M devices/system.c → devices/system.c

@@ -7,12 +7,22 @@ #define SYSTEM_STATE 0x00
 #define SYSTEM_ERROR 0x01
 #define SYSTEM_PAGE 0x02
 #define SYSTEM_RANDOM 0x03
+#define SYSTEM_ON_ERROR 0x04
 #define SYSTEM_IMAGE_EXEC 0x06
 
+#define SYSTEM_STATE_RUNNING 0x01
+#define SYSTEM_STATE_ERROR 0x80
+
+#define XYW_ERROR_NONE 0
+
+/// Error handler tracking (accessible by xywrun.c for snapshot/reset)
+xyw_byte error_handler_entry_s = 0;
+
 void system_setup(xyw_byte *data)
 {
     (void)data;
     srand(time(NULL));
+    error_handler_entry_s = 0;
 }
 
 xyw_byte system_input(xyw_byte *data, xyw_byte addr, xyw_byte *error)
@@ -33,3 +43,34 @@ if (target != 0)
             xyw_request_exec(target);
     }
 }
+
+void system_tick(xyw_byte *data)
+{
+    // Check if returning from error handler (after RTS popped the frame)
+    if ((data[SYSTEM_STATE] & SYSTEM_STATE_ERROR) &&
+        error_handler_entry_s != 0 &&
+        xyw_vm_get_system_depth() == error_handler_entry_s)
+    {
+        data[SYSTEM_STATE] &= ~SYSTEM_STATE_ERROR;
+        error_handler_entry_s = 0;
+    }
+
+    // Check for new error condition
+    if (data[SYSTEM_ERROR] != XYW_ERROR_NONE && !(data[SYSTEM_STATE] & SYSTEM_STATE_ERROR))
+    {
+        xyw_word on_error_handler = XYW_PEEKW(&data[SYSTEM_ON_ERROR]);
+        if (on_error_handler != 0)
+        {
+            XYW_DBG("Error occurred: %02X, jumping to error handler at %04X\n", data[SYSTEM_ERROR], on_error_handler);
+            data[SYSTEM_STATE] |= SYSTEM_STATE_ERROR;
+            error_handler_entry_s = xyw_vm_get_system_depth();
+            xyw_vm_push_frame(*pc);
+            *pc = on_error_handler;
+        }
+        else
+        {
+            // No error handler: halt execution
+            data[SYSTEM_STATE] &= ~SYSTEM_STATE_RUNNING;
+        }
+    }
+}

M devices/system.h → devices/system.h

@@ -2,4 +2,8 @@ #include "../xyw.h"
 
 void system_setup(xyw_byte *data);
 xyw_byte system_input(xyw_byte *data, xyw_byte addr, xyw_byte *error);
-void system_output(xyw_byte *data, xyw_byte addr, xyw_byte *error);+void system_output(xyw_byte *data, xyw_byte addr, xyw_byte *error);
+void system_tick(xyw_byte *data);
+
+/// Error handler stack depth tracking (saved/restored in snapshots)
+extern xyw_byte error_handler_entry_s;

M xyw.h → xyw.h

@@ -27,6 +27,7 @@ typedef void (*xyw_teardown)(xyw_byte *data);
 typedef int (*xyw_poll)(xyw_byte *data); // returns: 1=dispatched, 0=inactive, -1=active but no event
 typedef void (*xyw_save)(xyw_byte *data, xyw_byte *state);
 typedef void (*xyw_restore)(xyw_byte *data, const xyw_byte *state);
+typedef void (*xyw_tick)(xyw_byte *data);
 
 #define XYW_DEVICE_STATE_SIZE 64
 
@@ -40,6 +41,7 @@ xyw_teardown teardown;
     xyw_poll poll;
     xyw_save save;
     xyw_restore restore;
+    xyw_tick tick;
 } xyw_device;
 
 // Main Globals

M xywrun.c → xywrun.c

@@ -26,7 +26,6 @@ #define SYSTEM_STATE 0xff00
 #define SYSTEM_ERROR 0xff01
 #define SYSTEM_PAGE 0xff02
 #define SYSTEM_RANDOM 0xff03
-#define SYSTEM_ON_ERROR 0xff04
 
 typedef enum
 {
@@ -183,7 +182,6 @@ return return_addr;
 }
 
 //// Internal VM state
-xyw_byte error_handler_entry_s = 0;
 
 static int system_error_state()
 {
@@ -378,42 +376,24 @@ //// Initialize devices
 
 xyw_device xyw_devices[XYW_TOTAL_DEVICES] = {
     // System device
-    {&xyw_memory[0xff00], system_setup, system_input, system_output, 0, 0, 0, 0},
+    {&xyw_memory[0xff00], system_setup, system_input, system_output, 0, 0, 0, 0, system_tick},
     // Terminal device
-    {&xyw_memory[0xff10], terminal_init, terminal_input, terminal_output, terminal_teardown, terminal_poll, terminal_save, terminal_restore},
+    {&xyw_memory[0xff10], terminal_init, terminal_input, terminal_output, terminal_teardown, terminal_poll, terminal_save, terminal_restore, 0},
     // Clock device
-    {&xyw_memory[0xff20], clock_setup, clock_input, clock_output, 0, clock_poll, 0, 0},
+    {&xyw_memory[0xff20], clock_setup, clock_input, clock_output, 0, clock_poll, 0, 0, 0},
     // File device
-    {&xyw_memory[0xff30], file_setup, file_input, file_output, 0, 0, 0, 0},
+    {&xyw_memory[0xff30], file_setup, file_input, file_output, 0, 0, 0, 0, 0},
     // Beeper device
-    {&xyw_memory[0xff40], 0, beeper_input, beeper_output, beeper_teardown, 0, 0, 0},
+    {&xyw_memory[0xff40], 0, beeper_input, beeper_output, beeper_teardown, 0, 0, 0, 0},
     // ...
 };
 // clang-format on
 
-static int process_events()
+static int has_poll_devices(void)
 {
-    // Error handling
-    if (xyw_memory[SYSTEM_ERROR] != XYW_ERROR_NONE && !system_error_state())
-    {
-        xyw_word on_error_handler = XYW_PEEKW(&xyw_memory[SYSTEM_ON_ERROR]);
-        // If an error handler is set, jump to it
-        if (on_error_handler != 0)
-        {
-            XYW_DBG("Error occurred: %02X, jumping to error handler at %04X\n", xyw_memory[SYSTEM_ERROR], on_error_handler);
-            // Enter error state
-            xyw_memory[SYSTEM_STATE] |= SYSTEM_STATE_ERROR;
-            error_handler_entry_s = s; // Record stack depth before pushing return address
-            ss_push_frame(*pc);
-            *pc = on_error_handler;
-        }
-        else
-        {
-            // No error handler: halt execution
-            xyw_memory[SYSTEM_STATE] &= ~SYSTEM_STATE_RUNNING;
-            return xyw_memory[SYSTEM_ERROR];
-        }
-    }
+    for (int i = 0; i < XYW_TOTAL_DEVICES; i++)
+        if (xyw_devices[i].poll)
+            return 1;
     return 0;
 }
 
@@ -600,14 +580,6 @@ restore_snapshot(&exec_stack[--exec_stack_depth]);
     }
 }
 
-static int has_poll_devices(void)
-{
-    for (int i = 0; i < XYW_TOTAL_DEVICES; i++)
-        if (xyw_devices[i].poll)
-            return 1;
-    return 0;
-}
-
 //// Main evaluation function - runs from current pc until BRK
 int xyw_eval(xyw_word start_pc)
 {
@@ -663,7 +635,10 @@ }
             break;          // no parent -- genuinely done
         }
 
-        process_events();
+        // Tick devices (error handling, etc.)
+        for (int i = 0; i < XYW_TOTAL_DEVICES; i++)
+            if (xyw_devices[i].tick)
+                xyw_devices[i].tick(xyw_devices[i].data);
         handle_exec_requests();
         if (!system_running_state())
         {
@@ -724,11 +699,6 @@ /* JCN */ OPC_SR1(0x1D, , xyw_word addr = ADDR(ARG); xyw_byte cond = us_pop(); if (cond) { *pc = addr-1; });
             /* JSR */ OPC_SR1(0x1E, xyw_word addr = ADDR(ARG),  ss_push_frame(*pc+1); *pc = addr-1;);
             /* RTS */ case 0x1F: 
                 *pc = ss_pop_frame()-1; 
-                // If returning from error handler, clear flag to allow re-trigger
-                if ((system_error_state()) && s == error_handler_entry_s) {
-                    xyw_memory[SYSTEM_STATE] &= ~SYSTEM_STATE_ERROR;
-                    error_handler_entry_s = 0;
-                }
                 break;
             // clang-format on
         }