diff --git a/ivl_target.h b/ivl_target.h
index 3ff1e4503..5f69916f4 100644
--- a/ivl_target.h
+++ b/ivl_target.h
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT) && !defined(macintosh)
-#ident "$Id: ivl_target.h,v 1.69 2001/06/19 03:01:10 steve Exp $"
+#ident "$Id: ivl_target.h,v 1.70 2001/06/30 23:03:16 steve Exp $"
 #endif
 
 #ifdef __cplusplus
@@ -317,12 +317,17 @@ typedef int (ivl_scope_f)(ivl_scope_t net, void*cd);
  *    A design has a root named scope that is an instance of the top
  *    level module in the design. This is a hook for naming the
  *    design, or for starting the scope scan.
+ *
+ * ivl_design_time_precision
+ *    A design as a time precision. This is the size in seconds (a
+ *    signed power of 10) of a simulation tick.
  */
 
 extern const char* ivl_design_flag(ivl_design_t des, const char*key);
 extern int         ivl_design_process(ivl_design_t des,
 				      ivl_process_f fun, void*cd);
 extern ivl_scope_t ivl_design_root(ivl_design_t des);
+extern int         ivl_design_time_precision(ivl_design_t des);
 
 /*
  * These methods apply to ivl_net_const_t objects.
@@ -884,6 +889,10 @@ _END_DECL
 
 /*
  * $Log: ivl_target.h,v $
+ * Revision 1.70  2001/06/30 23:03:16  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.69  2001/06/19 03:01:10  steve
  *  Add structural EEQ gates (Stephan Boettcher)
  *
diff --git a/t-dll-api.cc b/t-dll-api.cc
index 63b7fcc28..cdd379a31 100644
--- a/t-dll-api.cc
+++ b/t-dll-api.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT) && !defined(macintosh)
-#ident "$Id: t-dll-api.cc,v 1.51 2001/06/16 23:45:05 steve Exp $"
+#ident "$Id: t-dll-api.cc,v 1.52 2001/06/30 23:03:16 steve Exp $"
 #endif
 
 # include  "t-dll.h"
@@ -47,6 +47,11 @@ extern "C" ivl_scope_t ivl_design_root(ivl_design_t des)
       return des->root_;
 }
 
+extern "C" int ivl_design_time_precision(ivl_design_t des)
+{
+      return des->time_precision;
+}
+
 extern "C" ivl_expr_type_t ivl_expr_type(ivl_expr_t net)
 {
       if (net == 0)
@@ -1227,6 +1232,10 @@ extern "C" ivl_statement_t ivl_stmt_sub_stmt(ivl_statement_t net)
 
 /*
  * $Log: t-dll-api.cc,v $
+ * Revision 1.52  2001/06/30 23:03:16  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.51  2001/06/16 23:45:05  steve
  *  Add support for structural multiply in t-dll.
  *  Add code generators and vvp support for both
diff --git a/t-dll.cc b/t-dll.cc
index 6f03128af..08e07ba46 100644
--- a/t-dll.cc
+++ b/t-dll.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT) && !defined(macintosh)
-#ident "$Id: t-dll.cc,v 1.51 2001/06/19 03:01:10 steve Exp $"
+#ident "$Id: t-dll.cc,v 1.52 2001/06/30 23:03:16 steve Exp $"
 #endif
 
 # include  "compiler.h"
@@ -318,6 +318,7 @@ bool dll_target::start_design(const Design*des)
 
 	// Initialize the design object.
       des_.self = des;
+      des_.time_precision = des->get_precision();
       des_.root_ = new struct ivl_scope_s;
       des_.root_->name_ = strdup(des->find_root_scope()->name().c_str());
       des_.root_->child_ = 0;
@@ -1381,6 +1382,10 @@ extern const struct target tgt_dll = { "dll", &dll_target_obj };
 
 /*
  * $Log: t-dll.cc,v $
+ * Revision 1.52  2001/06/30 23:03:16  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.51  2001/06/19 03:01:10  steve
  *  Add structural EEQ gates (Stephan Boettcher)
  *
diff --git a/t-dll.h b/t-dll.h
index 9584c13ca..c4e29a66b 100644
--- a/t-dll.h
+++ b/t-dll.h
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT) && !defined(macintosh)
-#ident "$Id: t-dll.h,v 1.51 2001/06/30 21:07:26 steve Exp $"
+#ident "$Id: t-dll.h,v 1.52 2001/06/30 23:03:16 steve Exp $"
 #endif
 
 # include  "target.h"
@@ -38,6 +38,8 @@ typedef shl_t ivl_dll_t;
 
 struct ivl_design_s {
 
+      int time_precision;
+
       ivl_scope_t root_;
 
       ivl_process_t threads_;
@@ -539,6 +541,10 @@ struct ivl_statement_s {
 
 /*
  * $Log: t-dll.h,v $
+ * Revision 1.52  2001/06/30 23:03:16  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.51  2001/06/30 21:07:26  steve
  *  Support non-const right shift (unsigned).
  *
diff --git a/tgt-vvp/vvp.c b/tgt-vvp/vvp.c
index 8242852a0..aff2f9559 100644
--- a/tgt-vvp/vvp.c
+++ b/tgt-vvp/vvp.c
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT) && !defined(macintosh)
-#ident "$Id: vvp.c,v 1.8 2001/05/22 02:14:47 steve Exp $"
+#ident "$Id: vvp.c,v 1.9 2001/06/30 23:03:16 steve Exp $"
 #endif
 
 /*
@@ -71,6 +71,15 @@ int target_design(ivl_design_t des)
 
       draw_execute_header(des);
 
+      { int pre = ivl_design_time_precision(des);
+        char sign = '+';
+        if (pre < 0) {
+	      pre = -pre;
+	      sign = '-';
+	}
+        fprintf(vvp_out, ":vpi_time_precision %c %d;\n", sign, pre);
+      }
+
       draw_module_declarations(des);
 
       root = ivl_design_root(des);
diff --git a/vvp/README.txt b/vvp/README.txt
index 7ee92ef02..65fb93a37 100644
--- a/vvp/README.txt
+++ b/vvp/README.txt
@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2001 Stephen Williams (steve@icarus.com)
  *
- *  $Id: README.txt,v 1.31 2001/06/18 00:51:23 steve Exp $
+ *  $Id: README.txt,v 1.32 2001/06/30 23:03:16 steve Exp $
  */
 
 VVP SIMULATION ENGINE
@@ -47,6 +47,18 @@ the rest of the program is compiled. The compiler looks in the
 standard VPI_MODULE_PATH for files named "name.vpi", and tries to
 dynamic load them.
 
+* :vpi_time_precision [+|-]<value>;
+
+This header statement specifies the time precision of a single tick of
+the simulation clock. This is mostly used for display (and VPI)
+purposes, because the engine itself does not care about units. The
+compiler scales time values ahead of time.
+
+The value is the size of a simulation tick in seconds, and is
+expressed as a power of 10. For example, +0 is 1 second, and -9 is 1
+nano-second. If the record is left out, then the precision is taken to
+be +0.
+
 LABELS AND SYMBOLS
 
 Labels and symbols consist of the characters:
diff --git a/vvp/compile.cc b/vvp/compile.cc
index 347503048..23b48909b 100644
--- a/vvp/compile.cc
+++ b/vvp/compile.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: compile.cc,v 1.82 2001/06/30 21:07:26 steve Exp $"
+#ident "$Id: compile.cc,v 1.83 2001/06/30 23:03:16 steve Exp $"
 #endif
 
 # include  "arith.h"
@@ -245,6 +245,11 @@ void compile_load_vpi_module(char*name)
       free(name);
 }
 
+void compile_vpi_time_precision(long pre)
+{
+      vpip_set_time_precision(pre);
+}
+
 /*
  *  Add a functor to the symbol table
  */
@@ -1450,6 +1455,10 @@ vvp_ipoint_t debug_lookup_functor(const char*name)
 
 /*
  * $Log: compile.cc,v $
+ * Revision 1.83  2001/06/30 23:03:16  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.82  2001/06/30 21:07:26  steve
  *  Support non-const right shift (unsigned).
  *
diff --git a/vvp/compile.h b/vvp/compile.h
index ab451b5da..f67ef0ae1 100644
--- a/vvp/compile.h
+++ b/vvp/compile.h
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: compile.h,v 1.28 2001/06/16 23:45:05 steve Exp $"
+#ident "$Id: compile.h,v 1.29 2001/06/30 23:03:17 steve Exp $"
 #endif
 
 # include  <stdio.h>
@@ -48,6 +48,8 @@ extern unsigned compile_errors;
 extern const char* module_path;
 extern void compile_load_vpi_module(char*name);
 
+extern void compile_vpi_time_precision(long pre);
+
 /*
  * This function is called by the parser to compile a functor
  * statement. The strings passed in are allocated by the lexor, but
@@ -198,6 +200,10 @@ extern void compile_net(char*label, char*name,
 
 /*
  * $Log: compile.h,v $
+ * Revision 1.29  2001/06/30 23:03:17  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.28  2001/06/16 23:45:05  steve
  *  Add support for structural multiply in t-dll.
  *  Add code generators and vvp support for both
diff --git a/vvp/lexor.lex b/vvp/lexor.lex
index 4e537f166..bd17713b5 100644
--- a/vvp/lexor.lex
+++ b/vvp/lexor.lex
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: lexor.lex,v 1.23 2001/06/18 03:10:34 steve Exp $"
+#ident "$Id: lexor.lex,v 1.24 2001/06/30 23:03:17 steve Exp $"
 #endif
 
 # include  "parse_misc.h"
@@ -32,6 +32,7 @@
 
   /* These are some special header keywords. */
 ^":vpi_module" { return K_vpi_module; }
+^":vpi_time_precision" { return K_vpi_time_precision; }
 
 
   /* A label is any non-blank text that appears left justified. */
@@ -145,6 +146,10 @@ int yywrap()
 
 /*
  * $Log: lexor.lex,v $
+ * Revision 1.24  2001/06/30 23:03:17  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.23  2001/06/18 03:10:34  steve
  *   1. Logic with more than 4 inputs
  *   2. Id and name mangling
diff --git a/vvp/parse.y b/vvp/parse.y
index 06e190b91..7844bb025 100644
--- a/vvp/parse.y
+++ b/vvp/parse.y
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: parse.y,v 1.32 2001/06/16 23:45:05 steve Exp $"
+#ident "$Id: parse.y,v 1.33 2001/06/30 23:03:17 steve Exp $"
 #endif
 
 # include  "parse_misc.h"
@@ -60,7 +60,7 @@ extern FILE*yyin;
 %token K_UDP K_UDP_C K_UDP_S
 %token K_MEM K_MEM_P K_MEM_I
 %token K_VAR K_VAR_S K_vpi_call K_vpi_func K_disable K_fork
-%token K_vpi_module
+%token K_vpi_module K_vpi_time_precision
 
 %token <text> T_INSTR
 %token <text> T_LABEL
@@ -93,6 +93,10 @@ header_lines
 header_line
 	: K_vpi_module T_STRING ';'
 		{ compile_load_vpi_module($2); }
+	| K_vpi_time_precision '+' T_NUMBER ';'
+		{ compile_vpi_time_precision($3); }
+	| K_vpi_time_precision '-' T_NUMBER ';'
+		{ compile_vpi_time_precision(-$3); }
 	;
 
   /* A program is simply a list of statements. No other structure. */
@@ -474,6 +478,10 @@ int compile_design(const char*path)
 
 /*
  * $Log: parse.y,v $
+ * Revision 1.33  2001/06/30 23:03:17  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.32  2001/06/16 23:45:05  steve
  *  Add support for structural multiply in t-dll.
  *  Add code generators and vvp support for both
diff --git a/vvp/vpi_priv.cc b/vvp/vpi_priv.cc
index 4f5260fe4..ee33a41b5 100644
--- a/vvp/vpi_priv.cc
+++ b/vvp/vpi_priv.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: vpi_priv.cc,v 1.6 2001/06/21 22:54:12 steve Exp $"
+#ident "$Id: vpi_priv.cc,v 1.7 2001/06/30 23:03:17 steve Exp $"
 #endif
 
 # include  "vpi_priv.h"
@@ -44,8 +44,7 @@ static int vpip_get_global(int property)
       switch (property) {
 
 	  case vpiTimePrecision:
-	    fprintf(stderr, "vpi Sorry: vpiTimePrecision not supported\n");
-	    return 0;
+	    return vpip_get_time_precision();
 
 	  default:
 	    fprintf(stderr, "vpi error: bad global property: %d\n", property);
@@ -152,6 +151,10 @@ extern "C" void vpi_sim_vcontrol(int operation, va_list ap)
 
 /*
  * $Log: vpi_priv.cc,v $
+ * Revision 1.7  2001/06/30 23:03:17  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.6  2001/06/21 22:54:12  steve
  *  Support cbValueChange callbacks.
  *
diff --git a/vvp/vpi_priv.h b/vvp/vpi_priv.h
index be8b22d03..6151d3a28 100644
--- a/vvp/vpi_priv.h
+++ b/vvp/vpi_priv.h
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: vpi_priv.h,v 1.17 2001/06/21 22:54:12 steve Exp $"
+#ident "$Id: vpi_priv.h,v 1.18 2001/06/30 23:03:17 steve Exp $"
 #endif
 
 # include  "vpi_user.h"
@@ -249,8 +249,15 @@ extern void vpip_execute_vpi_call(vthread_t thr, vpiHandle obj);
 
 vpiHandle vpip_sim_time(void);
 
+extern int vpip_get_time_precision(void);
+extern void vpip_set_time_precision(int pres);
+
 /*
  * $Log: vpi_priv.h,v $
+ * Revision 1.18  2001/06/30 23:03:17  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.17  2001/06/21 22:54:12  steve
  *  Support cbValueChange callbacks.
  *
diff --git a/vvp/vpi_time.cc b/vvp/vpi_time.cc
index 9de1782e8..b63141996 100644
--- a/vvp/vpi_time.cc
+++ b/vvp/vpi_time.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: vpi_time.cc,v 1.2 2001/04/03 03:46:14 steve Exp $"
+#ident "$Id: vpi_time.cc,v 1.3 2001/06/30 23:03:17 steve Exp $"
 #endif
 
 # include  "vpi_priv.h"
@@ -25,6 +25,9 @@
 # include  <stdio.h>
 # include  <assert.h>
 
+
+static int vpi_time_precision = 0;
+
 static struct __vpiSystemTime {
       struct __vpiHandle base;
       struct t_vpi_time value;
@@ -73,8 +76,23 @@ vpiHandle vpip_sim_time(void)
       return &time_handle.base;
 }
 
+int vpip_get_time_precision(void)
+{
+      return vpi_time_precision;
+}
+
+void vpip_set_time_precision(int pre)
+{
+      vpi_time_precision = pre;
+}
+
+
 /*
  * $Log: vpi_time.cc,v $
+ * Revision 1.3  2001/06/30 23:03:17  steve
+ *  support fast programming by only writing the bits
+ *  that are listed in the input file.
+ *
  * Revision 1.2  2001/04/03 03:46:14  steve
  *  VPI access time as a decimal string, and
  *  stub vpi access to the scopes.