uboot一般不会要求开启rtc，只是还是支持rtc以备特殊需求的。

底层驱动移植前面两篇已经介绍。这里介绍顶层的调用过程。顶层在uboot/common/cmd_date.c

/*

* (C) Copyright 2001

* Wolfgang Denk, DENX Software Engineering, wd@denx.de.

*

* See file CREDITS for list of people who contributed to this

* project.

*

* This program is free software; you can redistribute it and/or

* modify it under the terms of the GNU General Public License as

* published by the Free Software Foundation; either version 2 of

* the License, or (at your option) any later version.

*

* This program is distributed in the hope that it will be useful,

* but WITHOUT ANY WARRANTY; without even the implied warranty of

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

* GNU General Public License for more details.

*

* You should have received a copy of the GNU General Public License

* along with this program; if not, write to the Free Software

* Foundation, Inc., 59 Temple Place, Suite 330, Boston,

* MA 02111-1307 USA

*/

/*

* RTC, Date & Time support: get and set date & time

*/

include

include

include

include

ifdef CONFIG_RELOC_FIXUP_WORKS

define RELOC(a) a

else

define RELOC(a) ((typeof(a))((unsigned long)(a) + gd->reloc_off))

endif

int mk_date (char , struct rtc_time );

int do_date (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])

{

struct rtc_time tm;

int rcode = 0;

int old_bus;

/* switch to correct I2C bus */

old_bus = I2C_GET_BUS();

I2C_SET_BUS(CONFIG_SYS_RTC_BUS_NUM);

switch (argc) {

case 2:         /* set date & time */

    if (strcmp(argv[1],"reset") == 0) {

        puts ("Reset RTC...\n");

        rtc_reset ();

    } else {

        /* initialize tm with current time */

        rcode = rtc_get (&tm);

        if(!rcode) {

            /* insert new date & time */

            if (mk_date (argv[1], &tm) != 0) {

                puts ("## Bad date format\n");

                break;

            }

            /* and write to RTC */

            rcode = rtc_set (&tm);

            if(rcode)

                puts("## Set date failed\n");

        } else {

            puts("## Get date failed\n");

        }

    }

    /* FALL TROUGH */

case 1:         /* get date & time */

    rcode = rtc_get (&tm);

    if (rcode) {

        puts("## Get date failed\n");

        break;

    }

    printf ("Date: %4d-%02d-%02d (%sday)    Time: %2d:%02d:%02d\n",

        tm.tm_year, tm.tm_mon, tm.tm_mday,

        (tm.tm_wday<0 || tm.tm_wday>6) ?

            "unknown " : RELOC(weekdays[tm.tm_wday]),

        tm.tm_hour, tm.tm_min, tm.tm_sec);

    break;

default:

    cmd_usage(cmdtp);

    rcode = 1;

}

/* switch back to original I2C bus */

I2C_SET_BUS(old_bus);

return rcode;

}

/*

* simple conversion of two-digit string with error checking

*/

static int cnvrt2 (char *str, int *valp)

{

int val;

if ((*str < '0') || (*str > '9'))

    return (-1);

val = *str - '0';

++str;

if ((*str < '0') || (*str > '9'))

    return (-1);

*valp = 10 * val + (*str - '0');

return (0);

}

/*

* Convert date string: MMDDhhmm[[CC]YY][.ss]

*

* Some basic checking for valid values is done, but this will not catch

* all possible error conditions.

*/

int mk_date (char *datestr, struct rtc_time *tmp)

{

int len, val;

char *ptr;

ptr = strchr (datestr,'.');

len = strlen (datestr);

/* Set seconds */

if (ptr) {

    int sec;

    *ptr++ = '\0';

    if ((len - (ptr - datestr)) != 2)

        return (-1);

    len = strlen (datestr);

    if (cnvrt2 (ptr, &sec))

        return (-1);

    tmp->tm_sec = sec;

} else {

    tmp->tm_sec = 0;

}

if (len == 12) {        /* MMDDhhmmCCYY */

    int year, century;

    if (cnvrt2 (datestr+ 8, &century) ||

        cnvrt2 (datestr+10, &year) ) {

        return (-1);

    }

    tmp->tm_year = 100 * century + year;

} else if (len == 10) {     /* MMDDhhmmYY   */

    int year, century;

    century = tmp->tm_year / 100;

    if (cnvrt2 (datestr+ 8, &year))

        return (-1);

    tmp->tm_year = 100 * century + year;

}

switch (len) {

case 8:         /* MMDDhhmm */

    /* fall thru */

case 10:        /* MMDDhhmmYY   */

    /* fall thru */

case 12:        /* MMDDhhmmCCYY */

    if (cnvrt2 (datestr+0, &val) ||

        val > 12) {

        break;

    }

    tmp->tm_mon  = val;

    if (cnvrt2 (datestr+2, &val) ||

        val > ((tmp->tm_mon==2) ? 29 : 31)) {

        break;

    }

    tmp->tm_mday = val;

    if (cnvrt2 (datestr+4, &val) ||

        val > 23) {

        break;

    }

    tmp->tm_hour = val;

    if (cnvrt2 (datestr+6, &val) ||

        val > 59) {

        break;

    }

    tmp->tm_min  = val;

    /* calculate day of week */

    GregorianDay (tmp);

    return (0);

default:

    break;

}

return (-1);

}

/*****************************************/

U_BOOT_CMD(

date, 2, 1, do_date,

“get/set/reset date & time”,

“[MMDDhhmm[[CC]YY][.ss]]\ndate reset\n”

” - without arguments: print date & time\n”

” - with numeric argument: set the system date & time\n”

” - with ‘reset’ argument: reset the RTC”

);

这里反向分析：

第一步是注冊 date命令

U_BOOT_CMD(

date, 2, 1, do_date,

“get/set/reset date & time”,

“[MMDDhhmm[[CC]YY][.ss]]\ndate reset\n”

” - without arguments: print date & time\n”

” - with numeric argument: set the system date & time\n”

” - with ‘reset’ argument: reset the RTC”

);

这个命令就是rtc的控制命令了 调用的函数是 do_date

int do_date (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])

能够看到这命令是调用了rtc里面注冊的rtc_reset、rtc_get、rtc_set

分为case1 ：获取当年的时间

case2 设置时间；

时间转换函数mk_date 能够将我们输入的字符串转化成为时间的年月日 供rtc_set 配置下去去