RMINCNT
unsigned char buf[] = { RSECCNT, RMINCNT, RHRCNT,
ret = ret ? ret : write_reg(dev, RMINCNT, bin2bcd(dt->tm_min));
tm->tm_min = bcd2bin(readb(rtc->regbase + RMINCNT));
writeb(bin2bcd(tm->tm_min), rtc->regbase + RMINCNT);