/*
 * http://wiki.osdev.org/OSDev_Wiki:General_disclaimer
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
#include "libsaio.h"

#define CURRENT_YEAR        2012                            // Change this each year!

static int century_register = 0x00;                                // Set by ACPI table parsing code if possible(... in FADT table)

enum {
    cmos_address = 0x70,
    cmos_data    = 0x71
};


static int get_update_in_progress_flag() {
    outb(cmos_address, 0x0A);
    return (inb(cmos_data) & 0x80);
}


static unsigned char get_RTC_register(int reg) {
    outb(cmos_address, reg);
    return inb(cmos_data);
}

void rtc_read_clock(struct tm *time) {
    unsigned char century = 0;
    unsigned char last_second;
    unsigned char last_minute;
    unsigned char last_hour;
    unsigned char last_day;
    unsigned char last_month;
    unsigned char last_year;
    unsigned char last_century;
    unsigned char registerB;
    
    unsigned char second;
    unsigned char minute;
    unsigned char hour;
    unsigned char day;
    unsigned char month;
    unsigned int year;
    // Note: This uses the "read registers until you get the same values twice in a row" technique
    //       to avoid getting dodgy/inconsistent values due to RTC updates
    
    while (get_update_in_progress_flag());                // Make sure an update isn't in progress
    second = get_RTC_register(0x00);
    minute = get_RTC_register(0x02);
    hour = get_RTC_register(0x04);
    day = get_RTC_register(0x07);
    month = get_RTC_register(0x08);
    year = get_RTC_register(0x09);
    if(century_register != 0) {
        century = get_RTC_register(century_register);
    }
    
    do {
        last_second = second;
        last_minute = minute;
        last_hour = hour;
        last_day = day;
        last_month = month;
        last_year = year;
        last_century = century;
        
        while (get_update_in_progress_flag());           // Make sure an update isn't in progress
        second = get_RTC_register(0x00);
        minute = get_RTC_register(0x02);
        hour = get_RTC_register(0x04);
        day = get_RTC_register(0x07);
        month = get_RTC_register(0x08);
        year = get_RTC_register(0x09);
        if(century_register != 0) {
            century = get_RTC_register(century_register);
        }
    } while( (last_second == second) && (last_minute == minute) && (last_hour == hour) &&
            (last_day == day) && (last_month == month) && (last_year == year) &&
            (last_century == century) );
    
    registerB = get_RTC_register(0x0B);
    
    // Convert BCD to binary values if necessary
    
    if (!(registerB & 0x04)) {
        second = (second & 0x0F) + ((second / 16) * 10);
        minute = (minute & 0x0F) + ((minute / 16) * 10);
        hour = ( (hour & 0x0F) + (((hour & 0x70) / 16) * 10) ) | (hour & 0x80);
        day = (day & 0x0F) + ((day / 16) * 10);
        month = (month & 0x0F) + ((month / 16) * 10);
        year = (year & 0x0F) + ((year / 16) * 10);
        if(century_register != 0) {
            century = (century & 0x0F) + ((century / 16) * 10);
        }
    }    
    
    // Calculate the full (4-digit) year
    
    if(century_register != 0) {
        year += century * 100;
    } else {
        //year += (CURRENT_YEAR / 100) * 100;
        //if(year < CURRENT_YEAR) year += 100;        
        
        if ((year += 1900) < 1970)
            year += 100;
    }
    
    time->tm_sec = second;
    time->tm_min = minute;
    time->tm_hour = hour;
    time->tm_mday = day;
    time->tm_mon = month;
    time->tm_year = year;
}