diff --git a/interpreter/core_methods.c b/interpreter/core_methods.c
index 89f169c..b7c26a2 100644
--- a/interpreter/core_methods.c
+++ b/interpreter/core_methods.c
@@ -271,16 +271,19 @@ char bci_cm_jmp(uint8_t small_arg, machine_state_t state)
 // else: do nothing
 char bci_cm_cjmp(uint8_t small_arg, machine_state_t state)
 {
-	uint16_t arg;
+	uint16_t arg = small_arg;
 	BCI_CORE_REGISTER_CHECK(small_arg);
+#ifdef DEBUG
+	printf("MSG: cjmp: arg=0x%x (=0x%x)\n", arg, state->data_reg[arg]);
+#endif
 	arg = state->data_reg[arg];
 
 	if(state->status_reg)
 	{
 		state->program_counter = arg;
+		state->status_reg = 0;
 		return 0;
 	}
-	state->status_reg = 0;
 
 	return machine_state_t_default_afterexec(state, 0);
 }
diff --git a/interpreter/interpreter.c b/interpreter/interpreter.c
index c628bc9..4089fdd 100644
--- a/interpreter/interpreter.c
+++ b/interpreter/interpreter.c
@@ -50,7 +50,7 @@ machine_state_t machine_state_t_new( void * cache_function_data
 	int i;
 	for(i = 0; i < BCI_CORE_NUM_REG; i++)
 	{
-		state->data_reg[BCI_CORE_NUM_REG] = 0;
+		state->data_reg[i] = 0;
 	}
 	state->stack = NULL;
 
@@ -95,6 +95,9 @@ char update_cache(machine_state_t state, uint16_t offset)
 
 	if(cached != state->cache_size)
 	{
+		#ifdef DEBUG
+		printf("ERROR: should have cached %zu words, but got %zu.\n", state->cache_size, cached);
+		#endif
 		return 1;
 	}
 	state->cache_offset = cache_offset;
@@ -121,6 +124,9 @@ char machine_state_t_get_word(machine_state_t state, uint16_t offset, uint16_t *
 	{
 		if(update_cache(state, offset))
 		{
+			#ifdef DEBUG
+			printf("ERROR: failed to update cache\n");
+			#endif
 			state->error = 0b01000000 | 2;
 			return 0b01000000 | 2;
 		}
@@ -144,6 +150,12 @@ char machine_state_t_exec_cycle(machine_state_t state)
 		return res;
 	}
 
+#ifdef DEBUG
+	printf("MSG: opcode = 0x%x, small_arg = 0x%x\n"
+			, opcode & BCI_CORE_OPCODE_MASK
+			, opcode & BCI_CORE_SMALL_ARG_MASK);
+#endif
+
 	bci_core_method_t method = dispatch_tree_t_dispatch(
 					state->method_dispatcher
 					, opcode & BCI_CORE_OPCODE_MASK);
@@ -189,3 +201,17 @@ char machine_state_t_set_mem(machine_state_t state, uint16_t offset, uint16_t da
 	state->memory[offset] = data;
 	return 0;
 }
+
+
+
+
+char machine_state_t_exec(machine_state_t state)
+{
+	char status = 0;
+	while((!status) && (!state->shutdown_reg))
+	{
+		status = machine_state_t_exec_cycle(state);
+	}
+	state->error = status;
+	return status;
+}
diff --git a/interpreter/interpreter.h b/interpreter/interpreter.h
index aab2a30..4829148 100644
--- a/interpreter/interpreter.h
+++ b/interpreter/interpreter.h
@@ -88,6 +88,16 @@ void machine_state_t_del(machine_state_t state);
  * */
 char machine_state_t_exec_cycle(machine_state_t state);
 
+
+/*
+ * Runs ``machine_state_t_exec_cycle`` until either this function
+ * returns a non-zero value or a non-zero value is stored in
+ * ``state->shutdown_reg``. 
+ * Sets ``state->error`` to the last return value of ``machine_state_t_exec_cycle``
+ * and returns it.
+ * */
+char machine_state_t_exec(machine_state_t state);
+
 /*
  * Do the default updates on the machine state.
  * This will be basically increasing the program counter.