RTC_SECONDS_MASK
second = readb(ioaddr + RTC_SECONDS) & RTC_SECONDS_MASK;
sec &= RTC_SECONDS_MASK;
writeb(bin2bcd(tm->tm_sec) & RTC_SECONDS_MASK, ioaddr + RTC_SECONDS);
sec &= RTC_SECONDS_MASK;
writeb(bin2bcd(tm->tm_sec) & RTC_SECONDS_MASK, ioaddr + RTC_SECONDS);
second = readb(ioaddr + RTC_SECONDS) & RTC_SECONDS_MASK;
second = readb(ioaddr + RTC_SECONDS) & RTC_SECONDS_MASK;
writeb(bin2bcd(tm->tm_sec) & RTC_SECONDS_MASK, ioaddr + RTC_SECONDS);