RDAYCNT
RDAYCNT, RMONCNT, RYRCNT };
ret = ret ? ret : write_reg(dev, RDAYCNT, bin2bcd(dt->tm_mday));
tm->tm_mday = bcd2bin(readb(rtc->regbase + RDAYCNT));
writeb(bin2bcd(tm->tm_mday), rtc->regbase + RDAYCNT);