From: Justin Wind <justin.wind@gmail.com>
Date: Sat, 12 May 2012 18:55:51 +0000 (-0700)
Subject: further changes for v1.7: cpu fixes, support for 'hardware' devices, display to vnc
X-Git-Url: https://git.squeep.com/?a=commitdiff_plain;h=0a1b4588f79e3719af9431a98da44350030df754;p=dcpu16

further changes for v1.7: cpu fixes, support for 'hardware' devices, display to vnc

small changes throughout for 1.7, normalized some variable names, all registers now indexable in array.  fixed behavior of branch-skip.  changes to hw interfaces.
added initial clock, keyboard, and display modules.
display module now supports rendering as vnc server.

hardware devices are still somewhat incomplete and lack testing.
---

diff --git a/Makefile b/Makefile
index f0f3b71..263c8e3 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,8 @@ CC = clang
 endif
 
 PROGRAMS = as-dcpu16 vm-dcpu16
-SOURCES = common.c dcpu16.c as-dcpu16.c vm-dcpu16.c display.c
+SOURCES = common.c dcpu16.c as-dcpu16.c vm-dcpu16.c \
+		  hw_clock.c hw_keyboard.c hw_lem1802.c
 
 CPPFLAGS += -DDEBUG
 
@@ -25,6 +26,8 @@ ifeq ($(UNAME),Linux)
 CPPFLAGS += -DHAVE_FOPENCOOKIE -D_GNU_SOURCE
 endif
 
+CPPFLAGS += -DHAVE_LIBVNCSERVER -I/opt/local/include
+LDFLAGS += -L/opt/local/lib -lvncserver
 
 all:	$(PROGRAMS)
 
@@ -37,7 +40,7 @@ depend:	.depend
 include .depend
 
 
-vm-dcpu16:	vm-dcpu16.o dcpu16.o common.o display.o
+vm-dcpu16:	vm-dcpu16.o dcpu16.o common.o hw_clock.o hw_keyboard.o hw_lem1802.o
 
 as-dcpu16:	as-dcpu16.o dcpu16.o common.o
 
diff --git a/dcpu16.c b/dcpu16.c
index 75c6cf0..d7b3d48 100644
--- a/dcpu16.c
+++ b/dcpu16.c
@@ -18,10 +18,6 @@
  *  
  *  Justin Wind <justin.wind@gmail.com>
  *    2012 04 05 - implementation started
- *    2012 04 06 - first functionality achieved
- *    2012 04 09 - minor cleanups
- *    2012 04 10 - moved cli to separate module
- *    2012 04 12 - added basic callback support for address accesses
  *    2012 05 05 - start of v1.7 revisions
  *    2012 05 08 - v1.7 revisions mostly complete
  *
@@ -42,7 +38,23 @@ static const char * const src_id_ = "$Id$";
 #define OPCODE_OPERAND_B_BITS 5
 #define OPCODE_OPERAND_A_BITS 6
 
-static const char * const regnames_ = "ABCXYZIJ";
+const char * const dcpu16_reg_names[] = {
+    "A",
+    "B",
+    "C",
+    "X",
+    "Y",
+    "Z",
+    "I",
+    "J",
+    "PC",
+    "SP",
+    "EX",
+    "IA",
+    NULL
+};
+
+static void printf_null_(char *fmt, ...) { (void)fmt; }
 
 /* some default warning and debug reporting functions, which can be overridden by clients */
 #define WARN(...) do { if (warn_cb_) warn_cb_(__VA_ARGS__); } while (0)
@@ -60,7 +72,10 @@ void warn_(char *fmt, ...) {
 }
 static void (*warn_cb_)(char *fmt, ...) = warn_;
 void dcpu16_warn_cb_set(void (*fn)(char *fmt, ...)) {
-    warn_cb_ = fn;
+    if (fn)
+        warn_cb_ = fn;
+    else
+        warn_cb_ = printf_null_;
 }
 
 #ifdef DEBUG
@@ -88,7 +103,10 @@ static void (*trace_cb_)(char *fmt, ...) =
 #endif
     ;
 void dcpu16_trace_cb_set(void (*fn)(char *fmt, ...)) {
-    trace_cb_ = fn;
+    if (fn)
+        trace_cb_ = fn;
+    else
+        trace_cb_ = printf_null_;
 }
 
 
@@ -106,21 +124,16 @@ void acct_event_(struct dcpu16 *vm, dcpu16_acct_event ev, DCPU16_WORD addr) {
     }
 }
 
-/* convert register name to index into register array */
-static inline
-off_t reg_index_(int reg) {
-    return strchr(regnames_, reg) - regnames_;
-}
 
 /* add an entry to the interrupt queue */
 static
-int interrupt_enqueue_(struct dcpu16 *d, DCPU16_WORD message) {
-    d->interrupts_[d->interrupts_tail_] = message;
-    d->interrupts_tail_ += 1;
-    d->interrupts_tail_ %= DCPU16_INTERRUPT_QUEUE_SIZE;
+int interrupt_enqueue_(struct dcpu16 *vm, DCPU16_WORD message) {
+    vm->interrupts_[vm->interrupts_tail_] = message;
+    vm->interrupts_tail_ += 1;
+    vm->interrupts_tail_ %= DCPU16_INTERRUPT_QUEUE_SIZE;
 
-    if (d->interrupts_tail_ == d->interrupts_head_) {
-        d->on_fire_ = 1;
+    if (vm->interrupts_tail_ == vm->interrupts_head_) {
+        vm->on_fire_ = 1;
         WARN("interrupt queue overflow (system is now on fire)");
         return -1;
     }
@@ -129,17 +142,17 @@ int interrupt_enqueue_(struct dcpu16 *d, DCPU16_WORD message) {
 }
 
 static
-DCPU16_WORD interrupt_dequeue_(struct dcpu16 *d) {
+DCPU16_WORD interrupt_dequeue_(struct dcpu16 *vm) {
     DCPU16_WORD message;
 
-    if (d->interrupts_tail_ == d->interrupts_head_) {
+    if (vm->interrupts_tail_ == vm->interrupts_head_) {
         WARN("interrupt underflow");
         return 0;
     }
 
-    message = d->interrupts_[d->interrupts_head_];
-    d->interrupts_head_ += 1;
-    d->interrupts_head_ %= DCPU16_INTERRUPT_QUEUE_SIZE;
+    message = vm->interrupts_[vm->interrupts_head_];
+    vm->interrupts_head_ += 1;
+    vm->interrupts_head_ %= DCPU16_INTERRUPT_QUEUE_SIZE;
 
     return message;
 }
@@ -152,20 +165,20 @@ DCPU16_WORD interrupt_dequeue_(struct dcpu16 *d) {
  * e_addr is set to a referenced address, for accounting callback
  * pc_adjust is set to how to change the program counter
  * stack_adjust is set to how to change the stack pointer
- * cycles is set to number of cycles spent looking up operand
+ * cycle_adjust is set to number of cycles spent looking up operand
  *
  * zero all adjustables before decoding first operand, and pass in these values when
  * decoding next operand..
  *
  */
 static inline
-void value_decode_(struct dcpu16 *d, DCPU16_WORD value, unsigned int value_is_a, DCPU16_WORD value_data,
+void value_decode_(struct dcpu16 *vm, DCPU16_WORD value, unsigned int value_is_a, DCPU16_WORD value_data,
                   DCPU16_WORD *work_v, DCPU16_WORD **v, DCPU16_WORD *e_addr,
                   short *pc_adjust, short *sp_adjust, unsigned int *cycle_adjust) {
     assert(value <= 0x3f);
 
-    DCPU16_WORD pc = (DCPU16_WORD)(d->pc + *pc_adjust),
-                sp = (DCPU16_WORD)(d->sp + *sp_adjust);
+    DCPU16_WORD pc = (DCPU16_WORD)(vm->reg[DCPU16_REG_PC] + *pc_adjust),
+                sp = (DCPU16_WORD)(vm->reg[DCPU16_REG_PC] + *sp_adjust);
 
     TRACE("%s: pc:0x%04x sp:0x%04x value_data:0x%04x\n", 
           __func__,
@@ -174,21 +187,21 @@ void value_decode_(struct dcpu16 *d, DCPU16_WORD value, unsigned int value_is_a,
           value_data);
 
     if (value <= 0x07) { /* register */
-        *v = d->reg + value;
-        TRACE("%s>>     %c (0x%04x)",
+        *v = vm->reg + value;
+        TRACE("%s>>     %s (0x%04x)",
               __func__,
-              regnames_[value],
+              dcpu16_reg_names[value],
               **v);
         return;
     }
 
     if (value <= 0x0f) { /* [register] */
-        *v = &(d->ram[ d->reg[value & 0x07] ]);
-        *e_addr = d->reg[value & 0x07];
-        TRACE("%s>>     [%c] [0x%04x] (0x%04x)",
+        *v = &(vm->ram[ vm->reg[value & 0x07] ]);
+        *e_addr = vm->reg[value & 0x07];
+        TRACE("%s>>     [%s] [0x%04x] (0x%04x)",
               __func__,
-              regnames_[value & 0x07],
-              d->reg[value & 0x07],
+              dcpu16_reg_names[value & 0x07],
+              vm->reg[value & 0x07],
               **v);
         return;
     }
@@ -196,13 +209,13 @@ void value_decode_(struct dcpu16 *d, DCPU16_WORD value, unsigned int value_is_a,
     if (value <= 0x17) { /* [next word + register] */
         *pc_adjust += 1; /* consume next word */
         *cycle_adjust += 1;
-        *e_addr = value_data + d->reg[value & 0x07];
-        *v = d->ram + *e_addr;
-        TRACE("%s>>     [nextword + %c] [0x%04x + 0x%04x] (0x%04x)",
+        *e_addr = value_data + vm->reg[value & 0x07];
+        *v = vm->ram + *e_addr;
+        TRACE("%s>>     [nextword + %s] [0x%04x + 0x%04x] (0x%04x)",
               __func__,
-              regnames_[value & 0x07],
+              dcpu16_reg_names[value & 0x07],
               value_data,
-              d->reg[value & 0x07],
+              vm->reg[value & 0x07],
               **v);
         return;
     }
@@ -210,12 +223,12 @@ void value_decode_(struct dcpu16 *d, DCPU16_WORD value, unsigned int value_is_a,
     switch (value) {
         case 0x18: /* PUSH/[--SP] or POP/[SP++] */
         if (value_is_a == 0) { /* b */
-            *v = &(d->ram[sp - 1]);
+            *v = &(vm->ram[sp - 1]);
             *sp_adjust -= 1;
             *e_addr = sp - 1;
             TRACE("%s>>     PUSH [0x%04x] (0x%04x)", __func__, sp - 1, **v);
         } else { /* a */
-            *v = &(d->ram[sp]);
+            *v = &(vm->ram[sp]);
             *sp_adjust += 1;
             *e_addr = sp;
             TRACE("%s>>     POP [0x%04x] (0x%04x)", __func__, sp, **v);
@@ -223,7 +236,7 @@ void value_decode_(struct dcpu16 *d, DCPU16_WORD value, unsigned int value_is_a,
         break;
 
         case 0x19: /* PEEK/[SP] */
-        *v = &(d->ram[sp]);
+        *v = &(vm->ram[sp]);
         *e_addr = sp;
         TRACE("%s>>     PEEK [0x%04x] (0x%04x)",
               __func__,
@@ -235,7 +248,7 @@ void value_decode_(struct dcpu16 *d, DCPU16_WORD value, unsigned int value_is_a,
         *pc_adjust += 1;
         *cycle_adjust += 1;
         *e_addr = sp + value_data;
-        *v = d->ram + *e_addr;
+        *v = vm->ram + *e_addr;
         TRACE("%s>>     PICK 0x%04x [0x%04x] (0x%04x)",
               __func__,
               value_data,
@@ -244,26 +257,26 @@ void value_decode_(struct dcpu16 *d, DCPU16_WORD value, unsigned int value_is_a,
         break;
 
         case 0x1b: /* SP */
-        *v = &(d->sp);
+        *v = &(vm->reg[DCPU16_REG_SP]);
         TRACE("%s>>     %s (0x%04x)",
               __func__,
-              "SP",
+              dcpu16_reg_names[DCPU16_REG_SP],
               **v);
         break;
 
         case 0x1c: /* PC */
-        *v = &(d->pc);
+        *v = &(vm->reg[DCPU16_REG_PC]);
         TRACE("%s>>     %s (0x%04x)",
               __func__,
-              "PC",
+              dcpu16_reg_names[DCPU16_REG_PC],
               **v);
         break;
 
         case 0x1d: /* EX */
-        *v = &(d->ex);
+        *v = &(vm->reg[DCPU16_REG_EX]);
         TRACE("%s>>     %s (0x%04x)",
               __func__,
-              "EX",
+              dcpu16_reg_names[DCPU16_REG_EX],
               **v);
         break;
 
@@ -271,7 +284,7 @@ void value_decode_(struct dcpu16 *d, DCPU16_WORD value, unsigned int value_is_a,
         *pc_adjust += 1;
         *cycle_adjust += 1;
         *e_addr = value_data;
-        *v = d->ram + *e_addr;
+        *v = vm->ram + *e_addr;
         TRACE("%s>>     [nextword] [0x%04x] (0x%04x)",
               __func__,
               value_data,
@@ -310,7 +323,7 @@ struct opcode_entry {
 /* opcode doesn't adjust its own PC, the step function which invoked it handles that */
 /* opcode does adjust stack and cycle count */
 
-#define OP_IMPL(x) static void op_##x(struct dcpu16 *d, DCPU16_WORD val_b, DCPU16_WORD val_b_data, DCPU16_WORD val_a, DCPU16_WORD val_a_data)
+#define OP_IMPL(x) static void op_##x(struct dcpu16 *vm, DCPU16_WORD val_b, DCPU16_WORD val_b_data, DCPU16_WORD val_a, DCPU16_WORD val_a_data)
 
 #define OP_TYPE(op_type) DCPU16_WORD *a, *b;\
     DCPU16_WORD ev_a_addr = 0, ev_b_addr = 0;\
@@ -318,15 +331,15 @@ struct opcode_entry {
     unsigned int cycle_adjust = 0;\
     do {\
         op_type;\
-        value_decode_(d, val_a, 1, val_a_data,\
-                      &d->reg_work_[1], &a, &ev_a_addr,\
+        value_decode_(vm, val_a, 1, val_a_data,\
+                      &vm->reg_work_[1], &a, &ev_a_addr,\
                       &pc_adjust, &sp_adjust, &cycle_adjust);\
-        d->sp += sp_adjust;\
-        d->cycle += cycle_adjust;\
+        vm->reg[DCPU16_REG_SP] += sp_adjust;\
+        vm->cycle += cycle_adjust;\
     } while (0)
 #define OP_NBI_ (void)val_b, (void)b, (void)ev_b_addr, (void)val_b_data
-#define OP_BASIC_ value_decode_(d, val_b, 0, val_b_data,\
-                                &d->reg_work_[0], &b, &ev_b_addr,\
+#define OP_BASIC_ value_decode_(vm, val_b, 0, val_b_data,\
+                                &vm->reg_work_[0], &b, &ev_b_addr,\
                                 &pc_adjust, &sp_adjust, &cycle_adjust)
 #define OP_BASIC(x) OP_TYPE(OP_BASIC_)
 #define OP_NBI(x) OP_TYPE(OP_NBI_)
@@ -337,9 +350,9 @@ struct opcode_entry {
     accounting helpers, these fire off the related callbacks for memory reads,
     memory writes, and execution of reserved instructions
  */
-#define ACCT_R(addr) do { acct_event_(d, DCPU16_ACCT_EV_READ, addr); } while (0)
-#define ACCT_W(addr) do { acct_event_(d, DCPU16_ACCT_EV_WRITE, addr); } while (0)
-#define ACCT_ILL(addr) do { acct_event_(d, DCPU16_ACCT_EV_NOP, addr); } while (0)
+#define ACCT_R(addr) do { acct_event_(vm, DCPU16_ACCT_EV_READ, addr); } while (0)
+#define ACCT_W(addr) do { acct_event_(vm, DCPU16_ACCT_EV_WRITE, addr); } while (0)
+#define ACCT_ILL(addr) do { acct_event_(vm, DCPU16_ACCT_EV_NOP, addr); } while (0)
 
 /* extended opcodes */
 
@@ -355,10 +368,10 @@ OP_IMPL(nbi__reserved_) {
     /* reserved for future expansion */
 
     /* fire an illegal instruction event for current instruction */
-    DCPU16_WORD future_opcode = (d->ram[d->pc - pc_adjust] >> (OPCODE_BASIC_BITS + OPCODE_OPERAND_B_BITS));
+    DCPU16_WORD future_opcode = (vm->ram[vm->reg[DCPU16_REG_PC] - pc_adjust] >> (OPCODE_BASIC_BITS + OPCODE_OPERAND_B_BITS));
     WARN("reserved future opcode 0x%04x invoked", future_opcode);
 
-    ACCT_ILL(d->pc - pc_adjust);
+    ACCT_ILL(vm->reg[DCPU16_REG_PC] - pc_adjust);
 }
 
 OP_IMPL(nbi_jsr) {
@@ -367,12 +380,12 @@ OP_IMPL(nbi_jsr) {
 
     ACCT_R(ev_a_addr);
 
-    d->ram[ --d->sp ] = d->pc;
-    d->pc = *a;
+    vm->ram[ --vm->reg[DCPU16_REG_SP] ] = vm->reg[DCPU16_REG_PC];
+    vm->reg[DCPU16_REG_PC] = *a;
 
-    d->cycle += 2;
+    vm->cycle += 2;
 
-    ACCT_W(d->sp + 1);
+    ACCT_W(vm->reg[DCPU16_REG_SP] + 1);
 }
 
 OP_IMPL(nbi__reserved2_) {
@@ -381,7 +394,7 @@ OP_IMPL(nbi__reserved2_) {
 
     WARN("reserved nbi opcode invoked");
 
-    ACCT_ILL(d->pc - pc_adjust);
+    ACCT_ILL(vm->reg[DCPU16_REG_PC] - pc_adjust);
 }
 
 OP_IMPL(nbi_int) {
@@ -389,29 +402,29 @@ OP_IMPL(nbi_int) {
 
     ACCT_R(ev_a_addr);
 
-    if (d->ia) {
-        if ( interrupt_enqueue_(d, *a) ) {
+    if (vm->reg[DCPU16_REG_IA]) {
+        if ( interrupt_enqueue_(vm, *a) ) {
             WARN("failed to queue interrupt");
             return;
         }
 
-        if (d->interrupts_deferred_)
+        if (vm->interrupts_deferred_)
             return;
 
-        d->interrupts_deferred_ = 1;
-        d->ram[--d->sp] = d->pc;
-        d->ram[--d->sp] = d->reg[reg_index_('A')];
-        d->pc = d->ia;
-        d->reg[0] = *a;
+        vm->interrupts_deferred_ = 1;
+        vm->ram[--vm->reg[DCPU16_REG_SP]] = vm->reg[DCPU16_REG_PC];
+        vm->ram[--vm->reg[DCPU16_REG_SP]] = vm->reg[DCPU16_REG_A];
+        vm->reg[DCPU16_REG_PC] = vm->reg[DCPU16_REG_IA];
+        vm->reg[0] = *a;
     }
 
-    d->cycle += 4;
+    vm->cycle += 4;
 }
 
 OP_IMPL(nbi_iag) {
     OP_NBI(nbi_iag);
 
-    *a = d->ia;
+    *a = vm->reg[DCPU16_REG_IA];
 
     ACCT_W(ev_a_addr);
 }
@@ -419,7 +432,7 @@ OP_IMPL(nbi_iag) {
 OP_IMPL(nbi_ias) {
     OP_NBI(nbi_ias);
 
-    d->ia = *a;
+    vm->reg[DCPU16_REG_IA] = *a;
 
     ACCT_R(ev_a_addr);
 }
@@ -428,18 +441,18 @@ OP_IMPL(nbi_ias) {
 OP_IMPL(nbi_rfi) {
     OP_NBI(nbi_rfi);
 
-    d->interrupts_deferred_ = 0;
-    d->reg[reg_index_('A')] = d->ram[d->sp++];
-    d->pc = d->ram[d->sp++];
+    vm->interrupts_deferred_ = 0;
+    vm->reg[DCPU16_REG_A] = vm->ram[vm->reg[DCPU16_REG_SP]++];
+    vm->reg[DCPU16_REG_PC] = vm->ram[vm->reg[DCPU16_REG_SP]++];
 }
 
 OP_IMPL(nbi_iaq) {
     OP_NBI(nbi_iaq);
 
     if (*a) {
-        d->interrupts_deferred_ = 1;
+        vm->interrupts_deferred_ = 1;
     } else {
-        d->interrupts_deferred_ = 0;
+        vm->interrupts_deferred_ = 0;
     }
 
     ACCT_R(ev_a_addr);
@@ -450,9 +463,9 @@ OP_IMPL(nbi_hwn) {
 
     ACCT_W(ev_a_addr);
 
-    *a = d->hw_table_entries_;
+    *a = vm->hw_table_entries_;
 
-    d->cycle += 2;
+    vm->cycle += 2;
 }
 
 OP_IMPL(nbi_hwq) {
@@ -460,23 +473,23 @@ OP_IMPL(nbi_hwq) {
 
     ACCT_R(ev_a_addr);
 
-    if (*a >= d->hw_table_entries_) {
+    if (*a >= vm->hw_table_entries_) {
         WARN("hardware query for non-extant device 0x%04x", *a);
-        d->reg[reg_index_('A')] = 0;
-        d->reg[reg_index_('B')] = 0;
-        d->reg[reg_index_('C')] = 0;
-        d->reg[reg_index_('X')] = 0;
-        d->reg[reg_index_('Y')] = 0;
+        vm->reg[DCPU16_REG_A] = 0;
+        vm->reg[DCPU16_REG_B] = 0;
+        vm->reg[DCPU16_REG_C] = 0;
+        vm->reg[DCPU16_REG_X] = 0;
+        vm->reg[DCPU16_REG_Y] = 0;
         return;
     }
 
-    d->reg[reg_index_('A')] = d->hw_table_[*a].id_l;
-    d->reg[reg_index_('B')] = d->hw_table_[*a].id_h;
-    d->reg[reg_index_('C')] = d->hw_table_[*a].ver;
-    d->reg[reg_index_('X')] = d->hw_table_[*a].mfg_l;
-    d->reg[reg_index_('Y')] = d->hw_table_[*a].mfg_h;
+    vm->reg[DCPU16_REG_A] = vm->hw_table_[*a].id_l;
+    vm->reg[DCPU16_REG_B] = vm->hw_table_[*a].id_h;
+    vm->reg[DCPU16_REG_C] = vm->hw_table_[*a].ver;
+    vm->reg[DCPU16_REG_X] = vm->hw_table_[*a].mfg_l;
+    vm->reg[DCPU16_REG_Y] = vm->hw_table_[*a].mfg_h;
 
-    d->cycle += 4;
+    vm->cycle += 4;
 }
 
 OP_IMPL(nbi_hwi) {
@@ -484,13 +497,16 @@ OP_IMPL(nbi_hwi) {
 
     ACCT_R(ev_a_addr);
 
-    if (*a > d->hw_table_entries_) {
+    if (*a > vm->hw_table_entries_) {
         WARN("interrupt for non-extant device 0x%04x", *a);
         return;
     }
 
-    d->cycle += 4;
-    d->hw_table_[*a].int_fn(d, d->hw_table_[*a].data);
+    vm->cycle += 4;
+    if (vm->hw_table_[*a].hwi)
+        vm->hw_table_[*a].hwi(vm, vm->hw_table_[*a].data);
+    else
+        WARN("hardware 0x%04x has no interrupt handler", *a);
 }
 
 OP_IMPL(nbi_hcf) {
@@ -498,10 +514,10 @@ OP_IMPL(nbi_hcf) {
 
     ACCT_R(ev_a_addr);
 
-    d->on_fire_ = 1;
+    vm->on_fire_ = 1;
     WARN("system on fire");
 
-    d->cycle += 9;
+    vm->cycle += 9;
 }
 
 static const struct opcode_entry opcode_nbi_entries[] = {
@@ -533,7 +549,7 @@ static const struct opcode_entry opcode_nbi_entries[] = {
 /* basic opcodes */
 
 /*
-    N.B. the following function does not decode values, (thus does not advance sp)
+    N.B. the following function does not decode values.
     Decoding is handled by the secondary opcode functions it calls.
 */
 OP_IMPL(_nbi_) {
@@ -551,7 +567,7 @@ OP_IMPL(_nbi_) {
     assert(e->impl != NULL);
 
     TRACE(">> %s 0x%04x", e->name, val_b);
-    e->impl(d, 0, 0, val_a, val_a_data);
+    e->impl(vm, 0, 0, val_a, val_a_data);
 }
 
 OP_IMPL(set) {
@@ -566,7 +582,7 @@ OP_IMPL(set) {
      */
     *b = *a;
 
-    d->cycle += 1;
+    vm->cycle += 1;
 
     ACCT_W(ev_b_addr);
 }
@@ -580,9 +596,9 @@ OP_IMPL(add) {
     ACCT_R(ev_a_addr);
 
     *b = acc;
-    d->ex = (acc > 0xffff);
+    vm->reg[DCPU16_REG_EX] = (acc > 0xffff);
 
-    d->cycle += 2;
+    vm->cycle += 2;
 
     ACCT_W(ev_b_addr);
 }
@@ -596,9 +612,9 @@ OP_IMPL(sub) {
     ACCT_R(ev_a_addr);
 
     *b = acc;
-    d->ex = (acc > 0xffff);
+    vm->reg[DCPU16_REG_EX] = (acc > 0xffff);
 
-    d->cycle += 2;
+    vm->cycle += 2;
 
     ACCT_W(ev_b_addr);
 }
@@ -612,9 +628,9 @@ OP_IMPL(mul) {
     ACCT_R(ev_a_addr);
 
     *b = acc;
-    d->ex = acc >> 16;
+    vm->reg[DCPU16_REG_EX] = acc >> 16;
 
-    d->cycle += 2;
+    vm->cycle += 2;
 
     ACCT_W(ev_b_addr);
 }
@@ -628,9 +644,9 @@ OP_IMPL(mli) {
     ACCT_R(ev_a_addr);
 
     *b = acc;
-    d->ex = acc >> 16;
+    vm->reg[DCPU16_REG_EX] = acc >> 16;
 
-    d->cycle += 2;
+    vm->cycle += 2;
 
     ACCT_W(ev_b_addr);
 }
@@ -644,13 +660,13 @@ OP_IMPL(div) {
 
     if (*a == 0) {
         *b = 0;
-        d->ex = 0;
+        vm->reg[DCPU16_REG_EX] = 0;
     } else {
         *b = *b / *a;
-        d->ex = (*b << 16) / *a;
+        vm->reg[DCPU16_REG_EX] = (*b << 16) / *a;
     }
 
-    d->cycle += 3;
+    vm->cycle += 3;
 
     ACCT_W(ev_b_addr);
 }
@@ -664,13 +680,13 @@ OP_IMPL(dvi) {
 
     if (*a == 0) {
         *b = 0;
-        d->ex = 0;
+        vm->reg[DCPU16_REG_EX] = 0;
     } else {
         *b = (short)*b / (short)*a;
-        d->ex = (short)(*b << 16) / (short)*a;
+        vm->reg[DCPU16_REG_EX] = (short)(*b << 16) / (short)*a;
     }
 
-    d->cycle += 3;
+    vm->cycle += 3;
 
     ACCT_W(ev_b_addr);
 }
@@ -688,7 +704,7 @@ OP_IMPL(mod) {
         *b = *b % *a;
     }
 
-    d->cycle += 3;
+    vm->cycle += 3;
 
     ACCT_W(ev_a_addr);
 }
@@ -706,7 +722,7 @@ OP_IMPL(mdi) {
         *b = (short)*b % (short)*a;
     }
 
-    d->cycle += 3;
+    vm->cycle += 3;
 
     ACCT_W(ev_b_addr);
 }
@@ -720,7 +736,7 @@ OP_IMPL(and) {
 
     *b = *b & *a;
 
-    d->cycle += 1;
+    vm->cycle += 1;
 
     ACCT_W(ev_b_addr);
 }
@@ -734,7 +750,7 @@ OP_IMPL(bor) {
 
     *b = *b | *a;
 
-    d->cycle += 1;
+    vm->cycle += 1;
 
     ACCT_W(ev_b_addr);
 }
@@ -748,7 +764,7 @@ OP_IMPL(xor) {
 
     *b = *b ^ *a;
 
-    d->cycle += 1;
+    vm->cycle += 1;
 
     ACCT_W(ev_b_addr);
 }
@@ -762,9 +778,9 @@ OP_IMPL(shr) {
     ACCT_R(ev_a_addr);
 
     *b = acc & 0xffff;
-    d->ex = (*b << 16) >> *a;
+    vm->reg[DCPU16_REG_EX] = (*b << 16) >> *a;
 
-    d->cycle += 2;
+    vm->cycle += 2;
 
     WARN("IMPLEMENT");
 
@@ -780,9 +796,9 @@ OP_IMPL(asr) {
     ACCT_R(ev_a_addr);
 
     *b = acc & 0xffff;
-    d->ex = (*b << 16) >> *a;
+    vm->reg[DCPU16_REG_EX] = (*b << 16) >> *a;
 
-    d->cycle += 2;
+    vm->cycle += 2;
 
     WARN("IMPLEMENT");
 
@@ -799,9 +815,9 @@ OP_IMPL(shl) {
 
     *b = acc;
 
-    d->ex = acc >> 16;
+    vm->reg[DCPU16_REG_EX] = acc >> 16;
 
-    d->cycle += 2;
+    vm->cycle += 2;
 
     ACCT_W(ev_b_addr);
 }
@@ -816,11 +832,11 @@ OP_IMPL(ifb) {
     if ((*b & *a) != 0) {
         /* */
     } else {
-        d->skip_ = 1;
-        d->cycle += 1;
+        vm->skip_ = 1;
+        vm->cycle += 1;
     }
 
-    d->cycle += 2;
+    vm->cycle += 2;
 }
 
 OP_IMPL(ifc) {
@@ -831,13 +847,13 @@ OP_IMPL(ifc) {
     ACCT_R(ev_a_addr);
 
     if ((*b & *a) == 0) {
-        
+        /* */
     } else {
-        d->skip_ = 1;
-        d->cycle += 1;
+        vm->skip_ = 1;
+        vm->cycle += 1;
     }
 
-    d->cycle += 2;
+    vm->cycle += 2;
 }
 
 OP_IMPL(ife) {
@@ -850,11 +866,11 @@ OP_IMPL(ife) {
     if (*b == *a) {
         /* */
     } else {
-        d->skip_ = 1;
-        d->cycle += 1;
+        vm->skip_ = 1;
+        vm->cycle += 1;
     }
 
-    d->cycle += 2;
+    vm->cycle += 2;
 }
 
 OP_IMPL(ifn) {
@@ -867,11 +883,11 @@ OP_IMPL(ifn) {
     if (*b != *a) {
         /* */
     } else {
-        d->skip_ = 1;
-        d->cycle++;
+        vm->skip_ = 1;
+        vm->cycle++;
     }
 
-    d->cycle += 2;
+    vm->cycle += 2;
 }
 
 OP_IMPL(ifg) {
@@ -884,11 +900,11 @@ OP_IMPL(ifg) {
     if (*b > *a) {
         /* */
     } else {
-        d->skip_ = 1;
-        d->cycle++;
+        vm->skip_ = 1;
+        vm->cycle++;
     }
 
-    d->cycle += 2;
+    vm->cycle += 2;
 }
 
 OP_IMPL(ifa) {
@@ -901,11 +917,11 @@ OP_IMPL(ifa) {
     if (*b > *a) {
         /* */
     } else {
-        d->skip_ = 1;
-        d->cycle += 1;
+        vm->skip_ = 1;
+        vm->cycle += 1;
     }
 
-    d->cycle += 2;
+    vm->cycle += 2;
 }
 
 OP_IMPL(ifl) {
@@ -918,11 +934,11 @@ OP_IMPL(ifl) {
     if (*b < *a) {
         /* */
     } else {
-        d->skip_ = 1;
-        d->cycle++;
+        vm->skip_ = 1;
+        vm->cycle++;
     }
 
-    d->cycle += 2;
+    vm->cycle += 2;
 }
 
 OP_IMPL(ifu) {
@@ -935,11 +951,11 @@ OP_IMPL(ifu) {
     if (*b < *a) {
         /* */
     } else {
-        d->skip_ = 1;
-        d->cycle += 1;
+        vm->skip_ = 1;
+        vm->cycle += 1;
     }
 
-    d->cycle += 2;
+    vm->cycle += 2;
 }
 
 OP_IMPL(adx) {
@@ -950,14 +966,14 @@ OP_IMPL(adx) {
     ACCT_R(ev_b_addr);
     ACCT_R(ev_a_addr);
 
-    acc = *b + *a + d->ex;
+    acc = *b + *a + vm->reg[DCPU16_REG_EX];
     *b = acc & 0xffff;
     if (acc > 0xffff)
-        d->ex = 0x0001;
+        vm->reg[DCPU16_REG_EX] = 0x0001;
     else
-        d->ex = 0x0000;
+        vm->reg[DCPU16_REG_EX] = 0x0000;
 
-    d->cycle += 3;
+    vm->cycle += 3;
 
     ACCT_W(ev_b_addr);
 }
@@ -970,14 +986,14 @@ OP_IMPL(sbx) {
     ACCT_R(ev_b_addr);
     ACCT_R(ev_a_addr);
 
-    acc = *b - *a + d->ex;
+    acc = *b - *a + vm->reg[DCPU16_REG_EX];
     *b = acc & 0xffff;
     if (acc > 0xffff)
-        d->ex = 0xffff;
+        vm->reg[DCPU16_REG_EX] = 0xffff;
     else
-        d->ex = 0;
+        vm->reg[DCPU16_REG_EX] = 0;
 
-    d->cycle += 3;
+    vm->cycle += 3;
 
     ACCT_W(ev_b_addr);
 }
@@ -990,10 +1006,10 @@ OP_IMPL(sti) {
     ACCT_R(ev_a_addr);
 
     *b = *a;
-    d->reg[reg_index_('I')] += 1;
-    d->reg[reg_index_('J')] += 1;
+    vm->reg[DCPU16_REG_I] += 1;
+    vm->reg[DCPU16_REG_J] += 1;
 
-    d->cycle += 2;
+    vm->cycle += 2;
 
     ACCT_W(ev_b_addr);
 }
@@ -1006,10 +1022,10 @@ OP_IMPL(std) {
     ACCT_R(ev_a_addr);
 
     *b = *a;
-    d->reg[reg_index_('I')] -= 1;
-    d->reg[reg_index_('J')] -= 1;
+    vm->reg[DCPU16_REG_I] -= 1;
+    vm->reg[DCPU16_REG_J] -= 1;
 
-    d->cycle += 2;
+    vm->cycle += 2;
 
     ACCT_W(ev_b_addr);
 }
@@ -1019,7 +1035,7 @@ OP_IMPL(_reserved_) {
 
     WARN("reserved opcode invoked");
 
-    ACCT_ILL(d->pc - pc_adjust);
+    ACCT_ILL(vm->reg[DCPU16_REG_PC] - pc_adjust);
 }
 
 static const struct opcode_entry opcode_basic_entries[] = {
@@ -1061,11 +1077,11 @@ static const struct opcode_entry opcode_basic_entries[] = {
 static inline
 void dump_operand_value_(DCPU16_WORD value, DCPU16_WORD nextword, unsigned int value_position) {
     if (value <= 0x07) {
-        printf(" %c", regnames_[value]);
+        printf(" %s", dcpu16_reg_names[value]);
     } else if (value <= 0x0f) {
-        printf(" [%c]", regnames_[value & 0x07]);
+        printf(" [%s]", dcpu16_reg_names[value & 0x07]);
     } else if (value <= 0x17) {
-        printf(" [0x%04x + %c]", nextword, regnames_[value & 0x07]);
+        printf(" [0x%04x + %s]", nextword, dcpu16_reg_names[value & 0x07]);
     } else switch (value) {
         case 0x18:
             if (value_position == 0) { /* b */
@@ -1160,13 +1176,13 @@ DCPU16_WORD dcpu16_mnemonify_buf(DCPU16_WORD *buf) {
     print the words of the instruction at addr, followed by its assembly representation
     returns the length of the instruction in words
  */
-DCPU16_WORD dcpu16_disassemble_print(struct dcpu16 *d, DCPU16_WORD addr) {
+DCPU16_WORD dcpu16_disassemble_print(struct dcpu16 *vm, DCPU16_WORD addr) {
     DCPU16_WORD opcode, b, a, instr_len, i, *b_data, *a_data;
-    DCPU16_WORD buf[3] = { d->ram[addr], d->ram[(DCPU16_WORD)(addr + 1)], d->ram[(DCPU16_WORD)(addr + 2)] };
+    DCPU16_WORD buf[3] = { vm->ram[addr], vm->ram[(DCPU16_WORD)(addr + 1)], vm->ram[(DCPU16_WORD)(addr + 2)] };
     unsigned int indent = 0;
     unsigned int partial = 0;
 
-    if (!d) return 0;
+    if (!vm) return 0;
 
 #if 0
     /*
@@ -1175,7 +1191,7 @@ DCPU16_WORD dcpu16_disassemble_print(struct dcpu16 *d, DCPU16_WORD addr) {
         could be data which happen to match instructions..
     */
     for (i = 3; i; i--) {
-        instruction_decode_(d->ram, (DCPU16_WORD)(addr - i), &opcode, &b, &b_data, &a, &a_data, &instr_len);
+        instruction_decode_(vm->ram, (DCPU16_WORD)(addr - i), &opcode, &b, &b_data, &a, &a_data, &instr_len);
         if (instr_len > i)
             partial++;
         if (instr_len == i
@@ -1187,12 +1203,12 @@ DCPU16_WORD dcpu16_disassemble_print(struct dcpu16 *d, DCPU16_WORD addr) {
 #endif
 
     /* just need instr_len */
-    instruction_decode_(d->ram, addr, &opcode, &b, &b_data, &a, &a_data, &instr_len);
+    instruction_decode_(vm->ram, addr, &opcode, &b, &b_data, &a, &a_data, &instr_len);
 
     /* show the raw words */
-    printf("%04x", d->ram[addr]);
+    printf("%04x", vm->ram[addr]);
     for (i = 1; i < instr_len; i++) {
-        printf(" %04x", d->ram[addr + i]);
+        printf(" %04x", vm->ram[addr + i]);
     }
 
     /* align things neatly, show the instruction */
@@ -1207,64 +1223,78 @@ DCPU16_WORD dcpu16_disassemble_print(struct dcpu16 *d, DCPU16_WORD addr) {
     return instr_len;
 }
 
+int dcpu16_interrupt(struct dcpu16 *vm, DCPU16_WORD message) {
+    TRACE("%s>> message:0x%04x", __func__, message);
+    return interrupt_enqueue_(vm, message);
+}
+
 /* execute the next instruction */
-void dcpu16_step(struct dcpu16 *d) {
+void dcpu16_step(struct dcpu16 *vm) {
     DCPU16_WORD opcode, b, a, instr_len, *b_data, *a_data;
+    size_t i;
     const struct opcode_entry *e;
 
-    if (!d) return;
-
-    acct_event_(d, DCPU16_ACCT_EV_CYCLE, d->pc);
+    if (!vm) return;
 
-    /* if we're currently servicing interrupts */
-    if (d->interrupts_deferred_ == 0) {
-        /* and there are interrupts to be serviced */
-        if (d->interrupts_head_ != d->interrupts_tail_) {
-            DCPU16_WORD message;
-            message = interrupt_dequeue_(d);
+    /* signal interested parties that a new cycle has ticked */
+    TRACE("%s: sending global cycle event", __func__);
+    acct_event_(vm, DCPU16_ACCT_EV_CYCLE, vm->reg[DCPU16_REG_PC]);
 
-            if (d->ia) {
-                TRACE("servicing interrupt IA:0x%04x message:0x%04x \n", d->ia, message);
-                /* then service the next interrupt */
-                d->interrupts_deferred_ = 1;
-                d->ram[--d->sp] = d->pc;
-                d->ram[--d->sp] = d->reg[reg_index_('A')];
-                d->pc = d->ia;
-                d->reg[0] = message;
-            } else {
-                TRACE("ignoring interrupt IA:0");
-            }
+    /* signal attached hardware */
+    for (i = 0; i < vm->hw_table_entries_; i++) {
+        if (vm->hw_table_[i].cycle) {
+            TRACE("%s: sending cycle to %s", __func__, vm->hw_table_[i].name_);
+            vm->hw_table_[i].cycle(vm, vm->hw_table_[i].data);
         }
     }
 
-    /* and make sure to execute an instruction after an interrupt */
+    instruction_decode_(vm->ram, vm->reg[DCPU16_REG_PC], &opcode, &b, &b_data, &a, &a_data, &instr_len);
 
-    instruction_decode_(d->ram, d->pc, &opcode, &b, &b_data, &a, &a_data, &instr_len);
+    /* consume what we decoded */
+    /* this happens immediately as PC might be re-set as an operation */
+    vm->reg[DCPU16_REG_PC] += instr_len;
 
+    /* run the operation */
     for (e = opcode_basic_entries; e->impl; e++) {
         if (e->value == opcode) {
             TRACE("%s>> %s 0x%04x, 0x%04x", __func__, e->name, b, a);
-            e->impl(d, b, b_data ? *b_data : 0, a, a_data ? *a_data : 0);
+            e->impl(vm, b, b_data ? *b_data : 0, a, a_data ? *a_data : 0);
             break;
         }
     }
 
-    /* get ready for the next one */
-    d->pc += instr_len;
-
     /* and jump over next instr(s) if needed */
-    if (d->skip_) {
-        instruction_decode_(d->ram, d->pc, &opcode, &b, &b_data, &a, &a_data, &instr_len);
-        d->pc += instr_len;
+    while (vm->skip_) {
+        instruction_decode_(vm->ram, vm->reg[DCPU16_REG_PC], &opcode, &b, &b_data, &a, &a_data, &instr_len);
+        vm->reg[DCPU16_REG_PC] += instr_len;
         TRACE("++ SKIPPED %x words", instr_len);
         if (opcode >= 0x10 && opcode <= 0x17) {
             /* skipping a branch instruction? skip branch's skippable instruction as well */
-            d->cycle += 1;
-            instruction_decode_(d->ram, d->pc, &opcode, &b, &b_data, &a, &a_data, &instr_len);
-            d->pc += instr_len;
-            TRACE("++ SKIPPED %x words", instr_len);
+            vm->cycle += 1;
+        } else {
+            vm->skip_ = 0;
+        }
+    }
+
+    /* if we're currently servicing interrupts */
+    if (vm->interrupts_deferred_ == 0) {
+        /* and there are interrupts to be serviced */
+        if (vm->interrupts_head_ != vm->interrupts_tail_) {
+            DCPU16_WORD message;
+            message = interrupt_dequeue_(vm);
+
+            if (vm->reg[DCPU16_REG_IA]) {
+                TRACE("servicing interrupt IA:0x%04x message:0x%04x \n", vm->reg[DCPU16_REG_IA], message);
+                /* then service the next interrupt */
+                vm->interrupts_deferred_ = 1;
+                vm->ram[--vm->reg[DCPU16_REG_SP]] = vm->reg[DCPU16_REG_PC];
+                vm->ram[--vm->reg[DCPU16_REG_SP]] = vm->reg[DCPU16_REG_A];
+                vm->reg[DCPU16_REG_PC] = vm->reg[DCPU16_REG_IA];
+                vm->reg[DCPU16_REG_A] = message;
+            } else {
+                TRACE("ignoring interrupt IA:0");
+            }
         }
-        d->skip_ = 0;
     }
 }
 
@@ -1272,41 +1302,41 @@ void dcpu16_step(struct dcpu16 *d) {
     print the current state of the machine
     shows current cycle count, registers, and next instruction
 */
-void dcpu16_state_print(struct dcpu16 *d) {
+void dcpu16_state_print(struct dcpu16 *vm) {
     unsigned int i;
 
-    if (!d) return;
+    if (!vm) return;
 
     printf("  ");
     for (i = 0; i < 8; i++)
-        printf("  %c:0x%04x", regnames_[i], d->reg[i]);
+        printf("  %s:0x%04x", dcpu16_reg_names[i], vm->reg[i]);
     printf("\n");
 
     printf("(0x%08llx) %2s:0x%04x %2s:0x%04x %2s:0x%04x %2s:0x%04x [%2s]:",
-           d->cycle,
-           "EX", d->ex,
-           "SP", d->sp,
-           "PC", d->pc,
-           "IA", d->ia,
+           vm->cycle,
+           dcpu16_reg_names[DCPU16_REG_EX], vm->reg[DCPU16_REG_EX],
+           dcpu16_reg_names[DCPU16_REG_SP], vm->reg[DCPU16_REG_SP],
+           dcpu16_reg_names[DCPU16_REG_PC], vm->reg[DCPU16_REG_PC],
+           dcpu16_reg_names[DCPU16_REG_IA], vm->reg[DCPU16_REG_IA],
            "PC");
 
-    dcpu16_disassemble_print(d, d->pc);
+    dcpu16_disassemble_print(vm, vm->reg[DCPU16_REG_PC]);
     printf("\n");
 }
 
 /*  dcpu16_dump_ram
  *  print raw ram contents from start to stop
  */
-void dcpu16_dump_ram(struct dcpu16 *d, DCPU16_WORD start, DCPU16_WORD end) {
+void dcpu16_dump_ram(struct dcpu16 *vm, DCPU16_WORD start, DCPU16_WORD end) {
     unsigned int i, j;
     const unsigned int n = 8; /* words per line */
 
-    if (!d) return;
+    if (!vm) return;
 
     for (i = start, j = 0; i <= end; i++, j++) {
         if (j % n == 0)
             printf("0x%04x:\t", i);
-        printf(" %04x%s", d->ram[i], (j % n) == (n - 1) ? "\n" : "");
+        printf(" %04x%s", vm->ram[i], (j % n) == (n - 1) ? "\n" : "");
     }
     if ((j % n) != (n - 1))
         printf("\n");
@@ -1319,6 +1349,11 @@ int dcpu16_hw_add(struct dcpu16 *vm, struct dcpu16_hw *hw) {
     if (!vm || !hw)
         return -1;
 
+    if (vm->hw_table_entries_ == 0xffff) {
+        WARN("maximum hardware entries reached");
+        return -1;
+    }
+
     if (vm->hw_table_entries_ == vm->hw_table_allocated_) {
         size_t new_entries = vm->hw_table_allocated_ + 32;
         void *tmp_ptr = realloc(vm->hw_table_, new_entries * sizeof * (vm->hw_table_));
@@ -1343,6 +1378,9 @@ int dcpu16_hw_add(struct dcpu16 *vm, struct dcpu16_hw *hw) {
 int dcpu16_acct_add(struct dcpu16 *vm, dcpu16_acct_event mask, dcpu16_ev_cb_t *fn, void *data) {
     struct dcpu16_acct_cb cb;
 
+    if (!vm)
+        return -1;
+
     cb.mask = mask;
     cb.fn = fn;
     cb.data = data;
@@ -1367,19 +1405,30 @@ int dcpu16_acct_add(struct dcpu16 *vm, dcpu16_acct_event mask, dcpu16_ev_cb_t *f
 /*  dcpu16_reset
  *  signals cpu to reset, clearing runstate and ram, then reload any init callbacks
  */
-void dcpu16_reset(struct dcpu16 *d) {
-    if (!d) return;
-
-    d->cycle = 0;
-    memset(d->reg, 0, sizeof d->reg);
-    d->pc = 0;
-    d->sp = 0;
-    d->ex = 0;
-    d->ia = 0;
-    d->skip_ = 0;
-    memset(d->ram, 0, sizeof d->ram);
-
-    acct_event_(d, DCPU16_ACCT_EV_RESET, 0);
+void dcpu16_reset(struct dcpu16 *vm) {
+    size_t i;
+
+    if (!vm)
+        return;
+
+    vm->skip_ = 0;
+    vm->interrupts_deferred_ = 0;
+    vm->on_fire_ = 0;
+    memset(vm->interrupts_, 0, sizeof vm->interrupts_);
+    vm->interrupts_head_ = 0;
+    vm->interrupts_tail_ = 0;
+
+    /* signal attached hardware */
+    for (i = 0; i < vm->hw_table_entries_; i++) {
+        if (vm->hw_table_[i].reset) 
+            vm->hw_table_[i].reset(vm, vm->hw_table_[i].data);
+    }
+
+    memset(vm->reg, 0, sizeof vm->reg);
+    memset(vm->ram, 0, sizeof vm->ram);
+    vm->cycle = 0;
+
+    acct_event_(vm, DCPU16_ACCT_EV_RESET, 0);
 }
 
 /*  dcpu16_new
@@ -1392,6 +1441,9 @@ struct dcpu16 *dcpu16_new(void) {
     if (vm == NULL)
         WARN("%s: %s(%zu): %s", __func__, "calloc", strerror(errno));
 
+    vm->warn_cb_ = warn_cb_;
+    vm->trace_cb_ = trace_cb_;
+
     return vm;
 }
 
@@ -1399,7 +1451,8 @@ struct dcpu16 *dcpu16_new(void) {
  *  release a dcpu16 instance
  */
 void dcpu16_delete(struct dcpu16 **vm) {
-    if (!vm || !*vm) return;
+    if (!vm || !*vm)
+        return;
 
     free(*vm);
     *vm = NULL;
diff --git a/dcpu16.h b/dcpu16.h
index 35c1fe8..f2bf787 100644
--- a/dcpu16.h
+++ b/dcpu16.h
@@ -10,8 +10,28 @@ typedef unsigned short DCPU16_WORD;
 #define DCPU16_RAM 0x10000
 #define DCPU16_INTERRUPT_QUEUE_SIZE 256
 
+extern const char * const dcpu16_reg_names[];
+enum dcpu16_register_indexes {
+    DCPU16_REG_A = 0,
+    DCPU16_REG_B,
+    DCPU16_REG_C,
+    DCPU16_REG_X,
+    DCPU16_REG_Y,
+    DCPU16_REG_Z,
+    DCPU16_REG_I,
+    DCPU16_REG_J,
+    DCPU16_REG_PC,
+    DCPU16_REG_SP,
+    DCPU16_REG_EX,
+    DCPU16_REG_IA,
+    DCPU16_REG__NUM
+};
+
 /* a self-contained dcpu16 core */
 struct dcpu16 {
+    void (*warn_cb_)(char *fmt, ...);
+    void (*trace_cb_)(char *fmt, ...);
+
     struct dcpu16_acct_cb *cb_table_;   /* list of callbacks to invoke for certain events */
     size_t cb_table_entries_;           /* callback list maintenance */
     size_t cb_table_allocated_;         /* callback list maintenance */
@@ -29,11 +49,7 @@ struct dcpu16 {
     size_t interrupts_tail_;            /* interrupt queue maintenance */
 
     unsigned long long cycle;           /* number of cycles this core has executed */
-    DCPU16_WORD reg[8];                 /* system registers, a b c x y z i j */
-    DCPU16_WORD pc;                     /* program counter */
-    DCPU16_WORD sp;                     /* stack pointer */
-    DCPU16_WORD ex;                     /* overflow */
-    DCPU16_WORD ia;                     /* interrupt address */
+    DCPU16_WORD reg[DCPU16_REG__NUM];   /* system registers, a b c x y z i j */
     DCPU16_WORD ram[DCPU16_RAM];        /* memory */
 };
 
@@ -51,15 +67,21 @@ struct dcpu16_acct_cb {
     dcpu16_acct_event mask;
 };
 
+typedef void (dcpu16_hw_signal_t)(struct dcpu16 *, void *);
 /* these are used to define hardware attached to the system */
 struct dcpu16_hw {
+    struct dcpu16 *vm;  /* which system do I belong to */
     char *name_;
+
     DCPU16_WORD id_l;
     DCPU16_WORD id_h;
     DCPU16_WORD ver;
     DCPU16_WORD mfg_l;
     DCPU16_WORD mfg_h;
-    void (*int_fn)(struct dcpu16 *, void *);
+
+    dcpu16_hw_signal_t *hwi;
+    dcpu16_hw_signal_t *cycle;
+    dcpu16_hw_signal_t *reset;
     void *data;
 };
 
@@ -93,6 +115,8 @@ void dcpu16_step(struct dcpu16 *);
 /* release a core */
 void dcpu16_delete(struct dcpu16 **);
 
+int dcpu16_interrupt(struct dcpu16 *, DCPU16_WORD);
+
 /* register callbacks to handle warning and debug messages, default is writing to stderr, may be set to null */
 void dcpu16_warn_cb_set(void (*)(char *, ...));
 void dcpu16_trace_cb_set(void (*)(char *, ...));
diff --git a/display.c b/display.c
deleted file mode 100644
index 0fbfbf5..0000000
--- a/display.c
+++ /dev/null
@@ -1,499 +0,0 @@
-#include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
-#include <errno.h>
-#include <sysexits.h>
-#include <time.h>
-#include <assert.h>
-
-#ifdef HAVE_LIBPNG
-#include <setjmp.h>
-#include <png.h>
-#endif /* HAVE_LIBPNG */
-
-#include "dcpu16.h"
-#include "display.h"
-#include "chargen-4x8.h"
-
-/*
-    preliminary attempt at handling display
-
-    currently keeps raw display output in a pixel buffer, which is updated on every write to cpu's memory in display-space.
-    every [n] cycles, display buffer is rendered into an image file (png or pnm) in memory
-
-    TODO: blinking
-*/
-
-#define DISPLAY_BASE 0x8000
-#define DISPLAY_END  0x8179
-#define DISPLAY_CELL_MAP 0x8180
-#define DISPLAY_MISC 0x8280
-
-#define CELL_X 32
-#define CELL_Y 12
-
-#define CELL_X_SZ 4
-#define CELL_Y_SZ 8
-
-#define PIX_X 160
-#define PIX_Y 128
-#define PIX_BORDER 16
-
-/* total display is 160 pixels by 128 pixels */
-/* active display is 32x12 cells (each 4x8 pixels), surrounded by 16 pixel border */
-/* cells are rendered from cell map, which is bitmap of two words, defining four eight-bit columns */
-
-struct pixel_ {
-    unsigned char r;
-    unsigned char g;
-    unsigned char b;
-};
-
-/* buf will hold image file in memory */
-struct memstream_cookie_ {
-    char *buf;
-    size_t allocated;
-    size_t endpos;
-    off_t offset;
-    size_t chunk_size;
-};
-
-struct dcpu16_display_ {
-    char *outfile;
-    struct pixel_ *pixbuf; /* raw pixels */
-    struct memstream_cookie_ memstream_cookie; /* streambuffer contains rendered image file from pixbuf */
-    unsigned long long cycle_last_write;
-    unsigned int pixbuf_dirty : 1;
-    unsigned int file_dirty : 1;
-};
-
-static inline
-struct pixel_ pcolor_(unsigned int c) {
-    struct pixel_ p = { 0, 0, 0 };
-
-    switch (c) {
-        case 0x1: p.r=0x00, p.g=0x00, p.b=0xaa; break;  /* dark blue */
-        case 0x2: p.r=0x00, p.g=0xaa, p.b=0x00; break;  /* green */
-        case 0x3: p.r=0x00, p.g=0xaa, p.b=0xaa; break;  /* cyan */
-        case 0x4: p.r=0xaa, p.g=0x00, p.b=0x00; break;  /* red */
-        case 0x5: p.r=0xaa, p.g=0x00, p.b=0xaa; break;  /* magenta */
-        case 0x6: p.r=0xaa, p.g=0xaa, p.b=0x55; break;  /* yellow [] */
-        case 0x7: p.r=0xaa, p.g=0xaa, p.b=0xff; break;  /* pale blue */
-        case 0x8: p.r=0x55, p.g=0x55, p.b=0x55; break;  /* grey */
-        case 0x9: p.r=0x55, p.g=0x55, p.b=0xff; break;  /* also blue */
-        case 0xa: p.r=0x55, p.g=0xff, p.b=0x55; break;  /* light green */
-        case 0xb: p.r=0x55, p.g=0xff, p.b=0xff; break;  /* light cyan */
-        case 0xc: p.r=0xff, p.g=0x55, p.b=0x55; break;  /* light red */
-        case 0xd: p.r=0xff, p.g=0x55, p.b=0xff; break;  /* light magenta */
-        case 0xe: p.r=0xff, p.g=0xff, p.b=0x55; break;  /* light yellow */
-        case 0xf: p.r=0xff, p.g=0xff, p.b=0xff; break;  /* white */
-        default:  p.r=0x00, p.g=0x00, p.b=0x00;         /* black */
-    }
-
-    return p;
-}
-
-/* support functions for writing streams into memory buffer */
-static
-void memstream_cookie_init_(struct memstream_cookie_ *c, size_t chunk_size) {
-    assert(c);
-    assert(chunk_size);
-
-    c->buf = NULL;
-    c->allocated = 0;
-    c->endpos = 0;
-    c->offset = 0;
-    c->chunk_size = chunk_size;
-}
-
-static
-void memstream_cookie_fini_(struct memstream_cookie_ *c) {
-    assert(c);
-
-    free(c->buf);
-    c->allocated = c->endpos = c->offset = 0;
-}
-
-static
-/* of course these can't be the same */
-#ifdef HAVE_FOPENCOOKIE
-ssize_t memstream_write_fn_(void *c, const char *buf, size_t size)
-#else /* HAVE_FOPENCOOKIE */
-int memstream_write_fn_(void *c, const char *buf, int size)
-#endif /* HAVE_FOPENCOOKIE */
-{
-    struct memstream_cookie_ *cookie = c;
-
-    while ((size_t)size + cookie->offset > cookie->allocated) {
-        size_t new_allocated = cookie->allocated + cookie->chunk_size;
-        void *tmp_ptr = realloc(cookie->buf, new_allocated);
-        if (tmp_ptr == NULL) {
-            return -1;
-        }
-        cookie->buf = tmp_ptr;
-        cookie->allocated = new_allocated;
-    }
-
-    memcpy(cookie->buf + cookie->offset, buf, size);
-    cookie->offset += size;
-    if (cookie->offset > (off_t)cookie->endpos) {
-        cookie->endpos = cookie->offset;
-    }
-
-    return size;
-}
-
-/* should this just flood-fill entire display? */
-static inline
-void display_draw_border_(struct pixel_ *pixbuf, struct pixel_ color) {
-    size_t x, y;
-    size_t i;
-
-    /* top */
-    for (y = 0; y < PIX_BORDER; y++) {
-        for (x = 0; x < PIX_X; x++) {
-            i = (y * PIX_X) + x;
-            pixbuf[i] = color;
-            i = ((PIX_Y - y) * PIX_X) + x;
-            pixbuf[i] = color;
-        }
-    }
-
-    /* sides */
-    for (y = PIX_BORDER; y < (PIX_Y - PIX_BORDER + 1); y++)
-        for (x = 0; x < PIX_BORDER; x++) {
-            i = (y * PIX_X) + x;
-            pixbuf[i] = color;
-            pixbuf[i + (PIX_X - PIX_BORDER)] = color;
-        }
-
-}
-
-/* render a character cell to the display */
-static inline
-void display_draw_cell_(struct pixel_ *pixbuf, DCPU16_WORD *cell_map, DCPU16_WORD index, int cell_x, int cell_y, struct pixel_ fg, struct pixel_ bg) {
-    struct pixel_ *cellstart = pixbuf; /* start of display */
-    unsigned int pix_x, pix_y;
-    unsigned char *cell_bitmap = (unsigned char *)(cell_map + (index * sizeof index));
-
-    assert(cell_x < CELL_X);
-    assert(cell_y < CELL_Y);
-
-    cellstart += (PIX_X * PIX_BORDER); /* skip top border */
-
-    cellstart += (CELL_Y_SZ * PIX_X) * cell_y; /* skip down to row */
-
-    cellstart += PIX_BORDER; /* skip side border */
-
-    cellstart += (CELL_X_SZ) * cell_x; /* skip to column */
-
-    for (pix_x = 0; pix_x < CELL_X_SZ; pix_x++) {
-        for (pix_y = 0; pix_y < CELL_Y_SZ; pix_y++) {
-            if ((cell_bitmap[pix_x] >> pix_y) & 0x01)
-                cellstart[((CELL_Y_SZ - pix_y - 1) * PIX_X) + pix_x] = fg;
-            else
-                cellstart[((CELL_Y_SZ - pix_y - 1) * PIX_X) + pix_x] = bg;
-        }
-    }
-}
-
-#ifdef HAVE_LIBPNG
-/* write status callback */
-static
-void display_png_write_row_cb_(png_structp png_ptr, png_uint_32 row, int pass) {
-    (void)png_ptr, (void)row, (void)pass;
-    /*
-    fprintf(stderr, "%s:%u:%d\n", __func__, row, pass);
-    */
-}
-
-static
-void display_png_user_error_fn_(png_structp png_ptr, png_const_charp error_msg) {
-    (void)png_ptr;
-    fprintf(stderr, "PNG:ERROR:%s\n", error_msg);
-    exit(EX_SOFTWARE);
-}
-
-static
-void display_png_user_warning_fn_(png_structp png_ptr, png_const_charp warning_msg) {
-    (void)png_ptr;
-    fprintf(stderr, "PNG:WARNING:%s\n", warning_msg);
-    return;
-}
-
-/* write png file */
-static
-void display_png_write_(struct dcpu16_display_ *d) {
-    FILE *f;
-    png_structp png_ptr;
-    png_infop info_ptr;
-    size_t i;
-
-    png_voidp user_error_ptr = NULL;
-
-#ifdef HAVE_FOPENCOOKIE
-    /* linux-style memory stream */
-    cookie_io_functions_t cookie_io_functions = {
-        .read = NULL,
-        .write = memstream_write_fn_,
-        .seek = NULL,
-        .close = NULL
-    };
-    f = fopencookie(&d->memstream_cookie, "wb", cookie_io_functions);
-    if (f == NULL) {
-        fprintf(stderr, "%s():%s\n", "fopencookie", strerror(errno));
-        return;
-    }
-
-#else /* HAVE_FOPENCOOKIE */
-#ifdef HAVE_FUNOPEN
-    /* BSD-style memory stream */
-    f = funopen(&d->memstream_cookie,
-                NULL, /* don't care about read */
-                memstream_write_fn_,
-                NULL, /* don't care about seek */
-                NULL /* don't care about close */
-                );
-    if (f == NULL) {
-        fprintf(stderr, "%s():%s\n", "funopen", strerror(errno));
-        return;
-    }
-
-#else /* HAVE_FUNOPEN */
-    /* default to writing file if we can't buffer in memory */
-    f = fopen(d->outfile, "wb");
-    if (f == NULL) {
-        return;
-    }
-#endif /* HAVE_FUNOPEN */
-#endif /* HAVE_FOPENCOOKIE */
-
-    png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, user_error_ptr, display_png_user_error_fn_, display_png_user_warning_fn_);
-    if (png_ptr == NULL) {
-        goto f_done;
-    }
-
-    info_ptr = png_create_info_struct(png_ptr);
-    if (info_ptr == NULL) {
-        png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
-        goto f_done;
-    }
-
-    if (setjmp(png_jmpbuf(png_ptr))) {
-        png_destroy_write_struct(&png_ptr, &info_ptr);
-        goto f_done;
-}
-
-    png_init_io(png_ptr, f);
-    png_set_write_status_fn(png_ptr, display_png_write_row_cb_);
-
-    /* png_set_filter(png_ptr, 0, PNG_FILTER_NONE); */
-    /* png_set_compression_level(png_ptr, Z_BEST_COMPRESSION); */
-
-    png_set_IHDR(png_ptr, info_ptr, PIX_X, PIX_Y, 8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
-
-    png_write_info(png_ptr, info_ptr);
-
-    for (i = 0; i < PIX_Y; i++) {
-        png_write_row(png_ptr, (unsigned char *)(d->pixbuf + (i * PIX_X)));
-    }
-
-    png_write_end(png_ptr, info_ptr);
-
-    png_destroy_write_struct(&png_ptr, &info_ptr);
-
-f_done:
-    fclose(f);
-}
-#else /* HAVE_LIBPNG */
-
-/* if PNG not available, just write pnm file */
-static
-void display_pnm_write_(struct dcpu16_display_ *d) {
-    size_t i;
-    FILE *f;
-
-    f = fopen(d->outfile, "w");
-    if (f == NULL) {
-        fprintf(stderr, "%s('%s'):%s\n", "fopen", filename, strerror(errno));
-        return;
-    }
-
-    /* write header... */
-    /* PNM binary */
-    /* x y */
-    /* max value */
-    fprintf(f, "P6\n%d %d\n255\n", PIX_X, PIX_Y);
-
-    /* write out image bytes in r g b order */
-    for (i = 0; i < PIX_X * PIX_Y; i++) {
-        fwrite(&d->pixbuf[i].r, 1, 1, f);
-        fwrite(&d->pixbuf[i].g, 1, 1, f);
-        fwrite(&d->pixbuf[i].b, 1, 1, f);
-    }
-
-    fclose(f);
-}
-
-#endif /* HAVE_LIBPNG */
-
-static
-void display_image_render_(struct dcpu16_display_ *d) {
-#ifdef HAVE_LIBPNG
-    display_png_write_(d);
-#else /* HAVE_LIBPNG */
-    display_pnm_write_(d);
-#endif /* HAVE_LIBPNG */
-    d->file_dirty = 1;
-}
-
-
-/* the callback to register to be run on display init/reset */
-/* currently this populates the chargen map 'from rom'.. */
-/* and clears the display buffers */
-void display_reset_fn(struct dcpu16 *vm, dcpu16_acct_event e, DCPU16_WORD addr, void *data) {
-    struct dcpu16_display_ *d = (struct dcpu16_display_ *)data;
-
-    (void)e, (void)addr;
-
-    memcpy(vm->ram + DISPLAY_CELL_MAP, chargen_4x8_glyphs, sizeof chargen_4x8_glyphs);
-
-    memset(vm->ram + DISPLAY_BASE, 0, (DISPLAY_END - DISPLAY_BASE) * sizeof *(vm->ram));
-
-    memset(d->pixbuf, 0, PIX_X * PIX_Y * sizeof *(d->pixbuf));
-
-    d->pixbuf_dirty = 1;
-}
-
-/* the callback to register with the cpu for occasionally doing something with the display buffer */
-void display_cycle_fn(struct dcpu16 *vm, dcpu16_acct_event e, DCPU16_WORD addr, void *data) {
-    struct dcpu16_display_ *d = (struct dcpu16_display_ *)data;
-
-    const unsigned long long min_cycles_between_writes = 1536;
-    const time_t min_seconds_between_file_write = 5;
-
-    static time_t last_file_write_ = 0;
-    time_t now;
-
-    (void)e, (void)addr;
-
-    if (d->pixbuf_dirty) {
-        if (vm->cycle > d->cycle_last_write + min_cycles_between_writes) {
-            display_image_render_(d);
-            d->pixbuf_dirty = 0;
-            d->cycle_last_write = vm->cycle;
-        }
-    }
-
-    if (d->file_dirty) {
-        now = time(NULL);
-        if (now > last_file_write_ + min_seconds_between_file_write) {
-            FILE *of;
-
-            of = fopen(d->outfile, "wb");
-            if (of == NULL) {
-                fprintf(stderr, "%s('%s'):%s\n", "fopen", d->outfile, strerror(errno));
-                return;
-            }
-
-            fwrite(d->memstream_cookie.buf, d->memstream_cookie.endpos, 1, of);
-            fclose(of);
-
-            d->file_dirty = 0;
-            last_file_write_ = now;
-        }
-    }
-}
-
-/* the callback to register with the cpu for watching memory updates */
-/* 'data' is an allocated display buffer */
-void display_fn(struct dcpu16 *vm, dcpu16_acct_event e, DCPU16_WORD addr, void *data) {
-    DCPU16_DISPLAY *d = (DCPU16_DISPLAY *)data;
-    unsigned char index, blink, bg, fg;
-    unsigned int cell_x, cell_y;
-
-    (void)e;
-
-    if (addr < DISPLAY_BASE || addr > DISPLAY_MISC)
-        return;
-
-    if (addr > DISPLAY_END && addr < DISPLAY_MISC) {
-        unsigned char updated_index = addr - DISPLAY_CELL_MAP;
-        /* a cell map was updated, refresh entire screen */
-        for (cell_x = 0; cell_x < CELL_X; cell_x++) {
-            for (cell_y = 0; cell_y < CELL_Y; cell_y++) {
-                addr = DISPLAY_BASE + cell_x + (cell_y * CELL_X);
-                index = vm->ram[addr] & 0x7f;
-                if (index != updated_index)
-                    continue;
-                blink = (vm->ram[addr] >> 7) & 0x01;
-                bg = (vm->ram[addr] >> 8) & 0x0f;
-                fg = (vm->ram[addr] >> 12) & 0x0f;
-                display_draw_cell_(d->pixbuf, vm->ram + DISPLAY_CELL_MAP, index, cell_x, cell_y, pcolor_(fg), pcolor_(bg));
-            }
-        }
-
-        d->pixbuf_dirty = 1;
-        return;
-    }
-
-    if (addr == DISPLAY_MISC) {
-        /* new border color */
-        char border = vm->ram[addr] & 0x0f;
-        display_draw_border_(d->pixbuf, pcolor_(border));
-
-        d->pixbuf_dirty = 1;
-        return;
-    }
-
-    cell_x = (addr - DISPLAY_BASE) % CELL_X;
-    cell_y = (addr - DISPLAY_BASE) / CELL_X;
-
-    index = vm->ram[addr] & 0x7f;
-    blink = (vm->ram[addr] >> 7) & 0x01;
-    bg = (vm->ram[addr] >> 8) & 0x0f;
-    fg = (vm->ram[addr] >> 12) & 0x0f;
-
-    display_draw_cell_(d->pixbuf, vm->ram + DISPLAY_CELL_MAP, index, cell_x, cell_y, pcolor_(fg), pcolor_(bg));
-
-    d->pixbuf_dirty = 1;
-}
-
-/* init the pixel buffer */
-DCPU16_DISPLAY *display_new(const char *filename) {
-    DCPU16_DISPLAY *d = calloc(1, sizeof *d);
-    if (d == NULL)
-        return NULL;
-
-    d->pixbuf = calloc(PIX_X * PIX_Y, sizeof *(d->pixbuf));
-    if (d->pixbuf == NULL) {
-        free(d);
-        return NULL;
-    }
-
-    d->outfile = strdup(filename);
-    if (d->outfile == NULL) {
-        free(d->pixbuf);
-        free(d);
-        return NULL;
-    }
-
-    memstream_cookie_init_(&d->memstream_cookie, 1024 * 8);
-
-    d->cycle_last_write = 0;
-    d->pixbuf_dirty = 0;
-    d->file_dirty = 0;
-
-    return d;
-}
-
-void display_free(DCPU16_DISPLAY *d) {
-    if (d) {
-        free(d->pixbuf);
-        d->pixbuf = NULL;
-        free(d->outfile);
-        d->outfile = NULL;
-        memstream_cookie_fini_(&d->memstream_cookie);
-    }
-    free(d);
-}
diff --git a/display.h b/display.h
deleted file mode 100644
index fe88cc3..0000000
--- a/display.h
+++ /dev/null
@@ -1,14 +0,0 @@
-#ifndef DISPLAY_H_MJYI1IAV
-#define DISPLAY_H_MJYI1IAV
-
-#include "dcpu16.h"
-
-typedef struct dcpu16_display_ DCPU16_DISPLAY;
-
-void display_reset_fn(struct dcpu16 *, dcpu16_acct_event, DCPU16_WORD, void *);
-void display_cycle_fn(struct dcpu16 *, dcpu16_acct_event, DCPU16_WORD, void *);
-void display_fn(struct dcpu16 *, dcpu16_acct_event, DCPU16_WORD, void *);
-DCPU16_DISPLAY *display_new(const char *);
-void display_free(DCPU16_DISPLAY *);
-
-#endif /* DISPLAY_H_MJYI1IAV */
diff --git a/hw_clock.c b/hw_clock.c
new file mode 100644
index 0000000..89d5912
--- /dev/null
+++ b/hw_clock.c
@@ -0,0 +1,112 @@
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+#include "dcpu16.h"
+#include "hw_clock.h"
+
+static dcpu16_hw_signal_t clock_reset_;
+static dcpu16_hw_signal_t clock_cycle_;
+static dcpu16_hw_signal_t clock_hwi_;
+static struct dcpu16_hw hw_ = {
+    .name_  = "Generic Clock (compatible)",
+    .id_l   = 0xb402,
+    .id_h   = 0x12d0,
+    .ver    = 0x0001,
+    .mfg_l  = 0x0000,
+    .mfg_h  = 0x0000,
+    .hwi    = clock_hwi_,
+    .cycle  = clock_cycle_,
+    .reset  = clock_reset_,
+    .data   = (struct clock_ *)NULL
+};
+
+struct clock_ {
+    DCPU16_WORD cycle_;
+    DCPU16_WORD rate;
+    DCPU16_WORD tick;
+    DCPU16_WORD interrupt_message;
+};
+
+static
+void clock_reset_(struct dcpu16 *vm, void *data) {
+    struct clock_ *clock = (struct clock_ *)data;
+
+    (void)vm;
+
+    memset(clock, 0, sizeof *clock);
+}
+
+static
+void clock_cycle_(struct dcpu16 *vm, void *data) {
+    struct clock_ *clock = (struct clock_ *)data;
+
+    /* cycle is only called 100000 times per second */
+    /* maximum rate is 60hz / word_max = 3932160 */
+
+    if (clock->rate == 0)
+        return;
+
+    clock->cycle_++;
+    if (clock->cycle_ >= clock->rate) {
+        /* THIS CHECK IS WRONG, JUST A PLACEHOLDER */
+        clock->cycle_ = 0;
+        clock->tick += 1;
+
+        if (clock->interrupt_message) {
+            if (dcpu16_interrupt(vm, clock->interrupt_message))
+                vm->warn_cb_("%s: could not send interrupt", hw_.name_);
+        }
+    }
+}
+
+static
+void clock_hwi_(struct dcpu16 *vm, void *data) {
+    struct clock_ *clock = (struct clock_ *)data;
+    DCPU16_WORD reg_a = vm->reg[DCPU16_REG_A];
+    DCPU16_WORD reg_b = vm->reg[DCPU16_REG_B];
+
+    switch (reg_a) {
+        case 0: /* set tick gather rate, 60hz/B */
+            clock->rate = reg_b;
+            break;
+
+        case 1: /* fetch elapsed count since rate was set */
+            vm->reg[DCPU16_REG_C] = clock->tick;
+            break;
+
+        case 2:
+            clock->interrupt_message = reg_b;
+            break;
+    }
+}
+
+/* instantitate a new clock */
+struct dcpu16_hw *clock_new(struct dcpu16 *vm) {
+    struct dcpu16_hw *hw;
+
+    hw = calloc(1, sizeof *hw);
+    if (hw == NULL) {
+        vm->warn_cb_("%s():%s", "calloc", strerror(errno));
+        return NULL;
+    }
+    memcpy(hw, &hw_, sizeof *hw);
+    hw->data = calloc(1, sizeof hw->data);
+    if (hw->data == NULL) {
+        vm->warn_cb_("%s():%s", "calloc", strerror(errno));
+        free(hw);
+        return NULL;
+    }
+
+    return hw;
+}
+
+void clock_del(struct dcpu16_hw **hw) {
+    if (hw) {
+        free((*hw)->data);
+        (*hw)->data = NULL;
+
+        free((*hw));
+        *hw = NULL;
+    }
+}
diff --git a/hw_clock.h b/hw_clock.h
new file mode 100644
index 0000000..263c03b
--- /dev/null
+++ b/hw_clock.h
@@ -0,0 +1,7 @@
+#ifndef CLOCK_H_P5G2G9FA
+#define CLOCK_H_P5G2G9FA
+
+struct dcpu16_hw *clock_new(struct dcpu16 *);
+void clock_del(struct dcpu16_hw **);
+
+#endif /* CLOCK_H_P5G2G9FA */
diff --git a/hw_keyboard.c b/hw_keyboard.c
new file mode 100644
index 0000000..71e016f
--- /dev/null
+++ b/hw_keyboard.c
@@ -0,0 +1,123 @@
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+#include "dcpu16.h"
+#include "hw_keyboard.h"
+
+#define BUF_SZ 32
+
+static dcpu16_hw_signal_t keyboard_reset_;
+static dcpu16_hw_signal_t keyboard_cycle_;
+static dcpu16_hw_signal_t keyboard_hwi_;
+static struct dcpu16_hw hw_ = {
+    .name_  = "Generic Keyboard (compatible)",
+    .id_l   = 0x7406,
+    .id_h   = 0x30cf,
+    .ver    = 0x0001,
+    .mfg_l  = 0x0000,
+    .mfg_h  = 0x0000,
+    .hwi    = keyboard_hwi_,
+    .cycle  = keyboard_cycle_,
+    .reset  = keyboard_reset_,
+    .data   = (struct keyboard_ *)NULL
+};
+
+struct keyboard_ {
+    char *buf;
+    size_t buf_sz;
+    DCPU16_WORD interrupt_message;
+};
+
+static
+void keyboard_reset_(struct dcpu16 *vm, void *data) {
+    struct keyboard_ *keyboard = (struct keyboard_ *)data;
+
+    (void)vm;
+
+    keyboard->interrupt_message = 0;
+    memset(keyboard->buf, 0, keyboard->buf_sz);
+}
+
+static
+void keyboard_cycle_(struct dcpu16 *vm, void *data) {
+    struct keyboard_ *keyboard = (struct keyboard_ *)data;
+
+    (void)vm, (void)keyboard;
+}
+
+static
+void keyboard_hwi_(struct dcpu16 *vm, void *data) {
+    struct keyboard_ *keyboard = (struct keyboard_ *)data;
+    DCPU16_WORD reg_a = vm->reg[DCPU16_REG_A];
+    DCPU16_WORD reg_b = vm->reg[DCPU16_REG_B];
+    size_t i;
+
+    switch (reg_a) {
+        case 0: /* clear keyboard buffer */
+            memset(keyboard->buf, 0, keyboard->buf_sz);
+            break;
+
+        case 1: /* get next key from buffer as C */
+            vm->reg[DCPU16_REG_C] = keyboard->buf[0];
+            for (i = 1; i < keyboard->buf_sz; i++) {
+                keyboard->buf[i-1] = keyboard->buf[i];
+            }
+            keyboard->buf[i] = '\0';
+            break;
+
+        case 2: /* get currently-pressed-state of key in B as C */
+            vm->warn_cb_("IMPLEMENT");
+            (void)reg_b;
+            vm->reg[DCPU16_REG_C] = 0;
+            break;
+
+        case 3: /* set interrupt state */
+            keyboard->interrupt_message = reg_b;
+            break;
+
+    }
+}
+
+struct dcpu16_hw *keyboard_new(struct dcpu16 *vm) {
+    struct dcpu16_hw *hw;
+    char *b;
+
+    hw = calloc(1, sizeof *hw);
+    if (hw == NULL) {
+        vm->warn_cb_("%s():%s", "calloc", strerror(errno));
+        return NULL;
+    }
+    memcpy(hw, &hw_, sizeof *hw);
+    hw->data = calloc(1, sizeof hw->data);
+    if (hw->data == NULL) {
+        vm->warn_cb_("%s():%s", "calloc", strerror(errno));
+        free(hw);
+        return NULL;
+    }
+
+    b = calloc(BUF_SZ, sizeof *b);
+    if (b == NULL) {
+        vm->warn_cb_("%s():%s", "calloc", strerror(errno));
+        free(hw->data);
+        free(hw);
+        return NULL;
+    }
+    ((struct keyboard_ *)(hw->data))->buf = b;
+    ((struct keyboard_ *)(hw->data))->buf_sz = BUF_SZ;
+
+    return hw;
+}
+
+void keyboard_del(struct dcpu16_hw **hw) {
+    if (hw) {
+        free(((struct keyboard_ *)((*hw)->data))->buf);
+        ((struct keyboard_ *)((*hw)->data))->buf = NULL;
+
+        free((*hw)->data);
+        (*hw)->data = NULL;
+
+        free(*hw);
+        *hw = NULL;
+    }
+}
diff --git a/hw_keyboard.h b/hw_keyboard.h
new file mode 100644
index 0000000..cf7eb4c
--- /dev/null
+++ b/hw_keyboard.h
@@ -0,0 +1,7 @@
+#ifndef KEYBOARD_H_Y2G5EOAS
+#define KEYBOARD_H_Y2G5EOAS
+
+struct dcpu16_hw *keyboard_new(struct dcpu16 *);
+void keyboard_del(struct dcpu16_hw **);
+
+#endif /* KEYBOARD_H_Y2G5EOAS */
diff --git a/hw_lem1802.c b/hw_lem1802.c
new file mode 100644
index 0000000..72af16a
--- /dev/null
+++ b/hw_lem1802.c
@@ -0,0 +1,509 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+
+#ifdef HAVE_LIBPNG
+#include <setjmp.h>
+#include <png.h>
+#endif /* HAVE_LIBPNG */
+
+#ifdef HAVE_LIBVNCSERVER
+#include <rfb/rfb.h>
+#include <rfb/keysym.h>
+#endif /* HAVE_LIBVNCSERVER */
+
+#include "dcpu16.h"
+#include "chargen-4x8.h"
+#include "hw_lem1802.h"
+
+static dcpu16_hw_signal_t lem1802_reset_;
+static dcpu16_hw_signal_t lem1802_cycle_;
+static dcpu16_hw_signal_t lem1802_hwi_;
+static struct dcpu16_hw hw_ = {
+    .name_  = "LEM1802 - Low Energy Monitor",
+    .id_l   = 0xf615,
+    .id_h   = 0x7349,
+    .ver    = 0x1802,
+    .mfg_l  = 0x8b36,
+    .mfg_h  = 0x1c6c,
+    .hwi    = lem1802_hwi_,
+    .cycle  = lem1802_cycle_,
+    .reset  = lem1802_reset_,
+    .data   = (struct lem1802_ *)NULL
+};
+
+#define PIX_X 160
+#define PIX_Y 128
+#define PIX_BORDER 16
+#define CELL_X_SZ 4
+#define CELL_Y_SZ 8
+
+#define PALETTE_ENTRIES 16
+static const DCPU16_WORD palette_default_[PALETTE_ENTRIES] = {
+    0x0000, /* black */
+    0x000a, /* blue */
+    0x00a0, /* green */
+    0x00aa, /* cyan */
+    0x0a05, /* red */
+    0x0a0f, /* magenta */
+    0x0aa5, /* yellow */
+    0x0aaf, /* pale blue */
+    0x0555, /* grey */
+    0x055f, /* light blue */
+    0x05f5, /* light green*/
+    0x05ff, /* light cyan */
+    0x0f55, /* light red */
+    0x0f5f, /* light magenta */
+    0x0ff5, /* light yellow */
+    0x0fff, /* white */
+};
+
+struct pixel_ {
+    unsigned char r;
+    unsigned char g;
+    unsigned char b;
+    unsigned char a;
+};
+
+struct lem1802_ {
+    long long cycle_activated; /* for tracking 'turn on delay' */
+
+    DCPU16_WORD video_base;
+    DCPU16_WORD font_base;
+    DCPU16_WORD palette_base;
+    DCPU16_WORD border_color;
+    struct pixel_ *pixbuf;
+
+    unsigned int refresh_rate; /* redraw every n cycles */
+    unsigned int refresh_tally_; /* tick */
+    
+    unsigned int blink_rate; /* toggle every n cycles? still figuring this out.. */
+    unsigned int blink_tally_; /* tick */
+    unsigned int blink_state;
+
+    int (*render)(void *, struct pixel_ *, size_t, size_t);
+    void *renderer_data;
+};
+
+static inline
+void pixel_color_(struct pixel_ *pix, DCPU16_WORD color) {
+    pix->r = (color & 0x000f) | ((color & 0x000f) << 8);
+    pix->g = ((color & 0x00f0) >> 8) | (color & 0x00f0);
+    pix->b = ((color & 0x0f00) >> 8) | ((color & 0x0f00) >> 16);
+    pix->a = ((color & 0xf000) >> 16) | ((color & 0xf000) >> 24);
+}
+
+static
+void pixbuf_border_paint_(struct pixel_ *pixbuf, struct pixel_ *border) {
+    size_t x, y, i;
+
+    /* top */
+    for (y = 0; y < PIX_BORDER; y++) {
+        for (x = 0; x < PIX_X; x++) {
+            i = (y * PIX_X) + x;
+            pixbuf[i] = *border;
+            i = ((PIX_Y - y) * PIX_X) + x;
+            pixbuf[i] = *border;
+        }
+    }
+
+    /* sides */
+    for (y = PIX_BORDER; y < (PIX_Y - PIX_BORDER + 1); y++)
+        for (x = 0; x < PIX_BORDER; x++) {
+            i = (y * PIX_X) + x;
+            pixbuf[i] = *border;
+            pixbuf[i + (PIX_X - PIX_BORDER)] = *border;
+        }
+}
+
+static
+void font_tile_paint_(struct pixel_ *p, struct pixel_ *fg, struct pixel_ *bg, DCPU16_WORD *tile) {
+    size_t pix_x, pix_y;
+    unsigned char *font_bitmap = (unsigned char *)tile;
+
+    for (pix_x = 0; pix_x < CELL_X_SZ; pix_x++) {
+        for (pix_y = 0; pix_y < CELL_Y_SZ; pix_y++) {
+            if ((font_bitmap[pix_x] >> pix_y) & 0x01)
+                p[((CELL_Y_SZ - pix_y - 1) * PIX_X) + pix_x] = *fg;
+            else
+                p[((CELL_Y_SZ - pix_y - 1) * PIX_X) + pix_x] = *bg;
+        }
+    }
+}
+
+static
+void pixbuf_addr_paint_(struct pixel_ *pixbuf, DCPU16_WORD *mem, DCPU16_WORD addr, DCPU16_WORD *palette, DCPU16_WORD *tiles, unsigned int blink_state) {
+    struct pixel_ *tilestart = pixbuf; /* start of display */
+    unsigned int cell_x = addr % (PIX_X / CELL_X_SZ),
+                 cell_y = addr / (PIX_X / CELL_X_SZ);
+    struct pixel_ fg, bg;
+    DCPU16_WORD *font_bitmap;
+    int blink;
+
+    cell_x = addr % (PIX_X / CELL_X_SZ);
+    cell_y = addr / (PIX_X / CELL_X_SZ);
+
+    blink = mem[addr] & 0x0080;
+
+    /* tiles take two words each */
+    font_bitmap = tiles + (2 * (mem[addr] & 0x7f));
+
+    pixel_color_(&bg, palette[(mem[addr] >> 8) & 0x0f]);
+    if (blink && blink_state)
+        pixel_color_(&fg, palette[(mem[addr] >> 8) & 0x0f]);
+    else
+        pixel_color_(&fg, palette[(mem[addr] >> 12) & 0x0f]);
+
+    tilestart += (PIX_X * PIX_BORDER); /* skip top border */
+    tilestart += (CELL_Y_SZ * PIX_X) * cell_y; /* skip down to row */
+
+    tilestart += PIX_BORDER; /* skip side border */
+    tilestart += (CELL_X_SZ) * cell_x; /* skip to column */
+
+    font_tile_paint_(tilestart, &fg, &bg, font_bitmap);
+}
+
+static
+void lem1802_pixbuf_refresh_full_(struct lem1802_ *display, DCPU16_WORD *mem) {
+    struct pixel_ border;
+    size_t tile;
+
+    if (display->video_base == 0) {
+        /* disconnected, blank display.  static might be fun, too */
+        memset(display->pixbuf, 0, PIX_X * PIX_Y * sizeof *display->pixbuf);
+        return;
+    }
+
+    pixel_color_(&border, display->border_color);
+    pixbuf_border_paint_(display->pixbuf, &border);
+
+    for (tile = 0; tile < (PIX_X / CELL_X_SZ) * (PIX_Y / CELL_Y_SZ); tile++) {
+        pixbuf_addr_paint_(display->pixbuf,
+                           mem,
+                           display->video_base + tile,
+                           display->palette_base ? mem + display->palette_base : palette_default_,
+                           display->font_base ? mem + display->font_base : (unsigned short *)chargen_4x8_glyphs,
+                           display->blink_state);
+    }
+}
+
+static
+int pixbuf_render_pnm_(void *data, struct pixel_ *pixbuf, size_t x, size_t y) {
+    FILE *f = (FILE *)data;
+    size_t i;
+    fprintf(f, "P6\n"
+               "%lu %lu\n"
+               "255\n",
+               x, y);
+    for (i = 0; i < x * y; i++) {
+        fwrite(&pixbuf[i].r, 1, 1, f);
+        fwrite(&pixbuf[i].g, 1, 1, f);
+        fwrite(&pixbuf[i].b, 1, 1, f);
+    }
+    fclose(f);
+
+    return 0;
+}
+
+#ifdef HAVE_LIBPNG
+static
+void pixbuf_render_png_user_warning_(png_structp png, png_const_charp msg) {
+    (void)png, (void)msg;
+}
+static
+void pixbuf_render_png_user_error_(png_structp png, png_const_charp msg) {
+    (void)png, (void)msg;
+}
+static
+int pixbuf_render_png_(void *data, struct pixel_ *pixbuf, size_t x, size_t y) {
+    FILE *f = (FILE *)data;
+    int retval = 0;
+    png_structp png;
+    png_infop info;
+    size_t i;
+
+    png = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, pixbuf_render_png_user_error_, pixbuf_render_png_user_warning_);
+    if (png == NULL) {
+        goto f_done;
+    }
+
+    info = png_create_info_struct(png);
+    if (info == NULL) {
+        png_destroy_write_struct(&png, (png_infopp)NULL);
+        goto f_done;
+    }
+
+    if (setjmp(png_jmpbuf(png))) {
+        png_destroy_write_struct(&png, &info);
+        goto f_done;
+    }
+
+    png_init_io(png, f);
+    png_set_IHDR(png, info, x, y, 8, PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+    png_set_invert_alpha(png);
+    png_write_info(png, info);
+    for (i = 0; i < y; i++) {
+        png_write_row(png, (unsigned char *)(pixbuf + (i * x)));
+    }
+    png_write_end(png, info);
+
+    png_destroy_write_struct(&png, &info);
+
+f_done:
+    fclose(f);
+
+    return retval;
+}
+#endif /* HAVE_LIBPNG */
+
+#ifdef HAVE_LIBVNCSERVER
+struct vnc_server_ {
+    rfbScreenInfoPtr rfbScreen;
+};
+
+/* create and return a new struct vnc_server_, for use as a vnc renderer's generic data */
+void *lem1802_vnc_init_data(int argc, char *argv[], struct dcpu16_hw *hw) {
+    struct vnc_server_ *s;
+    struct pixel_ *pixbuf = ((struct lem1802_ *)(hw->data))->pixbuf;
+    int paddedWidth = PIX_X + ( (PIX_X & 3) ? (4 - (PIX_X & 3)) : 0 );
+    int height = PIX_Y;
+    int bitsPerSample = 8;
+    int samplesPerPixel = 3;
+    int bytesPerPixel = 4;
+
+    s = calloc(1, sizeof *s);
+    if (s == NULL)
+        return NULL;
+
+    s->rfbScreen = rfbGetScreen(&argc, argv, paddedWidth, height, bitsPerSample, samplesPerPixel, bytesPerPixel);
+    if (s->rfbScreen == NULL) {
+        free(s);
+        return NULL;
+    }
+
+    s->rfbScreen->desktopName = "lem1802";
+    s->rfbScreen->alwaysShared = TRUE;
+
+#if 0
+    s->rfbScreen->kbdAddEvent = HandleKey; */
+    s->rfbScreen->httpDir = "../classes";
+#endif
+
+    s->rfbScreen->frameBuffer = (char *)pixbuf;
+
+    rfbInitServer(s->rfbScreen);
+
+    rfbRunEventLoop(s->rfbScreen,-1,TRUE);
+
+    return s;
+}
+
+static
+int pixbuf_render_vnc_(void *data, struct pixel_ *pixbuf, size_t x, size_t y) {
+    int retval = 0;
+    struct vnc_server_ *s = (struct vnc_server_ *)data;
+
+    (void)pixbuf;
+
+    /* derp */
+    rfbMarkRectAsModified(s->rfbScreen,0,0,x,y);
+
+    return retval;
+}
+#endif /* HAVE_LIBVNCSERVER */
+
+
+static
+void lem1802_reset_(struct dcpu16 *vm, void *data) {
+    struct lem1802_ *display = (struct lem1802_ *)data;
+
+    display->cycle_activated = vm->cycle;
+
+    display->video_base = 0;
+    display->font_base = 0;
+    display->palette_base = 0;
+    display->border_color = 0;
+
+    memset(display->pixbuf, 0, PIX_X * PIX_Y * sizeof *display->pixbuf);
+
+    display->refresh_tally_ = 0;
+    display->blink_tally_ = 0;
+    display->blink_state = 0;
+}
+
+static
+void lem1802_cycle_(struct dcpu16 *vm, void *data) {
+    struct lem1802_ *display = (struct lem1802_ *)data;
+
+    (void)vm;
+    /*
+        maybe just step through video memory (if set)
+        one word per clock..?  could just cheat and
+        use accounting callbacks..
+
+        for now just count cycles and issue a full refresh/render
+        every so often
+     */
+
+    display->blink_tally_++;
+    if (display->blink_tally_ >= display->blink_rate)
+        display->blink_state ^= 1;
+
+    display->refresh_tally_++;
+    if (display->refresh_tally_ >= display->refresh_rate) {
+        display->refresh_tally_ = 0;
+        if (display->render)
+            display->render(display->renderer_data, display->pixbuf, PIX_X, PIX_Y);
+    }
+
+    if (display->render) {
+        lem1802_pixbuf_refresh_full_(display, vm->ram);
+        display->render(display->renderer_data, display->pixbuf, PIX_X, PIX_Y);
+    }
+}
+
+static
+void lem1802_hwi_(struct dcpu16 *vm, void *data) {
+    struct lem1802_ *display = (struct lem1802_ *)data;
+    DCPU16_WORD reg_a = vm->reg[DCPU16_REG_A];
+    DCPU16_WORD reg_b = vm->reg[DCPU16_REG_B];
+    size_t i;
+
+    switch (reg_a) {
+        case 0: /* MEM_MAP_SCREEN */
+            if (display->cycle_activated == 0 && reg_b) {
+                display->cycle_activated = vm->cycle;
+            }
+            display->video_base = reg_b;
+            break;
+
+        case 1: /* MEM_MAP_FONT */
+            display->font_base = reg_b;
+            break;
+
+        case 2: /* MEM_MAP_PALETTE */
+            display->palette_base = reg_b;
+            break;
+
+        case 3: /* SET_BORDER_COLOR */
+            display->border_color = reg_b & 0x000f;
+            break;
+
+        case 4: /* MEM_DUMP_FONT */
+            for (i = 0; i < 128 ; i++) {
+                vm->ram[reg_b] = chargen_4x8_glyphs[reg_b][0] << 8;
+                vm->ram[reg_b] |= chargen_4x8_glyphs[reg_b][1];
+                reg_b += 1;
+                vm->ram[reg_b] = chargen_4x8_glyphs[reg_b][2] << 8;
+                vm->ram[reg_b] |= chargen_4x8_glyphs[reg_b][3];
+                reg_b += 1;
+            }
+            vm->cycle += 256;
+            break;
+
+        case 5: /* MEM_DUMP_PALETTE */
+            for (i = 0; i < 16; i++) {
+                vm->ram[reg_b] = palette_default_[i];
+                reg_b += 1;
+            }
+            vm->cycle += 16;
+            break;
+    }
+}
+
+static struct renderer_ {
+    char *name;
+    char *args;
+    int (*renderer)(void *, struct pixel_ *, size_t, size_t);
+} lem1802_renderers_[] = {
+    { "pnm", "filename", pixbuf_render_pnm_ },
+#ifdef HAVE_LIBPNG
+    { "png", "filename", pixbuf_render_png_ },
+#endif /* HAVE_LIBPNG */
+#ifdef HAVE_LIBVNCSERVER
+    { "vnc", "", pixbuf_render_vnc_ },
+#endif /* HAVE_LIBVNCSERVER */
+    { "none", "", NULL },
+    { NULL, NULL, NULL }
+};
+
+int lem1802_renderer_set(struct dcpu16_hw *hw, const char *renderer, void *data) {
+    struct renderer_ *r;
+
+    for (r = lem1802_renderers_; r->renderer; r++) {
+        if (strcmp(renderer, r->name) == 0) {
+            ((struct lem1802_ *)(hw->data))->render = r->renderer;
+            ((struct lem1802_ *)(hw->data))->renderer_data = data;
+            return 0;
+        }
+    }
+
+    return -1;
+}
+
+char *lem1802_renderers_iter(void **iterp, char **name, char **args) {
+    struct renderer_ **r = (struct renderer_ **)iterp;
+
+    if (*r == NULL)
+        *r = lem1802_renderers_;
+    else
+        (*r)++;
+
+    if ((*r)->name == NULL) {
+        *r = NULL;
+        return NULL;
+    }
+
+    *name = (*r)->name;
+    *args = (*r)->args;
+
+    return (*r)->name;
+}
+
+/* instantitate a new display */
+struct dcpu16_hw *lem1802_new(struct dcpu16 *vm) {
+    struct dcpu16_hw *hw;
+
+    hw = calloc(1, sizeof *hw);
+    if (hw == NULL) {
+        vm->warn_cb_("%s():%s", "calloc", strerror(errno));
+        return NULL;
+    }
+
+    memcpy(hw, &hw_, sizeof *hw);
+
+    hw->data = calloc(1, sizeof(struct dcpu16_hw));
+    if (hw->data == NULL) {
+        vm->warn_cb_("%s():%s", "calloc", strerror(errno));
+        free(hw);
+        return NULL;
+    }
+
+    ((struct lem1802_ *)(hw->data))->pixbuf = calloc(1, PIX_X * PIX_Y * sizeof *((struct lem1802_ *)(hw->data))->pixbuf);
+    if (((struct lem1802_ *)(hw->data))->pixbuf == NULL) {
+        vm->warn_cb_("%s():%s", "calloc", strerror(errno));
+        free(hw->data);
+        free(hw);
+        return NULL;
+    }
+
+    return hw;
+}
+
+void lem1802_del(struct dcpu16_hw **hw) {
+    if (hw) {
+        if (*hw) {
+            if ((*hw)->data) {
+                if (((struct lem1802_ *)(*hw)->data)->pixbuf) {
+                    free(((struct lem1802_ *)(*hw)->data)->pixbuf);
+                    ((struct lem1802_ *)(*hw)->data)->pixbuf = NULL;
+                }
+                free((*hw)->data);
+                (*hw)->data = NULL;
+            }
+            free(*hw);
+        }
+        *hw = NULL;
+    }
+}
diff --git a/hw_lem1802.h b/hw_lem1802.h
new file mode 100644
index 0000000..fb739f4
--- /dev/null
+++ b/hw_lem1802.h
@@ -0,0 +1,12 @@
+#ifndef LEM1802_H_WH5E5NOE
+#define LEM1802_H_WH5E5NOE
+
+#include "dcpu16.h"
+
+struct dcpu16_hw *lem1802_new(struct dcpu16 *);
+void lem1802_del(struct dcpu16_hw **);
+int lem1802_renderer_set(struct dcpu16_hw *, const char *, void *);
+char *lem1802_renderers_iter(void **, char **, char **);
+void *lem1802_vnc_init_data(int argc, char *argv[], struct dcpu16_hw *hw);
+
+#endif /* LEM1802_H_WH5E5NOE */
diff --git a/vm-dcpu16.c b/vm-dcpu16.c
index 5924074..6324717 100644
--- a/vm-dcpu16.c
+++ b/vm-dcpu16.c
@@ -12,7 +12,8 @@
 
 #include "dcpu16.h"
 #include "common.h"
-#include "display.h"
+
+#include "hw_lem1802.h"
 
 /*
  *  shell-like driver for dcpu16 core
@@ -21,6 +22,7 @@
  *  Justin Wind <justin.wind@gmail.com>
  *    2012 04 10 - implementation started
  *    2012 04 12 - cleanup, better shell loop
+ *    2012 05 12 - support v1.7 style devices
  *
  *  TODO
  *    handle quotes in shell command parsing
@@ -65,7 +67,7 @@ void usage_(char *prog, unsigned int full) {
     if (full) {
         fprintf(f, "\nOptions:\n"
                 "\t [file] -- ram image to load initially\n"
-                "\t -v -- displays slightly more information\n"
+                "\t -v -- prints slightly more information while operating\n"
                 "\t -h -- this screen\n");
 
         fprintf(f, "\n%78s\n", src_id_);
@@ -140,6 +142,7 @@ int file_load_(struct dcpu16 *vm, char *filename, DCPU16_WORD addr) {
     return 0;
 }
 
+
 /*
     Here follows the various commands the shell can execute.
 
@@ -235,7 +238,7 @@ COMMAND_IMPL(dump) {
             return 0;
         }
     }
-    if (arg_count < 2) addr[0] = vm->pc;
+    if (arg_count < 2) addr[0] = vm->reg[DCPU16_REG_PC];
     if (arg_count < 3) addr[1] = addr[0];
 
     if (addr[1] < addr[0]) {
@@ -266,7 +269,7 @@ COMMAND_IMPL(disassemble) {
             return 0;
         }
     }
-    if (arg_count < 2) addr[0] = vm->pc;
+    if (arg_count < 2) addr[0] = vm->reg[DCPU16_REG_PC];
     if (arg_count < 3) addr[1] = addr[0];
 
     if (addr[1] < addr[0]) {
@@ -298,7 +301,7 @@ COMMAND_IMPL(step) {
         errno = 0;
         count = strtoul(arg_vector[1], &ep, 0);
         if (errno
-        ||  !(*arg_vector[0] && *ep == '\0') ) {
+        ||  !(*arg_vector[1] && *ep == '\0') ) {
             fprintf(stderr, "count '%s' is not a valid number: %s\n", arg_vector[1], strerror(errno));
             return 0;
         }
@@ -310,7 +313,7 @@ COMMAND_IMPL(step) {
     }
 
     while (count--) {
-        dcpu16_disassemble_print(vm, vm->pc);
+        dcpu16_disassemble_print(vm, vm->reg[DCPU16_REG_PC]);
         printf("\n");
         dcpu16_step(vm);
 
@@ -328,6 +331,46 @@ COMMAND_HELP(step) {
 }
 
 
+COMMAND_IMPL(set) {
+    int addr, value;
+    DCPU16_WORD *v;
+
+    (void)arg_count;
+
+    /* check if addr is a register */
+    for (addr = 0; dcpu16_reg_names[addr]; addr++) {
+        if (strcasecmp(arg_vector[1], dcpu16_reg_names[addr]) == 0)
+            break;
+    }
+    if (addr < DCPU16_REG__NUM) {
+        v = vm->reg + addr;
+    } else {
+        addr = str_to_word(arg_vector[1]);
+        if (addr < 0) {
+            fprintf(stderr, "address '%s' is not a valid word: %s\n", arg_vector[1], strerror(errno));
+            return 0;
+        }
+        v = vm->ram + addr;
+    }
+
+    value = str_to_word(arg_vector[2]);
+    if (value < 0) {
+        fprintf(stderr, "address '%s' is not a valid word: %s\n", arg_vector[2], strerror(errno));
+        return 0;
+    }
+
+    *v = value;
+
+    return 0;
+}
+
+COMMAND_HELP(set) {
+    fprintf(f, "\tset addr value\n");
+    if (summary) return;
+
+    fprintf(f, "Sets addr to value.");
+}
+
 COMMAND_IMPL(run) {
     struct sigaction act;
     (void)arg_count, (void)arg_vector;
@@ -348,7 +391,7 @@ COMMAND_IMPL(run) {
         if (opt_.verbose > 1)
             dcpu16_state_print(vm);
         else if (opt_.verbose) {
-            dcpu16_disassemble_print(vm, vm->pc);
+            dcpu16_disassemble_print(vm, vm->reg[DCPU16_REG_PC]);
             printf("\n");
         }
     }
@@ -373,53 +416,82 @@ static const char * const display_filename_default_ =
 #endif /* HAVE_LIBPNG */
 ;
 COMMAND_IMPL(display) {
-    static DCPU16_DISPLAY *display = NULL;
-    const char *filename = display_filename_default_;
+    struct dcpu16_hw *hw = lem1802_new(vm);
+    const char *renderer = arg_vector[1];
+    const char *renderer_arg = NULL;
+    void *renderer_data = NULL;
 
-    if (arg_count == 2) {
-        filename = arg_vector[1];
-    }
+    if (arg_count == 3)
+        renderer_arg = arg_vector[2];
 
-    if (display) {
-        printf("display already enabled..\n");
+    if (hw == NULL) {
+        fprintf(stderr, "failed to initialize new display\n");
         return 0;
     }
 
-    display = display_new(filename);
+    /* handle per-renderer setup of data.. */
+    /* FIXME: these are awkward */
+    if (strcmp(renderer, "pnm") == 0) {
+        if (renderer_arg == NULL)
+            renderer_arg = display_filename_default_;
+        renderer_data = (void *)renderer_arg;
+    }
 
-    if (display == NULL) {
-        fprintf(stderr, "failed to initialize display buffer\n");
-        return 0;
+#ifdef HAVE_LIBPNG
+    if (strcmp(renderer, "png") == 0) {
+        if (renderer_arg == NULL)
+            renderer_arg = display_filename_default_;
+        renderer_data = (void *)renderer_arg;
     }
+#endif /* HAVE_LIBPNG */
 
-    if (dcpu16_acct_add(vm, DCPU16_ACCT_EV_WRITE, display_fn, display)) {
-        fprintf(stderr, "failed to register display update callback\n");
-        return 0;
+#ifdef HAVE_LIBVNCSERVER
+    if (strcmp(renderer, "vnc") == 0) {
+        int argc = 1;
+        char *argv[] = { "vm-dcpu16", NULL };
+
+        renderer_data = lem1802_vnc_init_data(argc, argv, hw);
+
+        /* FIXME: keep refs to vnc displays around somewhere, in global list maybe.. */
+        /* keyboards will want to attach to them as well.. */
+
+        if (renderer_data == NULL) {
+            fprintf(stderr, "failed to initialize vnc\n");
+            lem1802_del(&hw);
+            return 0;
+        }
     }
+#endif /* HAVE_LIBVNCSERVER */
 
-    if (dcpu16_acct_add(vm, DCPU16_ACCT_EV_RESET, display_reset_fn, display)) {
-        fprintf(stderr, "failed to register display reset callback\n");
+    if (lem1802_renderer_set(hw, renderer, renderer_data)) {
+        fprintf(stderr, "failed to set back-end renderer for display\n");
+        lem1802_del(&hw);
         return 0;
     }
 
-    if (dcpu16_acct_add(vm, DCPU16_ACCT_EV_CYCLE, display_cycle_fn, display)) {
-        fprintf(stderr, "failed to register display cycle callback\n");
+    if (dcpu16_hw_add(vm, hw)) {
+        fprintf(stderr, "failed to attach new display\n");
+        lem1802_del(&hw);
         return 0;
     }
 
-    /* init display as if reset occurred */
-    display_reset_fn(vm, DCPU16_ACCT_EV_RESET, 0, display);
-
     return 0;
 }
 COMMAND_HELP(display) {
-    fprintf(f, "\tdisplay [file]\n");
+    char *name, *args;
+    void *iter;
+
+    fprintf(f, "\tdisplay renderer [renderer data]\n");
     if (summary) return;
 
-    fprintf(f, "Attaches display interface, begins updating an image file of display contents...\n"
-               "Image filename may be specified, defaults to '%s'\n",
-               display_filename_default_
+    fprintf(f, "Attaches new display unit, using 'renderer' as back-end output.\n"
             );
+
+    fprintf(f, "Supported renderers:\n");
+    iter = NULL;
+    while ( (lem1802_renderers_iter(&iter, &name, &args)) ) {
+        fprintf(f, "\t%s %s\n", name, args);
+    }
 }
 
 /* gather all these together into a searchable table */
@@ -436,8 +508,9 @@ static struct command_ command_table_[] = {
     COMMAND_ENTRY(disassemble, 0, 2),
     COMMAND_ENTRY(step, 0, 1),
     COMMAND_ENTRY(run, 0, 0),
+    COMMAND_ENTRY(set, 2, 2),
     COMMAND_ENTRY(reset, 0, 0),
-    COMMAND_ENTRY(display, 0, 1),
+    COMMAND_ENTRY(display, 1, 2),
     { NULL, 0, 0, NULL, NULL }
 };
 
@@ -519,13 +592,13 @@ int main(int argc, char **argv) {
     for (line = line_prev = NULL,
          tok_v = tok_v_prev = NULL,
          tok_c = tok_c_prev= 0,
-         snprintf(prompt, sizeof prompt, prompt_fmt, vm->pc),
+         snprintf(prompt, sizeof prompt, prompt_fmt, vm->reg[DCPU16_REG_PC]),
          dcpu16_state_print(vm);
 
          (line = readline(prompt));
 
          printf("\n"),
-         snprintf(prompt, sizeof prompt, prompt_fmt, vm->pc),
+         snprintf(prompt, sizeof prompt, prompt_fmt, vm->reg[DCPU16_REG_PC]),
          dcpu16_state_print(vm)) {
         const char whitespace[] = " \t";
         char *line_start;