+void chime(); /* RTI interrupt */
+
+/* internal helpers, also could be called from outside world */
+extern inline void chime_on() { bset((void*)&_io_ports[M6811_PORTA], PORTA_CHIME); }
+extern inline void chime_off() { bclr((void*)&_io_ports[M6811_PORTA], PORTA_CHIME);}
+