add: rtc support

headers/rtc.h

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <stdint.h>
+
+#define SECOND_REGISTER 0x00
+#define MINUTE_REGISTER 0x02
+#define HOUR_REGISTER 0x04
+#define DAY_OF_THE_MONTH_REGISTER 0x07
+#define MONTH_REGISTER 0x08
+#define YEAR_REGISTER 0x09
+#define CENTURY_REGISTER 0x32
+
+#define REGISTER_A 0x0A
+#define REGISTER_B 0x0B
+
+enum {
+      CMOS_ADDRESS = 0x70,
+      CMOS_DATA    = 0x71
+};
+
+struct rtc_date {
+    uint8_t second;
+    uint8_t minute;
+    uint8_t hour;
+
+    uint8_t index_of_the_day;
+    uint8_t day;
+    uint8_t month;
+    uint32_t year;
+};
+
+struct rtc_date get_date(void);

src/rtc/rtc.c

@@ -0,0 +1,56 @@
+#include "sys/io.h"
+
+#include "rtc.h"
+
+#include "kprintf.h"
+
+static uint16_t raw_read_register(uint16_t cmos_register)
+{
+    //selecting the register
+    outb(CMOS_ADDRESS, cmos_register);
+    //read value of the selectect register
+    return inb(CMOS_DATA);
+}
+
+static uint8_t update_is_in_progress(void)
+{
+    return raw_read_register(REGISTER_A) & 0x80;
+}
+
+static uint16_t read_register(uint16_t cmos_register)
+{
+    while (update_is_in_progress())
+        kprintf(0, "%d\n", update_is_in_progress());
+    return raw_read_register(cmos_register);
+}
+
+uint8_t bcd_mode_to_bin(uint8_t value)
+{
+    return (value & 0x0F) + ((value/ 16) * 10);
+}
+
+struct rtc_date get_date(void)
+{
+    struct rtc_date rv;
+    uint8_t century;
+
+    rv.second = read_register(SECOND_REGISTER);
+    rv.minute = read_register(MINUTE_REGISTER);
+    rv.hour = read_register(HOUR_REGISTER);
+    rv.day = read_register(DAY_OF_THE_MONTH_REGISTER);
+    rv.month = read_register(MONTH_REGISTER);
+    rv.year += read_register(YEAR_REGISTER);
+    century = read_register(CENTURY_REGISTER);
+
+    if (!(read_register(REGISTER_B) & 0x04)) {
+        rv.second = bcd_mode_to_bin(rv.second);
+        rv.minute = bcd_mode_to_bin(rv.minute);
+        rv.hour = bcd_mode_to_bin(rv.hour);
+        rv.day = bcd_mode_to_bin(rv.day);
+        rv.month = bcd_mode_to_bin(rv.month);
+        rv.year = bcd_mode_to_bin(rv.year);
+        century = bcd_mode_to_bin(century);
+    }
+    rv.year += century * 100 - 108; // -108 = bozo offset
+    return rv;
+}