CHAN_A
c = (ch->ch_nr == 1) ? CHAN_A : CHAN_B;
ip = scc_getmreg(bas, CHAN_A, RR_IP);
bes = scc_getmreg(bas, CHAN_A, CR_RSTXSI);
src = scc_getmreg(bas, CHAN_A, RR_SRC);