From 0a8fd50c4af30c449ac25937e75f6bd416b45a2f Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Fri, 13 Jun 2008 13:59:48 +0100
Subject: [PATCH] Find assignments that could be initializers

---
 tgt-vhdl/process.cc     |  7 ++++++-
 tgt-vhdl/stmt.cc        | 32 +++++++++++++++++++++++---------
 tgt-vhdl/vhdl_syntax.hh |  6 ++++++
 3 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/tgt-vhdl/process.cc b/tgt-vhdl/process.cc
index b43e0ee64..ac11cefa5 100644
--- a/tgt-vhdl/process.cc
+++ b/tgt-vhdl/process.cc
@@ -36,7 +36,12 @@ static int generate_vhdl_process(vhdl_entity *ent, ivl_process_t proc)
    // parent link won't be valid (and draw_stmt needs this
    // to add information to the architecture)
    vhdl_process *vhdl_proc = new vhdl_process();
-   ent->get_arch()->add_stmt(vhdl_proc);   
+   ent->get_arch()->add_stmt(vhdl_proc);
+
+   // If this is an initial process, push signal initialisation
+   // into the declarations
+   if (ivl_process_type(proc) == IVL_PR_INITIAL)
+      vhdl_proc->set_initial(true);
    
    ivl_statement_t stmt = ivl_process_stmt(proc);
    int rc = draw_stmt(vhdl_proc, vhdl_proc->get_container(), stmt);
diff --git a/tgt-vhdl/stmt.cc b/tgt-vhdl/stmt.cc
index 4013dafac..1e80d11b4 100644
--- a/tgt-vhdl/stmt.cc
+++ b/tgt-vhdl/stmt.cc
@@ -192,13 +192,25 @@ static int draw_nbassign(vhdl_process *proc, stmt_container *container,
          return 1;
       vhdl_expr *rhs = rhs_raw->cast(decl->get_type());
 
-      // The type here can be null as it is never actually needed
-      vhdl_var_ref *lval_ref = new vhdl_var_ref(signame, NULL);
-
-      vhdl_nbassign_stmt *nbassign = new vhdl_nbassign_stmt(lval_ref, rhs);
-      if (after != NULL)
-         nbassign->set_after(after);
-      container->add_stmt(nbassign);
+      // If this is an `inital' process and we haven't yet
+      // generated a `wait' statement then initializing the
+      // signal here is equivalent to initializing to in the
+      // declaration
+      // The second test ensures that we only try to initialise
+      // internal signals not ports
+      if (proc->is_initial()
+          && !proc->get_parent()->get_parent()->get_decl(signame)) {
+         std::cout << "Pushing " << signame << " init up" << std::endl;
+      }
+      else {
+         // The type here can be null as it is never actually needed
+         vhdl_var_ref *lval_ref = new vhdl_var_ref(signame, NULL);
+         
+         vhdl_nbassign_stmt *nbassign = new vhdl_nbassign_stmt(lval_ref, rhs);
+         if (after != NULL)
+            nbassign->set_after(after);
+         container->add_stmt(nbassign);
+      }
    }
    else {
       error("Only signals as lvals supported at the moment");
@@ -244,9 +256,12 @@ static int draw_delay(vhdl_process *proc, stmt_container *container,
       // is caught here instead
       if (ivl_statement_type(sub_stmt) != IVL_ST_NOOP)
          draw_stmt(proc, container, sub_stmt);
-   
    }
    
+   // Any further assignments occur after simulation time 0
+   // so they cannot be used to initialize signal declarations
+   proc->set_initial(false);
+   
    return 0;
 }
 
@@ -278,7 +293,6 @@ static void edge_detector(ivl_nexus_t nexus, vhdl_process *proc,
    }
 }
 
-
 /*
  * A wait statement waits for a level change on a @(..) list of
  * signals.
diff --git a/tgt-vhdl/vhdl_syntax.hh b/tgt-vhdl/vhdl_syntax.hh
index 441c6c1bb..27607d076 100644
--- a/tgt-vhdl/vhdl_syntax.hh
+++ b/tgt-vhdl/vhdl_syntax.hh
@@ -420,6 +420,9 @@ private:
 
 /*
  * Container for sequential statements.
+ * Verilog `initial' processes are used for variable
+ * initialisation whereas VHDL initialises variables in
+ * their declaration.
  */
 class vhdl_process : public vhdl_conc_stmt {
 public:
@@ -431,11 +434,14 @@ public:
    void add_decl(vhdl_decl *decl);
    void add_sensitivity(const char *name);
    bool have_declared_var(const std::string &name) const;
+   void set_initial(bool i) { initial_ = i; }
+   bool is_initial() const { return initial_; }
 private:
    stmt_container stmts_;
    decl_list_t decls_;
    std::string name_;
    string_list_t sens_;
+   bool initial_;
 };