diff --git a/src/meta/debug.h b/src/meta/debug.h
index 94291bf4..3e591402 100644
--- a/src/meta/debug.h
+++ b/src/meta/debug.h
@@ -35,6 +35,7 @@ typedef enum {
     GOING
 } stepping_type_t;
 
+// FIXME TODO : make opaque type ...
 typedef struct stepping_struct_t {
     stepping_type_t step_type;
     uint16_t step_count;
@@ -43,6 +44,7 @@ typedef struct stepping_struct_t {
     bool should_break;
     time_t timeout;
     const char *step_text;
+    const bool step_deterministically;
 } stepping_struct_t;
 
 #define DEBUGGER_BUF_X  39
@@ -85,7 +87,7 @@ extern const struct opcode_struct *opcodes;
 void c_interface_debugging();
 #endif
 
-void debugger_setInputText(const char *text);
+void debugger_setInputText(const char *text, const bool deterministically);
 void c_debugger_go(void);
 bool c_debugger_should_break(void);
 void c_debugger_set_timeout(const unsigned int secs);
diff --git a/src/meta/debugger.c b/src/meta/debugger.c
index 3c7069c0..3c9e301f 100644
--- a/src/meta/debugger.c
+++ b/src/meta/debugger.c
@@ -33,6 +33,7 @@
 const struct opcode_struct *opcodes;
 
 static char input_str[1024] = { 0 }; // ASCII values
+static bool input_deterministically = false; // slows down testing ...
 
 static stepping_struct_t stepping_struct = { 0 };
 static unsigned int stepping_timeout = 0;
@@ -1126,15 +1127,13 @@ static int begin_cpu_stepping() {
     cpu_altscale_factor = CPU_SCALE_FASTEST;
     timing_initialize();
 
-    unsigned int idx = 0;
-    size_t textlen = 0;
-    if (stepping_struct.step_text) {
-        textlen = strlen(stepping_struct.step_text);
+    if (stepping_struct.step_text && stepping_struct.step_text[0] == '\0') {
+        stepping_struct.step_text = NULL;
     }
 
     do {
-        if (textlen && !((apple_ii_64k[0][0xC000] & 0x80) || (apple_ii_64k[1][0xC000] & 0x80)) ) {
-            uint8_t text_ch = (uint8_t)stepping_struct.step_text[idx];
+        if (stepping_struct.step_text && !((apple_ii_64k[0][0xC000] & 0x80) || (apple_ii_64k[1][0xC000] & 0x80)) ) {
+            uint8_t text_ch = (uint8_t)stepping_struct.step_text[0];
             if (text_ch == '\n') {
                 text_ch = '\r';
             }
@@ -1142,9 +1141,9 @@ static int begin_cpu_stepping() {
             apple_ii_64k[0][0xC000] = text_ch | 0x80;
             apple_ii_64k[1][0xC000] = text_ch | 0x80;
 
-            ++idx;
-            if (idx >= textlen) {
-                textlen = 0;
+            ++stepping_struct.step_text;
+            if (stepping_struct.step_text[0] == '\0') {
+                stepping_struct.step_text = NULL;
             }
         }
 
@@ -1160,7 +1159,7 @@ static int begin_cpu_stepping() {
             break;
         }
 #endif
-        if ( (stepping_struct.step_type == TYPING) && (idx > textlen) ) {
+        if ( (stepping_struct.step_type == TYPING) && (!stepping_struct.step_text || stepping_struct.step_text[0] == '\0') ) {
             break; // finished typing
         }
         if (stepping_timeout && (stepping_struct.timeout < time(NULL))) {
@@ -1190,6 +1189,7 @@ bool c_debugger_should_break() {
         RELEASE_BREAK();
     }
 
+    bool break_stepping = false;
     if (at_haltpt()) {
         stepping_struct.should_break = true;
     } else {
@@ -1249,12 +1249,17 @@ bool c_debugger_should_break() {
 
             case GOING:
             case TYPING:
+            // basically force CPU thread to execute one instruction at a time so we can feed characters to the emulator
+            // in a deterministic way
+            break_stepping = (stepping_struct.step_deterministically && stepping_struct.step_text && stepping_struct.step_text[0] != '\0');
+            break;
+
             case LOADING:
             break;
         }
     }
 
-    return stepping_struct.should_break;
+    return break_stepping ?: stepping_struct.should_break;
 }
 
 /* -------------------------------------------------------------------------
@@ -1493,8 +1498,9 @@ void c_interface_debugging() {
 /* -------------------------------------------------------------------------
     debugger testing-driven API
    ------------------------------------------------------------------------- */
-void debugger_setInputText(const char *text) {
+void debugger_setInputText(const char *text, const bool deterministically) {
     strcat(input_str, text);
+    input_deterministically = deterministically;
 }
 
 void c_debugger_go(void) {
@@ -1503,8 +1509,11 @@ void c_debugger_go(void) {
         buf = STRDUP(input_str);
         input_str[0] = '\0';
     }
+    bool deterministically = input_deterministically;
+    input_deterministically = false;
 
     stepping_struct_t s = (stepping_struct_t){
+        .step_deterministically = deterministically,
         .step_text = buf,
         .step_type = GOING,
         .timeout = time(NULL) + stepping_timeout
diff --git a/src/test/testcommon.c b/src/test/testcommon.c
index 20b7db76..681dd726 100644
--- a/src/test/testcommon.c
+++ b/src/test/testcommon.c
@@ -20,7 +20,7 @@ void test_common_setup(void) {
 }
 
 void test_type_input(const char *input) {
-    debugger_setInputText(input);
+    debugger_setInputText(input, false);
 }
 
 void test_breakpoint(void *arg) {