MC_DOW
dt->dt_wday = chiptime[MC_DOW];
chiptime[MC_DOW] = dt->dt_wday;
mc146818_write(sc, MC_DOW, dt->dt_wday + 1);
rtclk[MC_DOW] = dt->dt_wday + 1;
regs[MC_DOW] = dt.dt_wday;
dt->dt_wday = FROMREG((*sc->sc_mcread)(sc, MC_DOW));
(*sc->sc_mcwrite)(sc, MC_DOW, TOREG(dt->dt_wday));