diff --git a/vvp/README.txt b/vvp/README.txt
index a95f84a3e..204c549ef 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 1.22 2001/05/02 04:05:17 steve Exp $
+ *  $Id: README.txt,v 1.23 2001/05/02 23:16:50 steve Exp $
  */
 
 VVP SIMULATION ENGINE
@@ -170,10 +170,6 @@ A UDP functor instance is created so:
 Where <label> identifies the functor, <type> is the label of a UDP
 defined earlier, and <symbol_list> is a list of symbols, one for each
 input of the UDP.
-
-ATTN: The "<name>" attribute of the UDP is pretty useless, and may go
-away in future versions.  It may be useful for diagnostic messages,
-though.
  
 
 VARIABLE STATEMENTS:
@@ -334,18 +330,15 @@ initializes four memory bits.  Two bits form each byte for each memory
 bit, in the ususal encoding.
 
 Procedural access to the memory employs an index register to address a
-bit location in the mememory, via the commands:
+bit location in the memory, via the commands:
 
-	%load/mem   <bit>, <memid>[<ix>] ;
-	%set/mem    <memid>[<ix>], <bit> ;
-	%assign/mem <memid>[<ix>], <delay>, <bit> ;
+	%load/m   <bit>, <memid> ;
+	%set/m    <memid>, <bit> ;
+	%assign/m <memid>, <delay>, <bit> ;
 
-???  is "/mem" required, or shall functors and memories share a
-namespace? ???
-
-<ix> identifies one of the four index registers of the current
-thread.  The value of register <ix> is the index in the memories bit
-space, where each data word occupies a multiple of four bits.
+The memory bit is addressed by index register 3.  The value of
+register 3 is the index in the memory's bit space, where each data
+word occupies a multiple of four bits.
 
 
 EVENT STATEMENTS
diff --git a/vvp/codes.h b/vvp/codes.h
index 0f313da65..4786e51d3 100644
--- a/vvp/codes.h
+++ b/vvp/codes.h
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: codes.h,v 1.22 2001/05/02 01:57:25 steve Exp $"
+#ident "$Id: codes.h,v 1.23 2001/05/02 23:16:50 steve Exp $"
 #endif
 
 
@@ -52,6 +52,7 @@ extern bool of_INV(vthread_t thr, vvp_code_t code);
 extern bool of_IX_ADD(vthread_t thr, vvp_code_t code);
 extern bool of_IX_LOAD(vthread_t thr, vvp_code_t code);
 extern bool of_IX_MUL(vthread_t thr, vvp_code_t code);
+extern bool of_IX_SUB(vthread_t thr, vvp_code_t code);
 extern bool of_JMP(vthread_t thr, vvp_code_t code);
 extern bool of_JMP0(vthread_t thr, vvp_code_t code);
 extern bool of_JMP0XZ(vthread_t thr, vvp_code_t code);
@@ -126,6 +127,13 @@ extern void codespace_dump(FILE*fd);
 
 /*
  * $Log: codes.h,v $
+ * Revision 1.23  2001/05/02 23:16:50  steve
+ *  Document memory related opcodes,
+ *  parser uses numbv_s structures instead of the
+ *  symbv_s and a mess of unions,
+ *  Add the %is/sub instruction.
+ *        (Stephan Boettcher)
+ *
  * Revision 1.22  2001/05/02 01:57:25  steve
  *  Support behavioral subtraction.
  *
diff --git a/vvp/compile.cc b/vvp/compile.cc
index 2aec081d3..5f1d69801 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 1.52 2001/05/02 04:05:17 steve Exp $"
+#ident "$Id: compile.cc,v 1.53 2001/05/02 23:16:50 steve Exp $"
 #endif
 
 # include  "compile.h"
@@ -56,9 +56,8 @@ enum operand_e {
       OA_CODE_PTR,
 	/* The operand is a variable or net pointer */
       OA_FUNC_PTR,
-        /* The operand is a memory, with index ... */
-      OA_MEM_X3, /* ... hardwired index register 3  */
-      OA_MEM_I1  /* ... index register in bit1      */
+        /* The operand is a pointer to a memory */
+      OA_MEM_PTR,
 };
 
 struct opcode_table_s {
@@ -73,7 +72,7 @@ const static struct opcode_table_s opcode_table[] = {
       { "%add",    of_ADD,    3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%and",    of_AND,    3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%assign", of_ASSIGN, 3,  {OA_FUNC_PTR, OA_BIT1,     OA_BIT2} },
-      { "%assign/m",of_ASSIGN_MEM,3,{OA_MEM_X3, OA_BIT1,     OA_BIT2} },
+      { "%assign/m",of_ASSIGN_MEM,3,{OA_MEM_PTR,OA_BIT1,     OA_BIT2} },
       { "%cmp/s",  of_CMPS,   3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%cmp/u",  of_CMPU,   3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%cmp/x",  of_CMPX,   3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
@@ -84,19 +83,20 @@ const static struct opcode_table_s opcode_table[] = {
       { "%ix/add", of_IX_ADD, 2,  {OA_BIT1,     OA_NUMBER,   OA_NONE} },
       { "%ix/load",of_IX_LOAD,2,  {OA_BIT1,     OA_NUMBER,   OA_NONE} },
       { "%ix/mul", of_IX_MUL, 2,  {OA_BIT1,     OA_NUMBER,   OA_NONE} },
+      { "%ix/sub", of_IX_SUB, 2,  {OA_BIT1,     OA_NUMBER,   OA_NONE} },
       { "%jmp",    of_JMP,    1,  {OA_CODE_PTR, OA_NONE,     OA_NONE} },
       { "%jmp/0",  of_JMP0,   2,  {OA_CODE_PTR, OA_BIT1,     OA_NONE} },
       { "%jmp/0xz",of_JMP0XZ, 2,  {OA_CODE_PTR, OA_BIT1,     OA_NONE} },
       { "%jmp/1",  of_JMP1,   2,  {OA_CODE_PTR, OA_BIT1,     OA_NONE} },
       { "%join",   of_JOIN,   0,  {OA_NONE,     OA_NONE,     OA_NONE} },
       { "%load",   of_LOAD,   2,  {OA_BIT1,     OA_FUNC_PTR, OA_NONE} },
-      { "%load/m", of_LOAD_MEM,2, {OA_BIT2,     OA_MEM_I1,   OA_NONE} },
+      { "%load/m", of_LOAD_MEM,2, {OA_BIT1,     OA_MEM_PTR,  OA_NONE} },
       { "%mov",    of_MOV,    3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%noop",   of_NOOP,   0,  {OA_NONE,     OA_NONE,     OA_NONE} },
       { "%nor/r",  of_NORR,   3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%or",     of_OR,     3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%set",    of_SET,    2,  {OA_FUNC_PTR, OA_BIT1,     OA_NONE} },
-      { "%set/m",  of_SET_MEM,2,  {OA_MEM_I1,   OA_BIT1,     OA_NONE} },
+      { "%set/m",  of_SET_MEM,2,  {OA_MEM_PTR,  OA_BIT1,     OA_NONE} },
       { "%sub",    of_SUB,    3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%wait",   of_WAIT,   1,  {OA_FUNC_PTR, OA_NONE,     OA_NONE} },
       { "%xnor",   of_XNOR,   3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
@@ -692,8 +692,7 @@ void compile_code(char*label, char*mnem, comp_operands_t opa)
 		  code->number = opa->argv[idx].numb;
 		  break;
 
-        	case OA_MEM_I1:
-	        case OA_MEM_X3:
+        	case OA_MEM_PTR:
 		  if (opa->argv[idx].ltype != L_SYMB) {
 			yyerror("operand format");
 			break;
@@ -701,26 +700,7 @@ void compile_code(char*label, char*mnem, comp_operands_t opa)
 
 		  code->mem = memory_find(opa->argv[idx].symb.text);
 		  if (code->mem == 0) {
-			yyerror("functor undefined");
-			break;
-		  }
-
-		  if (opa->argv[idx].symb.idx >= 4) {
-		        yyerror("index operand out of range (0..3)");
-		        break;
-		  }
-
-		  switch(op->argt[idx]) {
-		      case OA_MEM_I1:
-		        code->bit_idx1 = (unsigned short) 
-			  opa->argv[idx].symb.idx;
-		        break;
-		      case OA_MEM_X3:
-		        if (opa->argv[idx].symb.idx != 3)
-			      yyerror("index operand must be 3");
-			break;
-		      default:
-			break;
+			yyerror("memory undefined");
 		  }
 
 		  free(opa->argv[idx].symb.text);
@@ -1064,6 +1044,13 @@ void compile_dump(FILE*fd)
 
 /*
  * $Log: compile.cc,v $
+ * Revision 1.53  2001/05/02 23:16:50  steve
+ *  Document memory related opcodes,
+ *  parser uses numbv_s structures instead of the
+ *  symbv_s and a mess of unions,
+ *  Add the %is/sub instruction.
+ *        (Stephan Boettcher)
+ *
  * Revision 1.52  2001/05/02 04:05:17  steve
  *  Remove the init parameter of functors, and instead use
  *  the special C<?> symbols to initialize inputs. This is
diff --git a/vvp/opcodes.txt b/vvp/opcodes.txt
index 0d8dfb1be..a0e392dc5 100644
--- a/vvp/opcodes.txt
+++ b/vvp/opcodes.txt
@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 2001 Stephen Williams (steve@icarus.com)
  *
- *  $Id: opcodes.txt,v 1.16 2001/05/02 01:57:26 steve Exp $
+ *  $Id: opcodes.txt,v 1.17 2001/05/02 23:16:50 steve Exp $
  */
 
 
@@ -41,6 +41,15 @@ the assignment takes place. The delay may be 0. For blocking
 assignments, see %set. The <bit> is the address of the thread register
 that contains the bit value to assign.
 
+
+* %assign/m <memory-label>, <delay>, <bit>
+
+This instruction does a non-blocking assignment to a bit in a memory
+from the specified thread register <bit>.  The memory bit is addressed
+by index register 3.  Bit address zero is the LSB of the first memory
+word.
+
+
 * %cmp/u <bit-l>, <bit-r>, <wid>
 * %cmp/s <bit-l>, <bit-r>, <wid>
 
@@ -129,6 +138,16 @@ number. The idx value selects the index register, and may be 0, 1, 2
 or 3.
 
 
+* %ix/add <idx>, <value>
+* %ix/sub <idx>, <value>
+* %ix/mul <idx>, <value>
+
+This instruction adds, subtracts, or multiplies an immediate value to
+the addressed index register. The index register holds numeric values,
+so the <value> is a number. The <idx> value selects the index register,
+and may be 0, 1, 2 or 3.
+
+
 * %jmp <code-label>
 
 The %jmp instruction performs an unconditional branch to a given
@@ -169,6 +188,14 @@ functor within a vector of functors. This instruction loads only a
 single bit.
 
 
+* %load/m <bit>, <memory-label>
+
+This instruction loads a value from a memory bit into the specified
+thread register bit. The memory bit is addressed by index register 3.
+Bit address zero is the LSB of the first memory word.  This
+instruction loads only a single bit.
+
+
 * %mov <dst>, <src>, <wid>
 
 This instruction copies a vector from one place in register space to
@@ -211,6 +238,14 @@ be read out of the variable. The <bit> is the address of the thread
 register that contains the bit value to assign.
 
 
+* %set/m <memory-label>, <bit>
+
+This instruction set a bit in a memory from the specified thread
+register bit. The memory bit is addressed by index register 3.  Bit
+address zero is the LSB of the first memory word.  This instruction
+sets only a single bit.
+
+
 * %sub <bit-l>, <bit-r>, <wid>
 
 This instruction arithmetically subtracts the right vector out of the
diff --git a/vvp/parse.y b/vvp/parse.y
index 9f2fd738c..752c4e056 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 1.24 2001/05/02 04:05:17 steve Exp $"
+#ident "$Id: parse.y,v 1.25 2001/05/02 23:16:50 steve Exp $"
 #endif
 
 # include  "parse_misc.h"
@@ -45,6 +45,8 @@ extern FILE*yyin;
       struct symb_s  symb;
       struct symbv_s symbv;
 
+      struct numbv_s numbv;
+
       struct symb_s vect;
 
       struct argv_s argv;
@@ -66,7 +68,8 @@ extern FILE*yyin;
 %token <vect> T_VECTOR
 
 %type <symb>  symbol symbol_opt
-%type <symbv> symbols symbols_net numbers
+%type <symbv> symbols symbols_net
+%type <numbv> numbers
 %type <text> label_opt
 %type <opa>  operand operands operands_opt
 %type <table> udp_table
@@ -426,6 +429,13 @@ int compile_design(const char*path)
 
 /*
  * $Log: parse.y,v $
+ * Revision 1.25  2001/05/02 23:16:50  steve
+ *  Document memory related opcodes,
+ *  parser uses numbv_s structures instead of the
+ *  symbv_s and a mess of unions,
+ *  Add the %is/sub instruction.
+ *        (Stephan Boettcher)
+ *
  * Revision 1.24  2001/05/02 04:05:17  steve
  *  Remove the init parameter of functors, and instead use
  *  the special C<?> symbols to initialize inputs. This is
diff --git a/vvp/parse_misc.cc b/vvp/parse_misc.cc
index dcc6ffd82..275c8d265 100644
--- a/vvp/parse_misc.cc
+++ b/vvp/parse_misc.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: parse_misc.cc,v 1.4 2001/05/01 01:09:39 steve Exp $"
+#ident "$Id: parse_misc.cc,v 1.5 2001/05/02 23:16:50 steve Exp $"
 #endif
 
 # include  "parse_misc.h"
@@ -46,6 +46,12 @@ void symbv_add(struct symbv_s*obj, struct symb_s item)
       obj->cnt += 1;
 }
 
+void numbv_init(struct numbv_s*obj)
+{
+      obj->cnt = 0;
+      obj->nvec = 0;
+}
+
 void numbv_add(struct numbv_s*obj, long item)
 {
       obj->nvec = (long*) realloc(obj->nvec, (obj->cnt+1) * sizeof(long));
@@ -69,6 +75,13 @@ void argv_add(struct argv_s*obj, vpiHandle item)
 
 /*
  * $Log: parse_misc.cc,v $
+ * Revision 1.5  2001/05/02 23:16:50  steve
+ *  Document memory related opcodes,
+ *  parser uses numbv_s structures instead of the
+ *  symbv_s and a mess of unions,
+ *  Add the %is/sub instruction.
+ *        (Stephan Boettcher)
+ *
  * Revision 1.4  2001/05/01 01:09:39  steve
  *  Add support for memory objects. (Stephan Boettcher)
  *
diff --git a/vvp/parse_misc.h b/vvp/parse_misc.h
index bfac815aa..ec516f77d 100644
--- a/vvp/parse_misc.h
+++ b/vvp/parse_misc.h
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: parse_misc.h,v 1.4 2001/05/01 01:09:39 steve Exp $"
+#ident "$Id: parse_misc.h,v 1.5 2001/05/02 23:16:50 steve Exp $"
 #endif
 
 
@@ -50,17 +50,18 @@ struct symb_s {
 
 struct symbv_s {
       unsigned cnt;
-      union {
-            struct symb_s*vect;
-	    long*nvec;
-      };
+      struct symb_s*vect;
 };
 
 extern void symbv_init(struct symbv_s*obj);
 extern void symbv_add(struct symbv_s*obj, struct symb_s item);
 
-#define numbv_s    symbv_s
-#define numbv_init symbv_init
+struct numbv_s {
+      unsigned cnt;
+      long*nvec;
+};
+
+extern void numbv_init(struct numbv_s*obj);
 extern void numbv_add(struct numbv_s*obj, long item);
 
 
@@ -75,6 +76,13 @@ extern void argv_add(struct argv_s*obj, vpiHandle);
 
 /*
  * $Log: parse_misc.h,v $
+ * Revision 1.5  2001/05/02 23:16:50  steve
+ *  Document memory related opcodes,
+ *  parser uses numbv_s structures instead of the
+ *  symbv_s and a mess of unions,
+ *  Add the %is/sub instruction.
+ *        (Stephan Boettcher)
+ *
  * Revision 1.4  2001/05/01 01:09:39  steve
  *  Add support for memory objects. (Stephan Boettcher)
  *
diff --git a/vvp/vthread.cc b/vvp/vthread.cc
index f1bcaa95a..96db63395 100644
--- a/vvp/vthread.cc
+++ b/vvp/vthread.cc
@@ -17,7 +17,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #if !defined(WINNT)
-#ident "$Id: vthread.cc,v 1.33 2001/05/02 01:57:26 steve Exp $"
+#ident "$Id: vthread.cc,v 1.34 2001/05/02 23:16:50 steve Exp $"
 #endif
 
 # include  "vthread.h"
@@ -168,6 +168,7 @@ vthread_t vthread_new(unsigned long pc, struct __vpiScope*scope)
       thr->is_scheduled = 0;
       thr->i_have_ended = 0;
       thr->waiting_for_event = 0;
+      thr->is_scheduled = 0;
 
       thr_put_bit(thr, 0, 0);
       thr_put_bit(thr, 1, 1);
@@ -626,20 +627,24 @@ bool of_INV(vthread_t thr, vvp_code_t cp)
 
 
 /*
-** Index registers, signed arithmetic.
+** Index registers, unsigned arithmetic.
 */
 
 bool of_IX_ADD(vthread_t thr, vvp_code_t cp)
 {
-  int number = (int)cp->number; // signed
-  thr->index[cp->bit_idx1 & 3] += number;
+  thr->index[cp->bit_idx1 & 3] += cp->number;
+  return true;
+}
+
+bool of_IX_SUB(vthread_t thr, vvp_code_t cp)
+{
+  thr->index[cp->bit_idx1 & 3] -= cp->number;
   return true;
 }
 
 bool of_IX_MUL(vthread_t thr, vvp_code_t cp)
 {
-  int number = (int)cp->number; // signed
-  thr->index[cp->bit_idx1 & 3] *= number;
+  thr->index[cp->bit_idx1 & 3] *= cp->number;
   return true;
 }
 
@@ -714,9 +719,8 @@ bool of_LOAD(vthread_t thr, vvp_code_t cp)
 bool of_LOAD_MEM(vthread_t thr, vvp_code_t cp)
 {
       assert(cp->bit_idx1 >= 4);
-      assert(cp->bit_idx2 < 4);
-      unsigned char val = memory_get(cp->mem, thr->index[cp->bit_idx1]);
-      thr_put_bit(thr, cp->bit_idx2, val);
+      unsigned char val = memory_get(cp->mem, thr->index[3]);
+      thr_put_bit(thr, cp->bit_idx1, val);
       return true;
 }
 
@@ -809,9 +813,8 @@ bool of_SET(vthread_t thr, vvp_code_t cp)
 
 bool of_SET_MEM(vthread_t thr, vvp_code_t cp)
 {
-      assert(cp->bit_idx2 < 4);
-      unsigned char val = thr_get_bit(thr, cp->bit_idx2);
-      memory_set(cp->mem, thr->index[cp->bit_idx1], val);
+      unsigned char val = thr_get_bit(thr, cp->bit_idx1);
+      memory_set(cp->mem, thr->index[3], val);
 
       return true;
 }
@@ -966,6 +969,13 @@ bool of_ZOMBIE(vthread_t thr, vvp_code_t)
 
 /*
  * $Log: vthread.cc,v $
+ * Revision 1.34  2001/05/02 23:16:50  steve
+ *  Document memory related opcodes,
+ *  parser uses numbv_s structures instead of the
+ *  symbv_s and a mess of unions,
+ *  Add the %is/sub instruction.
+ *        (Stephan Boettcher)
+ *
  * Revision 1.33  2001/05/02 01:57:26  steve
  *  Support behavioral subtraction.
  *