scc_getmreg
ip = scc_getmreg(bas, CHAN_A, RR_IP);
bes = scc_getmreg(bas, CHAN_A, CR_RSTXSI);
src = scc_getmreg(bas, CHAN_A, RR_SRC);
bes = scc_getmreg(bas, CHAN_B, CR_RSTXSI);
src = scc_getmreg(bas, CHAN_B, RR_SRC);