rtc_time.c

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/*
 * Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * 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 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., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

/** @file
 *
 * RTC-based time source
 *
 */

#include <stdint.h>
#include <time.h>
#include <rtc.h>
#include <ipxe/time.h>

/**
 * Read RTC register
 *
 * @v address           Register address
 * @ret data            Data
 */
static unsigned int rtc_readb ( int address ) {
        outb ( address, CMOS_ADDRESS );
        return inb ( CMOS_DATA );
}

/**
 * Check if RTC update is in progress
 *
 * @ret is_busy         RTC update is in progress
 */
static int rtc_is_busy ( void ) {
        return ( rtc_readb ( RTC_STATUS_A ) & RTC_STATUS_A_UPDATE_IN_PROGRESS );
}

/**
 * Read RTC BCD register
 *
 * @v address           Register address
 * @ret value           Value
 */
static unsigned int rtc_readb_bcd ( int address ) {
        unsigned int bcd;

        bcd = rtc_readb ( address );
        return ( bcd - ( 6 * ( bcd >> 4 ) ) );
}

/**
 * Read RTC time
 *
 * @ret time            Time, in seconds
 */
static time_t rtc_read_time ( void ) {
        unsigned int status_b;
        int is_binary;
        int is_24hour;
        unsigned int ( * read_component ) ( int address );
        struct tm tm;
        int is_pm;
        unsigned int hour;
        time_t time;

        /* Wait for any in-progress update to complete */
        while ( rtc_is_busy() ) {}

        /* Determine RTC mode */
        status_b = rtc_readb ( RTC_STATUS_B );
        is_binary = ( status_b & RTC_STATUS_B_BINARY );
        is_24hour = ( status_b & RTC_STATUS_B_24_HOUR );
        read_component = ( is_binary ? rtc_readb : rtc_readb_bcd );

        /* Read time values */
        tm.tm_sec = read_component ( RTC_SEC );
        tm.tm_min = read_component ( RTC_MIN );
        hour = read_component ( RTC_HOUR );
        if ( ! is_24hour ) {
                is_pm = ( hour >= 80 );
                hour = ( ( ( ( hour & 0x7f ) % 80 ) % 12 ) +
                         ( is_pm ? 12 : 0 ) );
        }
        tm.tm_hour = hour;
        tm.tm_mday = read_component ( RTC_MDAY );
        tm.tm_mon = ( read_component ( RTC_MON ) - 1 );
        tm.tm_year = ( read_component ( RTC_YEAR ) +
                       100 /* Assume we are in the 21st century, since
                            * this code was written in 2012 */ );

        DBGC ( RTC_STATUS_A, "RTCTIME is %04d-%02d-%02d %02d:%02d:%02d "
               "(%s,%d-hour)\n", ( tm.tm_year + 1900 ), ( tm.tm_mon + 1 ),
               tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec,
               ( is_binary ? "binary" : "BCD" ), ( is_24hour ? 24 : 12 ) );

        /* Convert to seconds since the Epoch */
        time = mktime ( &tm );

        return time;
}

/**
 * Get current time in seconds
 *
 * @ret time            Time, in seconds
 */
static time_t rtc_now ( void ) {
        time_t time = 0;
        time_t last_time;

        /* Read time until we get two matching values in a row, in
         * case we end up reading a corrupted value in the middle of
         * an update.
         */
        do {
                last_time = time;
                time = rtc_read_time();
        } while ( time != last_time );

        return time;
}

PROVIDE_TIME ( rtc, time_now, rtc_now );