寻求高人帮助

nigel_d

在linux下调用了sys_stime和sys_gettimeofday以后日期和时间是怎样写入CMOS  RTC时钟的?

static int set_rtc_mmss(unsigned long nowtime)
{
        int retval = 0;
        int real_seconds, real_minutes, cmos_minutes;
        unsigned char save_control, save_freq_select;

        /* gets recalled with irq locally disabled */
        spin_lock(&rtc_lock);
        save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
        CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);

        save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
        CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);

        cmos_minutes = CMOS_READ(RTC_MINUTES);
        if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
                BCD_TO_BIN(cmos_minutes);

        /*
         * since we're only adjusting minutes and seconds,
         * don't interfere with hour overflow. This avoids
         * messing with unknown time zones but requires your
         * RTC not to be off by more than 15 minutes
         */
        real_seconds = nowtime % 60;
        real_minutes = nowtime / 60;
        if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
                real_minutes += 30;                /* correct for half hour time zone */
        real_minutes %= 60;

        if (abs(real_minutes - cmos_minutes) < 30) {
                if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
                        BIN_TO_BCD(real_seconds);
                        BIN_TO_BCD(real_minutes);
                }
                CMOS_WRITE(real_seconds,RTC_SECONDS);
                CMOS_WRITE(real_minutes,RTC_MINUTES);
        } else {
                printk(KERN_WARNING
                       "set_rtc_mmss: can't update from %d to %d\n",
                       cmos_minutes, real_minutes);
                retval = -1;
        }

        /* The following flags have to be released exactly in this order,
         * otherwise the DS12887 (popular MC146818A clone with integrated
         * battery and quartz) will not reset the oscillator and will not
         * update precisely 500 ms later. You won't find this mentioned in
         * the Dallas Semiconductor data sheets, but who believes data
         * sheets anyway ...                           -- Markus Kuhn
         */
        CMOS_WRITE(save_control, RTC_CONTROL);
        CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
        spin_unlock(&rtc_lock);

        return retval;
}

我只找到这一个同步时候用的函数是往回写的,可看样子不像是设置时间后写入硬件的那个,哪位大哥知道请尽快给俺解答,急~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~