RR_SRC
src = scc_getmreg(bas, CHAN_A, RR_SRC);
src = scc_getmreg(bas, CHAN_B, RR_SRC);
src = uart_getmreg(bas, RR_SRC);
src = uart_getmreg(bas, RR_SRC);
src = uart_getmreg(bas, RR_SRC);