data type. */
+      return 0;
+}
+
 ivl_variable_type_t type_of_nexus(ivl_nexus_t net)
 {
       unsigned idx;