Add gettimeofday() syscall and LibC wrappers gettimeofday() and time().

This only has second accuracy right now, I'll work out subseconds later.

Kernel/RTC.cpp

@@ -0,0 +1,90 @@
+#include "RTC.h"
+#include "CMOS.h"
+
+namespace RTC {
+
+static time_t s_bootTime;
+
+void initialize()
+{    
+    byte cmosMode = CMOS::read(0x0b);
+    cmosMode |= 2; // 24 hour mode
+    cmosMode |= 4; // No BCD mode
+    CMOS::write(0x0b, cmosMode);
+
+    s_bootTime = now();
+}
+
+time_t bootTime()
+{
+    return s_bootTime;
+}
+
+static bool updateInProgress()
+{
+    return CMOS::read(0x0a) & 0x80;
+}
+
+inline bool isLeapYear(unsigned year)
+{
+    return ((year % 4 == 0) && ((year % 100 != 0) || (year % 400) == 0));
+}
+
+static unsigned daysInMonthsSinceStartOfYear(unsigned month, unsigned year)
+{
+    switch (month) {
+    case 11: return 30;
+    case 10: return 31;
+    case 9: return 30;
+    case 8: return 31;
+    case 7: return 31;
+    case 6: return 30;
+    case 5: return 31;
+    case 4: return 30;
+    case 3: return 31;
+    case 2:
+        if (isLeapYear(year))
+            return 29;
+        return 28;
+    case 1: return 31;
+    default: return 0;
+    }
+}
+
+static unsigned daysInYearsSinceEpoch(unsigned year)
+{
+    unsigned days = 0;
+    while (year > 1969) {
+        days += 365;
+        if (isLeapYear(year))
+            ++days;
+        --year;
+    }
+    return days;
+}
+
+time_t now()
+{
+    // FIXME: We should probably do something more robust here.
+    //        Perhaps read all the values twice and verify that they were identical.
+    //        We don't want to be caught in the middle of an RTC register update.
+    while (updateInProgress())
+        ;
+
+    unsigned year = (CMOS::read(0x32) * 100) + CMOS::read(0x09);
+    unsigned month = CMOS::read(0x08);
+    unsigned day = CMOS::read(0x07);
+    unsigned hour = CMOS::read(0x04);
+    unsigned minute = CMOS::read(0x02);
+    unsigned second = CMOS::read(0x00);
+
+    return daysInYearsSinceEpoch(year - 1) * 86400
+         + daysInMonthsSinceStartOfYear(month - 1, year) * 86400
+         + day * 86400
+         + hour * 3600
+         + minute * 60
+         + second;
+}
+
+}
+