M xyw.h → xyw.h

@@ -37,7 +37,7 @@ 
 // clang-format off
 #define XYW_PEEKW(d) (*(d) << 8 | (d)[1])
 #define XYW_POKEW(d, v) { *(d) = (v) >> 8; (d)[1] = (v); }
-#define XYW_DBG(...) do { if (xyw_debug) fprintf(stdout, __VA_ARGS__); } while(0)
+#define XYW_DBG(...) do { if (xyw_debug) fprintf(stderr, __VA_ARGS__); } while(0)
 // clang-format on
 
 // Devices API

M xywrun.c → xywrun.c

@@ -221,7 +221,6 @@ {
         xyw_memory[SYSTEM_ERROR] = XYW_SYSTEM_ERROR_USER_STACK_OVERFLOW;
         return;
     }
-    XYW_DBG(" => %02X\n", val);
     user_stack[u++] = val;
 }
 
@@ -234,7 +233,6 @@ return;
     }
     user_stack[u]     = (xyw_byte)(val >> 8);
     user_stack[u + 1] = (xyw_byte)(val & 0xFF);
-    XYW_DBG(" => %04X\n", val);
     u += 2;
 }
 
@@ -471,6 +469,39 @@ }
     return 0;
 }
 
+// Reconstruct the modes given an opcode (used for debugging)
+static const char *mode_suffix(xyw_byte opcode)
+{
+    static char buf[4];
+    int i = 0;
+    if (opcode & XYW_MODE_X) buf[i++] = 'x';
+    if (opcode & XYW_MODE_Y) buf[i++] = 'y';
+    if (opcode & XYW_MODE_W) buf[i++] = 'w';
+    buf[i] = '\0';
+    return buf;
+}
+
+// Format the first four bytes on the stack (used for debugging)
+static const char *format_stack_peek(xyw_byte mode_w)
+{
+    static char buf[24];
+    if (mode_w)
+    {
+        xyw_word top    = u >= 2 ? (xyw_word)((user_stack[u-2] << 8) | user_stack[u-1]) : 0;
+        xyw_word second = u >= 4 ? (xyw_word)((user_stack[u-4] << 8) | user_stack[u-3]) : 0;
+        snprintf(buf, sizeof(buf), "[ %04X %04X ]", second, top);
+    }
+    else
+    {
+        xyw_byte b3 = u >= 4 ? user_stack[u-4] : 0;
+        xyw_byte b2 = u >= 3 ? user_stack[u-3] : 0;
+        xyw_byte b1 = u >= 2 ? user_stack[u-2] : 0;
+        xyw_byte b0 = u >= 1 ? user_stack[u-1] : 0;
+        snprintf(buf, sizeof(buf), "[%02X %02X %02X %02X]", b3, b2, b1, b0);
+    }
+    return buf;
+}
+
 //// Main evaluation function - runs from current pc until BRK
 int xyw_eval(xyw_word start_pc)
 {
@@ -533,7 +564,10 @@ 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);
+        XYW_DBG(" -- PC:%04X  %s%-3s  U:%02X S:%02X X:%02X Y:%02X XW:%04X YW:%04X  stk:%s\n",
+            *pc, xyw_instructions[xyw_memory[*pc] & 0x1F], mode_suffix(xyw_memory[*pc]),
+            u, s, *x, *y, *xw, *yw,
+            format_stack_peek(xyw_memory[*pc] & XYW_MODE_W));
         switch (xyw_memory[*pc])
         {
             // clang-format off