diff --git a/apps/dvxbasic/runtime/vm.c b/apps/dvxbasic/runtime/vm.c
index 1081f6d..24568f5 100644
--- a/apps/dvxbasic/runtime/vm.c
+++ b/apps/dvxbasic/runtime/vm.c
@@ -20,6 +20,11 @@
 // Prototypes
 // ============================================================
 
+// Steps to execute between doEvents yields during subroutine calls.
+// This keeps the GUI responsive without excessive overhead from
+// calling doEvents on every instruction.
+#define SUB_YIELD_INTERVAL 500
+
 static BasCallFrameT *currentFrame(BasVmT *vm);
 static void           defaultPrint(void *ctx, const char *text, bool newline);
 static BasVmResultE   execArith(BasVmT *vm, uint8_t op);
@@ -37,6 +42,51 @@ static uint16_t       readUint16(BasVmT *vm);
 static void           runtimeError(BasVmT *vm, int32_t errNum, const char *msg);
 
 
+// ============================================================
+// runSubLoop -- shared inner loop for basVmCallSub variants
+// ============================================================
+//
+// Executes instructions until callDepth drops back to savedCallDepth
+// (meaning the subroutine returned). Periodically yields via the
+// doEvents callback to keep the GUI responsive during long-running
+// event handlers.
+
+static bool runSubLoop(BasVmT *vm, int32_t savedPc, int32_t savedCallDepth, bool savedRunning) {
+    int32_t stepsSinceYield = 0;
+
+    while (vm->running && vm->callDepth > savedCallDepth) {
+        BasVmResultE result = basVmStep(vm);
+
+        if (result == BAS_VM_HALTED) {
+            break;
+        }
+
+        if (result != BAS_VM_OK) {
+            vm->pc        = savedPc;
+            vm->callDepth = savedCallDepth;
+            vm->running   = savedRunning;
+            return false;
+        }
+
+        // Yield periodically to keep the GUI responsive
+        if (++stepsSinceYield >= SUB_YIELD_INTERVAL) {
+            stepsSinceYield = 0;
+
+            if (vm->doEventsFn) {
+                if (!vm->doEventsFn(vm->doEventsCtx)) {
+                    vm->running = false;
+                    break;
+                }
+            }
+        }
+    }
+
+    vm->pc      = savedPc;
+    vm->running = savedRunning;
+    return true;
+}
+
+
 // ============================================================
 // basVmCallSub
 // ============================================================
@@ -70,26 +120,7 @@ bool basVmCallSub(BasVmT *vm, int32_t codeAddr) {
     vm->pc      = codeAddr;
     vm->running = true;
 
-    // Run until the SUB returns (callDepth drops back).
-    // No step limit -- event handlers must run to completion.
-    while (vm->running && vm->callDepth > savedCallDepth) {
-        BasVmResultE result = basVmStep(vm);
-
-        if (result == BAS_VM_HALTED) {
-            break;
-        }
-
-        if (result != BAS_VM_OK) {
-            vm->pc        = savedPc;
-            vm->callDepth = savedCallDepth;
-            vm->running   = savedRunning;
-            return false;
-        }
-    }
-
-    vm->pc      = savedPc;
-    vm->running = savedRunning;
-    return true;
+    return runSubLoop(vm, savedPc, savedCallDepth, savedRunning);
 }
 
 
@@ -127,24 +158,7 @@ bool basVmCallSubWithArgs(BasVmT *vm, int32_t codeAddr, const BasValueT *args, i
     vm->pc      = codeAddr;
     vm->running = true;
 
-    while (vm->running && vm->callDepth > savedCallDepth) {
-        BasVmResultE result = basVmStep(vm);
-
-        if (result == BAS_VM_HALTED) {
-            break;
-        }
-
-        if (result != BAS_VM_OK) {
-            vm->pc        = savedPc;
-            vm->callDepth = savedCallDepth;
-            vm->running   = savedRunning;
-            return false;
-        }
-    }
-
-    vm->pc      = savedPc;
-    vm->running = savedRunning;
-    return true;
+    return runSubLoop(vm, savedPc, savedCallDepth, savedRunning);
 }
 
 
@@ -181,25 +195,12 @@ bool basVmCallSubWithArgsOut(BasVmT *vm, int32_t codeAddr, const BasValueT *args
     vm->pc      = codeAddr;
     vm->running = true;
 
-    while (vm->running && vm->callDepth > savedCallDepth) {
-        BasVmResultE result = basVmStep(vm);
+    bool ok = runSubLoop(vm, savedPc, savedCallDepth, savedRunning);
 
-        if (result == BAS_VM_HALTED) {
-            break;
-        }
-
-        if (result != BAS_VM_OK) {
-            vm->pc        = savedPc;
-            vm->callDepth = savedCallDepth;
-            vm->running   = savedRunning;
-            return false;
-        }
-    }
-
-    // Read back modified locals before restoring state.
+    // Read back modified locals before the frame is reused.
     // The frame at savedCallDepth still has the data even
     // though callDepth was decremented by RET.
-    if (outArgs && outCount > 0) {
+    if (ok && outArgs && outCount > 0) {
         BasCallFrameT *doneFrame = &vm->callStack[savedCallDepth];
 
         for (int32_t i = 0; i < outCount && i < BAS_VM_MAX_LOCALS; i++) {
@@ -207,9 +208,7 @@ bool basVmCallSubWithArgsOut(BasVmT *vm, int32_t codeAddr, const BasValueT *args
         }
     }
 
-    vm->pc      = savedPc;
-    vm->running = savedRunning;
-    return true;
+    return ok;
 }