M41T94_REG_HOURS
buf[M41T94_REG_HOURS] = bin2bcd(tm->tm_hour);
buf[M41T94_REG_HOURS] |= M41T94_BIT_CEB;
buf[M41T94_REG_HOURS] |= M41T94_BIT_CB;
hour = spi_w8r8(spi, M41T94_REG_HOURS);