M devices/system.c → devices/system.c

@@ -8,24 +8,17 @@ #define SYSTEM_ERROR 0x01
 #define SYSTEM_PAGE 0x02
 #define SYSTEM_RANDOM 0x03
 #define SYSTEM_IMAGE_EXEC 0x06
-#define SYSTEM_IMAGE_EXEC_TRIGGER 0x08
-
-#define SYSTEM_IMAGE_EXEC_DIRECTION 0x01 // 0 = exec child, 1 = return to parent
-#define SYSTEM_IMAGE_EXEC_PRESERVE  0x02 // EXEC only: snapshot self to be able to return to previous image
 
 void system_setup(xyw_byte *data)
 {
     (void)data;
-    // Initialize random generator seed
     srand(time(NULL));
 }
 
 xyw_byte system_input(xyw_byte *data, xyw_byte addr, xyw_byte *error)
 {
     if (addr == SYSTEM_RANDOM)
-    {
         return (xyw_byte)(rand() & 0xFF);
-    }
     (void)error;
     return data[addr];
 }
@@ -33,20 +26,10 @@ 
 void system_output(xyw_byte *data, xyw_byte addr, xyw_byte *error)
 {
     (void)error;
-    if (addr == SYSTEM_IMAGE_EXEC_TRIGGER && data[SYSTEM_IMAGE_EXEC_TRIGGER] != 0)
+    if (addr == SYSTEM_IMAGE_EXEC + 1)
     {
-        xyw_byte trig = data[SYSTEM_IMAGE_EXEC_TRIGGER];
-        data[SYSTEM_IMAGE_EXEC_TRIGGER] = 0;
-        if (trig & SYSTEM_IMAGE_EXEC_DIRECTION)
-        {
-            xyw_request_return();
-        }
-        else
-        {
-            xyw_word target = XYW_PEEKW(&data[SYSTEM_IMAGE_EXEC]);
-            if (target != 0) {
-                xyw_request_exec(target, trig & SYSTEM_IMAGE_EXEC_PRESERVE);
-            }
-        }
+        xyw_word target = XYW_PEEKW(&data[SYSTEM_IMAGE_EXEC]);
+        if (target != 0)
+            xyw_request_exec(target);
     }
-}+}

M xyw.h → xyw.h

@@ -54,6 +54,5 @@ int xyw_assemble(const char *input, const char *output);
 int xyw_run(const char *input);
 int xyw_eval(xyw_word pc);
 void xyw_request_exec(xyw_word path_addr, int preserve);
-void xyw_request_return(void);
 
 #endif // XYW_H

M xywrun.c → xywrun.c

@@ -453,9 +453,7 @@ 
 static xyw_image_snapshot exec_stack[MAX_IMAGE_EXEC_DEPTH];
 static int exec_stack_depth = 0;
 static int exec_pending = 0;
-static int exec_preserve = 0;
 static char exec_path_buf[MAX_IMAGE_EXEC_PATH_LENGTH];
-static int return_pending = 0;
 
 // Read a null-terminated string out of VM memory into a local buffer
 static void get_string_from_memory(xyw_word addr, char *buf, size_t bufsize)
@@ -466,16 +464,10 @@ buf[i] = xyw_memory[addr + i];
     buf[i] = '\0';
 }
 
-void xyw_request_exec(xyw_word path_addr, int preserve)
+void xyw_request_exec(xyw_word path_addr)
 {
     get_string_from_memory(path_addr, exec_path_buf, sizeof(exec_path_buf));
-    exec_preserve = preserve;
     exec_pending = 1;
-}
-
-void xyw_request_return(void)
-{
-    return_pending = 1;
 }
 
 static void split_exec_string(char *full, char **path, char **argstart)
@@ -595,44 +587,27 @@ if (xyw_devices[i].setup)
             xyw_devices[i].setup(xyw_devices[i].data);
 }
 
-static void handle_exec_return_requests(void)
+static void handle_exec_requests(void)
 {
-    if (exec_pending)
-    {
-        exec_pending = 0;
-        if (exec_preserve)
-        {
-            if (exec_stack_depth >= MAX_IMAGE_EXEC_DEPTH)
-            {
-                xyw_memory[SYSTEM_ERROR] = XYW_ERROR_EXEC_DEPTH_EXCEEDED;
-                return;
-            }
-            save_snapshot(&exec_stack[exec_stack_depth++]);
-        }
-        // preserve == 0: one-way handoff — no push, no way back to this image
+    if (!exec_pending)
+        return;
+    exec_pending = 0;
 
-        char path_copy[MAX_IMAGE_EXEC_PATH_LENGTH];
-        strncpy(path_copy, exec_path_buf, sizeof(path_copy) - 1);
-        path_copy[sizeof(path_copy) - 1] = '\0';
-        char *path, *argstart;
-        split_exec_string(path_copy, &path, &argstart);
-
-        reset_vm_state();
-        load_and_launch(path, argstart);
-    }
-    else if (return_pending)
+    if (exec_stack_depth >= MAX_IMAGE_EXEC_DEPTH)
     {
-        return_pending = 0;
-        if (exec_stack_depth > 0)
-        {
-            restore_snapshot(&exec_stack[--exec_stack_depth]);
-        }
-        else
-        {
-            // No parent to return to — behaves like HLT
-            xyw_memory[SYSTEM_STATE] &= ~SYSTEM_STATE_RUNNING;
-        }
+        xyw_memory[SYSTEM_ERROR] = XYW_ERROR_EXEC_DEPTH_EXCEEDED;
+        return;
     }
+    save_snapshot(&exec_stack[exec_stack_depth++]);
+
+    char path_copy[MAX_IMAGE_EXEC_PATH_LENGTH];
+    strncpy(path_copy, exec_path_buf, sizeof(path_copy) - 1);
+    path_copy[sizeof(path_copy) - 1] = '\0';
+    char *path, *argstart;
+    split_exec_string(path_copy, &path, &argstart);
+
+    reset_vm_state();
+    load_and_launch(path, argstart);
 }
 
 //// Main evaluation function - runs from current pc until BRK
@@ -650,13 +625,28 @@ if (xyw_debug)
     {
         xyw_memory[SYSTEM_STATE] |= SYSTEM_STATE_DEBUG;
     }
-    while ((system_running_state()) && *pc < DEVICE_AREA_START)
+    while (1)
     {
+        if (*pc >= DEVICE_AREA_START)
+        {
+            xyw_memory[SYSTEM_STATE] &= ~SYSTEM_STATE_RUNNING;
+        } 
+        if (!system_running_state())
+        {
+            if (exec_stack_depth > 0)
+            {
+                restore_snapshot(&exec_stack[--exec_stack_depth]);
+                continue;   // resume the parent exactly where it left off
+            }
+            break;          // no parent -- genuinely done
+        }
+
         process_events();
         dispatch_vectors();
-        handle_exec_return_requests();
-        if (!system_running_state()) {
-            break;   // exec/return may have halted or swapped mid-iteration
+        handle_exec_requests();
+        if (!system_running_state())
+        {
+            continue;
         }
         XYW_DBG(" -- PC: %04X -> %02X (%s) [U:%02X|S:%02X|X:%02X|Y:%02X|XW:%04X|YW:%04X]\n", *pc, xyw_memory[*pc], xyw_instructions[xyw_memory[*pc] & 0x1F], u, s, *x, *y, *xw, *yw);
         switch (xyw_memory[*pc])