#include "rtc.h"
#include "io.h"

char bcd;

unsigned char read_register(unsigned char reg) {
    __asm__ volatile("cli");
    outb(RTC_COMMAND, reg);
    return inb(RTC_DATA);
    __asm__ volatile("sti");
}

void write_register(unsigned char reg, unsigned char value) {
    __asm__ volatile("cli");
    outb(RTC_COMMAND, reg);
    outb(RTC_DATA, value);
    __asm__ volatile("sti");
}

unsigned char bcd2bin(unsigned char in_bcd) {
    return (bcd) ? ((in_bcd >> 4) * 10) + (in_bcd & 0x0F) : in_bcd;
}

int rtc_init() {
    __asm__ volatile("cli");
    unsigned char status;
    status = read_register(RTC_STATUS);
    status |= 0x02;         // 24 hour clock
    status |= 0x10;         // update ended interrupts
    status &= ~0x20;        // no alarm interrupts
    status &= ~0x40;        // no periodic interrupt
    bcd = !(status & 0x04); // check if data type is BCD
    write_register(RTC_STATUS, status);

    outb(0x70, 0x8B);		// select register B, and disable NMI
    char prev=inb(0x71);	// read the current value of register B
    outb(0x70, 0x8B);		// set the index again (a read will reset the index to register D)
    outb(0x71, prev | 0x40);	// write the previous value ORed with 0x40. This turns on bit 6 of register B
    __asm__ volatile("sti");
    return 0;
}