vm: Initial support for calling bytecode functions w/o C stack ("stackless").
diff --git a/py/mpconfig.h b/py/mpconfig.h
index ae5e776..94e2737 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -125,6 +125,11 @@
 #define MICROPY_QSTR_BYTES_IN_LEN (1)
 #endif
 
+// Avoid using C stack when making Python function calls.
+#ifndef MICROPY_STACKLESS
+#define MICROPY_STACKLESS (0)
+#endif
+
 /*****************************************************************************/
 /* Micro Python emitters                                                     */