OSDev.org

#define CURRENT_YEAR        2018                            // Change this each year!
int century_register = 0x00;
unsigned char second;
unsigned char minute;
unsigned char hour;
unsigned char day;
unsigned char month;
unsigned int year;

enum {
      cmos_address = 0x70,
      cmos_data    = 0x71
};
int get_update_in_progress_flag() {
      outportb(cmos_address, 0x0A);
      return (inportb(cmos_data) & 0x80);
}

unsigned char get_RTC_register(int reg) {
      outportb(cmos_address, reg);
      return inportb(cmos_data);
}

void read_rtc() {

   
    unsigned char century;
    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;

      // 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);
            }
      }


      // Convert 12 hour clock to 24 hour clock if necessary

      if (!(registerB & 0x02) && (hour & 0x80)) {
            hour = ((hour & 0x7F) + 12) % 24;
      }

      // 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;
      }


      //print_digit(year);

}

uint16 *textmemptr;

void putch(char c)
{
  uint16 *where;
  uint16 att = attrib << 8;

  /* Handle a backspace, by moving the cursor back one space */
  if(c == 0x08)
  {
      if(csr_x != 0) csr_x--;
  }
  /* Handles a tab by incrementing the cursor's x, but only
  *  to a point that will make it divisible by 8 */
  else if(c == 0x09)
  {
      csr_x = (csr_x + 8) & ~(8 - 1);
  }
  /* Handles a 'Carriage Return', which simply brings the
  *  cursor back to the margin */
  else if(c == '\r')
  {
      csr_x = 0;
  }
  /* We handle our newlines the way DOS and the BIOS do: we
  *  treat it as if a 'CR' was also there, so we bring the
  *  cursor to the margin and we increment the 'y' value */
  else if(c == '\n')
  {
      csr_x = 0;
      csr_y++;
  }
  /* Any character greater than and including a space, is a
  *  printable character. The equation for finding the index
  *  in a linear chunk of memory can be represented by:
  *  Index = [(y * width) + x] */
  else if(c >= ' ')
  {
      where = textmemptr + (csr_y * 80 + csr_x);
      *where = c | att;   /* Character AND attributes: color */
      csr_x++;
  }

  /* If the cursor has reached the edge of the screen's width, we
  *  insert a new line in there */
  if(csr_x >= 80)
  {
      csr_x = 0;
      csr_y++;
  }

  /* Scroll the screen if needed, and finally move the cursor */
  scroll();
  //move_csr();
}

void print_digit(int num)
{
    textmemptr = (uint16*) 0xb8000;
    int index = 1;
    char str[80] = "";
while ( num > 0 )
{
    str[index]= '0'+ num%10;
    num = num/10;
    index++;
}
while ( index > 0 )
{
    putch(str[index]);
    index--;
}
}

void k_main(void)
{
cls();             //clear the screen with blank spaces before use
///upper_line(0,9);
//
    upper_line(0,9); //Line at the top
   read_rtc(); // initializing and print the current time.

print("\n");

print_xy_clr("&&&&&&$                &&&&&&&         &&&&&&&&&\n"
             "&&     &&             &&       &&     &&\n"
             "&&       &          &&          &&   &&\n"
             "&&     &&           &&          &&    &&\n"
             "&&&&&&&             &&          &&     &&&&&&&&&\n"
             "&&         &&&&&&   &&          &&              &&\n"
             "&&                  &&          &&               &&\n"
             "&&                    &&       &&               &&\n"
             "&&                      &&&&&&&         &&&&&&&& \n",15,7,15,0);

    print_xy_clr("Loading\n",37,10,9,0);


    upper_line(11,9); //Line at the bottom

}

print("\n Current CPU time is - ");
print_digit(hour);
print(":");
print_digit(minute);
print(":");
print_digit(second);

//First time
print("hello");
//I got a printed text "hello"

//Second time
print("hello");
cls();
//I got empty black screen

void cls()
{
  /* Fill screen with blank spaces (with current attribute)
attribute stands for current forecolor and backcolor so it fills the screen with current backcolor and no forecolor bcs of blank spaces

*/
   uint16 blank = 0x20 | (attrib << 8);

  textmemptr = (uint16 *) 0xB8000;

  memsetw ( ( uint16 *) textmemptr, blank, 80 * 25);

}